SYSTEM,POWERPLANT&ELECTRICS
1-Which of the fo1lowing statements concerning the stresses "TORSION" and "TENSION" is correct?
A)Tension is caused by twisting and torsion resists a force pulling it apart.
B)Torsion is caused by twisting and tension resists a force pulling it apart.
C)Torsion is caused by two layers sliding apart and tension resists a force pulling it apart.
D)Torsion is caused by twisting and tension is a crushing force.
2-Define the term "FATIGUE":
A)a one off loading that breaks the material.
B)a loading on the material but it returns fully to its former state when the load is removed.
C)if a material is continually loaded and unloaded it will eventually break even though the load remains the
same.
D)the material suffers progressively more permanent damage each time that it is loaded and unloaded.
(Refer to figure 021-E51)
The life of an airframe is limited by fatigue, caused by the load cycles imposed during takeoff, landing and
pressurisation. This life has been calculated over the years by using different design philosophies, these being
safe-life, failsafe, and damage-tolerant.
3-Among the different types of aircraft structures, the shell structures efficiently transmit the:
1)normal bending stresses
2)tangent bending stresses
3)torsional moment
4)shear stresses
The combination regrouping all the correct statements is:
A)1,2,4
B)2,3,4
C) 1,3,4
D) 1,2,3
(Refer to figures 021-E49 and 021-E50)
Reinforced shell structure is a development on the semi-monocoque type. The formers (or frames) are attached,
together with the stringers and longerons, to the stressed skin. The skin takes the most of the load, the longerons
provide a rigidity of the skeleton structure and the stringers keep the shape. As in all structures, the areas around
openings such as doors, windows and hatches must be especially strengthened.
4-What are the most frequently used materials in a monocoque or semi-monocoque structure?
A)Aluminium or magnesium alloy.
B)Steel.
C)Wood.
D)Composite fibers.
Initially, aircraft structures consisted of wooden frames over which were affixed panels of fabric and plywood.
As aircraft weight, manoeuvrability and speeds changed and aircraft structural loading increased, wood was
replaced by light weight metal and the skin eventually became, at least on some aircraft, part of the load bearing
structure. Pure aluminium was initially used but, although corrosion resistant, the metal lacks strength, has a low
melting point and is difficult to work. The metal developed, in the fullness of time, to an aluminium alloy
sandwich known as duralumin that also contains other alloys such as copper, manganese and magnesium. The
alloy is lightweight and of high strength. Other alloys, for example titanium, are for specialist applications;
particularly, where very high-speed aircraft are concerned and where high strength in the presence of high
temperatures is required. The search for lighter and stronger materials is ongoing. Most materials have a specific
use and are resistant to particular forms of stress. Materials can be welded, bolted, screwed or bonded together
(special glue and/ or heat process). The materials used in semi-monocoque construction are principally metal,
with high strength aluminium alloy being the commonest, especially in smaller aircraft. In larger aircraft steel
and titanium alloys are often used for major load-bearing components. Secondary and non load-bearing
components are increasingly made from fibreglass, kevlar, graphite-based compounds and composite materials.
Cabin floors, for example, are often made from aluminium and fibreglass honeycomb sandwiched between
aluminium sheeting.
5-In flight, a cantilever wing of an airplane containing fuel undergoes vertical loads which produce a
bending mo-moment:
A) highest at the wing root.
B) equal to the zero fuel weight multiplied by the span.
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SYSTEM,POWERPLANT&ELECTRICS
C) equal to half the weight of the aircraft multiplied by the semi span.
D)lowest at the wing root.
Cantilever wings are wings without any external support (without any bracing struts or wires). They are attached
to the fuselage only at the wing root. Wings of an aeroplane in flight are subject to the bending stress. As the
wings develop lift they have a tendency to bend upwards. Since they are attached to the fuselage on their
inboard end, there is no possibility of bending at this end. Instead, the wing-tips which are free to move
vertically as they do not have, any attachment holding them in a fixed position do bend upward as a result of lift.
This upward-bending force coupled together with the very long arm represented by the length of the wing
creates a very high bending force at the wing root. It is therefore extremely important to limit these bending
loads within the design envelope of the aeroplane.
6-On a non-stressed skin type wing, the wing structure elements which take up the vertical bending
moments Mx are:
A)spars
B)ribs
C)skin
D) stringers
(Refer to figures 021-E49 and 021-E50)
The wing spars of modern aircraft are made of metal, formed into a beam either by extrusion or by built-up
construction. The wing ribs are the formers that maintain the aerofoil section of the wing and have to be strong
enough to resist the torsional stress tending to twist the wing. These twisting forces are much less than the
upward bending loads (carried mainly by the spars) and the ribs are there-fore of relatively light construction.
7-In flight the wing of an aircraft containing fuel is subjected to vertical loads that produce a bending
moment which is:
A)equal to half the weight of the aircraft multiplied by the semi span.
B)equal to the zero-fuel weight multiplied by the span.
C) highest at the wing root.
D) lowest at the wing root.
For explanation refer to question #5.
8-The advantage of mounting the tailplane on top of the vertical stabilizer is:
A)to withdraw it from the influence of wing turbulence.
B)to decrease fuel consumption by creating a tail heavy situation.
C)to have greater effectiveness at high speed.
D) that it does not require a de-icing system.
In a "T-tail" configuration, where the horizontal stabilizer is mounted on top of the vertical stabilizer, the
horizontal
tailplane surfaces are kept well out of the airflow behind the wing (wing down-wash). This results in a smoother
airflow ,more predictable design characteristics, and better pitch control. This is especially important for
airplanes operating at low speed, where smooth airflow is required for maintaining positive control. In addition,
rear mounting of the engines is a very good reason why the tail plane is put on top of the fin .Rear mounting the
engines gives a "clean" wing .
However, one undesirable property of the "T-tail" is the possibility of a "super stall" condition. Basically, if the
wing stalls, the turbulent airflow from the wing envelops the tailplane and nose down elevator is ineffective.
9-What is the reason for putting the horizontal stabiliser on top of the fin?
A)To be more efficient at high speed.
B)No need for anti-icing .
C)Create a pitch up by making the aeroplane tail heavy.
D)To be out of the way of the wing down wash.
For explanation refer to question #8 on this page.
10-A wing structure consists primarily of:
A) A front and rear main spar.
B) a front and rear main spar with ribs and stringers.
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C) ribs and stringers only.
D) ribs only to give optimum and cost effective simple construction.
(Refer to figures 021-E49 and 021-E50)
The bending stresses to which the wing is subjected may be carried by one or more transverse beams, known as
spars, or by building the wing as a box structure in which almost all the stresses are carried by the external skin.
The latter is known as stressed-skin construction. Torsional stress, due largely to the effects of movement of the
centre of pressure, is taken up by chord-wise ribs that give greater rigidity. The ribs also provide the aerofoil
shape. Stringers run spanwise, between the spars, to provide attachment points for the skin and to provide
additional span-wise rigidity.
11-The empennage consists of the:
A)horizontal stabilizer only.
B)horizontal and vertical stabilizer.
C)vertical stabilizer only.
D)tailplane only.
Empennage is a term used to describe the tail portion of an aircraft. The empennage is also known as the tail or
tail assembly. The empennage gives stability to the aircraft and controls the night dynamics of pitch and yaw.
Structurally, the empennage consists of the entire tail assembly, including the night tailplane and the part of the
fuselage to which these are attached. The front section of the tailplane is called the horizontal stabilizer. The rear
section is called the elevator and is usually hinged to the horizontal stabilizer. The elevator is a movable airfoil
that controls changes in pitch, the up-and-down motion of the aircraft's nose.
The vertical tail structure (or fin) has a fixed front section called the vertical stabilizer, used to restrict side-toside motion of the aircraft (yawing). The rear section of the vertical fin is the rudder, a movable airfoil that is
used to turn the aircraft in combination with the ailerons.
Note: the aircraft's "black box" (cockpit voice recorder and flight data recorder) are of ten located in the
empennage, because the aft of the aircraft better survives the destructive forces (in most crash scenarios).
12-The two deformation modes that cause wing flutter are:
A)torsion and shearing.
B)torsion and bending.
C)bending and elongation.
D)shearing and elongation.
(Refer to figure 021-E51)
Flutter is an aerodynamic phenomenon that can occur at any speed but usually occurs at the higher speed end of
the operating envelope. Flutter is cyclical movement of a control surface that starts because of some disturbance,
a gust for example, the effect of which can be divergent in character. It is a form of structural vibration in which
the surface twists. Flutter creates torsion and bending moments. The bending is caused by the aerodynamic lift
forces acting on the wing from the root to the wing tip (bending is greatest at the wing root). Wings are subject
to torsional forces for example at the wing tip sections -caused by the movement of the ailerons. If the
aerodynamic flutter is uncorrected the control surface could detach from its structure and major damage will
occur. The aircraft speed envelope is often restricted because of this and VMO will be limited to the just-before
flutter value. The remedy for flutter is to do with mass balance and to this end, the weight of a control surface is
biased towards the hinge line. Often, balance weights are fitted to the control surface, ahead of the hinge line.
13-Which part of a wing, other than stressed skin construction, takes upward loads?
A)Ribs
B)Skin
C)Spars
D)Webs
For explanation refer to question #6.
14-The torsion box of a modern aircraft wing structure consists of:
A)spars, skin, frames and stringers.
B)spars, skin, frames and ribs.
C)spars, skin, longerons and ribs.
D)spars, skin, stringers and ribs.
(Refer to figures 021-E49 and 021-E50)
A torsion box consists of two skins applied to a core material, usually a grid or spars, stringers and ribs. The
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torsion box functions as a beam, but is considerably lighter than a solid beam of the same size without losing
much strength. On a wing, the torsion box is typically formed by the front spar and the rear spar with ribs in
between these two and upper and lower skin with stringers covering the structure as a whole.
15-How can wing bending moments be reduced in flight?
A)By using aileron up float and keeping the centre section fuel tanks full for as long as possible,
B)By having tail-mounted engines and using aileron down float.
C)By using aileron up float and using the fuel in the wings last.
D)By having wing-mounted engines and using the wing fuel first.
16-When do you say that an aircraft has a cantilever wing?
A)When the wing is attached to the fuselage at or near one end only.
B)When the wing planform is other than rectangular.
C)When the wing is supported by braces or strut, linked to the fuselage.
D)When the wing is attached to the lower part of the fuselage.
In some aircraft, where the wings are of a relatively light construction, the loads are in part taken by bracing
struts or wires for example see-the bracing struts on a Cessna 152 or a 172. This type of wing design is called
"braced". However, in most cases, the wings are designed on what is known as the "cantilever" principle, where
structural rigidity is provided entirely by the wing structural members, without any external support.
17-Stall fences mounted on an aircraft wing are used:
A)to increase the maximum speed of the aircraft.
B)to avoid the formation of shock waves.
C)to increase the lift coefficient in landing.
D)to prevent the tendency of the outer portion of the wing to stall first .
Wing stall-fences are flat metal plates fixed to the upper surfaces (and often wrapping around the leading edge)
parallel to the airflow. They are often seen on swept-wing aircraft. They obstruct spanwise airflow along the
wing, and prevent the entire wing from stalling at once. They prevent the wing tip's tendency (on a swept wing)
to stalling before the wing root. Wing fences are often used in addition to or instead of slats.
As a swept-wing aircraft slows toward the stall speed of the wing, the angle of the leading edge forces some of
the airflow sidewise, toward the wing tip. This process is progressive, airflow near the middle of the wing is
affected not only by the leading edge angle, but also the spanwise airflow from the wing root. At the wing tip
the airflow can end up being almost all spanwise, as opposed to front-to-back over the wing, meaning that the
effective airspeed drops well below the stall. Because the geometry of swept wings typically places the wing
tips of an aircraft's aft of its center of gravity, lift generated at the wing tips tends to create a nose-down pitching
moment. When the wing tips stall, both the lift and the associated nose-down pitching moment rapidly diminish.
The loss of the nose-down pitching moment leaves the previously balanced aircraft with a net nose up pitching
moment. This forces the nose of the aircraft up, increasing the angle of attack and leading to stall over a greater
portion of the wing. The result is a rapid and powerful pitch-up followed by a complete stall, a difficult situation
for a pilot to recover from. Wing fences delay, or eliminate, this effect by preventing the spanwise flow from
moving too far along the wing and gaining speed. When meeting the fence, the air is directed back over the
wing surface
18-What mission does the strut have, often observed between the fuselage and the wing, on small high
wing sir-craft?
A)Serves as a facilitating access to the upper side of the wing .
B)Supporting the wing while the aircraft is on ground only.
C)Supporting the wing while the aircraft is on ground and when airborne.
D)Supporting the wing if the airplane should become inverted.
For explanation refer to question 16.
19-Wings without exterior support are called:
A)mono-lever
B)monocoque
C)cantilever
D)sweepback
For explanation refer to question 16.
20-On modern transport aircraft, cockpit windows are protected against icing by:
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A) vinyl coating.
B) electric heating.
C) anti-icing fluid.
D) rain repellent system
The use of electrical heating elements built into flight deck wind screens is widely used in modern transport
aircraft. A conductive film (typically a gold film) is applied to the inner surface of the outer glass panel to
permit electrical heating for anti-icing and de-fogging .The use of electrical heating elements built in to flight
deck wind-screens also increases windshield resistance against bird-strikes and/or hail impact, because the
heated glass is structurally stronger than unheated. If the window heating fails the flight manual may state a
pressurisation limit and/or speed limit below a specified speed, pressurisation and heating loads.
21-Torque links on an undercarriage come under most stress when:
A)during crosswind landings.
B)during pushback.
C)making tight turns when taxiing.
D)after takeoff.
When the aircraft is taxiing on the ground and enters a turn only the nose-wheel is steered. The main wheels are
prevented from castoring by the torque links. Therefore, as the aircraft turns on the ground the main wheels
would tend to turn as well, but are prevented from doing so by the torque links , which results in loads being
applied the torque links. These are highest especially when making tight turns.
22-The part of the flight that will cause the highest loads the torsion link in a bogie gear is:
A) braking with an inoperative anti-skid system
B) taxiing with a small turning radius
C)touch down with crosswind.
D) gear down selection
(Refer to figure 021-E09) A bogie is a beam to which 4 (or more) wheels are attached it is typically used on
large transport aeroplanes used for long-haul operations such as' B747 or A330. The unit is attached to, and
pivots around, the oleo leg. The unit carries all hydraulic and electrical components that provide power and
warning functions to the relevant equipment. Examples are: wheel brakes and anti-skid units; The temperature
indications; hydraulic brake system components stall warning systems; cabin conditioning facilities and some
deicing facilities On bogie-type units there is a certain distance between the front and rear wheel axles -they can
have a relatively large "foot-print(e.g. B777 has 3 sets of wheels in a row). This arrangement can cause
excessive loads in some situations, such as during turning on the ground with relatively small radius of turn
during taxi, be cause the bogie arrangement causes a crab. Typically, such aircraft have rather a limited turning
capabilities = large turning radius. To minimize these loads some installations feature a turning (steering)
capability of the individual bogie axles
23-The Maximum Zero Fuel Weight:
1)is a limitation set by regulation.
2)is designed for a maximum load factor.
3)is due to the maximum bending moment at wing root.
4)requires to empty external tanks first.
5)requires to empty internal tanks first.
The correct combination of true statements is:
A) 2,5
B) 1,2,3
C) 2,4
D) 1,3,5
If the fuselage weight was to increase beyond the maximum safe value, the force acting between the landing
gear legs(aeroplane on the ground) would increase and eventually cause very large and unacceptable loads at the
wing roots. To prevent such an event, the weight of the aircraft is limited to a maximum zero fuel mass
(MZFM). one of the most important aircraft limitations. The maximum zero-fuel mass (MZFM) is defined as
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the maximum permissible mass of an aeroplane with no usable fuel. If an aeroplane were to be airborne with no
fuel in the wings (e.g. only with fuel in the centre tank located in the fuselage), the upward bending stress on the
wing structure could exceed its design limitations. Since there will always be some fuel in the wings (counterbalancing the upward bending force that the wings are subject to), then these limitations will not be exceeded. In
a heavy landing for example, not only is the landing gear likely to sustain damage but the wing spar attachment
points are likely to sustain damage due to the large forces as the wings move rapidly downwards. In addition,
the fuselage might be subjected to excessive loading stress. The MZFM is a limitation imposed by the
manufacturer and is stated in the operating manual. It also takes into account the maximum load factors likely to
be experienced by the aeroplane in flight.
24. MZFM is:
A) the recommended maximum mass of the aircraft with out usable fuel.
B)the total maximum permissible mass of the aircraft without usable
C) the actual maximum mass of the aircraft without us able fuel.
D) the minimum allowable mass of the aircraft without usable fuel.
For explanation refer to question #23.
25-(Refer to figure 021-01)
If piston A has an area of 2 cm2 and piston B has an area of 10 Cm2, when piston B moves down by 5 cm,
how far will piston A have moved?
A) 25 cm
B) 10 cm
C) 5 cm
D) 0.5 cm
Hydraulic fluid is incompressible -therefore in a closed circuit hydraulic system the Input Force x Input
Distance (travelled by the piston) '" Output Force x Output Distance (travelled by the piston). The general
principle used in aircraft hydraulic systems is the fact that a small input force exerted on a piston with a small
area produces a greater output force from a piston with a larger area. The volume displaced by the force on one
side must be compensated for on the other side. We can use the formula: Area (A) x distance (A) = Area (B) x
Distance (B). When we enter the numbers we get: 2 x? = 10 x 5 .... => 10 x 5 ÷ 2 => 25 cm.
26-Hydraulic power is a function of:
A)pump RPM only.
B)system pressure and volume flow.
C)system pressure and tank capacity.
D)pump size and volume flow.
Thanks to Mr. Pascal we know that if a force is applied to a confined fluid the resulting pressure is transmitted
equally in all directions. Providing that the fluid is not compressed by the action of the applied force, then the
pressure transmitted in each and every direction is undiminished by distance .The amount of force a hydraulic
system can provide is related to the pressure produced and the area on which the force is acting. The relationship
between force, pressure and area are related as follows and transposing where necessary:
•Force= Pressure x Area
•Pressure = Force ÷ Area
•Area = Force÷ Pressure
Another relationship is that which is to do with the distance travelled by the piston, the volume of the liquid
displaced and the area of the piston. The appropriate transposed formulae are given below and it can be
assumed, for example, that area is the area of a piston, volume is the volume of the liquid displaced by piston
movement and distance is the distance the piston moves:
•Volume = Area x Distance
•Distance = Volume ÷ Area
•Area = Volume ÷ Distance Relationship between Work, Power and Time in hydromechanics:
Definition / Formula
Units
Work = Force x Distance
Pounds x feet = foot pounds
Newton x metres = Newton metres
Power= work done : Time
Foot pounds per second
Newton metre per second
Volume Distance =
Square inches x inches = inches3
Area x Distance
Square metres x metres = metres3
Flow rate = Volume : Time
Cubic inches per second
Cubic metres per second
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SYSTEM,POWERPLANT&ELECTRICS
Gallons or litres per minute
Note: Work done is Force x Distance and is equal to Pressure x Volume. Also, Power is Pressure x Flow rate. A
powerful pump will provide a high pressure with a high flow rate, say, 3.000 PSI at 25 gpm. A powerful
actuator will operate as fast as it needs to for safe operation of the aircraft. This is to reduce required flow rates
and reduce component size and weight. For example, flaps move slowly but flying controls move rapidly.
27-(Refer to figure 021-03)
In the hydraulic press schematically shown, what balancing force would be acting on the right hand side?
A) 20 N
B) 1 N
C) 4 N
D) 100 N
Hydraulic fluid is incompressible -therefore in a closed circuit hydraulic system the pressure remains the same.
In order to calculate the Force on the right side of the press, we need to know the formula "Force = Pressure x
2
2
Area". Using this formula we can find out that the system pressure is 2N/cm (20 N ÷ 10 CM ). Using this
information we can easily solve the problem on the right side. Force = Pressure x Area => 2 x 2 = 4 N. We can
also solve this question without using any formula: the area of the piston on the left is 5x larger than the area of
the piston on the right. Therefore the output force resulting on the right side will be 5x less than the input force
on the left side .
28-(Refer to figure 021-02)
In the diagram (not to scale), the balancing force required on the right hand side is:
A)1 N
B)1.000 N
C)20 N
D)100 N
Hydraulic fluid is incompressible -therefore in a closed circuit hydraulic system the pressure remains the same.
In order to calculate the Force on the right side of the press, we need to know the formula "Force == Pressure x
2
2
Area". Using this formula we can find out that the system pressure is 200 N/m (10 N ÷ 0,05 m ). Using this
information we can easily solve the problem on the right side. Force =: Pressure x Area => 200 x 0,5 == 100 N.
29-The viscosity of a hydraulic fluid should be:
A)the highest to minimize power consumption and resistance to flow.
B)the lowest to provide excellent lubrication properties.
C)the lowest to minimize power consumption and resistance to flow.
D)the highest to provide excellent lubrication properties.
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional
stress. In other words, it is the tendency of a fluid or gas to resist flow .In everyday terms (and for fluids only),
viscosity is "thickness". Thus, water is "thin", having a lower viscosity ,while honey or oil is "thick" having a
higher viscosity. Water will flow a lot easier than honey or oil. The viscosity of a hydraulic fluid must be
minimum so as to reduce the internal friction of the fluid -it must easily flow through the entire hydraulic system
pipes, hoses and the individual components.
30-Viscosity is:
A)the temperature dependence of an oil.
B)the tendency of a liquid or gas to resist flow.
C)the pressure resistance of an oil.
D)the flow velocity inside the oil lines.
For explanation refer to question #29.
31-Relationships between the force. pressure and area is:
A)force = pressure x area
B)pressure = force x area
C)pressure = area x distance
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SYSTEM,POWERPLANT&ELECTRICS
D)force = volume / area
For explanation refer to question #26.
32-Pascal's law states that:
A) for every action there is an opposite and equal reaction.
B) the volume of a Liquid is constant, regardless of pressure and temperature.
C) the force produced by a fluid depends only on the amount of fluid.
D) pressure in an enclosed container is transmitted equally and undiminished to all parts of
the container and acts at right angles to the enclosing walls.
One of the fundamental principles of hydraulic transmission of pressure is stated by a physicist called Pascal
(Pascal's Law): "The pressure in an enclosed vessel acts at right angles to the walls enclosing the fluid, and that
the pressure is transmitted equally and undiminished to all parts of the vessel". In simple terms, if a pressure is
produced in a pump, which is then supplied via pipelines to a service, that pressure is sensed immediately
throughout that system.
33-The tanks of a hydraulic system are pressurized:
A) in flight only.
B) by bleed air coming from the turbine-engine.
C) by the air conditioning system.
D) by an auxiliary system.
For aircraft that fly at high altitude where the atmospheric pressure is correspondingly low, the hydraulic fluid
reservoirs are usually pressurized, typically to between 10 psi and 30 psi depending on the manufacturer.
Pressurizing the hydraulic fluid reservoir is typically done using a filtered bleed air from the turbine engine
compressor stage and the desired pressure is controlled by a pressure relief valve. Pressurization of the
reservoirs ensures that the system receives a constant supply of fluid already at a certain positive pressure before
entering the hydraulic pump and that hydraulic pump cavitation is avoided. Cavitation (bubbles of gas or air
enter the supply of a hydraulic pump causing its stall and decrease in pressure output) occurs (typically on the
inlet or suction side of a hydraulic pump) when the fluid pressure is so low that cavities form due to entrapped
gas expansion.
34-The function of the selector valve is to:
A) discharge some hydraulic fluid if the system pressure is too high.
B) automatically activate the hydraulic system.
C) select the system to which the hydraulic pump should supply pressure.
D) communicate system pressure to either side of an actuator.
(Refer to figure 021-E25)
In a complex hydraulic system, control valves or selector valves are needed to control fluid flow. Selector
valves are used to control the path of the hydraulic fluid operating a hydraulic. component. See the diagram of a
simple hydraulic system with a selector valve and how it operates a hydraulic component -based on the direction
how the valve is positioned the system operates the piston either up or down.
35-In a hydraulic system, the reservoir is pressurized in order to:
A)reduce fluid combustibility.
B)seal the system.
C)keep the hydraulic fluid at optimum temperature.
D)prevent pump cavitation.
Pressurizing the hydraulic fluid reservoir (typically using the bleed air from the turbine engine compressor
stage) ensures that the system receives a constant supply of fluid already at a certain pressure before entering the
hydraulic pump and that hydraulic pump cavitation is avoided (typical pressurization values of the reservoirs are
between 5 and 15 psi). Cavitation(bubbles of gas or air enter the supply of a hydraulic pump
causing its stall and decrease in pressure output) occurs (typically on the inlet or suction side of a hydraulic
pump) when the fluid pressure is so low that cavities form due to entrapped gas expansion. Foaming can be
prevalent when the outside air pressure falls to a low level. After entering the reservoir, the fluid will be deaerated.
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SYSTEM,POWERPLANT&ELECTRICS
36-The hydraulic fluid, entering the hydraulic pump, is slightly pressurized to:
A)prevent vapour locking.
B)ensure sufficient pump output.
C)prevent overheating of the pump.
D)prevent cavitation in the pump.
For explanation refer to question #35.
37-The component that transforms the hydraulic pressure into a linear motion is called:
A)an accumulator.
B)a hydraulic pump.
C)an actuator or jack.
D)a pressure regulator.
The function of a hydraulic actuator (jack) is the reverse of that of a pump where the actuator converts hydraulic
power into mechanical 'energy. Hydraulically operated actuators can be linear or rotary they can be used in
many applications. The linear actuator operates in a straight line; whereas, the rotary machine produces a
turning moment or torque. The former type is designed to operate directly on to the service required; the rotary
actuator operates components such as screw jacks for tail planes and flaps for example. The actuators can be
also divided into single-acting and double acting
• single acting jack = moves under hydraulic pressure in one direction, and in the other direction under the
influence of a non hydraulic force, such as a spring. A common application of the single acting jack is door
locks.
• double acting jack = the movement in either direction is due to hydraulic pressure, and is controlled by means
of a selector valve. The jack may be compensated (balanced) or non-compensated. In the first case the area on
either side of the piston is identical, since there is a piston rod or ram on both sides of the piston. In the second
case the area on the side of the piston which is remote from the rod or ram is greater than on the other side. A
non-compensated system is normally used for landing gear and flap systems, where a greater force is needed in
raising the gear or extending the flaps than in lowering the gear or retracting the flaps.
38-Synthetic hydraulic fluids:
A)do not require special care.
B)cause high fire risk.
C) are irritating to eyes and skin.
D) are irritating to eyes and skin and cause high fire risk.
39-The low pressure switch of a hydraulic circuit sets off an alarm if:
A)the pump output pressure is insufficient.
B)the reservoir level is at the normal operation limit.
C)there is a leak in the reservoir return line.
D)the pump power accumulator is deflated.
40-In a modern transport aircraft what type of hydraulic fluid is typically used?
A) Synthetic.
B) Mineral.
C)Mineral/alcohol.
D)Vegetable..
41-A shuttle valve is used to:
A)restrict the rate of operation of a system.
B)select the most suitable system pressure.
C)allow two supplies to be available to a service.
D)to allow a constant volume pump to idle.
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SYSTEM,POWERPLANT&ELECTRICS
42-Internal leakage in a hydraulic system will cause:
A)fluid loss.
B)a decreased fluid temperature.
C)an increased fluid temperature.
D)an increased fluid pressure.
43-Hydraulic fluids of synthetic origin are:
A)pink
B)purple
C)blue
D)red
44-Hydraulic fluids must have the following characteristics:
1)thermal stability
2)low emulsifying characteristics
3)corrosion resistance
4)good resistance to combustion
5)high compressibility
6)high volatility
7)high viscosity
The combination regrouping all the correct statements is:
A)1,2,5,7
B)1,2,3,4
C)2, 3,4,5
D)1,3,4,6
45. Large transport aeroplane hydraulic systems usually operate with a system pressure of
approximately:
A)4.000 psi
B)3.000 psi
C)2.000 psi
D)1.000 psi
46-What colour is the hydraulic liquid in a modern jet-powered aircraft'?
A)Purple
B)Red
C)Yellow
D)Pink
47-An automatic cut-out valve is used in a:
A)fixed volume pressure control system.
B)constant pressure system.
C)neither of these.
D)both of these.
(Refer to figure 021-E81)
In case of a constant delivery system (fixed volume type pump= a spur gear type) the pump cannot regulate the
system pressure. A constant pressure is maintained by an automatic cut-out valve which divides fluid between
the system and scavenge lines.
48-An accumulator in a hydraulic system will:
A) reduce fluid temperature and pressure.
B) reduce fluid temperature only.
C)store fluid under pressure.
D)increase pressure surges within the system.
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SYSTEM,POWERPLANT&ELECTRICS
49-A pressure regulator is used in a hydraulic system:
A)in conjunction with a constant delivery type pump.
B)in conjunction with a variable delivery type pump.
C)to ensure that an equal pressure flow is delivered to critical components such as servo actuators.
D)as an interface between the system and the cockpit indicators.
(Refer to figure 021-E81)
In the constant delivery system the pump, known as a constant displacement pump, is operating continuously
and is driven by the engine. This type of pump will move a given amount of fluid for each revolution and is used
when a fairly large volume of fluid needs to be moved at a relatively low pressure. It means, though, that once
the required pressure has been attained a cut-out, or pressure relief valve, will be required to prevent any further
increase in pressure. A hydraulic accumulator will normally be found in any system using a constant
displacement pump.
50-Filters in hydraulic systems often incorporate pop out indicators to:
A)warn of a hydraulic system overheat.
B)indicate that the filter is clogged and unfiltered oil is passing around the system.
C)warn of an impending by-pass situation.
D)indicate that the filter is due maintenance.
The tiny particles of metal, dust and seal material that accumulate in a hydraulic system would cause significant
damage if allowed to circulate freely. To prevent this, filters are installed in the pressure and return lines. A
hydraulic filter consists of a renewable "element", usually made of cellulose material, situated in a bowl-shaped
container. Hydraulic fluid enters the bowl and must pass through the cylindrical filter element in order to reach
the hydraulic system. Return filters normally incorporate a spring-loaded by-pass valve. As the element starts to
become clogged the pressure differential across the filter starts to increase and a pop-out indicator operates (or a
warning light in the cockpit illuminates) indicating an impending filter by-pass-when this happens, the filter is
still able to filter the fluid (it is not completely clogged soon .When the differential reaches a pre-set critical
valves opens and allows unfiltered fluid to pass direct to the hydraulic system ( filter is completely blocked).
51-Filtration in a hydraulic system is usually ensured by:
A)a filter on the return line only.
B)a filter in the pressure line only.
C)filters in both the pressure and return lines.
D)the use of sealed containers only during replenishment.
For explanation refer to question #50.
52-In hydraulic systems of large modern transport category aircraft the fluids used are:
A)vegetable oil.
B)mineral oil.
C)synthetic oil.
D)water and glycol.
53-One of the functions of an accumulator in a hydraulic system is:
A)to act as the primary fluid storage.
B)to damp pressure surges in the system.
C)to maintain constant system pressure.
D)to act as a pressure relief valve.
54-The color of a fresh synthetic hydraulic fluid is:
A)purple
B)pink
C)blue
D)red
55-The purpose of an accumulator in a hydraulic system is:
A)to eliminate the fluid flow variations.
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SYSTEM,POWERPLANT&ELECTRICS
B)to damp the fluid pressure variations.
C)to bypass the pumps in the hydraulic system.
D)to enable the starting of hydraulic devices.
56-The purpose of an accumulator in a hydraulic system is to:
A)act as a primary fluid storage.
B)store energy.
C)cool the fluid.
D)even-out the fluid temperature and pressure fluctuations.
57-The purpose of a hydraulic fuse is to:
A)reduce pressure to the braking system.
B)restrict return fluid from the anti-skid unit.
C)allow the parking brake to remain on.
D)prevent leakage if the hydraulic line breaks.
58-What happens with the hydraulic fluid level (in the reservoir) as you energize the system?
A)Stays the same.
B)Increases and then stays the same.
C)Decreases and then fluctuates.
D)Increases initially and then returns.
59-What is the normal pressure in a main hydraulic system of a modern turbojet aircraft?
A)1.000 psi
B)1.500 psi
C)3.000 psi
D)4.000 psi
For explanation refer to question #45.
60-What is the colour of synthetic hydraulic oil?
A) Purple
B) Red
C) Orange
D) Pink
61-What component converts hydraulic pressure into linear motion?
A)Accumulator
B)Hydraulic pump
C)Reservoir
D)Jack/actuator
For explanation refer to question #37.
62-In the event of the normal hydraulic pressure regulation system failure, the following component is
fitted in a typical hydraulic system:
A)an accumulator.
B)a pressure relief valve.
C)an automatic cut out valve.
D)a non-return valve.
63-The purpose of a hydraulic fuse is to:
A)allow the parking brake to remain on overnight if required.
B)allow a reduced pressure to the wheel brake system to avoid locking the wheels.
C)prevent over-pressurising the reservoir as altitude increases.
D)prevent loss of system fluid if the pipeline to a brake unit should rupture.
64-A "hydraulic fuse" will:
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SYSTEM,POWERPLANT&ELECTRICS
A)in case of a too high pressure in the system, open up and relieve the pressure by dumping the fluid overboard
or back to the reservoir.
B)detect a sufficient pressure drop across itself, or a specified volume of fluid passing through itself, and then
shut off the flow of fluid to prevent the system of emptying itself.
C)activate the actuators after the pilot has used the emergency hand pump.
D)direct the hydraulic fluid to the proper actuator according to the power pack and sequence valve.
65-The oil reservoir in a hydraulic system has the purpose to serve as:
A) the compartment that stores the fluid.
B) a point at which the fluid can purge itself of air.
C) an expansion chamber to provide a space for the fluid when its volume increases due to a high temperature.
D) all of the above alternatives are correct.
66-The reason for the pressure accumulator in the hydraulic system is:
A) it works as a backup fluid reservoir, which increases the capacity of the system.
B)it serves as a water reservoir that collects water from the hydraulic fluid.
C)the accumulator serves as an internal shock absorber for the hydraulic system.
D)the accumulator compensates for fluid-volume variation due to changes in temperature.
67-What is the purpose of a "relief valve" in the hydraulic system?
A)Make sure that the pressure in the system exceeds a certain minimum pressure.
B)Make sure that the pressure does not exceed the max. permitted pressure in the system.
C)To "even out" the pressure in the system.
D)Make sure that the emergency hand pump will produce enough pressure when used.
68-The purpose of pressurizing some hydraulic reservoirs is to:
A)provide emergency pressure if the pump should fail.
B)provide a positive pressure to the return line.
C)provide a positive feed to the main pump.
D)prevent cavitation at the pressure filter .
69-The illumination of the green landing gear light indicates that the landing gear is:
A)locked-down and its door is locked.
B)in the required position.
C)locked-down.
D)not in the required position.
(Refer to figure 021-E10)
Landing gear position is displayed by means of one indicator for each gear (nose, left main, right main) and
often takes the form of three lights which illuminate green when the gears are down , and locked in the down
position. Whilst the gear is traveling from UP to DOWN, or vice versa, a red light illuminates to indicate "gear
unlocked" or "gear in transfer ".This sometimes takes the form of a flashing red light in the gear operating
handle. When the gear is locked up, all lights are extinguished. The red light also indicates a disagreement in the
landing gear lever/selector position and the position of the gear == e.g. when the gear is not down and locked
while gear lever in the down position, the associated gear red light will also be showing. Note: typically there
are no cockpit indications relating to the position of the gear doors.
70-A main landing gear is said to be "locked down" when:
A) the actuating cylinder is at the end of its travel.
B) the corresponding indicator lamp is amber.
C)the strut is locked by an overcentre mechanism.
D)it is in the down position.
When the landing gear lever is selected DOWN, the main selector valve signals the doors to open. When the
doors are fully open, they operate a selector, which diverts hydraulic fluid to the main jack, which then extends
the landing gear. When in the fully down position, the down-lock automatically engages under spring pressure
and diverts fluid back to the main door jacks. The doors close. The landing gear is considered to be fully down
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SYSTEM,POWERPLANT&ELECTRICS
and locked once this overcentre locking mechanism engages and locks the gear in the down position, preventing
an inadvertent gear collapse on touchdown. Both the landing gear up locks and down locks are usually provided.
The locks are engaged by spring force and broken during retraction/extension by hydraulic pressure.
71-A red or an amber light on an undercarriage position indicator signifies:
A)at least one wheel is in the traveling or unlocked condition.
B)all wheels are up and locked.
C)all wheels are down and locked.
D)the landing has been selected down using the emergency extension system.
For explanation refer to question #69.
72-Overcentre mechanisms In landing gear systems are used to:
A)lock the landing gear in the up and/or down positions.
B)lock the landing gear in the up position only.
C)ensure that the nose-wheel does not exceed the maximum steering arc.
D)ensure the nose-wheel is positioned fore and aft prior to retraction.
For explanation refer o question 70
73-The damping element In a landing gear shock absorber used on large aircraft is:
A)oil
B)nitrogen
C)oxygen
D)springs
74The pilot may be prevented from retracting the landing gear whilst the aircraft is on the ground by:
A)a pneumatic interlock which disables the hydraulic up selector.
B)a guard on the selector switch which cannot be moved until the aircraft is airborne.
C)any attempt to select the landing gear up will result in a flashing warning light and a loud horn.
D) the electrical control system being routed through the weight on wheels switch
75-The systems used for emergency extension of landing systems may comprise of:
1)compressed CO2
2)compressed nitrogen
3)Compressed oxygen
)Auxiliary hydraulic system
5) freefall
The combination regrouping all the correct statements is:
A)1,3,4
B)1,2,5
C)2,3,4
D)2,4,5
76-VLE is the maxi mum:
A)speed authorized in flight.
B)speed at which the landing gear can be operated with full safety.
C)speed with flaps extended in a given position.
D)flight speed with landing gear down.
Where the landing gear is retractable it is typically selected "UP" as soon as a positive rate of climb is
established
following lift-off. There are typically 2 limiting speeds for the landing gear -exceeding these speeds could
subject the gear components (especially the landing gear bay doors and operating mechanisms) to excessive
aerodynamic forces that could result in structural damage of the gear and/ or its operating mechanisms.
VLO = Maximum landing gear operating speed. This is the maximum speed at which it is safe to extend or
retract the landing gear on a retractable gear aircraft. Often the VLO consists of 2 values -one being for the gear
retraction and a different max speed for the gear extension. This has to do mainly with the fact that often the
nose wheel retracts against the wind, thus an additional force that could damage the mechanism if the speed is
exceeded.
LE == Maximum landing gear extended speed. This is the maximum speed at which it is safe to fly a
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retractable gear aircraft with the landing gear extended.
77. VLO is the maximum:
A)speed at which the landing gear can be operated with full safety.
B)flight speed with landing gear down.
C)speed with flaps extended in a given position.
D)cruising speed not to be exceeded except in still air with caution.
For explanation 'refer to question #76.
78. An undercarriage leg is locked when:
A)amber light is on .
B)it is down.
C)mechanically locked by an over-centre mechanism.
D)actuating cylinder is at the end of its travel.
For explanation refer to question #70.
79. Green lights indicate the landing gear is:
A)locked down.
B)locked down and door locked.
C)unlocked but the doors are open.
D)up.
For explanation refer to question #69.
80. What do three green lights represent when the landing gear is selected down?
A)The gear is down.
B)The gear is down and locked.
C)The gear and doors are down and locked.
D)The gear is traveling between up and down.
81. To prevent the landing gear from collapsing when the aircraft is parked on the ground, following
device is used:
A)locking pins with flags.
B)hydraulic pressure.
C)chocks.
D)torque links.
82. If an aircraft is equipped with a fixed gear, which of the mentioned factors will differ from a
retractable landing gear?
A)Horizontal stability.
B)Induced drag .
C)Lift.
D) Parasite drag.
The reason for using retractable landing gear installations is the economy of the flight operation. Fixed landing
gear decreases the aerodynamic efficiency of the aircraft because it increases the parasite drag. The parasite drag
increases within creasing speed. Therefore, you will find a retractable landing gear installation typically on highspeed and high-altitude aircraft. For aircraft that operate at low speeds only(e.g. small single engine training
aircraft) it would be often rather uneconomical to install a retractable landing gear (compared to a fixed gear the
retractable gear is quite a complicated system).
83. The function of an accumulator in a hydraulic brake system is:
A)to supply a limited amount of brake energy in the event of failure of the hydraulic system normally supplying
the brakes.
B)to damp pressure fluctuations of the auto brake system.
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SYSTEM,POWERPLANT&ELECTRICS
C)to store the hydraulic energy recovered by the anti skid system to prevent wheel blocking.
D)to function as a buffer to assist the hydraulic system during heavy braking.
Accumulators in general are a common part of hydraulic system such as the brakes. Their function is to store
energy by using pressurized gas. Examples of accumulator uses are backup power for steering or brakes, or to
act as a shock
absorber for the hydraulic circuit. Typically their design is a tube with a floating piston -on one side of the
piston there is a charge of pressurized gas, and on the other side is the hydraulic fluid. Accumulators in the
brake system usually incorporate a pressure gauge on the gas pressure side. Under normal operation, when the
hydraulic pressure is supplied by the fluid the system hydraulic pressure is therefore displayed on a pressure
gauge (as the gas side is pressurized by the normally functioning hydraulic system). The brake accumulator
must have a sufficient pressure capacity in case of a hydraulic system failure to typically provide full 6 brake
applications .In the event of loss of main hydraulic supply the NRV (non return valve) prevents pressure loss
from the brake hydraulic sub-system to main system and the accumulator holds sufficient reserve pressure for a
number of brake applications(typically 6 to 10 brake applications). In many modern transport aircraft reserve
braking is also available by connecting an electric hydraulic pump to a reserve supply of fluid in the event of
loss of main hydraulic systems. In some
cases emergency brake operation employs pneumatic pressure.
84. The pressure for the braking system of a modern aircraft originates from:
A)bottled gas.
B)engine bleeds.
C)an accumulator.
D)the main hydraulic system.
85. The reason for fitting thermal plugs to aircraft wheels is that they:
A)prevent the brakes from overheating.
B)release air from the tire in case of overheating.
C)prevent heat transfer from the brake disks to the tires.
D)release air from the tire in case of overpressure.
86. Thermal plugs are installed in:
A)cabin windows.
B)cargo compartments.
C)wheel rims.
D)fire warning systems.
87. A tubeless tire is a tire:
1)Which requires solid or branched Wheels.
2)Whose valve can be sheared in sudden accelerations.
3)Whose mounting rim must be flawless.
4)Which requires no rim protection between rim flange and tire removing device.
5)Which does not burst In the event of a tire puncture.
6)Which eliminates internal friction between the tube and the tire.
The combination regrouping all the correct statements is:
A)1,5,6
B)3,4,5
C) 1,2,5
D) 2,3,6
88. The reason for fitting thermal plugs to aeroplane wheels is that they:
A)release air from the tire in the event of overpressure due to over-inflation.
B)prevent the brakes from overheating .
C)prevent heat transfer from the brake disks to the tires.
D)prevent tire burst.
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SYSTEM,POWERPLANT&ELECTRICS
89. To avoid the risk of tire burst from overheating there is:
A) a pressure relief valve situated in the filler valve.
B) a thermal plug that deflates the tire at a specific temperature.
C) the "Emergency Burst" function of the anti-skid system that adapts braking to the tire
temperature.
D) water injection triggered at a fixed temperature in order to lower tire temperature.
90. An under inflated tire on a dry runway:
A)increases wear on the crown.
B)increases wear on the shoulder.
C)decreases viscous aquaplaning speed.
D)will cause the tire temperature to reduce.
91. Where are thermal plugs fitted?
A) Wheel rim .
B) Cargo bay.
C)Fuel tank.
D)Oil tank.
92. For a JAR-25 aeroplane, spoilers are:
A)lower wing surface devices, their deflection is symmetrical or asymmetrical.
B)upper wing surface devices, their deflection is symmetrical or asymmetrical.
C) lower wing surface devices, their deflection is always asymmetrical.
D)upper wing surface devices, their deflection is always asymmetrical.
Spoilers are hinged to the wing upper surface (symmetrically on both wings) and, when extended, destroy some
of the lift generated. They can be used after touch down to prevent "floating" and to shorten the landing roll.
Their extension can be selected manually or automatically on landing after touchdown and wheel spin-up,
provided the lever is in the armed position, or for a rejected takeoff, automatically usually when reverse thrust is
selected above a particular speed (typically 60 kts). On the ground the spoilers extend symmetrically (on both
Wings) as well as in flight when they are used as a means to reduce the aircraft speed or to increase the rate of
descent.
Spoilers can also be used in flight in an asymmetrical manner to assist the ailerons in rolling the aircraft. In this
case the spoilers extend slightly on the "down-going" wing (to increase drag on this wing) while they stay
retracted on the up-going" Wing. This helps to counteract the effects of adverse yaw and to increase the rate of
roll. If the spoilers are used in the speed-brake mode (extended on both wings) and the pilot makes an input to
turn the airplane (roll) then the spoilers will retract almost to the stowed position on the "up-going" wing and
will again extend once the roll manoeuvre is completed to resume the speed-brake mode.
On most aeroplanes the spoilers are divided into two groups flight spoilers and ground spoilers. When used in
flight for the purpose of reducing speed and/or when assisting the ailerons in the roll control, only the flight
spoilers are used. When used on the ground to help in deceleration after landing both the flight and ground
spoilers are used. Greater degree of flight spoiler deflection is provided when used on the ground. For example
on a B737-300 there are 4 spoiler panels on each wing. The two inboard panels are used as flight spoilers and
the two outboard panels are used as ground spoilers.
93. The elevators of a conventional airplane are used to provide rotation about the:
A) longitudinal axis.
B) lateral axis.
C)directional axis.
D) vertical axis.
(Refer to figure 021-E01)
Elevators => provide pitch up/down control (around the lateral axis). Rudder => provides yaw to the left/right
(around the normal / vertical axis)
Ailerons => provide rolling to the left / right (around the longitudinal axis)
94. How do differential ailerons work?
A)Increase lift on down-going wing and decrease lift on up going wing.
B)Increase drag on up-going wing and decrease drag on down-going wing.
C)Equalise the drag on up -going and down-going wings.
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SYSTEM,POWERPLANT&ELECTRICS
D) Equalise the lift on up-going and down-going wings.
(Refer to figure 021-E07)
The ailerons, for roll control, are mounted on the outboard trailing edge of the wings -one moving upward to
decrease lift while the other one moving downward to increase lift. On most airplanes the ailerons are geared in
such a way that they have a different angular deflection downward and upward. The reason for this is to
overcome the secondary effect of rolling an aircraft -an adverse yaw. With differentially geared ailerons the upgoing aileron has a greater deflection than the down-going one. This causes an increased drag on the up-going
aileron (down-going wing) and thus counter-balancing the induced-drag created by the down-going aileron on
the other wing (up-going wing) => reducing the yawing effect.
95. The range of control surface movements is limited by:
A)leaving control cables a little stack.
B)tensioning control cables correctly.
C)defined limits is the Operations Manual.
D)providing control stops.
The function of the control stops is to limit the range of movement of the flight control surfaces -e.g. to avoid
overstress due to excessive loads. In other words it mechanically restricts the movement of the control surface to
within the correct control range. The primary control stops are physically located at the flight control surfaces
(or on the airframe adjacent to the control surface) -not on the control Wheel.
96. Over tensioned cables in a flight control system could result in:
A)no appreciable difference.
B)insufficient friction in the system.
C)excessive friction in the system.
D)restricted movement of control surfaces.
If a mechanically operated flight control system is fitted, the cables are tensioned to a correct pre-set value, to
compensate for thermal expansion. Increased temperature causes metal structures to expand. Both the cables as
well as the fuselage have a tendency to slightly expand under increased temperatures, but since the cables are
typically steel and the fuselage is an aluminium alloy, they expand differently. The fuselage has a tendency to
expand more than the steel cables ,therefore the tension in the cables increases. If this tension increase is
excessive, it can affect the cable system operation it might be difficult to operate the controls due to the
increased friction on the pulleys,
also resulting in excessive wear of the system components.
97. What is the purpose of inboard ailerons?
A)To reduce wing bending at high speed.
B)To reduce wing twist at high speed.
C)To reduce wing twist at low speed.
D)To reduce wing bending at low speed.
As the forces vary at different flight speeds or during turbulence, the wings must be able to flex to a certain
degree. It is important however that the wings, whilst able to flex up and down, do not twist when the ailerons
are used. For this reason typically two sets of ailerons are installed on each wing of a large transport airplane the outboard and the inboard aileron. At low speeds the outboard ailerons produce sufficient force for lateral
control, whereas at high speeds they would create excessive moments -large enough to cause possible structural
damage. Therefore, at low speeds both the outboard and inboard ailerons are used for roll control. Once the flaps
are retracted after takeoff and the aeroplane accelerates above a certain speed, the outboard ailerons become
locked in their neutral position and only the inboard ailerons are used (as they are mounted on a wing section
with a shorter lever arm to the aircraft CG as well as a more rigid wing in the inboard area). If roll spoilers are
fitted, they are also used during high-speed flight to assist the inboard ailerons. The reason for this is to avoid
excessive rolling moment that could be caused by the long lever arm between the CG position and the outboard
aileron at high speed and to avoid control reversal due to the flexing of the wing.
98. A control surface has its limitations in movement by:
A)control cable tension.
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SYSTEM,POWERPLANT&ELECTRICS
B)primary stops at the surface.
C)primary stops at the control column.
D)secondary stops at the control column.
For explanation refer to question #95.
99. A primary stop is mounted on an elevator control system in order to:
A)restrict the range of movement of the control column.
B)restrict the range of movement of the elevator.
C)maintain constant control cable tension.
D)prevent overloading of control cables.
For explanation refer to question #95.
100. The control surface that rotates the aircraft about its longitudinal axis is/are the:
A) elevator
B) ailerons
C)rudder
D)flaps
For explanation refer to question #93.
101. The function of the rudder limiter on some aircraft is to:
A) prevent that heavy gust damages the rudder.
B) prevent large rudder deflections on ground.
C)prevent excessive loads from acting on the rudder.
D)reduce rudder load during takeoff and landing.
Most transport category airplanes are equipped with rudder limiter systems that limit rudder deflection at higher
airspeeds ,which prevents single rudder inputs from causing structural overload (overstress due to excessive
loads). Most flight control surfaces are effective only up to a deflection angle of25°-30' and beyond these values
only the' drag increases substantially. Any aircraft rudder is subject to considerable forces that determine its
position via a force or torque balance equation. In extreme cases these forces can lead to loss of rudder control
or even destruction of the rudder. The largest achievable angle of a rudder in flight is called its blow down limit
;it is achieved when the force from the air or blow down equals the maximum available hydraulic pressure.
102. What is the name of the control surface that rotates an aeroplane about its longitudinal axis?
A)The elevator.
B)The rudder.
C)The trim tabs.
D)The ailerons.
For explanation refer to question #93.
103. Longitudinal stability involves the motion of the aircraft about its:
A)longitudinal axis.
B)lateral axis.
C)vertical axis.
D)centre of pressure.
(Refer to figure 021-E01)
The longitudinal stability of an aircraft refers to the aircraft's stability in the pitching plane = about its lateral
axis. The plane which describes the position of the aircraft's nose in relation to its tail and the horizon (other
stability modes are directional stability and lateral stability). If an aircraft is longitudinally stable, a small
increase in angle of attack will cause the pitching moment on the aircraft to change so that the angle of attack
decreases. Similarly, a small decrease in angle of attack will cause the pitching moment to change so that the
angle of attack increases.
104. If the control stick of an aircraft is moved forward and to the right, the left aileron will move:
A) up, and the elevator will move down.
B) up, and the elevator will move up.
C)down, and the elevator will move up.
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SYSTEM,POWERPLANT&ELECTRICS
D)down, and the elevator will move down.
Moving the stick forward and to the right causes the nose of the aircraft to pitch down and roll the aeroplane to
the right. For the nose to pitch down the tail must move up (aircraft "pivots" around its CG). For the tail to go up
the elevator must produce upward lift => since it is a conventional airfoil, the elevator control surface will be
JAA Test Prep Edition 2010 deflected down to increase the camber of the airfoil and thus create an upward lift.
To roll the aeroplane to the right the right wing must move down and the left wing must move up. To achieve
this, we have to decrease lift on the right wing and increase lift at the left wing. Therefore, the aileron (control
surface) on the left wing will move down to increase the camber of the left wing => increasing its lift. At the
same time the aileron on the right wing will move up to decrease the camber => decrease lift and by protruding
up increase drag significantly.
105. With which system is differential control associated?
A) Trim system.
B) Aileron system.
C)Rudder system.
D)Elevator system.
For explanation refer to question #94.
106. If the control stick of an aircraft with properly rigged flight controls is moved rearward and to the
left, the right aileron will move:
A)down and the elevator will move down.
B)up and the elevator will move down.
C)up and the elevator will move up.
D)down and the elevator will move up.
Moving the stick rearward and to the left causes the nose of the aircraft to pitch up and roll the aeroplane to the
left. For the nose to pitch up the tail must move down (aircraft "pivots" around its CG). For the tail to go down
the elevator must produce downward lift => since it is a conventional airfoil, the elevator control surface will be
deflected up to increase the negative camber of the airfoil and thus create a downward lift, To roll the aeroplane
to the left the left wing must move down and the right wing must move up. To achieve this, we have to decrease
lift on the left wing and increase lift at the right wing. Therefore, the aileron (control surface) on the right wing
will move down to increase' the camber of the right wing => increasing its lift. At the same time I the aileron on
the left wing will move up to decrease the camber => decrease lift and by protruding up increase drag
significantly.
107. The rudder limiters on several aircraft have a specific function, which is to:
A)prevent that heavy gust damages the rudder.
B)prevent large rudder deflections on ground.
C)prevent excessive loads from acting on the rudder.
D)reduce rudder load during takeoff and landing.
For explanation refer to question #101.
108. What is the name of the control surface that rotates an aeroplane about its vertical axis?
A)The elevator,
B)The rudder .
C)The trim tabs.
D)The ailerons.
For explanation refer to question# 93.
109. If the control stick of an aircraft is moved forward:
A) the elevator will move down.
B) the rudder will move up.
C)the aileron will move up.
D)the rudder will move down.
Moving the stick forward causes the nose of the aircraft to pitch down. For the nose to pitch down the tail
must move up (aircraft '''pivots'' around its CG). For the tail to go UP the elevator must produce upward lift =>
since it is a conventional airfoil, the elevator control surface will be deflected down to increase the camber of-
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SYSTEM,POWERPLANT&ELECTRICS
the airfoil and thus create an upward lift.
110. Which controls act together in a V-tail aircraft?
A)The stick in both axis (push, pull and turn). B)The stick in one axis and the throttle. C)The
stick in one axis and the rudder-pedals. D)The rudder-pedals and the mixture.
In aircraft, a V-tail is an unconventional arrangement of the tail control surfaces that replaces the traditional fin
and horizontal surfaces with two surfaces set in a V-shaped configuration when viewed from the front or rear of
the aircraft. The rear part of each surface is hinged, and these movable sections, sometimes called rudder-vators,
combine the tasks of the elevators and rudder. With fewer surfaces than a conventional three-aerofoil tail or a Ttail, the V-tail is lighter, has less wetted surface area, and thus produces less drag. However, the V-tail has not
been a popular choice for aircraft manufacturers. The most popular V-tailed aircraft in mass production was the
Beech craft Bonanza Model 35. Combining the pitch and yaw controls is difficult and requires a more complex
control system. The V-tail arrangement also places greater stress on the rear fuselage when pitching and yawing.
In the mid-1980s, the FAA grounded the Bonanza 35 due. to safety concerns. While the Bonanza met the initial
certification requirements, it had a history of fatal mid-air breakups during extreme stress, at a rate exceeding
the accepted norm.
111. The purpose of a trim tab (device) is to:
A)trim the aeroplane during normal flight.
B)reduce or to cancel control forces.
C)trim the aeroplane at low airspeed.
D)lower manoeuvring control forces.
(Refer to figure 021-E05)
Trim tabs are attached to the primary control surfaces and adjusted to eliminate the stick force needed to hold a
given control position (reduces hinge moment). They can be either fixed (adjustable only on the ground) or they
can be mechanically or electrically adjusted by the pilot in flight. They work on the principle that their
deflection will create a small aerodynamic force that moves the associated primary control surface in the
opposite direction to the movement of the trim tab. Once the force created by the trim tab and exerted on the
control surface is equal to the force created by the deflected primary control surface the control surface
movement will stop and it will remain in the given position without any need for pilot control input. Therefore,
even though the trim tabs reduce the control forces they reduce the effectiveness of the control surface as well
(by actually creating an opposite aerodynamic force to the control surface).
112. The reason for the trim switch on a control column to consist of two separate switches is:
A)to be able to use two different trim speeds, slow trim rate at high speed and high trim rate at low speed.
B)to prevent that both pilots perform opposite trim inputs.
C)because there are two trim motors.
D)to reduce the probability of a trim-runaway.
Strict requirements are set for the electrical powered trim systems. Precautions must be taken in their design as
to avoid inadvertent, improper or abrupt trim operation. It must be ensured that the airplane stays safely
controllable in case of apowered trim system malfunction during which the “runaway” occurs (uncommanded
continuous movement of the trim tab).In most electrical trim installations the pilot must simultaneously operate
two thumb-rocker switches in order to actuate the trim tab movement. One of the switches operates an electric
motor that drives the trimming mechanism while the other switch operates an electronic clutch. In case either of
these two switches or electric circuits malfunctions the electric trim system will not operate. In case of a trim
"runaway"(where the trimming continues after the trim switches are released by the pilot) the pilot must be
capable of overcoming the force on the controls manually while maintaining a safe and positive control of the
aircraft -for this reason the operating range of the electric trim is often limited on most large transport airplanes
(range of the electric trim is less
than the range of the manual trim).
113. The trim tab:
A)increases hinge moment and reduces control surface efficiency.
B)reduces .. hinge moment and increases control surface efficiency.
C)increases hinge moment and control surface efficiency.
D)reduces hinge moment and control surface efficiency.
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SYSTEM,POWERPLANT&ELECTRICS
For explanation refer to question #111.
114. Trailing edge flaps:
A)increase lift at a higher AOA.
B)increase lift at a lower AOA.
C)reduce lift at a higher AOA.
D)reduce lift at a lower AOA.
(Refer to figure 021-E04)
115. Flaps which not only move down, but also increase the wing area by extending backwards on
tracking are called:
A) slotted flap.
B) kruger flap.
C)fowler flap.
D)split flap.
116. A Kruger flap is:
A) a trailing edge flap which is operating automatically.
B) a leading edge flap type which is formed by extending an area of the wing downwards and
forward at the leading edge.
C) an anti-balanced type of flap with the purpose of making the controls smoother.
D) to give the aircraft better short field performance.
(Refer to figure 021-E03)
The Krueger flap is a leading edge lift augmentation device typically found on large turbine-powered transport
aeroplanes. When used on aeroplanes it is typically located on the wing's inboard section of the leading edge between the fuselage (wing root) and the engine pylon (between the wing root and the inner engine in case of a
4-engined aircraft). It is hinged along the underside of the leading edge of the wing (hinge located in the forward
edge of the flap) -when being deployed it swings down (into the airflow) and forward. Once in the deployed
position it dramatically increases the lift by increasing the wing camber. Krueger flaps do not form a slot in the
leading edge. Most transport aircraft employ leading edge slats on the outboard portion of the leading edge
(from the engine towards the wing tip), where more powerful flow control is required, and Krueger flaps on the
inboard portion of the leading edge (between the fuselage and the engine pylon).
117. The heating facility for the windshield of an aircraft is:
A) used only at low altitudes where there is a risk of ice formation.
B) harmful to the integrity of the windows in the event of a bird strike.
C) only used when hot air demisting is insufficient.
D) used on a continual basis as it reduces the thermal gradients which adversely affect the useful life of the
components.
The use of windshield electrical heating transparent conductive material (can be referred to as gold film) is
supplied power from the aircraft AC electrical system (usually 115 volt, 3 phase AC at 400 Hz). The heating
process will provide a non-shattering quality ro the window and the flight crew are provided with normal (ON)
and failure (OVERHEAT or OFF) indications. Heating of the windshields increases its resistance to withstand a
potential bird strike (a warm glass is stronger than a cold glass) -it is therefore used on a continuous basis during
the entire flight -typically switched on after the engine startup and switched off after the engine shutdown.
Therefore it is used on a preventive basis for the entire flight time as an anti-icing method (and to prevent
damaging consequences of bird strikes). Once switched ON it is thermostatically controlled (they automatically
cycle ON and OFF) so the temperature remains within the correct operating limits.
Another reason for a continuous use of the window heating system is to reduce the thermal gradients. When
window heat system is used, the window pane is maintained at a relatively constant temperature throughout the
entire flight. We need to realize that the temperatures at high altitude can be as low as for example -60C and it
would not do any good to the window pane material to be subject to constant rapid changes in temperatures as
the aircraft climbs and descends.
The inside (viewed from the cabin) glass panel is the load-bearing agent. The vinyl interlayer is the "fail-safe"
load carrying member and prevents the window shattering if the inner panel should fail. The outer glass panel
has no structural significance, it provides rigidity and a hard scratch resistant surface. A conductive film is
applied to the elements built into flight deck windscreens is widely used in modern transport aircraft. A layer of
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SYSTEM,POWERPLANT&ELECTRICS
inner surface of the outer glass panel to permit electrical heating for anti-icing and de-fogging. However damage
of the outer panel due to arcing can lead to visibility problems. For an electrical supply failure a limited amount
of de-fogging can be gained from the windscreen warm air de-misting supply. A conductive coating on the outer
panel also assists in dissipating static electricity from the windscreen.
118. Generally, for large aeroplanes, electrical heating for ice protection is used on:
A)slat leading edges.
B)fin leading edges.
C)pitot tubes.
D)elevator leading edges.
Electrical heating elements are fitted to pitot probes and AOA sensors. This is a requirement for all IFR certified
aircraft. On some aircraft the static ports are also heated. Pilot-static system heating elements are manually
controlled by the pilots-typically switched an after the engine startup and switched off after the engine shutdown
-they serve as preventive (anti icing) devices and are used for the entire flight time(especially when flying IFR).
Once switched on they are thermostatically controlled. On modern aircraft the pitot heaters operate at low power
on the ground and change over to high power when the aircraft is airborne. The AOA probes and autopilot and
air data probes switches may be switched via the pitot switches or they may have their own control switches
.The indication system in the cockpit is typically relatively simple -it typically involves ON / OFF switch, a
green "ON" light and an amber "OFF" light. On most transport category aircraft each pitot probe has its own
indicating lights (ON/OFF) and a common operating switch for all of the probes (sometimes 2 switches one for
the left side probes, one for the right side probes).Other electrical heating application includes for example antiice protection for the propellers. In any case, the electrical heating is quite demanding on the electrical system
and therefore it is typically used only for small areas (pitot probes, wind shields, propeller leading edges, etc).
Electrical heating is not used for ice protection of engine intakes or the leading edges of the airfoils (wings,
stabilizers ,etc.) of fixed-wing aircraft.
119. The elements specifically protected against icing on transport aircraft are:
1)engine air intake and pod
2)front glass shield
3)radome
4)pitot tubes and waste water exhaust masts
5)leading edge of wing
6)cabin windows
7)trailing edge of wings
8)electronic equipment compartment
The combination regrouping all the correct statements is:
A) 1,2,5,6
B)1,4,5,7
C)1,2,4,5
D)1,2,3,8
On aeroplanes certified for IFR flight in known icing conditions, the following airframe sections need to have
means of ice protection (either anti-icing or de-icing systems):
•Airfoil leading edges -Wings, horizontal and vertical stabilizers and leading edges of props. As the aeroplane
moves through the air at a high speed, it is typically only the leading edges that are prone to ice buildup.
•Engine air Intakes -turbojet engines require a laminar airflow to be supplied into the compressor. Therefore, if
ice was allowed to accumulate on the intake edges it could easily distort the airflow and thus decrease the engine
efficiency. In severe icing conditions partial blocking of airflow into the engine could be caused.
•Windshield -if ice was allowed to accumulate on the windshield without any means to remove it would be
difficult to land-imagine that you do not see anything in front of you and try to land.
•Pitot probes -if ice was allowed to accumulate on the pilot probes it could block the probe's sensing capabilities
rendering the pilot-static instrument inoperative. .
•Waste water outlets -on large transport aeroplanes that operate at high altitudes, where the temperatures are
very low (e.g. -5˚C) there must be systems in place that provide heating for the waste water outlets (water
drained from the wash-basins) -otherwise draining of the water would not be possible.
In general, anti-icing or de-icing systems are provided on such Components and sections of the aircraft that are
critical to its safe operation and where ice accumulation is likely in icing conditions. Among these components
and sections you will NOT find the radome (radar dome -typically the nose of the aeroplane); trailing edges of
the wings (ice will never accumulate on these parts due to the aerodynamic airflow properties); cabin windows
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SYSTEM,POWERPLANT&ELECTRICS
(there is no safety need for this) or electronic bays & compartments (as these are located inside the fuselage and
water will not get into them).
120. The anti-icing or de-icing system which is mostly used for the wings of modern turboprop aeroplanes
is:
A)fluid de-icing.
B)electrical heating.
C)thermal anti-icing.
D)pneumatic boots.
Some piston engined aircraft and most turbo-prop aircraft use pneumatically operated de-icing systems (known
as "boots") instead of thermal de-icing by hot air (as their engines usually would not have sufficient power for
hot bleed air extraction). The method of ice removal on this system design is mechanical. The system uses
rubberised (flexible neoprene rubber) flat inflatable tubes, closed at the ends, attached to the leading edges of
wings, tail planes and fin. The rubberised fabric tubes typically run parallel to the span of the flying surface -and
are placed around the leading edges. The tubes are connected to a vacuum source when the system is at rest or,
to a compressed air system when de-icing is selected. When at rest the boots are held tight up against the leading
edge by vacuum. When in use the boots are inflated by the compressed air (cycled => inflated and deflated) to
remove ice accretion from the wings and the tail surfaces. The boots are divided into sections that are inflated
sequentially to more efficiently de-ice the appropriate component with a higher pressure of the compressed air typically one group of boots is inflated at a time to minimize the demands on the compressed air (to reduce the
power off-take from the engine) and also to minimize the overall effects of the airflow disturbance around the
wings and tail surfaces (as the boot inflates it changes the profile of the airfoil momentarily). These can not be
used as anti-icing system -the ice has to accumulate on the leading edge first before the boots can be inflated. By
their inflation the ice is mechanically broken-off the leading edge surface. It is important that the operation of
the system is delayed until a sufficient layer of ice is present on the airfoil leading edge surface (about 1,5 cm),
otherwise the ice could build-up around the inflated boot rendering it unusable for subsequent de-icing. One
typical cycle of the boot operation lasts over 10 seconds.
121. The advantages of thermal anti-icing are:
1)simple and reliable system
2)profiles maintained
3)greater efficiency than that of an electrical resistor
4)direct use of the hot air from the jet engine without substantial reduction in engine thrust
The combination of correct statements is:
A) 1,2
B) 3,4
C) 1,3
D) 2,4
(Refer to figure 021-E29)
Large transport category aircraft typically use the thermal deicing for the ice protection of the wings and other
airfoils. This system is designed in such a way that hot bleed air is extracted from the compressor section of the
0
turbine engine (the temperature of this bleed air can be as high .as 300 C). It is then routed via a series of control
valves into so called "piccolo ducts" located under the leading edges of the wings and stabilizers. This causes
the temperature of the leading edges to rise and rid the leading edge of any ice accumulation. This is a very
effective de-icing system. However, the bleed air demand is quite high when the system operates, reducing the
power of the engine slightly -therefore it is usually not used throughout the entire flight time as an anti-icing
system. Instead, it is turned on by the pilots only after the ice accumulation is detected and turned off again once
the wing has been cleared from the ice accretion (= de-icing system). Typically not all sections of the leading
edge are protected by these systems -for example on a B737 the Krueger flap on the inboard section of the
leading edge and the last outboard slat close to the wing-tip are not protected by this system (to reduce bleed air
demands => bleed air extraction from the engine equals reduced engine performance/reduced maximum thrust).
As mentioned previously, this system is not only very effective in ice removal, but it is also advantageous over
the inflatable boot design in respect that it does not disrupt the airflow over the leading edge (unlike the
inflatable boots that modify the airflow when they inflate). The same system is typically used also for the ice
protection of the turbine engine intake. In this case, however, it is used as an ant/icing system (because the size
of the intake protected area is not so large). It is turned on by the pilots when icing conditions are anticipated
and turned off only after there is no doubt that icing will not be a factor.
122. A pneumatic de-icing system should be operated:
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SYSTEM,POWERPLANT&ELECTRICS
A)when there is approximately 1,5 cm of ice on leading edges.
B)when entering areas with icing conditions.
C)when there are approximately 5 cm of ice on leading edges.
D)only at takeoff and during approach.
For explanation refer to question 120.
123. The effect of frost on an aircraft:
A)is to cause an increase in boundary layer energy and so delay the onset of the stall.
B)can be generally Ignored.
C)has no significant effect on the aerodynamic contour or lift coefficient.
D)causes an increase in the surface roughness which in turn increases skin friction drag.
The presence of ice on an aircraft is not a situation, which should be taken lightly. On the one hand engines can
be damaged or, at the very least, lose power; on the other hand, alteration of the shape of a wing aerofoil section
and an unknown increase in weight by ice accretion can have, and has had, disastrous consequences. Knowledge
of all ice protection methods and protection procedures, on the ground as well as in flight, are an absolutely
essential part of the aviators store of information. Main effects of ice accretion:
•aerodynamic changes to wing, tailplane, control surfaces, fin,
propellers and flaps/slats; increase in skin friction drag;
•weight increase;
•vision obscured;
•systems supply air intakes and pitot and static vents blocked;
•the freezing up of moving parts such as flaps/slats, landing gear etc;
•engine intake airflow disrupted and engine compressor blade
aerodynamics changed which could cause flame-out, surge and loss of thrust.
124. During flight, the wing anti-icing system has to protect:
A)leading edges, slats and sometimes the leading edge flaps.
B)the whole upper wing surface and the flaps.
C)slats and the leading edge flaps only.
D)leading edges only.
On aeroplanes certified for IFR flight in known icing conditions, the wing leading edges need to have means of
ice protection (either anti-icing or de-icing systems). As the aeroplane moves through the air at a high speed, it
is typically only the leading edges that are prone to ice build-up. Either the entire leading edge of the wing or
only some of its sections are protected. For example on a B737 the Krueger flap on the inboard section of the
leading edge and the last outboard slat close to the wing-tip are not protected by thermal ice protection system
(to reduce bleed air demands => bleed air extraction from the engine equals reduced engine
performance/reduced maximum thrust). Therefore, typically the leading edge flaps are not protected, but the
leading edge without any lift augmentation devices + leading edge slats are protected.
125. With regard to pneumatic mechanical devices that afford ice protection the only correct statement is:
A)they can only be used as de-icing devices.
B)they are used extensively on modern aircraft as they are inexpensive and easy to maintain.
C)they can only be used as anti-icing devices.
D)they can be used as both de-icing and anti-icing devices.
For explanation refer to question 120.
126. In jet aeroplanes the thermal anti-icing system is primarily supplied by:
A)bleed air from the engines.
B)turbo compressors.
C)ram air, heated via a heat exchanger.
D)the APU.
For explanation refer to question #121.
127. In flight, the most commonly used anti-icing method for the wings of modern commercial aircraft
fitted with turbo-jet units is:
A)mechanical (pneumatic source which acts by deforming the profiles of the leading edge).
25
SYSTEM,POWERPLANT&ELECTRICS
B)physical/chemical (glycol-based liquid).
C)electrical (electrical resistances).
D)thermal (use of hot air).
For explanation refer to question 121.
128. The ice protection for propellers of modern turboprop aeroplanes works:
A)with anti-icing fluid.
B)pneumatically.
C)with hot air.
D)electrically.
De-icing systems are used to remove ice after it has built up. Just like the leading edges of the wings, also the
leading edges of the propellers are prone to ice accumulation in flight in icing conditions. Electrically heated
mats, affixed to the first third of a blade leading edge achieve electric propeller deicing. Power is transferred
from the power source (AC or DC) to the mats via slip rings and brushes. The blades are heated cyclically and
usually with a selection of timer intervals. Typically, a set of propellers is heated over a period of 90 seconds but
a selectable timer interval is set in accordance with the flight manual. Operation can be checked with the aid of
an ammeter. The heavier the ice, the shorter the cycle selected. The severity of icing is dependent upon outside
air temperature. When a mat is heated, the adhesion is broken between the heating mat and the layer of ice and
airflow and centrifugal force removes the ice and to such an extent in heavy icing that the ice strikes the
fuselage opposite the propeller. Double skinning or kevlar armour is fitted to protect the fuselage against such
damage. Some large installations include an AC generator per engine but some propeller deicing systems have
only say, one generator between two engines. In this case only one engine propeller is selected at a time.
129. The ice protection system currently used for the most modern jet aeroplanes is the:
A)liquid de-icing system.
B)electrical de-icing system.
C)hot air system.
D)pneumatic system with expandable boots.
For explanation refer to question 121.
130. Concerning the sequential pneumatic impulses used in certain leading edge de-icing devices, one can
affirm
that:
1)They prevent ice formation.
2)They are triggered from the flight deck after icing has become visible.
3) A cycle lasts more than ten seconds.
4) There are more than ten cycles per second.
The combination which regroups o11 the correct statements is:
A)2,4
B)2,3
C)1,3
D)1,4
For explanation refer to question 120 .
131. Usually, electric heating for ice protection is used on:
A)pitot tubes.
B)pitot tubes and engine intakes.
C)engine intakes.
D)wing and stabilizer leading edges.
For explanation refer to question 118.
132. The pneumatic ice protection system is mainly used for:
A)pitot tubes.
B)wings.
C)propellers.
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SYSTEM,POWERPLANT&ELECTRICS
D)engine intakes.
For explanation refer to question 120.
133. Concerning electrically powered ice protection devices, the only true statement is:
A) on modern aeroplanes, electrically powered thermal devices are used to prevent icing on small surfaces
(pitotstatic, windshield, etc.).
B) on modern aeroplanes, electrical power supply being available in excess, this system is often used for large
surfaces de-icing.
C) on modern aeroplanes, electrically powered thermal devices are very efficient, therefore they only need
little energy.
D) on modern aeroplanes, electrically powered thermal devices are used as de-icing devices for pitot -tubes,
static-ports, windshield etc.
Smaller surfaces which are prone to ice formation (pitot probes, windshield, propeller leading edges, etc.) may
be heated electrically. Larger surfaces are not heated electrically due to the availability of more efficient systems
for larger surfaces (pneumatic boots, bleed air de-icing systems, "weeping wings, etc.) -the electrical demand
would be simply too extensive for electrical heating of large surfaces. Electrical heating elements are manually
controlled by the pilots -typically switched on after the engine startup and switched off after the engine
shutdown -they typically serve as preventive (anti-icing) devices and are used for the entire flight time
(especially when flying IFR). Once switched on they are thermostatically controlled.
134.During flight,-the wing anti-icing system has to protect:
A)the whole upper wing surface and the flaps.
B)at least a part of the whole leading edge.
C)slats and the leading edge flaps only.
D)the whole leading edge and the whole upper wing surface.
For explanation refer to question 124.
135. Power for windscreen heating is usually:
A)115 volts DC.
B)single phase AC.
C)3 phase AC.
D)28 volts DC.
For explanation refer to question 117 .
136. Regarding a thermal wing anti-icing system, the correct statement is:
A)Aerodynamic performances of the wings are maintained and there is a reduction of maximum engine thrust.
B)Aerodynamic performances of the wings are not maintained and there is no reduction of maximum engine
thrust. C)Aerodynamic performances of the wings are maintained and there is no reduction of maximum engine
thrust. D)Aerodynamic performances of the wings are not maintained and there is a reduction of maximum
engine thrust. For explanation refer to question 121
137. The wing ice protection system currently used for most large turboprop transport aeroplanes is a(n):
A)pneumatic system with inflatable boots.
B)electrical de-icing system.
C)hot air system.
D)liquid de-icing system.
For explanation refer to question 120.
138. Windscreen heating systems usually:
A)depend upon the pilot monitoring the windscreen temperature probe for control of the heating system.
B)consist of warm air from the cabin conditioning system blown across the inner surface of the windscreen.
C)are powered from the emergency DC bus.
D)cycle on/off to maintain a windscreen temperature between approximately 18° and 35°C.
For explanation refer to question #117.
139. With regard to the pneumatic mechanical devices which afford protection against the formation of
ice, the only correct statement is:
27
SYSTEM,POWERPLANT&ELECTRICS
A)the pneumatic mechanical device can only be used as a deicing device.
B)the pneumatic mechanical device is used a lot on modern aircraft as it is inexpensive and easy to maintain.
C)the pneumatic mechanical device can only be used as an anti-icing device.
D)the inflatable de-icing boots of the pneumatic mechanical device are arranged perpendicular to the leading
edges.
For explanation refer to question 120.
140. In a bleed air anti-icing system the areas that are typically heated are:
A)the leading edge slats and flaps.
B)the whole surface of the aircraft.
C)the trailing edge flaps.
D) the leading edges of the wings and empennage.
For explanation refer to question 121.
141. When is windscreen heating active?
A)At low altitude and moderate icing.
B)High altitude.
C)When the de-fogger isn't keeping up.
D)All the time to increase integrity of the windscreen for bird strikes.
For explanation refer to question 117.
142. Anti-icing in a modern jet airliner is:
A)electric
B)mechanical
C)hot air
D)liquid
For explanation refer to question 121.
143. Pneumatic boot de-icing on wing leading edge:
A)has a cycle that lasts longer than 10 seconds.
B)has 10 cycles a second.
C)prevents ice buildup.
D) should be permanently selected on.
For explanation refer to question 120
144. In a bleed air anti-icing system the areas that are heated are:
A)the whole of the wing.
B)wing leading edge slats and flaps.
C)wing leading edges and slats.
D)trailing edge flaps.
For explanation refer to question 121.
145. Electrical heating devices:
A)consume little power.
B)are used for preventing ice on small areas -e.g. pitot head, Windscreen.
C)are used for de-icing small areas.
D)can de-ice large areas because there is a large excess of electrical power available.
For explanation refer to question 133.
146. The advantages of thermal anti-icing are?
A)There is less disruption to the leading edge airflow.
B)The engine performance is reduced.
C)Boots operate more effectively.
D)Generators can be paralleled.
For explanation refer to question 121.
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SYSTEM,POWERPLANT&ELECTRICS
147. The de-icing of a propeller by fluid is achieved through:
A)spray mats.
B)de-icing paste.
C)ground application of fluid only.
D)slinger rings.
Anti-icing systems for propellers are usually of electrical type(electrically heated mats) or of the liquid type. In
the liquid type design the system comprises a reservoir of isoprophyl alcohol == a liquid with a very low
freezing point. The fluid is either pumped from the reservoir or the reservoir is pressurized by compressed air so
as to maintain a reasonable fluid pressure at about 10 PSI. The fluid is directed to a "slinger-ring" via a check
valve (prevents siphoning when the system is switched OFF). A "slinger-ring" is a device that allows a pick up
of fluid from a stationary delivery pipe located behind the propeller hub, and then to each propeller blade, via
individual pipes, by centrifugal force. Some installations have over-boots fitted to the blades (for about a third of
the length) to assist in a more even distribution of fluid. One system supplies all engines and a rheostat may
control the application time.
148. In the case of a thermal de-icing system over-temperature, this is indicated by:
A)temperature gauges.
B)warning lights.
C)yellow flags.
D)a buzzer.
(Refer to figure 021-E29)
Large transport category aircraft typically use the thermal deicing for the ice protection of the wings and other
airfoils .This system is designed in such a way that hot bleed air is extracted from the compressor section of the
fl
turbine engine(the temperature of this bleed air can be as high as 300 C). It is then routed via a series of control
valves into so called "piccolo ducts" located under the leading edges of the wings and stabilizers. This causes
the temperature of the leading edges to rise and rid the leading edge of any ice accumulation. The operation of
this system is relatively simple. When the aeroplane is in the air, the engine bleed air valve is already opened,
because bleed air is used by multitude of critical systems, such as the pressurization system. The only action
required from the pilot is to turn the wing or engine anti-ice selector ON or OFF. The system indications
typically include a bleed air duct pressure gauge ==> indicating the pressure of the bleed air extracted from the
engines that is ready to be used for multiple of purposes (pressurization, anti-icing, . engine starting, etc.]. Other
indications of the pneumatic system include 3 warning lights:
•Pack Trip off == air conditioning (pressurization) pack/unit stopped operating -typically due to excessively
high operating temperature (working too hard);
•Wing Body Overheat == temperature has been exceeded somewhere in the bleed air duct -e.g. due to a leak of
the bleed air through the duct insulation;
•Bleed Trip off == the pressure or temperature of the bleed air extracted from the engine has been exceeded (this
is measured around the engine bleed air valve, before the bleed air is routed into the pneumatic system of the
aircraft). The thermal anti-icing system is usually automatically controlled when in operation (thermostatically).
The typical indications of the actual anti-icing system on most transport category aircraft are limited to ON/
OFF or DISAGREEMENT status. The disagreement status means that there is a disagreement between the
commanded position of the valves and their actual position -e.g. the pilot turns the system ON, but it remains
closed due to a malfunction of the valve == disagreement. In case of the engine anti-icing system an amber light
is typically provided that alerts the pilot of an over-pressure and/or over-temperature condition in this system.
149. The boots of a pneumatic de-icing system are normally made of:
A)neoprene rubber.
B)plastic.
C)porous metal.
D)synthetic rubber.
For explanation refer to question 120.
150. The accurate method of removing snow and ice that has accumulated on the aircraft during parking,
is:
A)hot water that melts the contamination.
B)the aeroplane's own de-icing equipment for five minutes.
C)hot air from the engines.
D)de-ice all surfaces with approved de-icing fluid.
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SYSTEM,POWERPLANT&ELECTRICS
If ice and snow accumulates on the aircraft during parking then it must be removed prior to the flight. The
regulations are very clear about this:
OPS 1.345 -Ice and other contaminants -ground procedures
(a) An operator shall establish procedures to be followed when ground de-icing and anti-icing and related
inspections of the aeroplane(s) are necessary.
(b) A commander shall not commence takeoff unless the external surfaces are clear of any deposit which might
adversely affect the performance and/or controllability of the aeroplane except as permitted in the Aeroplane
Flight Manual.
151. Fire precautions to be observed before refuelling are:
A)All bonding and earthing connections between ground equipment and the aircraft should be made before filler
caps are removed.
B)Ground Power Units (GPU) are not to be operated.
C) Passengers may be boarded (traversing the refuelling zone)provided suitable fire extinguishers are readily
available.
D)Aircraft must be more than 10 metres from radar or HF radio equipment under test.
An aircraft flying through the atmosphere will, to a greater or lesser extent, acquire electrostatic charges in the
metallic structure of the airframe. If different sections of the airframe acquire different electrical potentials then
current will flow between them, and sparking (arcing) across small gaps in the structure is liable to occur. At
best this will cause radio interference and at worst it could lead to fires. In order to prevent this the individual
parts of the airframe are electrically bonded together, using woven copper wire strips to provide a low resistance
path to discharge points on the structure .Same method of bonding is applied during refuelling –before the
refuelling is actually started (filler caps removed or pressure refuelling hose connected to the airplane) the
grounding wire has to be connected between the airplane and the refuelling truck, thus equalizing any possible
static electricity differential potential among the two, eliminating the possibility of spark. Another precaution
that should betaken is not to use the aircraft's main engine to power the electrical system during refuelling .Note:
there is a limitation imposed by many airlines that also prohibits starting or shutting-down the APU during
refuelling .It is OK for the APU to run, but it can not be started or shutdown while refueling .Obviously other
limitations prohibit the presence of passengers in the refuelling zone, although at some airports it is allowed for
the passengers to embark or disembark the aeroplane during refuelling (if certain other conditions are met) -but
the passengers are never allowed to traverse the refuelling zone
152. Fuel is pressurized to:
A) prevent cavitation.
B) prevent vapour lock.
C) keep constant fuel flow in negative G.
D) prevent fuel icing.
(Refer to figure 021-E17)
A vent system prevents damage to the fuel tank by positive or negative pressures and arranges for air to replace
fuel as the latter is used up. On a simple aircraft, a fuel tank is literally vented to the atmosphere, through a
single pipe located at the top of the tank and With appropriate arrangements to allow for aeroplane manoeuvres
(different attitudes). This sometimes involves routing of the vent pipe to the opposite side of the fuselage -if the
aeroplane banks in one direction the fuel will be prevented from spilling out as the pipe will always be facing
upwards even during steep banks .In larger aircraft, fuel tanks tend to be coupled to a common vent pipe within
a wing and in this case, and with large span-wise fuel tanks, the tanks are usually connected to the common vent
pipe at both the inboard and outboard parts of the tank. Flap valves, located over the ends of the vent pipe
,ensure that fuel does not flow into the system when the end of the vent is covered with fuel. This could be
caused by a failed refuelling shut-off valve for example or when the tank is full and just an outboard corner is
left as airspace. The vent pipes are connected to a vent or surge tank, located at the wing tip and vented to
atmosphere, from which any spilled fuel is pumped (fuel pump or jet pump) back into a fuel tank. EASA
certification rules state that the minimum volume of
the vent-space must be at least 2% of the tank capacity.
The purpose of the venting and pressurization of the fuel tanks by the ram air is to reduce the possibility of a
vapour lock by a positive feed of fuel into the fuel pumps or carburettors (note that some small . aeroplanes do
not have fuel pumps -e.g. C152) and to prevent loss of fuel due to evaporation at high altitudes. Tanks are also
equipped with relief valves (venting system) that prevent especially the decrease of pressure inside the tanks
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SYSTEM,POWERPLANT&ELECTRICS
caused by the fuel being used up -the space occupied by the used-up fuel must be allowed to be replaced with air
as negative pressure inside the tanks could result in damage to the tank's structural integrity and/or reduce or
stop the fuel flow. Also the over-pressurization of the tanks is prevented by the vent system -in this case the air
and fuel vapours are relieved into the atmosphere. Vapour lock = fuel vapours being collected and trapped in the
fuel lines around fuel line bends. This condition can cause a significant reduction of fuel flow into the engine or
completely block it. Under some conditions a vapour lock can occur in fuel system where the fuel is suction fed
into the engine (using a suction feed pump as opposed to a gravity feed fuel system) -conditions for occurrence
of a vapour lock are high fuel temperature, low fuel amount in the tanks, low ambient pressure and high angles
of attack of the aircraft. During the fuel system design the designers must provide a system capable of operation
without the occurrence of a vapour lock at fuel temperatures of up to 43˚C. When a vapour lock occurs it is
indicated by a reduced fuel pressure indication and auxiliary fuel pump must be switched on (if aircraft is
equipped with it) -this should increase the fuel pressure and force it through the fuel line areas affected by the
vapour lock.
153. The fuel temperature, at which, under standard conditions, the vapour ignites in contact with a
flame and extinguishes immediately, is the:
A) flash point.
B) combustion point.
C)fire point.
D)self ignition point.
The flash point of a flammable liquid is the lowest temperature at which it can form an ignitable mixture with
air. At this temperature the fuel produces sufficient vapour to be ignited by a small flame or spark. At this
temperature the fuel vapour may cease to burn when the source of ignition is removed. A slightly higher
temperature, the fire point, is defined as the temperature at which the vapour continues to burn after being
ignited. Neither of these parameters is related to the temperatures of the ignition source or of the burning liquid,
which are much higher. The flash point is often used as one descriptive characteristic of liquid fuel, but it is also
used to describe liquids that are not used
intentionally as fuels.
154. Fuel stored in aircraft tanks will accumulate moisture. The most practical way to minimize this when
a plane is used every day or so is to:
A) keep tanks topped off (full) when plane is not in use.
B) drain tanks at end of each day's flight.
C)use only high octane gasoline.
D)keep tank vents plugged and filler cap tight.
Fuel drains are inserted into the lowest points of a fuel tank and other parts of the system. These allow for either
complete tank and/ or fuel system draining such as for maintenance purposes or for collecting a small fuel
sample to check if water and/or other contaminant are not present in the fuel system. As the water is heavier
than the fuel any condensation within a tank would collect in the bottom of the tank.
Collecting a fuel sample from this section of the tank will clearly indicate the presence of contaminants or water
-seen either clearly as a layer of water below the layer of fuel or a cloudy fuel with the cloudy parts (suspended
water) slowly settling toward the bottom of the collection sample. These water drain checks have to be carried
out at laid down intervals -always at least before the first flight of the day and after each refuelling. Some
operators of small aeroplanes require these checks to be performed before each flight. Once the aircraft is
refuelled the most likely source of water contamination comes from the condensation within the tank itself typically when the aircraft is parked outside during a cool night. To minimize this effect it is a good practice to
top-off the fuel tanks after the last flight of the day so that the space inside the tanks where moist atmospheric
air can condensate is limited and instead of air taken-up by fuel.
155. Aircraft fuel tanks should be checked for water at least:
A)immediately after every refuelling.
B)before the first flight of the day.
C)during refuelling.
D)always before each flight.
For explanation refer to question 154.
156. On small aircraft the fuel content is typically measured by:
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SYSTEM,POWERPLANT&ELECTRICS
A) calculation of the centre of gravity of the helicopter.
B) the volume of fuel in the tank.
C)the weight of fuel in the tank.
D)the level of fuel in the tank.
The simplest way of measuring the fuel content in the tanks is using a float switch. This type of system is
typically found only on small aircraft and is quite susceptible to erroneous readouts due to changes in attitude of
the aircraft. The system uses a simple float (floating on top of the fuel inside the tank)attached to a resistor by its
mounting arm. As the fuel level is decreased during the flight so does the float change its position (settles lower
and lower inside the tank) and moves the mounting arm accordingly which in turn mechanically changes the
resistance of the electrical circuit => changes in the fuel content indications. This type of measurement system
therefore measures the level of the fluid in the tanks(regardless if it is water or fuel) and it can not compensate
for any changes in the
density of the fuel tank content.
157. Unusable fuel is:
A) always the same quantity irrespective of aircraft attitude or flight conditions
B)fuel drained from the aircraft due to water contamination.
C)sometimes mini mized by the incorporation of tank sump pads.
D)the amount of fuel not available for use but included on the fuel contents gauge.
Usable fuel = the total amount of fuel that can be supplied to the engines. Small amount of fuel always remains
inside the tanks due to the internal irregularities in the tank structure this small fuel amount (unusable fuel)
simply can not physically get to the fuel pumps an always remains inside the tanks (unless manually drained). It
is of course desirable to minimize the amount of unusable fuel as much as possible during the design of the
aircraft (such as the correct answer to one of the questions suggests using for example sump pad or making the
fuel tank bottom surface smooth and down sloping. toward the fuel pump). Unusable fuel is typically not
indicated on the fuel quantity indicators (When the indicator reads zero, it is actually usable, but there is still the
unusable fuel left in the tanks).
158. What does "octane rating" when applied to AVGAS refer to?
A)The anti-knock value of the fuel.
B)The volatility of the fuel.
C) The power the fuel produces per unit volume.
D) The specific gravity of the fuel.
The octane rating is a measure of the resistance of gasoline to detonation (engine knocking) in spark-ignition
internal combustion on egines. High-performance engines typically have higher compression. ratios and are
therefore more prone to detonation, so they require higher octane fuel. A lower-performance engine will not
generally perform better with high-octane fuel, since the compression ratio is fixed by the engine design. Antiknock value = a fuel's resistance to detonation. A fuel is said to have a good anti-knock value when its
detonation resisting quality is good, compared with other fuels under the same operating conditions .Aviation
gasoline (AVGAS) is only generally available as AVGAS 100LL (low lead). It is coloured blue, has a specific
gravity of approximately 0,72. AVGAS 100LL has an octane rating of 100/130 the 100 corresponding to the
anti-knock qualities when a lean mixture is used and the 130 to the antiknock qualities when a rich mixture is
used. There are two other categories of AVGAS which may be available: AVGAS100 is coloured green and has
identical anti knock characteristics to 100LL (100/130 octane rating under lean rich conditions), but obviously
contains more tetra-ethyl-lead(TEL) than 100LL and is therefore considered to be environmentally un friendly.
AVGAS 80 is coloured red and has a lean /
rich octane rating of 80 / 87.
159. Fuel tanks accumulate moisture. The most practical way to limit this in an aircraft flown daily is to:
A)secure the drain plugs and filler caps.
B)drain the tank at the end of each day.
the tank at the end of each flight.
D)drain the water prior to each flight.
For explanation refer to question 154.
160. If a fuel sample is cloudy and clears slowly from the top it is an indication of:
A)cold soaked fuel.
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SYSTEM,POWERPLANT&ELECTRICS
B)air in the fuel.
C)wax in the fuel.
D)water in the fuel.
For explanation refer to question 154.
161. Which statement is true concerning the structure and possible advantage of an integral fuel tank?
A)It is a separate metal container that is relatively light weight.
B)It is built internally using the aircraft structure, this saves weight and space.
C)It is constructed of rubber so it can be fitted into any free space within the aircraft.
D)It is a separate metal container that is relatively cheap to manufacture.
Integral tanks are areas inside the aircraft structure that have been sealed to allow fuel storage. An example of
this type is the "wet wing" commonly used in larger aircraft. They are formed from the spars, ribs and skin of
the aircraft structure. The whole assembly is made leak-proof by coating the assemblies in sealant before
assembly and then spraying the complete internal surface after assembly. Since these tanks are part of the
aircraft structure, they cannot be removed for service or inspection. Inspection panels must be provided to allow
internal inspection, repair, and overall servicing of the tank. Most large transport aircraft use this system, storing
fuel in the wings and/or tail of the airplane. The advantages of this type of fuel tank include maximum space
used for fuel storage and a weight saving. Rigid removable tanks are installed in a compartment designed to
accommodate the tank (typically the wings). They are typically made of aluminium alloy or reinforced plastic
and may be removed for inspection, replacement, or repair. The aircraft does not rely on the tank for structural
integrity. These tanks are commonly found in smaller general aviation aircraft, such as the Cessna 172.
Bladder tanks or sometimes called the "bag" or "flexible" tanks are reinforced rubberised bags installed in a
section of aircraft structure designed to accommodate the weight of the fuel. The bladder is rolled up and
installed into the compartment through the fuel filler neck or access panel, and is secured by means of metal
buttons or snaps inside the compartment. Many high-performance light aircraft and some smaller turboprops use
bladder tanks. The tank is supported by the aircraft structure into which it is inserted.
Generally, different types of tanks may be used on the same aircraft depending on the aircraft structure. The
integral tank offers the greatest advantages but the fuel tank walls, de-facto, form part of the structure and carry
stresses which must be catered for in the design (typically located in the wings and center fuselage on transport
aeroplanes). One further advantage of the integral tank is that a fuel leak may be the first indication of a
structural problem. Inspection points are included in the construction, through manholes, together with
refuelling points all of which are inserted into the upper skin of the tank.
162. What does the expression usable fuel mean?
A)The remaining fuel in the bottom of the tank when the
pump is no longer immersed in fuel.
B)The total fuel on board the aircraft at start up.
C)The total fuel remaining at any stage of flight.
D)The total amount of fuel that can be supplied to the engine.
For explanation refer to question 157.
163. If a fuel sample appears cloudy, this is:
A)an indication of air in the fuel.
B)normal.
C)because of fuel additives to improve engine performance.
D)an indication of water in the fuel.
For explanation refer to question #154.
164. The flash point of fuel is:
A) highest temperature of fluid.
B) lowest temperature of fluid.
C)lowest temperature of vapour.
D)highest temperature of vapour.
For explanation refer to question 153.
165. When checking the fuel for possible water content, the presence of water will be indicated by:
A) change in the color of the fuel.
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SYSTEM,POWERPLANT&ELECTRICS
B) impossible to tell because they will mix.
C)the water will be on top of the fuel in the fuel strainer because the water is lighter than the fuel.
D)the water will be found at the bottom of the strainer ,because it is heavier than the fuel.
For explanation refer to question #154.
166. The fuel tanks in small aircraft are mainly located:
A) in the wings
B) in the tail section of the aircraft.
C)in the fuselage.
D)close to the engine.
In small aeroplanes the fuel tanks are typically located in the wings -most frequently as an integral or rigid tank.
Typically the fuel tanks of large transport aeroplanes are integral tanks(they directly form part of the airframe
structure). Vast majority of transport aeroplanes will have fuel tanks located inside the wings (wing tanks,
typically referred to as main tanks) and in the lower section of the fuselage -in the center section (center tank)
around the wing attachment areas. Long-haul transport aeroplanes may also have additional tanks fitted in the
fin and use sophisticated fuel transfer mechanisms to allow transfer of this fuel to the front tanks (center or
Wing).Some aeroplanes may also have additional auxiliary (rigid)tanks fitted in parts of the cargo hold for
extended range of operations.
167. Fuel tank booster pumps are typically:
A)centrifugal, low pressure.
B)centrifugal, high pressure.
C)gear type, low pressure.
D)gear type, high pressure.
(Refer to figures 021-E14 and 021-E27)
Each tank of a large transport category aircraft usually contains two booster pumps (low pressure, centrifugal
type pumps), either of which can supply the needs of anyone engine. In the event of a failure of both pumps the
suction feed of the fuel into the engine-driven high pressure (HP) fuel pump will continue to supply the engine,
but aircraft operating altitude may have to be reduced in order to prevent vapour lock in the feed line. The
booster pumps are electrically driven, usually by an AC induction motor (115 V /400 Hz), whereas in light
aircraft the booster pump is usually operated by a DC motor (14 v or 28 V). Typically the pressure output of the
pumps is between 20 to 50 psi. Fuel is supplied from the aircraft fuel tanks, to the high-pressure (HP) enginedriven pump by a low-pressure (LP) boost pump system. The LP fuel pumps ensure a constant supply at a
suitable pressure to prevent vapour locking and cavitation of the HP pump supply to ensure satisfactory engine
operation. The LP system usually incorporates a fuel heater before the fuel is supplied to the filter and to the HP
pump to prevent the formation of ice crystals which would block the fuel filter. For aeroplanes that have
separate fuel output pressure indicators for each fuel pump the sensors are located on the output side of each LP
booster pump. On aeroplanes where only one fuel pressure indication is provided the sensor is located on the
output side of the HP fuel pump or on the HP fuel filter outlet.
168. On most transport aircraft, the low pressure pumps of the fuel system are:
A)piston pumps.
B)gear type pumps.
C)centrifugal pumps.
D)diaphragm pumps.
For explanation refer to question 167.
169. The fuel system boost pumps are used to:
A)feed the fuel control units, which inject the pressurized fuel into the engine.
B)avoid the bubbles accumulation.
C)feed the lines with fuel for directing it to the engine at a positive pressure.
D)avoid the bubbles accumulation and feed the lines with fuel for directing it to the engine at a positive
pressure.
For explanation refer to question 167.
170. The pressurization of tanks is maintained by the fuel:
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SYSTEM,POWERPLANT&ELECTRICS
A)vent system.
B)tank drains.
C)top off unit.
D)dump system.
For explanation refer to question 152.
171. On most transport jet aircraft, the low pressure pumps of the fuel system are supplied with electric
power of the following type:
A) 115 V DC
B)115 V AC
C)28 V DC
D)28 V AC
For explanation refer to question #167.
172. The fuel cross-feed system:
A)allows feeding of any engine from any fuel tank.
B)is only used to feed an engine from the tank of the opposite wing.
C)is only used on the ground for fuel transfer from one tank to another.
D) is only used in flight for fuel transfer from one tank to another.
(Refer to figures 021-E27 and 021-E26)
By the use of the cross-feed valves the fuel system can be operated in such a way that each engine draws from
its own tank (cross-feed valve closed) during normal operation '" left engine from left tank, right engine from
right tank. However the system is designed in such a way that any engine can be operated using fuel from any
tank. Using the combination of cross-feed valve opening and turning-off specific booster fuel pumps the pilot
can for example setup the fuel system to supply both engines with fuel from only the left tank; or incase of an
engine shut-down due
to a failure supply the remaining engine from both tanks; etc.
173. The high pressure fuel pumps are driven by:
A) hydraulic pressure.
B) air pressure.
C)the engine.
D)the electrical system.
In a booster pump fuel system the fuel is supplied from the fuel tanks to the high-pressure (HP) engine-driven
pump via a low-pressure (LP) boost pump system. The LP fuel pumps ensure a constant supply at a suitable
pressure to prevent vapour locking and cavitation of the HP (engine-driven) pump supply, to ensure satisfactory
engine operation. The LP system usually incorporates a fuel heater to prevent the formation of ice crystals
which would block the fuel filter. Fuel pressure sensors for the instrument indicators are typically located on the
HP pump outlet or on the HP fuel filter outlet. Other types of fuel system can be the gravity feed type where the
tanks are located above the engine and fuel is allowed to freely flow from the tanks into the engine, or the
suction type fuel system where the fuel is drawn into the engine by the engine-driven fuel pump only.
174. During refuelling operations:
A)the aircraft should be bonded to the refuelling truck before refuelling pipes are coupled.
B)a refuelling zone is to be established to at least 100 m.
C)passengers are forbidden to remain on the aircraft regardless of the type of fuel being replenished.
D)radio transmissions are not forbidden.
For explanation refer to question #151.
175. On most transport aircraft, the low pressure pumps of the fuel system are:
A)electro-mechanical wobble pumps, with self-regulated pressure.
B)mechanically driven by the engine's accessory gearbox.
C)removable only after the associated tank has been emptied.
D)centrifugal pumps, driven by an electric motor.
For explanation refer to question 167
176. Fuel pressure is measured:
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SYSTEM,POWERPLANT&ELECTRICS
A)at the outlet from the fuel control unit.
B)always at the outlet of the high pressure pump only.
C)in the line between the booster-pump and the engine or at the outlet of the high pressure filter.
D)in the line between the high pressure filter and the high pressure pump.
For explanation refer to question 167.
177. In the event of an engine fire:
A)an automatic shut-off valve is moved to the closed position controlled by the fire sensing system.
B)the fuel supply is disconnected by a quick release coupling.
C)the fuel supply is isolated from the engine by a pilot controlled fuel shut-off valve.
D)the fuel installation is protected by an automatic fire extinguishing system.
The fuel system shut-off valves are typically operated manually by the engine "start levers" which open or close
the
fuel supply to the engine. However, the fuel shut-off valve can also be closed automatically when the pilot pulls
the fire-handle. If a fire is detected in the engine the fire warning system annunciates this condition to the pilots
by sounding afire bell and illuminating the master fire warning light + the respective fire handle (corresponding
to the engine which is on fire). When the pilot pulls this handle a series of automated tasks is triggered -such as
closing the fuel valve of the respective engine; closing the bleed air valve; closing the hydraulic shut-off valve;
arming the fire extinguisher; tripping the generator; disabling the reverser, etc. By pulling the fire handle the
pilot basically stops the engine very quickly without needing to go through a long checklist before stopping it
(checklist of course
follows after pulling the fire handle).
178. The fuel cross-feed system enables:
A)the supply of the engines mounted on a wing from any fuel tank within that wing.
B)the supply of any engine from any fuel tank.
C)the supply of the outboard engines from any outboard fuel tank.
D)the transfer of fuel only from the centre tank to the wing tanks.
For explanation refer to question 172.
179. The ventilation system in a fuel tank:
A)prevents low pressure or excessive overpressure in the tank.
B)can be used to drain the tanks. for daily checks.
C)prevents fuel freezing during flight in Icing conditions
D)prevents vapour locking in the fuel lines.
For explanation refer to question 152.
180. In order to ensure that all fuel on board is available to any engine on a multi-engined aircraft, it
must be fitted with:
A)a jet pump.
B)a tank shut-off valve.
C)cross-feed.
D)booster pumps.
181. A volumetric top off valve on small aircraft works with:
A)pressure sensors.
B)flow rate sensors.
C)float switches.
D)capacitive sensing systems.
182. Which fuel tanks are heated?
A) Wing tanks.
B) Fuselage tanks.
C)All tanks.
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SYSTEM,POWERPLANT&ELECTRICS
D) None.
183. Low pressure fuel pumps are:
A)engine driven.
B)electrically driven centrifugal pumps.
C)driven by the accessory gearbox.
D)swash plate pumps with self governors.
For explanation refer to question 167.
184. Fuel tanks on large aircraft are located:
A) only in the wings.
B) in the wings and in the centre section.
C)in the wings, the centre section and sometimes the fin.
D)in the wings, the centre section and sometimes the fin or part of the hold.
For explanation refer to question 166.
185. On what principle does a fuel flow meter work?
A)Volume and viscosity.
B)Quantity of movement.
C)Capacitive dielectric.
D)Pressure and temperature.
186. On what principle does the fuel contents gauging system work on a modern large aircraft?
A)Capacity affected by dielectric therefore changing EMF of system.
B)Capacity affected by dielectric therefore changing resistivity of system.
C)Changes in dielectric causes changes in capacitance.
D)Change in dielectric causes change in distance between plates and therefore changes capacitance.
187. What is the purpose of a surge box inside a fuel tank?
A)Collect sediment at the bottom of the tank.
B)Ventilate the tank during high pressure refuelling.
C)Allow movement of fuel between tanks while refueling.
D)Prevent sloshing of fuel away from pump inlet during abnormal manoeuvres.
188. Fuel heaters are fitted:
A)in the wing fuel tanks.
B)in the fuselage fuel tanks.
C) in the engine fuel system mounted on the engine.
D) all of the above.
189. A volumetric top-off unit (VTO), is provided in a fuel system to:
A)vent the tank to atmosphere when its full.
B)allow a main feed tank to be maintained at a predetermined level automatically, while being fed from an
auxiliary tank.
C)allow the main tank to automatically maintain a predetermined fuel pressure.
D)prevent too much fuel from being dumped.
190. The precautions to be taken during refuelling are:
A)GPU may not be running during refuelling.
B)all earthing of aircraft parts to ground equipment must be completed before filler caps are removed.
C)passengers may be boarded (traversing the refuelling zone).
D)no radar or HF radios under test within 10 metres.
For explanation refer to question 151.
191. Aircraft fuel booster pumps are typically:
A)centrifugal and powered by DC induction motors.
B)centrifugal and powered by AC induction motors.
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SYSTEM,POWERPLANT&ELECTRICS
C)spur-gear and powered by DC induction motors.
D)spur-gear and powered by AC induction motors.
For explanation refer to question 167.
192-An electrically activated and operated fuel valve is called a/an:
A)motor valve.
B)solenoid valve.
C)electronic valve.
D)emergency valve.
Fuel shut-off valves on large transport aeroplanes are typically solenoid valves. A solenoid valve is an electromechanical valve for use with liquids -it is controlled by running or stopping an electric current through a
solenoid, which is a coil of wire, thus changing the state of the valve. The operation of a solenoid valve is
similar to that of a relay -but instead of controlling another electric circuit the solenoid mechanically controls the
flow of a liquid.
193-When baffles are fitted to aircraft fuel tanks, the purpose is to:
A)separate air from the fuel during fuelling operations.
B)reduce fire risk when fuelling.
C)control the fuel flow to the main feed.
D)prevent surge of fuel within the tank during flight.
194-The most widely used electrical frequency in aircraft is:
A)115 Hz
B)200 Hz
C)50 Hz
D)400 Hz
Typically modern aircraft utilize 3-phase AC systems with a frequency of 400 Hz (115V single-phase / 200V 3phase). The formula to calculate the AC generator output frequency = (rotor RPM x number of pairs of poles)
60. Constant frequency machines usually operate at 400 Hz so a 6-pole machine will be driven at 8.000 RPM
and an 8 pole machine will be driver at 6.000 RPM
195-Refer to figure 021-12)
Which of this circuit diagram symbols represents a relay?
A)A
B) B
C)C
D) D
(Refer to figures 021-E95 and 021-E96)
Relays are, in effect, electromagnetic switching devices electric switches that open and close an electrical
circuit under the control of another electrical circuit. Using a relay one electrical circuit can be controlled by
another -for example a high current circuit by low current circuit. Basically, a coil is energised or de-energised
open and close one pair or many pairs of electrical contacts operate other circuits. In addition to the contact
assembly designations relays are also classified by the order of making and breaking
196-A relay is:
A)an electrical security switch.
B)an electromagnetically operated switch.
C)a switch specially designed for AC circuits.
D)an electrical energy conversion unit.
For explanation refer to question #195.
197-The purpose of static wick dischargers is to:
A)dissipate static charge from the aircraft skin after landing.
B)dissipate static charge of the aircraft in flight thus avoiding radio interference as a result of static electricity.
C)provide a path to ground for static charges when refuelling.
D)be able to fly higher because of less electrical friction.
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SYSTEM,POWERPLANT&ELECTRICS
198-A circuit breaker :
A)is self resetting after the fault has been rectified.
B)may be reset manually after the fault has been rectified.
C)can only be reset after major maintenance.
D)can be reset on the ground only.
199-When an open circuit occurs in an electrical supply system, the:
A)load as indicated by the ammeter will increase.
B)fuse or CB should isolate the circuit due to excess current drawn.
C)components will operate normally, but will not switch off.
D)loss of continuity will prevent its working components from functioning.
An electric current is simply a flow of electrons through a conducting element and it is measured in amperes
(amps) by means of an ammeter. The lower the resistance to current flow, the greater the current flow and vice
versa. Maximum current will flow when a short circuit exists (a direct connection between supply and return),
and this causes an overload. No current will flow when an open circuit exists (when the circuit is broken, for
example by opening a switch). The break in the circuit has created a condition of infinite resistance.
200-If a current is passed through a conductor which is positioned in a magnetic field:
A)the current will increase.
B)a force will be exerted on the conductor.
C)there will be no effect unless the conductor is moved.
D)the intensity of the magnetic field will decrease.
When an electrical current flows through a conductor a magnetic field is created around the current-carrying
conductor. The greater the current flow through the conductor ,the greater the strength of the magnetic field
surrounding it .This is the principle upon which electromagnets work. If this conductor is positioned into a
magnetic field the two fields will interact with each other and this will exert a force on the conductor .
201-Fuses are rated to a value by:
A)their wattage.
B)the number of volts they will pass.
C)the number of amperes they will carry.
D)their resistance measured in ohms.
(Refer to figures 021-E95 and 021-E96)
202-The true statement among the following in relation to the application of Ohm's law is:
A)power in the circuit is inversely proportional to the square of the current.
B)the current in a circuit is directly proportional to the resistance of the circuit.
C)current in a circuit is directly proportional to the applied electromotive force.
D) current in a circuit is inversely proportional to the electromotive force.
Ohm's law applies to electrical circuits. It states that the current through a conductor between two points is
directly proportional to the potential difference or voltage across the two points, and inversely proportional to
the resistance between them. The mathematical equation that describes this relationship is: I = V : R, where "I"
is the current in amperes, "V" is the potential difference (voltage) in volts, and "R" is a circuit parameter called
the resistance (measured in ohms, also equivalent to volts per ampere).
Summary:
•current = voltage : resistance
•resistance = voltage: current
•voltage = current x resistance
203-A component consuming 80 watts at 8 amps would require a supply of:
A) 0,01 kV
B) 100 Volts
39
SYSTEM,POWERPLANT&ELECTRICS
C)5 Volts
D) 0,008 kV
Power is the rate of doing work where, in this case, the force is voltage and the rate is the Amperage. It,
therefore, follows that Power (P) = Voltage x Current. Power is measured in Watts (W). As a definition, 1 W is
the power used when 1 volt moves 1 coulomb (quantity) per sec through a conductor. There are 746 W in one
HP. To solve this question, simply use the formula P = V x 1=> 80 Watts = ? Volts x 8 Amps => ? equals 10
Volts. 1 kV equals 1000 Volts, therefore 10 Volts equal 0,01 kY.
204-A magnetic circuit breaker:
A)is a quick tripping response protective system.
B) permits over voltage for a short period of time.
C) has a slow response time.
D) can be reset without danger.
205-Circuit breakers protecting circuits may be:
A)reset at any time.
B) used only in AC circuits.
C)used only in DC circuits.
D) used in AC and DC circuits.
206-A diode:
A)allows current flow if its lags the voltage by 90˚
B)allows current flow if it is in phase with the voltage.
C)allows current to flow in one direction only.
D)can be used as an inverter.
A diode is a semiconductor device equipped with two terminals. The most common function of a diode is to
allow
an electric current to flow in one direction (called the for ward biased condition) and to block the current in the
opposite direction (the reverse biased condition). Thus, the diode can be thought of as an electronic version of a
check valve. In electrical schematics, the direction in which the current is allowed to flow is indicated by an
arrow.
A specific type of a diode is the Zener Diode -it will conduct electricity only under certain voltage conditions. It
is a type of diode that permits current in the forward direction just like abnormal diode, but also in the reverse
direction if the voltage is larger than the breakdown voltage. The breakdown voltage is a set voltage at which
the Zener diode will conduct, below this set voltage it acts as a normal diode. Zener diodes are Widely used to
regulate the voltage across a circuit. When connected in parallel with a variable voltage source so that it is
reverse biased, a Zener diode conducts when the voltage reaches the diode's reverse breakdown voltage. From
that point it keeps the voltage at that value.
207-arelay is:
A)a unit which is used to convert electrical energy into heat energy.
B)a device which is used to increase electrical power.
C)a magnetically operated switch.
D)another name for a solenoid valve.
For explanation refer to question 195.
208-Amagnetic circuit breaker:
A)is a protection system that has a quick tripping response.
B)permits an over current limited in time.
C)can be reset without any danger even when fault remains.
D)is a system with a slow response time.
209-A Zener diode is used for:
A)rectification.
B)voltage stabilisation.
C)reverse current protection.
40
SYSTEM,POWERPLANT&ELECTRICS
D)digital displays.
For explanation refer to question 206.
210-Regarding Ohm's law:
A)the power in the circuit is inversely proportional to the square of the current.
B)the current in a circuit is directly proportional to the resistance of the circuit.
C)the current in a circuit is directly proportional to voltage.
D)the current in a circuit is inversely proportional to voltage.
For explanation refer to question 202 .
211-The purpose of bonding the metallic parts of an aircraft is to:
1)prevent electrolytic corrosion between mating surfaces of similar metals.
2)ensure zero voltage difference between aircraft components.
3)isolate all components electrically.
4)keep all parts of the aircraft at the same potential.
The combination regrouping all the correct statements is :
A)2,4
B)1,4
C)2,3
D)1,3
212-When the supply frequency in a circuit with a capacitor is increased, the current in this circuit will:
A)increase.
B)be zero.
C)decrease.
D)remain the same.
213-The total resistance of a number of power consuming devices connected in series is equal to:
A)the sum of the individual resistances.
B)the sum of the reciprocals of the individual resistances.
C) the reciprocal of sum of the individual resistances.
D) the sum of the resistances divided by the total resistance.
214-Ohm's law states:
A)I=R ÷ V
B)R = I ÷ V
C) I=V ÷ R
D) I =V ×R
For explanation refer to question 202 .
215-Electrical potential is measured in:
A)watts
B)amperes
C)ohms
D)volts
Electromotive force, otherwise known as Voltage (symbol "U" or (V) is the difference of electrical potential
between two points of an electrical or electronic circuit, expressed in volts. It measures the potential energy of
an electric field to cause an electric current in an electrical conductor.
216-Electromotive force is measured in:
A) watts
B) ohms
C) volts
D) amperes
For explanation refer to question 215.
217-A fuse is rated by:
A) its resistance in ohms.
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SYSTEM,POWERPLANT&ELECTRICS
B) the current amperage it will carry.
C)the voltage it will carry.
D)the wattage it will pass.
For explanation refer to question 201.
218-You can use circuit breakers in:
A)AC circuits only.
B)DC circuits only.
C)AC or DC circuits.
D)re-settable systems.
219-The difference between (i) a fuse and (ii) a circuit breaker , is:
A) (i) suitable for high currents, (ii) not suitable for high currents.
B)(i) not resettable, (ii) resettable.
C)(i) not suitable for high currents, (ii) suitable for high currents.
D) (i) not resettable, (ii) not resettable.
220-The most common overload protection device used in aircraft is:
A) circuit breakers.
B) fuses.
C) blow torches.
D) relays.
221-The most common voltage/frequency used in jet transport aircraft is:
A) 115V AC /400 Hz
B)115V DC / 400 Hz
C)28V DC
D)400V AC /115 Hz
For explanation refer to question 194.
222-Modern aircraft can have many different types of circuit breakers (CB). Generally speaking a CB is
an electric component that:
A)when excessive current flows through it, it will open the circuit. It has to be replaced to regain a closed
electrical circuit.
B)when excessive current flows through it, it will open the circuit, but a closed circuit is regained when it is
reset. C)is seldom used in electrical systems.
D)prevents high voltage, but can not handle high values of current.
223-The commonly used symbol of voltage is:
A) I and it is measured in volts.
B) I and it is measured in amperes.
C) v and it is measured in volts
D) R and it is measured in volts.
For explanation refer to question 215
224-The current in a DC circuit, according to Ohm's law, can be described as:
A)proportional to both the voltage and the resistance.
B)inversely proportional to the resistance and proportional to the voltage.
C)equal to the voltage regardless of the resistance.
D)independent on both the voltage and the resistance.
For explanation refer to question #202.
225-The international symbol of electrical power is:
A)P and it is measured in watts.
B) I and it is measured in amperes.
C)U and it is measured in volts.
D)R and it is measured in ohms
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SYSTEM,POWERPLANT&ELECTRICS
Electric power is defined as the rate at which electrical energy is transferred by an electric circuit. The SI unit of
power is the Watt. Electric power, like mechanical power, is represented by the letter “P" in electrical equations.
When electric current flows in a circuit, it can transfer energy to do mechanical or thermodynamic work.
Devices convert electrical energy into many useful forms, such as heat (electric heaters), light (light bulbs),
motion (electric motors), sound (loudspeaker) or chemical changes. In DC resistive circuits, instantaneous
electrical power is calculated using Joule's Law: P = V x I(where “P” is the electric power, “V” the potential
difference ,and “I” the electric current).
226-Ohm's law claims the following:
A)The current flowing in a circuit is inversely proportional to the applied voltage, and proportional to the
resistance through which the current flows.
B)The current flowing in a circuit is proportional to the applied voltage, and inverse proportional to the
resistance through which the current flows.
C)The current flowing in a circuit is proportional to both the applied voltage and to the resistance through
which the current flows.
D)The current flowing in a circuit is inversely proportional to both the applied voltage and to the resistance
through which the current flows.
For explanation refer to question 202 .
227-The commonly used symbol of resistance is:
A)U and it is measured in volts.
B)R and it is measured in ohms.
C)P and it is measured in watts.
D)I and it is measured in amperes.
228-Which of the following materials is a semiconductor?
A) Fe
B) AI
C) H
D) Si
A semiconductor is a material that has an electrical resistivity between that of a .conductor and an insulator. An
external electrical field changes a semiconductor's resistivity. Devices made from semiconductor materials are
the foundation of modern electronics, including radio, computers, telephones, and many other devices.
Semiconductor devices include the transistor, solar cells, many kinds of diode's including the light-emitting
diode, the silicon controlled rectifier, and digital and analog integrated circuits. Solar photovoltaic panels are
large semiconductor devices that directly convert light energy into electrical energy. In a metallic conductor,
current is carried by the flow of electrons. In semiconductors, current can be carried either by the flow of
electrons or by the flow of positively-charged "holes" in the electron structure of the material. Typically,
Germanium (Ge) or Silicon (Si) is used as the semiconductor material. Semiconductor materials in their pure
state have 4 elections in their outer (valence) shell. Germanium atoms have a total of 32 electrons. Silicon atoms
have a total of 14 electrons. Both of these elements are highly resistive because the atoms of these materials
have a strong valence bond .In other words ,the electrons in the outer shell of each atom naturally pair with
those of adjacent atoms. Consequently there are no free electrons in these materials to act as current carriers.
229-Batteries are rated in:
A)amperes / volts.
B)amperes x hours.
C)watts.
D)ohms.
Batteries are rated according to their voltage and capacity. Battery capacity is measured in terms of ampere
hours. Ampere-hour (or Ah) is the unit of electrical capacity -it tells you how much power the battery will store.
Current (A) multiplied by time (Hr) in hours equals ampere hours. A current of one amp for one hour would be
one amp-hour; a current of 3 amps for 5 hours would be 15 Ah, a current of 4 amps for 10 hours would be 40
Ah, etc. The "Ah" rating is to do with how many amperes can be discharged over a period of time before the
battery is flat. For example if a battery had a rating of 30 ampere hours, it could discharge at 30 amps for 1 hour,
60 amps for 30 minutes, 15 amps for two hours and so on.
Amp-hour ratings will vary with temperature, and with the rate of discharge. For example, a battery rated at 100
Ah at the 6-hour rate would be rated at about 135 AH at the 48-hour rate. Terms such as "6 hour rate" or "20
hour rate" indicate that the battery is discharged steadily over 6 or 20 hours, and the Amp-hour capacity is
43
SYSTEM,POWERPLANT&ELECTRICS
measured by how much it puts out before reaching 80% DOD (Depth of Discharge). Batteries are usually said to
have an efficiency of about 80%. Therefore, if a 20 amp hour battery at the 1 hour rate was discharging at 20
amps, it should last (20 x 0,80) = 0,8 hours or 48 minutes. Battery capacity is checked at regular intervals -if it
falls below 80% of its rated capacity the battery is removed from aircraft service .
230-The capacity of a battery is expressed in terms of:
A)watts.
B)volts.
C)ampere hours.
D)internal resistance.
For explanation refer to question 229.
231-If one of the 12 cells of a Lead-acid battery is dead, the battery:
A)has 1/12 less capacity, but can still be used.
B)has 1/12 less voltage, but can still be used.
C)is unserviceable.
D)has 1/12 less voltage and less capacity, but can still be used.
Batteries are made out of individual battery cells -for Lead-acid batteries the nominal voltage of individual cells
is 2 -2,2 V; for NiCd it is 1,2 -1,25 V. The cells are connected in series for an output of 12 V or 24 V. Since the
cells are connected in series a failure of a single cell will make the battery unserviceable (the circuit within the
battery will be broken).
232-when a battery is almost fully discharged there is a tendency for the:
A)voltage to decrease under load.
B)voltage to increase due to the current available.
C) current produced to increase due to the reduced voltage.
D)electrolyte to "boil".
The principle underlying any battery or battery cell is a chemical reaction. A battery cell consists of two
dissimilar metals immersed in or surrounded by water and a conducting fluid called an electrolyte. The chemical
action of the electrolyte causes electron flow between the plates. One plate will become positive and the other
negative (surplus of electrons) and current will flow through any connected load .Over a period of time as the
battery is discharged, the plates of a NiCd battery deteriorate and oxygen is either taken up or given up, to or
from the electrolyte. This reduces the electrical potential between the plates => the battery's voltage and
subsequently the current decrease. Recharging the battery restores the chemical composition inside the battery
and restores the electrical potential to the original value .The voltage of a battery always drops when load
connected to the battery is increased -no matter if it is almost discharged or coming straight from the charger.
However, this effect is more pronounced when the battery is almost discharged. For example -for a healthy leadacid battery cell the "off-load" voltage is 2,2 V and the "on load" voltage is 2 V. When discharging at low rate,
the battery's energy is delivered more efficiently than at
higher discharge rates.
233-A test to assess the state of charge of a Lead-acid battery would involve:
A)checking the level of the electrolyte.
B)comparing the "on-load" and "off-load" battery voltages.
C)checking the discharge current of the battery "on load".
D)checking the battery voltage "off-load".
Lead-acid batteries The positive and negative plates are made of lead peroxide and lead, respectively. The
electrolyte is 30% sulphuric acid and 70% water. Over a period of time the composition of the battery elements
changes as sulphur from the electrolyte is taken up by the plates and converts to lead sulphate. At this point, the
battery condition would necessitate recharging from a source with a higher emf and the battery condition is
restored to normal. Whilst in storage they are usually held on a 'trickle' charge. Whilst being charged, the
electrolyte dissociates into hydrogen and water and a venting system is required in the installation to reduce the
explosive hazard provided by the hydrogen. Each cell has a nominal output of 2 to 2,2 V-therefore a 12 V
battery has 6 cells, 24 V battery has 12 cells.
Capacity checks:
It is possible to determine the state of charge of a lead-acid cell by using a hydrometer to check the specific
44
SYSTEM,POWERPLANT&ELECTRICS
gravity (SG) of the electrolyte. When fully charged the SG should be between 1,25 (hot) and 1,30 (cold), also
depending upon the age and condition of the cell. When fully discharged the SG is likely to have fallen to
approximately 1,17. •SG 1,275 to 1,3 = high state of charge;
•SG 1,24 to 1,275 = medium charge state;
•SG 1,2 to 1,24 = low charge state.
Voltage checks:
Battery voltage can be checked by measuring the battery output at the terminals with a voltmeter. Alternatively,
a known resistance or load is put across the terminals and the on-load voltage measured. If the battery is in poor
condition, the terminal PO will reduce. It is Usually better to make an assessment of condition by comparing the
off-load and on-load voltages.
Preflight voltage check:
A flight manual battery voltage check is sometimes specified and this will include switching on the batteries and
a pitot heater for example (to create an "on-load" condition for the battery). The load is maintained for a
specified time interval, usually 15 seconds, after which the voltage should be substantially the same or at least
above a stated limit.
Disadvantages over NiCd batteries (examples -not a full list):
•Give off noxious or explosive gasses.
•Cannot be stored in a discharged condition.
•Low energy density => poor weight-to-energy density limits use to , stationary and wheeled applications (too
heavy for a given output).
•Allows only a limited number of full discharge cycles; well suited for standby applications that require only
occasional deep discharges.
234-When carrying out battery condition check using the aeroplane's voltmeter:
A)a load should be applied to the battery in order to give a better indication of condition.
B)no load should be applied to the battery because it would depress the voltage.
C)the battery should be isolated.
D)the load condition is unimportant.
Voltage checks:
Battery voltage can be checked by measuring the battery output at the terminals with a voltmeter. Alternatively,
a known resistance or load is put across the terminals and the 'on-load' voltage measured. If the battery is in poor
condition, the terminal potential difference will reduce. It is usually better to make an assessment of condition
by comparing the off-load and on-load voltages.
Pre-flight voltage check:
A flight manual battery voltage check is sometimes specified and this wilt include switching on the batteries and
a pitot heater for example (to create an "on-load" condition for the battery). The load is maintained for a
specified time interval, usually 15 seconds, after which the voltage should be
substantially the same or at least above a stated limit.
235-The connection in parallel of two 12 volt / 40 Ah batteries, will create a unit with the following
characteristics:
A)24 volt / 40 Ah
B)12 volt /40 Ah
C)24 volt / 80 Ah
D)12 volt /80 Ah
If batteries are connected in SERIES, the output voltage becomes the sum of both, but the capacity (ampere
hour rate) remains as for a single unit. If, however, they are connected in PARALLEL, the voltage remains as
for a single unit, but the capacity becomes the sum of both. Therefore, if we have two batteries, each of 12 V /
40 Ah, then when connecting them in series the result will 24v/40AH when connecting them in parallel the
result will be 12v/80Ah
236-In aeronautics, the most commonly used batteries are NiCd because:
A) their output voltage is less constant than lead-acid batteries.
B)they weigh less than lead-acid batteries.
C)their electrolyte is neither corrosive nor dangerous.
D)they are cheaper than lead-acid batteries .
NiCD (Nickel cadmium) batteries
There are two types of NiCd batteries: sealed and vented. The positive plates are nickel hydroxide, the negative
plates are cadmium hydroxide and the electrolyte is a mixture of 70% distilled water . and 30% potassium
45
SYSTEM,POWERPLANT&ELECTRICS
hydroxide. The plates are supported on nickel plated steel supports. During charging the negative plates give up
oxygen and become cadmium, whilst the positive plates pick up oxygen to form nickel oxides. During discharge
the process is reversed. Servicing and frequent condition checks, monitoring, load and voltage checks are as for
other types of battery, but the nominal cell voltage Is 1,2 to 1,25 V per cell (compared to 2 V per cell for Lead
Acid batteries). Therefore a 12 V battery contains 10 cells, 24 V battery contains 20 cells connected in series.
The capacity of a NiCd battery is a direct function of the total plate area within the cells and may be up to 80
ampere hours (Ah) in a typical 24-volt battery. The Ah rating is always determined at a 5-hour discharge rate
unless otherwise specified.
Advantages over Lead-acid batteries
•Have a lower self-discharge rate (longer shelf-life).
•Longer life & are easier to store and they do not give off gases whilst charging.
•More robust = less prone to damage & tolerating deep discharge for long periods.
•Last longer, in terms of number of charge/discharge cycles and have faster charge and discharge rates than
lead-acid batteries.
•Much higher energy density. This means that, for a given battery capacity, a NiCd battery is smaller and lighter
than a comparable lead-acid battery.
•Battery voltage remains constant over almost the entire discharge cycle, falling significantly only as the battery
becomes fully discharged. This characteristic makes the NiCd battery particularly suitable for gas turbine engine
starting, where a long start cycle requires protracted battery discharge before the engine-driven generators can
supply power to recharge the battery (terminal voltage only changes a little as It discharges = minimal loss of
capacity even at high discharge rates).
Disadvantages over Lead-acid batteries
•More expensive to manufacture and extremely toxic.
•Very significant negative temperature coefficient = as the cell temperature rises, the internal resistance falls
This can pose significant charging problems with relatively simple charging systems employed for lead-acid
type batteries (thermal runaway).
•The specific gravity of the electrolyte is no indication of the state of charge of NiCd battery, nor can the state of
charge be determined by a voltage check against rated load, since voltage remains substantially constant over
most of the discharge period.
•NiCd batteries suffer from a "memory effect if they are recharged before they have been fully discharged. The
apparent symptom is that the battery "remembers" the point in its charge cycle where recharging began and
during subsequent use suffers a sudden drop in voltage at that point, as if the battery had been discharged.
237-A 12 volt Lead-acid battery has a broken connection In a cell. The battery:
th
A)provides 1/12 less voltage for the same time.
th
th
B)provides 1/12 less voltage for 1/12 less time.
C)is unserviceable.
D) will suffer from thermal runaway.
For explanation refer to question 231.
238-The voltage of a fully charged lead-acid battery cell is:
A)1,8 V
B)1,2 V
C)2,2 V
D)1,4 V
For explanation refer to question #233.
239-The capacity of a battery is the:
A)intensity withstood by the battery during charging.
B)number of cycles (charging and discharging) that a battery can withstand without deterioration of its cells.
C)no-load voltage of the battery multiplied by its rated output current.
D)amount of ampere-hours that a fully charged battery can supply.
For explanation refer to question 229.
240-Battery voltage is tested with:
A)a megometer
B)a voltmeter on rated load.
C)an ammeter on rated load.
D)a dummy load.
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SYSTEM,POWERPLANT&ELECTRICS
For explanation refer to question 234 .
241-A significant increase in battery temperature is an indication of:
A)thermal runaway.
B)excess load on the battery.
C)alternator failure.
D)voltage regulator failure.
Batteries will perform to their rated capacities as long as temperature conditions and charging rates are kept
within the specified limits. If either is exceeded a condition known as thermal runaway may occur, which causes
a significant increase of the battery electrolyte temperature. This increased electrolyte temperature lowers the
resistance of the battery, allowing more charging current to flow and further increasing the temperature of the
electrolyte; The result is a violent gassing and eventual melting of the plates and battery casing. Sometimes the
temperature can get so high so as to cause an explosion of the battery.
Thermal runaway, or vicious cycling, is a condition to which NiCd , batteries are particularly susceptible at high
charging rates. During overcharging, oxygen is formed at the positive plates of the battery. If this oxygen
reaches the negative plates it will recombine with the cadmium and generate heat as a result. If this process is
allowed to continue, the battery may be seriously damaged, or even explode . The condition is avoided by
keeping charge rates within safe limits and by monitoring battery temperature (if it exceeds safe values,
disconnecting the charge current automatically until the temp reduces again). Some aircraft NiCd batteries
incorporate a temperature sensor that activates an overheat-warning indicator, or a temperature gauge, in the
cockpit.
242-A lead-acid battery is checked for serviceability by:
A)using an ammeter.
B)measuring the specific gravity of the electrolyte.
C)using an ohmmeter.
D)measuring the level of the electrolyte.
For explanation refer to question 233.
243-The electrolyte in a Nickel-Cadmium battery is:
A)hydrogen peroxide.
B)nickel dioxide,
C)potassium hydroxide.
D)potassium chloride.
For explanation refer to question 236.
244-How do you test a battery on an aircraft with a voltmeter?
A)Off load.
B)On load.
C)There is no specific procedure.
D)It does not matter whether the batteries are on load or off load.
For explanation refer to question 234.
245-What are the advantages of NICD batteries?
A)Simple charging systems can be used.
B)Less cells required than in lead-acid battery with the same voltage.
C)Even voltage before rapid discharge.
D)Higher voltage than lead acid type.
For explanation refer to question 236.
246-If a 24 V secondary cell battery has 20 cells and one cell is dead:
A)you cannot use it.
B)1/20 of a reduction in voltage, but can still be used.
C)1/24 of a reduction in voltage and capacity, but can still be used.
D)1/20 of a reduction in capacity, voltage not reduced battery can still be used.
For explanation refer to question 231
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SYSTEM,POWERPLANT&ELECTRICS
247-With an almost discharged battery there will be:
A)an increase of current with decrease of voltage
B)a decrease of current with increasing load.
C)a decrease of voltage with increasing load.
D)an increase of voltage with increasing load.
For explanation refer to question 232.
248-When a battery is nearly discharged, the:
A)voltage decreases.
B)voltage and current decrease.
C)current increases because voltage has dropped.
D)electrolyte will boil.
For explanation refer to question 232.
249-The capacity of an accumulator is:
A)the number of cycles (charging and discharging) that a battery can withstand without deterioration of its cells.
B)the quantity of electricity that the battery can supply during discharge.
C)the no-load voltage of the battery multiplied by its rated output current.
D)the intensity withstood by the battery during charging.
For explanation refer to question 229.
250-One of the main functions of the battery in large transport aircraft is to:
A)provide electric power for heating.
B)be an emergency source of electric power.
C)provide DC power for certain equipment.
D)provide AC power for certain equipment.
Batteries used in aircraft applications are mostly of the NiCd type as these batteries offer a better weight/output
ratio and provide a relatively stable voltage during most of the discharge cycle. Typically the on-board batteries
are used only for a limited periods of time -such as for the engine starting .Once the engine is started and the
engine-driven generator starts operating, the batteries are recharged. Another important purpose of the on-board
batteries is to provide emergency source of electrical power in case of failure of all engine-driven generators.
This emergency power is of course available only for a limited period of time and only for the flight-critical
systems such as instruments, emergency lighting, etc. For example on a B737-300 a fully charged battery is
capable
of providing a minimum of 30 minutes of in-flight emergency power to critical systems -typically a sufficient
time
To quickly find a suitable airport and land.
251-Obvious disadvantages of using lead-acid batteries in airplanes are:
A)they only carry 12 volt, and most modern airplanes use 24volt circuits.
B)they are expensive compared to other batteries used in airplanes.
C)they have insufficient capacity and are volume and weight inefficient.
D)the lead-acid battery is too heavy.
For explanation refer to question 233.
252-What is the best way to test the charge level of a lead acid battery?
A)By using a voltmeter.
B)By using an ammeter.
C)By checking the level of the electrolyte.
D)By checking the specific gravity of the electrolyte.
For explanation refer to question 233.
253-The capacity of a typical lead-acid battery for use in small general aviation aircraft is:
A)24 V
B)12-18 Ah
C)4-8 Ah
D)12 Volts
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SYSTEM,POWERPLANT&ELECTRICS
Out of the given answer possibilities only the answers B) and C) describe the battery capacity. 4-8 Ah would be
quite low, considering the fact that the battery does not only serve as the source of power for the starter, but also
as an emergency (time-limited) source of electrical power should all electrical generators fail. Therefore the
capacity of 12-18 Ah is more appropriate
254-The frequency of an AC generator is dependent on the:
A)number of pairs of poles and the speed of the rotor.
B)number of individual poles and the field strength.
C)field strength and the speed of the rotor.
D)number of individual poles only.
(Refer to figures 021-E85, 021-E86, 021-E87, 021-E88, 021E89 and 021-E90)
AC generator frequency is dependent upon the number of pairs of poles and the generator rotational speed. The
output current frequency is measured in cycles per second or Hertz(Hz). Typically modem aircraft utilize AC
systems with a frequency of 400 Hz. The formula to calculate the AC generator output frequency = (rotor RPM
x number of pairs of poles) ÷ 60. Constant frequency machines usually operate at400 Hz so a 6-pole machine
(3-pole pairs) will be driven at8.000 RPM and an 8-pole machine will be driven at 6.000RPM.
255-The frequency of the current provided by an alternator depends on:
A)its rotation speed.
B)the strength of the excitation current.
C)its load .
D)its phase balance.
For explanation refer to question #254.
256-The purpose of a voltage regulator is to control the output voltage of the:
A)generators at varying speeds and the batteries at varying loads.
B)batteries at varying loads.
C)generator at varying loads and speeds.
D)output of the TRU.
(Refer to figures 021-E85, 021-E86, 021-E87, 021-E88, 021E89 and 021-E90
A generator voltage is proportional to the field strength(magnitude of field excitation). The field current and
therefore the output voltage of the generator is constantly adjusted by a voltage regulator. Voltage regulator is
required regardless of the fact that a generator is driven by a COD or directly by the engine accessory gearbox the rotational speed determines the frequency of the output current and not the voltage. Voltage regulators work
on the principle of sensing the generator output voltage and adjusting the field current to maintain voltage at a
constant value. Typically the voltage regulator is a transistorised unit that allows a set current to flow to the
alternator field coil when alternator output voltage falls below a set value (say 27,5 volts). When output voltage
rises above a set value (say 28,5 volts) it cuts off the current supply to the field coil. This cycle is repeated about
2000 times per second, maintaining alternator output voltage at about 28 volts.
257-On an aeroplane utilizing AC as primary power supplies, the batteries are charged in flight from:
A)the AC bus via current limiters.
B)a static inverter.
C)a DC transformer and rectifier.
D)a transformer rectifier unit.
258-The output of a generator is controlled by:
A)varying the field strength.
B)varying the speed of the engine.
C)varying the length of wire in the armature windings.
D)the reverse current relay circuit breaker.
259-A 3 phase AC generator has 3 separate stator windings spaced at:
A)90°
B)60°
C) 45°
D)120°
(Refer to figures 021-E85, 021-E86, 021-E87, 021-E88, 021E89 . and 021-E90)
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SYSTEM,POWERPLANT&ELECTRICS
The vast majority of large modern aircraft now employ AC motors and generators because the systems and
equipment are lighter, more efficient and more adaptable to further modification than are their DC equivalents.
AC generators can be designed to produce Single phase, two phase or three phase current but the most powerful
and common of these is the 3phase machine. The 3 'stator , Windings are electrically separated and there is only
one rotor inside the stator. The 3-phase windings are positioned so that their voltage outputs are sequentially
120° apart. This is the same as having 3 single phase generators, all driven by the same shaft. Each winding can
be used to supply single-phase loads or, alternatively, the outputs can be used together for 3phase (or 2-phase)
loads. For a given output this gives a more compact machine or a greater output for a given size.
260-In an aeroplane equipped with a DC main power system, AC for instrument operation may be
obtained from:
A)a rectifier.
B)an inverter.
C)a contactor.
D)a TRU.
Even on a DC aircraft, there are many systems that require AC supply and this is provided by an inverter, a
machine that converts DC to AC. There are two types of inverter units: the rotary unit and the static unit. In the
case of the rotary inverter, DC is used to drive a DC motor at constant speed. This in turn drives an alternator
(AC generator) to provide alternating current at constant frequency (usually 115 volt, 3phase AC at 400 HZ).
Static inverters, as their name suggests ,have no moving parts and achieve the same result electronically. They
are much more common in modern aircraft. The circuitry of the static inverter contains such electronic
components as diodes, transistors, capacitors and transformers. These solid-state components form an oscillator
circuit that converts DC input into a 400 Hz constant frequency AG output. Static inverters are usually designed
to produce single phase AG. Inverter power usually supplies instruments and flight systems equipment =>
generally low power devices requiring 200/115v° 400 Hz. Transformers are included to provide lower voltages,
for example, 26V AC. Inverters are also required on aircraft with AC electrical circuits simply because the
emergency power source is the battery = DC power source. Therefore, there have to be means of converting
emergency DC power to emergency AC power (e.g. for the instruments and radios) and this is achieved by the
inverters (typically the static inverters).
261-The function of the generator breaker is to close when the voltage of the:
A)battery is greater than the generator voltage and to open when the opposite is true.
B)generator is greater than battery voltage and to open when the opposite is true.
C)alternator is greater than the battery voltage and to open when the opposite is true.
D)battery is greater than the alternator voltage and to open when the opposite is true.
Generator cut-out: assuming that a DC generator and a battery are online together and connected to the same bus
bar. If the generator voltage falls below that of the battery a reverse current flow could occur (from the battery to
the generator) and the generator could, in certain conditions, for example low RPM, be driven by the battery, as
a motor. To avoid this undesirable situation, a cut-out relay (also referred to as the reverse current relay) is
installed so that the:
•generator will charge up the battery whenever the generator voltage is slightly higher than that of the battery, or
busbar.
•generator will be disconnected from the battery when the generator voltage is lower than that of the battery.
The reverse current relay is not requited on alternators because the diodes prevent current reversal. On a DC
generator the reverse current relay contacts are held open by spring-action, keeping the generator disconnected
from the busbar. Once a sufficient generator output voltage is built-up the relay closes by overcoming the spring
force. If the generator voltage decreases below the battery voltage the force holding the relay contacts closed
will not be sufficient to overcome the spring force and the contacts open and thus disconnect the generator from
the busbar.
262-The voltage regulator of a DC generator is connected in:
A)parallel with the armature.
B)series with the armature.
C) parallel with the shunt field coil.
D) series with the shunt field coil.
(Refer to figures 021-E85, 021-E86 and 021-E87)
On a shunt-wound DC generator the shunt field coil is in parallel with the armature. The field current depends
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SYSTEM,POWERPLANT&ELECTRICS
on the voltage and the resistance of the field. As load currents do not affect it, it has little in the way of
consumption and consists of a large number of turns of fine wire. As the generator load increases and the
generator emf falls so the emf across the coil decreases and field current reduces. However, reductions in
field current are not large and a voltage regulator placed in series with the coil maintains a fairly even control
over generator output. This type is used in a current turboprop aircraft and is rated at 28V DC, 9 KW; and 300
amps over
an engine speed range of 4500 RPM to 8500 RPM.
263-Assume a constant speed DC generator providing a constant output voltage. If the electrical load
increases, the voltage regulator will:
A)decrease the intensity of the excitation current.
B)change the direction of the excitation current.
C)maintain the intensity of the excitation current constant.
D)increase the intensity of the excitation current.
(Refer to figures 021-E85, 021-E86 and 021-E87)
On the series-wound generators the field is connected in series with the load so as the generator load increases,
the current flow in through the field and armature increases, field excitation increase and maintains a very wide
based generator emf. Large currents flow through the coil, which consists of a few turns of thick wire .
264-A DC generator fitted to a commercial aircraft is cooled by:
A)air via a ram air intake .
B)water at 8° centigrade from the air conditioning system.
C)a fan located before the generator.
D)air tapped from the low pressure compressor.
The alternators generate heat in the stator Windings due to the current flow. In order to prevent overtemperature, some means cooling have to be typically provided. This cooling is predominantly ( provided by
passing ram air over the heat-exposed sections of the, alternator. In the absence of ram air (ground operations)
fans can be used on some aircraft as well. However, the ram air method is the predominating one .
265-In an alternator rotor coil you can find:
A)AC.
B)three-phase AC.
C) only induced current.
D) DC.
(Refer to figures 021-E85, 021-E86, 021-E87, 021-E88, 021E89 and 021-E90)
ALTERNATOR ROTOR
The rotor consists of a coil of wire wrapped around an iron core. Current through the wire coil -called "field"
current produces a magnetic field around the core. The strength of the field current determines the strength of
the magnetic field .The field current is DC, or direct current. In other words, the current flows in one direction
only, and is supplied to the wire
coil by a set of brushes and slip rings. The magnetic field produced has, as any magnet, a north and a south pole.
The rotor is driven by the alternator pulley, rotating as the engine runs, hence the name "rotor."
ALTERNATOR STATOR
Surrounding the rotor is another set of coils, three in number ,called the stator. The stator is fixed to the shell of
the alternator, and does not turn. As the rotor turns within the
stator windings, the magnetic field of the rotor sweeps through the stator windings, producing an electrical
current in the windings Because of the rotation of the rotor, an
alternating current (Ac) is produced. As, for example, the North pole of the magnetic field approaches one of the
stator windings, there is little coupling taking place, and a weak current is produced, As the rotation continues,
the magnetic field moves to the centre of the Winding, where maximum.
coupling takes place, and the induced current is at its peak. As the rotation continues to the point that the
magnetic field is leaving the stator winding, the induced current is small. By this time, the South pole is
approaching the winding, producing a weak current in the opposite direction. As this continues, the current
produced in each winding plotted against the angle of rotation of the rotor has a sinusoidal form. The three stator
Windings are spaced inside the alternator 120° apart, producing three separate sinusoidal sets, or "phases," of
output voltages, spaced 120fl apart
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SYSTEM,POWERPLANT&ELECTRICS
266-Alternating current can be derived from direct current by:
A)the use of relays.
B)a series wound motor.
C) an alternating current motor.
D) an inverter.
For explanation refer to question 260 .
267-The moving part in an AC generator is usually referred to as the:
A)stator.
B)rotor.
C)oscillator.
D)slip ring.
For explanation refer to question #265.
268-In an electrical circuit the reverse current relay will open:
A) when battery voltage exceeds generator voltage.
B)when circuit voltage is less than generator voltage.
C)when the batteries are flat.
D)when the battery is being charged.
For explanation refer to question 261.
269-Generator cut-out (reverse current relay) contacts are kept open by:
A) magnetism.
B)spring tension.
C)generator speed.
D)current flow.
For explanation refer to question #261.
270-If the load on a DC generator is reduced the voltage regulator will the current in the exciter field.
A)decrease
B)increase
C)maintain constant
D)None of the above, voltage regulators are not used in DC generator systems.
For explanation refer to question 263 .
271-The frequency of an AC generator is dependent upon:
A)the RPM of the rotor.
B)the number of poles in the rotor.
C)the RPM and number of poles in the rotor.
D)the number of poles in the rotor and the number of phase windings in the stator.
For explanation refer to question 254.
272-The battery cut-out (reverse current relay). cuts out:
A)when the battery voltage is higher than the generator voltage.
B)when the battery voltage is lower than the generator voltage.
C)when the battery and generator voltage are the same.
D)whenever the engine is stopped.
For explanation refer to question #261.
273-The primary purpose of the reverse current relay is to:
A) prevent the generator from delivering current to the generator.
B) prevent the battery from delivering current to the generator.
C) prevent the generator from delivering too much current.
D) allow the battery to be charged.
For explanation refer to question #261
274-The output voltage of DC generators used in aircraft is normally regulated by:
A) varying the RPM of the generator.
B) controlling the current in the armature (anker) windings.
C) controlling the current in the field windings.
D) varying the torque applied to the generator.
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SYSTEM,POWERPLANT&ELECTRICS
275-The purpose of the voltage regulator is to:
A)keep a constant power output from the generator.
B)keep a constant current output from the generator.
C)keep a constant frequency.
D)keep a constant voltage output from the generator.
For explanation refer to question 256 .
276-When AC generators are operated in parallel, they must be of the same:
A)voltage and frequency.
B)voltage and amperage.
C)amperage and kVAR.
D)frequency and amperage.
(Refer to figures 021-E91, 021-E92 and 021-E93)
Generators connected in parallel must:
•be in phase,
•have the same voltage (within 10 V),
•have the same phase angle (Within 90°),
•have the same frequency (within 3-5 Hz).
•real and reactive load sharing must be effective.
277-If AC generators are connected in parallel, the reactive loads are balanced by:
A)frequency regulation.
B)torque of the CSD.
C)regulating the energizing current.
D)voltage regulation.
(Refer to figures 021-E91, 021-E92 and 021-E93)
For paralleled generators to equally share reactive load, their output frequencies and output voltages must be
equal. Output frequency is controlled by the rotational speed of the generator -therefore by the CSDu (Constant
Speed Drive unit). Output voltage is dependent upon voltage regulators and the generator field excitation
current. Suppose the excitation current is higher in one generator than in the other generators, because its
voltage regulator is set slightly above the mean system value. This will produce a reactive component of current
flowing in opposition to the reactive loads of the other generators. Consequently, its load is increased whilst the
loads of the other generators are reduced, resulting in unbalanced reactive load sharing.
•Real load sharing is provided through the control of the generator's speed and torque (drive mechanisms);
•Reactive load sharing is provided through the control of the generator's output voltage (via the voltage regulator
==> excitation currents).
278-As regards three-phase AC generators, the following conditions must be met for paralleling AC
generators: 1)equal voltage
2)equal current
3)equal frequencies
4)same phase rotation
5)voltages of same phase
The combination regrouping all the correct statements is:
A) 1.3.4.4
B) 1.2.3.4
C) 1.3.5
D) 1.4.5
279-To ensure correct load sharing between AC generators operating in parallel:
A)the matching of loads is unimportant.
B)both real and reactive loads must be matched.
C)only reactive loads need to be matched.
D)only real loads need to be matched.
For explanation refer to question 276.
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SYSTEM,POWERPLANT&ELECTRICS
280-"Frequency wild" in relation to a AC generation system means the generator:
A) output frequency varies with engine speed.
B) output frequency is too high.
C) voltage regulator is out of adjustment.
D) output frequency is too low.
Frequency wild AC systems are mainly confined only to light aircraft and turboprops. Frequency wild systems
cannot be paralleled. On frequency wild systems the generators are not rotated by the engines at a constant
speed -they do not employ any CSD units (Constant Speed Drive) -therefore the rotational speed of the
generator is dependent on the rotational speed of the engine. Since the rotational speed of the generator
determines its output frequency, then the frequency will vary with the engine speed.
281-When operating two AC generators unparalleled the phase relationship of each generator:
A)must be synchronous.
B)is unimportant.
C)must be in opposition.
D)must be 90° out of synchronisation.
(Refer to figure 021-E94)
In order to connect AC generators in parallel, all of the generators must be in phase, must have the voltage and
phase
angle, frequency, etc. However, in a split-bus system, where the generators are not paralleled, these parameters
do not have to be matched among the generators. In this type of electrical system each generator is powering its
own AC bus and does not "interact" with any other generator. However ,the generator output must of course
meet certain criteria ,such as the voltage and frequency required by the electrical system in order to be used to
power its busbar.
282-The measured output power components of a constant frequency AC system are:
A)volts and amperes.
B)kVA and kVAR.
C)volts and kilowatts.
D)amperes and kilowatts.
Power meters indicate total power being generated (kVA) and, in some cases the real power (kW) and the
reactive power (kVAR). Both real and reactive power displays may be combined in a Watt/VAR meter.
283-When two DC generators are operating in parallel, control of load sharing is achieved by:
A)the synchronous bulbar.
B)an equalisins circuit which, in turn, controls the speed of the generators.
C)carrying out systematic load-shedding procedures.
D)an equalizing circuit which, in conjunction with the voltage regulators, varies the field
excitation current of the generators.
In order to parallel two or more DC generators, their output voltage must be the same (or
almost the same as some minor fluctuations are OK). Voltage output of the generator is
controlled by a voltage regulator which regulates the field current => output voltage of the
generator. When two or more DC generators are paralleled, equalising coils are placed in the
voltage regulators, which sense the potential difference across the controlling coils. If one
generator is taking more load than another, its output voltage will be slightly higher' than the
others and the resultant higher current flow is arranged to reduce its field strength and,
therefore, its emf. The field strengths of the remaining generators will be strengthened and
their outputs will rise slightly.
284-In order for DC generators to achieve equal load sharing when operating in parallel, it is necessary
to ensure that;
A)their voltages are almost equal.
B)the synchronising busbar is disconnected from the busbar system.
C)equal loads are connected to each generator busbar before paralleling.
D)adequate voltage differences exists.
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SYSTEM,POWERPLANT&ELECTRICS
For explanation refer to question #283.
285-An aircraft electrical circuit which uses the aircraft structure as a return path to earth, may be
defined as a:
A) complete negative system.
B) single pole circuit.
C) double pole circuit.
D) semi-negative system.
(Refer to figure 021-E33)
Oversimplified for explanatory purposes: in electrical circuits the current needs to flow -therefore two terminals
are required on all of the electrical devices. Imagine a battery and 2 light-bulbs you must run two wires from the
battery to each light bulb for it to operate. If you interrupt any of the wires, the corresponding light-bulb will go
out. This would be an example of a di-pole electrical system. However , you can also connect one terminal of
each light bulb to a common conductive material (e.g. a metal plate) and then attach a cable from the battery to
this plate as well. With each light bulb having one "terminal connected to the battery with a cable and the other
terminal connected to the metal place, which in turn is also connected to-the other terminal of the battery, both
light bulbs will operate. This would be an example of a single-pole system as illustrated on the attached figure.
The single-pole (unit pole or "earth return") system is used on aircraft of metal construction. In this system, one
wire (the single pole) connects the electrical power supply to the equipment, and the return path from the
equipment to the power source is via the aircraft structure itself. The evident advantages of this design are
reduced weight (no need for additional wiring) and easier fault detection (fewer wires => easier to find the
problem). Also the possibility of a short circuit is reduced, because of the fewer wires. Typically the wires are
routed inside the fuselage in "bundles" or "harnesses" (many strings of wires bundled together by the use of
clamps, cable ties, etc.) -if the insulation of the wires is damaged for whatever reason (ageing, mechanically,
etc.) the likelihood of the "positive" wire getting in contact with the "negative" wire is minimized, because only
the positive wires are contained in the wire harness, which itself is again insulated as a whole to prevent contact
with the airframe (negative terminal).
286-A busbar is:
A) the stator of a moving coil instrument.
S) a device which may only be used in DC circuits.
C)a distribution point for electrical power.
D)a device permitting operation of two or more switches together.
(Refer to figures 021-E95 and 021-E96)
A busbar, sometimes called a bus, is a distribution point from which individual circuits take their power. It can
take the form of a strip of metal or a piece of heavy duty cable depending upon the load it is designed to carry,
and is connected to a source of electrical power. Individual names are sometimes given to indicate their source
and place in the system -for example AC BUS 1, DC BUS 1, BATTERYBUS, etc. In electrical systems of
transport aircraft
there are often several types of bus bars installed -to name a few important ones:
•NON-ESSENTIAL bus -typically non-essential (from the perspective of flight critical system point of view)
electrical devices are powered from this type of a bus -such as galley power for the ovens and coffee pots, noncritical aircraft systems, etc. When all generators fail and only emergency power from the battery is available,
this
bus is not powered.
•ESSENTIAL bus -this is the opposite of the non-essential bus .Critical flight systems and devices are powered
from this bus .In case of all generators fail and the battery is the only source of power in flight, this bus remains
powered.
•SWITCHED BATTERY bus -this bus can be powered from the battery if the battery switch is switched to ON.
•HOT BATTERY bus -this bus is connected directly to the battery without any switches. It is always powered.
The most critical systems are powered from this bus to ensure their operation in emergency under any
circumstances.
287-The services connected to a supply busbar are normally in:
A)parallel, so that isolation of loads decreases the busbar voltage.
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SYSTEM,POWERPLANT&ELECTRICS
B)series, so that isolation of loads increases the busbar voltage.
C)parallel, so that isolating individual loads decreases the busbar current consumption.
D)series, so that isolating one load increases the busbar current consumption.
When two or more generators or alternators are used in the electrical system they can each be supplying its own
busbar or they can be connected in parallel (if certain conditions are met such as their voltage, phase, loads, etc.
must be synchronized). This generator paralleling is achieved via paralleling the bus bars to which the individual
generators are connected. By parallel operation of the generators we obtain a system where the consumers
(electrical devices) can be fed from any power source -for example if one generator fails, the load will be taken
by the remaining generators and no aircraft onboard systems will lose power. Generators, when connected in
parallel to the same busbar, provide the same output voltage, but their output currents add up. For example, if
we have two 115 V generators, each supplying an output current of 100 A connected to the same bus, the
voltage on the bus will be 115 V, but the output current will be 200 A. Current depends on the loads connected
to the busbar. More load means more current will flow through the busbar. The total current consumed in a
circuit, where the power consuming devices are connected in parallel, the total current consumption equals to
the sum of the current consumptions of the individual devices (do not confuse with parallel connection of
resistors!). If some of the electrical consumers are switched off (or isolated via a circuit breaker) then the
voltage on the busbar will remain the same, put the total current flow will decrease.
288-In a two generator system, a differential relay will ensure that:
A) generator voltages are not equal, dependent on load .
B) one generator comes "on-line" before the other.
C) generator voltages are almost equal before the generators are paralleled.
D) only one generator can supply the bus bar at the same time.
The differential relay is used in electrical systems where two DC generators need to be paralleled. It works
much the same as the reverse current relay (that prevents current flow from the battery to the generator if the
generator output voltage is lower than the battery voltage). Assume the first generator is already connected to its
bus. We now connect the second generator, but its voltage is lower than the first generator. Without the
differential relay the current would flow from the first generator to the second generator. The differential relay
will prevent this by keeping both generators separated and paralleling will be allowed by this relay only when
their voltage outputs are equal.
289-When the AC generators are connected in parallel, the reactive loads are balanced by means of the:
A) frequency.
B)voltage.
C)torque of the constant speed drive (CSD).
D)energizing current.
For explanation refer to question #277.
290-Direct current generators are connected:
A) in parallel to provide maximum voltage
B) in series to provide maximum power.
C)in series to provide maximum voltage.
D)in parallel to provide maximum power .
For explanation refer to question #287 .
291-Generators, when connected to the same busbar are usually connected:
A) dependent on the type of generator.
B) in a series mode.
C) in a parallel mode.
D) dependent on the type of engine.
For explanation refer to question 287 .
292-When the AC generators are connected In paral1el, the reactive loads are balanced by means of the:
A)torque of the constant speed drive (CSD).
B)frequency or load controller.
C)voltage controller.
D) excitation current.
For explanation refer to question #277.
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SYSTEM,POWERPLANT&ELECTRICS
293-In a simple electrical circuit, if the power consuming devices are connected in parallel, the total
current consumed is equal to:
A)the sum of the currents taken divided by the number of devices.
B)the sum of the currents taken by the devices.
C)the sum of the reciprocals of the currents taken by the devices.
D)the sum of the individual resistances.
For explanation refer to question 287.
294-In an AC circuit:
A) the battery is connected in series.
B) the battery cannot be used because the voltage is low.
C)a battery is not fitted.
D)battery output must be inverted.
A battery is a DC (Direct Current) device. You can not connect a DC device into an AC circuit. Battery can only
be
connected to a DC circuit. In aircraft there are usually both AC and DC circuits. In transport aircraft the
electrical
systems are primarily AC systems, but DC supplementary systems are also installed. The aircraft battery is
connected to the DC supplementary system which often includes inverters(devices that convert DC to AC) these devices then provide initial power to the main AC circuit -such as for starting the APU, before the AC
generators
start producing the main AC power supply.
295-What is the purpose of the GCB (Generator Circuit Breaker)?
A) Controls the generator fixed excitation.
B)Connects a generator busbar to a paired generator.
C)Connects generator to its busbar.
D)Connects synchronising bus bars of paralleled generators.
(Refer to figure 021-E94)
A generator circuit breaker (GCB) connects the generator to the busbar. However, before closing the GCB the
output parameters of the generator are checked by the Generator Control Unit or by the Control & Protection
Unit. Only if the generator output parameters meet the required limits the generator is allowed to be connected
online (to its busbar).GCBs can be operated automatically by the control units or manually by the pilots from the
flight deck.
296-In a paralleled AC distribution system what regulates the real load?
A)Voltage regulator.
B)Main control unit.
C)Torque from the CSD.
D)Voltage sensing unit.
For explanation refer to question 277.
297-A changeover relay allows:
A)an APU to connect to its busbar.
B)a GPU to connect to its busbar.
C)connection of AC to an unserviceable generator's busbar.
D)an alternate source to supply an essential bus bar.
298-How are the loads on an aircraft busbar connected?
A)In parallel so that current reduces through the busbar as loads are switched off.
B)In parallel so that voltage reduces through the bus bar as loads are switched off.
C)In series so that current reduces through the busbar as loads are switched off.
D)In series so that voltage reduces through the busbar as loads are switched off.
For explanation refer to question 287.
299-Hot/direct busbars are:
A)heated directly by bleed air.
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SYSTEM,POWERPLANT&ELECTRICS
B)directly connected to the battery.
C)directly connected to the DC generator.
D)directly connected to the AC generator.
For explanation refer to question 286.
300-If AC generators are connected in parallel the reactive loads are balanced by adjusting:
A)frequency.
B)torque of the CSD.
C)energising current.
D)voltage.
For explanation refer to question 277.
301-What are the conditions necessary in order to parallel DC generators?
A)Voltage and RPM must be the same.
B)Voltage must be nearly the same.
C)Voltage and frequency must be the same.
D)Output frequency must be nearly the same.
For explanation refer to question #283.
302-In an AC distribution system what is the purpose of the GCB?
A) Maintains constant frequency.
B) Connects the load busbar to the synchronising busbar.
C) Controls generator field excitation.
D) Connects a generator output to its load bus bar.
For explanation refer to question #295.
303-The alternators, when connected, are usually connected :
A) in series mode.
B) in parallel mode.
C) dependant on the type of generator.
D) dependant on the type of engine.
For explanation refer to question 287.
304-Generator paralleling through bus bars is done to assure that:
A) the biggest generator gets the highest load.
B) different consumers can be fed from different sources.
C) all consumers receive the same generator voltage.
D) wiring is done properly, and so that we can easily detect errors in the system.
For explanation refer to question 287
305-The type of windings commonly used in DC starter motors are:
A) series-wound.
B) shunt-wound.
C)series shunt wound.
D)compound-wound.
(Refer to figure 021-E37)
Series-wound motors -to carry heavy current they are made up of a few turns of thick wire. Because of this, a
series motor is capable of starting on full load and has high starting torque and good acceleration. However,
speed varies inversely with the load and could overspeed leading to mechanical destruction. This type of motor
is used as an engine starter motor and similar high load applications. Motor torque is proportional to the square
of the armature current and, as an increase in load results in a reduction of the back emf, there is an increase in
armature current and a rapid increase in driving torque: good starting toque, poor speed control.
In Shunt-wound motors the field Windings are arranged in parallel with the motor armature. They are of high
resistance and consist of many turns of fine wire. Because of the parallel connection with the power supply, the
current is of constant value and is low in comparison with the load current and is started on little or no load. The
speed characteristic is constant and this type of motor is used where) low torque is required but which increases
with motor speed. Torque is proportional to armature current but, at or near full load, armature reaction weakens
the effect of the field: low starting torque, good speed control.
Compound-wound motor is used when continuous running over a: wide torque load range is required and
comprises of both series and, shunt fields where the best of their characteristics can be selected The motor is
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SYSTEM,POWERPLANT&ELECTRICS
used in continuous running applications, have good, starting torque and with a fairly constant speed. Usually the
series: and shunt field are wound in the same direction on the same pole faces and augment the effect of each
other.
306-What type of electrical motor is used as a starter motor?
A)Series-wound.
B)Shunt-wound.
C)Compound-wound.
D)Induction.
For explanation refer to question 305
307-What are the advantages or disadvantages of an asynchronous motor?
A)Low starting current and constant torque.
B)Low starting current and works also with only two connected phases.
C)Works on also with only two connected phases but high starting current.
D)None of the above is correct.
Open circuit -stator phase winding. If a phase circuit opens ,rotor RPM will drop to about 60% of normal RPM
and there will be a loud humming noise sometimes called single phasing. Provided torque is not too high the
motor will
continue to run. In addition, if the motor is operating a pump, which imposes an "on" and "off" load, it may well
be that the pump will cut in more frequently than is usual. The remaining phases will take more of the load and
all fuses
may have to be changed.
Operation -when power is switched to the motor, a three phase rotating field is set up in the stator windings. An
emf is induced into the stator windings and into the rotor. The two fields react, the rotor turns and speed
increases. The greater the relative speed between the rotor and stator fields, the greater the turning moment or
torque produced and the greater the current. At switch on, a large emf is induced into the rotor and as the rotor
speed increases, relative speed decreases, there is a reduction in induced emf and torque tends to reduce as slip
(lag of the rotor speed behind the field speed) decreases. A some speed, the rotor speed, rotor induced emf and
stator induced emf produce a turning moment that is just balanced by the load on the motor. At that point, rotor
speed becomes constant. ( the mechanical load increases, the rotor slows down, slip increases, induced power
increases and the speed either stabilises at the higher torque and current or increases marginally back towards
the original speed. Eventually, the slip is so great that the motor stops, or more correctly, it reaches its 'pull out'
point. Conversely, if the mechanical load decreases, slip decreases, induction decreases and the lower torque
tends to allow the rotor speed to return to normal.
308-What is the capacitor in the one phase asynchronous motor used for?
A)To generate an elliptic field used only for starting the motor operation.
B)To prevent the system from a short circuit.
C)To generate a second phase for a sinus field used for continuous motor operation.
D)To change the rotating direction.
(Refer to figure 021-E36)
The magnetic field of the stator of a single phase induction motor does not rotate, but rather it pulses on or off A
separate start winding is wound in the stator and the phase of the current is shifted 90° by a capacitor or inductor
so that it is different from the phase of the current in the run winding. The shifted phase and the run phase
together produce a rotating field. As soon as the rotor is turning at the correct speed, a centrifugal switch
automatically disconnects the start winding and the inertia of the rotor keeps it turning in the pulsing magnetic
field .
309-On a normally aspirated engine (non turbo-charged), the manifold pressure gauge always indicates:
A)a lower value than atmospheric pressure when the engine is running.
B)a greater value than atmospheric pressure when the engine is running.
C)zero on the ground when the engine is stopped.
D)a value equal to the QFE when the engine is at full power on the ground.
The MAP (Manifold Air Pressure) gauge indicates the pressure inside the cylinder intake manifold. Manifold
air pressure is controlled by the position of the throttle lever namely the throttle butterfly valve in the
carburettor. The more the valve opens, the more air (and therefore higher mass of the air/fuel mixture) is
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allowed into the cylinders and the higher the power output of the engine. Intake manifold is connected to the
engine air intake, therefore when the engine does not operate the gauge indicates the atmospheric pressure.
Once the engine is started (assuming normally aspirated engine) then at IDLE power the MAP gauge will
indicate lower pressure than atmospheric simply because the engine Is "sucking-in" the air through the intake
=> velocity of this air is increased => its pressure decreases. Increasing the MAP using power augmentation
devices such as super-chargers or turbochargers increases the density of air in the intake manifold and
therefore also the density of the air in the air/fuel mixture => higher mass of the air/fuel mixture > higher
power output of the engine.
Note: If the MAP gauge indicates atmospheric pressure even after the engine has been started and is running
at IDLE then this might be most likely caused by a leak in the pressure sensing fine between the intake
minified and the gauge -probably a leak in the line itself or its fittings to the intake manifold or the pressure
sensor gauge. As mentioned above, when a normally aspirated engine is running at IDLE, the MAP will
always be slightly lower than the atmospheric
310-In a four-stroke piston engine, the only DRIVING stroke is:
A)compression
B)induction
C)power
D)exhaust
311-The power of a piston engine which will be measured by using a friction brake is:
A)friction horse power.
B)brake horse power.
C)heat loss power.
D)indicated horse power.
Brake Horse Power (BHP) = Power available at crankshaft.
Indicated Horse Power (IHP) = Power developed in the cylinder.
Mechanical Efficiency = Brake Horse Power x 100% ÷ Indicated Horse Power.
Friction Horsepower (FHP) = the frictional and power losses due to engine driven accessories.
Power Output = torque x RPM (power = rate of doing work; work done per unit of time).
indicated Horsepower (IHP) takes no account of any work done within the engine to overcome friction. The
indicated horsepower is a purely theoretical value and is reduced by the friction horsepower to give brake
horsepower (BHP). This is the power actually delivered
by the crankshaft to the propeller gearing.
312-The part of piston engine that transforms reciprocating movement into rotary motion is termed
the:
A)crankshaft.
B)piston .
C)camshaft.
D)reduction gear.
(Refer to figures 021-E56, 021-E57 and 021-E58)
The crankshaft is the main rotating component of a piston engine" is made of high tensile steel, and takes all the
reciprocating and rotational loading. It basically transforms the reciprocal (up/down) movement of the pistons
and its connecting rods into rotary motion. The component is mounted in high pressure oil lubricated plain
bearings called main or journal bearings. The oil flow is supplier through a duct that runs down the centre of the
shaft and forms a high oil pressure distribution gallery. There are as many cranks and "big end" bearings as
there are cylinders and pistons.
313-The power output of a piston engine can be calculated by:
A)pressure times arm.
B)work times velocity.
C)force times distance,
D)torque times RPM ..
For explanation refer to question 311.
314-On four-stroke piston engines, the theoretical valve and ignition settings are readjusted in order to increase
the:
A)engine RPM.
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B)compression ratio.
C)piston displacement.
D)overall efficiency.
(Refer to figures 021-E56, 021-E57 and 021-E58)
The Theoretical Otto Cycle -in the theoretical Otto cycle (named after a German engineer), the strokes and
valve and ignition operation take place very conveniently every 180° This, however, does not take account of
mixture and gas momentum, flame rate, exhaust gas contamination of the incoming air mixture or speed (RPM)
or mixture strength. Therefore , modification of the cycle is required: Modified Otto Cycle: near the top and
bottom of its stroke the piston moves only a relatively small amount in a linear direction, this is called
ineffective crank angle, and accelerates towards the 90° position. The crank velocity though has not changed
throughout the revolution and relative speeds need to be taken into account. The top and bottom of a stroke is
celled top dead centre (TDC) and bottom dead centre (BDC), respectively. Also, the effective power exerted by
the expanding gasses during the power stroke reduces markedly (reducing mechanical advantage) after the crank
has passed the 90° position during piston descent. All of these mechanical features need to be taken into
account. As a result of these modifications the ignition of the air/fuel charge takes place before the piston
reaches the TDC position instead at the TDC position. Also a valve overlap is introduced -where the intake
valve opens a little bit earlier before the exhaust stroke is completed -for a brief moment both the intake and
exhaust valves are open at the end of the exhaust stroke -this improves scavenging (pushing out) of the exhaust
gases from the combustion chamber. All of these modifications therefore improve the efficiency of the engine .
315-Specific fuel consumption is defined as the:
A)designed fuel consumption for a given RPM.
B)mass of fuel required to produce unit power for unit time.
C)quantity of fuel required to run the engine for one minute at maximum operating conditions.
D)maximum fuel consumption of the aircraft.
Specific Fuel Consumption (SFC) is a ratio of mass of fuel required to produce a unit of power per unit of time.
The goal of engine designers is of course to get the highest amount of power out of the engine for the lowest
possible weight of fuel .The lower the SFC ratio" the better the fuel economy. For example -if an engine has
SFC of fl0,3"it can mean for example 0,3 lbs of fuel are required to produce 1 BHP per hour -in this case the
SFC
value will be written as .0,3 lb/BHP/Hr
316-Which components constitute a crank assembly?
A)Crankshaft, camshaft, valve springs.
B)Crankcase, crankshaft, pistons and connecting rods.
C)Crankshaft, pistons and connecting rods.
D)Propeller, crankshaft, connecting rods.
For explanation refer to question 312.
317-The correct formula to calculate the multi-cylinder engine displacement (engine capacity) is:
A) cylinder length x cylinder diameter
B) piston area x piston stroke x number of cylinders
C) piston area x piston stroke
D)cylinder volume x number of cylinders
318-The global output of a piston engine is of: (global output = thermal energy corresponding to the
available shaft power over the total thermal energy produced)
A)0,30
B)0,50
C)0,75
D)0,90
Thermal efficiency of a piston engine is the efficiency with which the heat energy contained in the fuel and
released during the combustion is converted into work done during the combustion process. Average thermal
efficiency of a piston engine is in the range of 30%. Thermal efficiency = (Heat converted to work ÷ Heat
energy available in the
fuel) x 100%.
319-The compression ratio of a piston engine is the ratio of the:
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SYSTEM,POWERPLANT&ELECTRICS
A) area of the piston to the cylinder volume.
B)weight of the air induced to its weight after compression.
C) volume of the cylinder with the piston at bottom dead centre to that with the piston at top dead centre.
D)diameter of the bore to the piston stroke.
320-The crankcase is the component which:
A) provides a mounting for an all cooler.
B)provides a mounting point for most of the engine components and in which are the main rotating assemblies
located.
C) converts reciprocating motion into rotary motion.
D) operates within the float chamber.
The crankcase of a piston engine is the housing for the crankshaft assembly and provides attachment points for
the
cylinders. The enclosure forms the largest cavity in the engine and also provides a sump for the engine oil at its
lower part. It is an aluminum alloy casting in two parts ,divided along the centerline of the engine and joined
by threaded studs and nuts. Cast into the casing are the housings for the crankshaft bearings and valve camshaft
bearings. At the sides of the crankcase are holes for the passage of the piston connecting rods, with machined
facings to which the cylinders will be bolted. The crankcase casting also includes the attachment points by
which the engine will be attached to the airframe in the engine nacelle of the aircraft.
321-Volumetric efficiency is:
A)the thermal conversion factors concerning swept volume.
B)swept volume + un swept volume divided by the swept volume.
C)IHP -FHP.
D)the amount of charge induced into a cylinder compared with that which would fill the swept volume.
Volumetric efficiency (VE) of a piston engine refers to the efficiency with which the engine can move the
charge into and out of the cylinders. More correctly, VE Is a ratio (or percentage) of what volume of fuel and air
actually enters the cylinder during induction to the actual capacity of the cylinder under static conditions (swept
volume). Therefore, those engines that can create higher induction manifold pressures above ambient -will have
VE greater than 100%. VE above100% can be reached by using forced induction such as supercharging or
turbo-charging. Normally aspirated engine will have a VE of about 75-85%. VE can be improved in a number of
ways, but most notably the size of the valve openings compared to the volume of the cylinder, number of valves
per cylinder and streamlining the valve ports. Engines with higher VE will generally be able to run at higher
speeds (RPM) and produce more overall power due to less parasitic power loss moving air in and out of the
engine. Volumetric "efficiency" should in no way be construed to be a measure of engine efficiency, the thermal
efficiency of the engine, although it may have an effect on it. One of the factors that decrease the VE is for
example a high Cylinder Head Temperature (CHT) high CHT means that the temperature of the intake air will
be higher => its density will be therefore reduced and lower mass of air will be sucked in during each induction
stroke.
322-In order to get the optimum efficiency of a piston engine the positions of the intake and exhaust
valve just after the power stroke are:
A) intake valve closed and exhaust valve open.
B) both valves open.
C) both valves closed.
D) exhaust valve closed and intake valve open.
323-The compression ratio of an engine may be defined as:
A)swept volume plus clearance volume divided by swap volume.
B)swept volume plus clearance volume divided by clearance volume.
C)swept volume divided by clearance volume plus swept volume.
D)total volume minus clearance volume divided by swept volume.
324-Valve overlap occurs between:
A) exhaust and induction stroke.
B) exhaust and power stroke.
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C)compression and power stroke.
D)induction and compression stroke.
325-Assuming the modified Otto cycle, what is the position of the inlet and exhaust valve at the end of
the exhaust stroke?
A)Inlet closed and exhaust open.
B)Both valves closed.
C)Both valves open.
D)Inlet open and exhaust closed.
326-In a piston engine the manifold pressure:
A) is affected only by altitude.
B)increases as the throttle is opened.
C)decreases as the throttle is opened.
D)is unaffected by throttle position.
For explanation refer to question #309.
327-A reciprocating spark ignition engine works on the principle of the:
A)constant volume Otto cycle.
B)constant pressure Otto cycle.
C)constant volume Brayton cycle.
D) constant pressure Brayton cycle.
A piston engine works on the principle of a so called "Otto cycle". It is a 4-stroke cycle involving induction,
Compression, Power and Exhaust. The piston engine works on a principle of a constant volume cycle, unlike a
turbine engine, which works on a principle of a constant pressure cycle. In the piston engine (constant volume
cycle), when the ignition occurs the piston does not move significantly (only a little bit to reach the TDC
position where the piston movement is not very large) -once the fuel/air mixture is ignited the pressure bulksup rapidly while the volume remains nearly the same -this pressure build-up them forces the piston to move
down during the power stroke. On the contrary on a turbine engine, the mixture is ignited in the combustion
chamber where it expands (volume increase) and is thus forced over the turbine assembly
328-IHP BHP and FHP are all terms related as follows:
A) IHP is the power measured at the prop shaft, BHP is the power produced in the cylinders and FHP is the
power available in the fuel due to the calorific value.
B) IHP is the power produced in the cylinders, BHP is the power produced at the crankshaft and FHP is the
difference between IHP and BHP.
C) IHP + BHP + FHP = mechanical efficiency
D) IHP -BHP = thermal efficiency.
For explanation refer to question 311.
329-During the compression stroke:
A)the volume decreases and the temperature increases.
B)the temperature remains constant and the volume decreases.
C)the volume increases and the temperature decreases.
D)the volume remains constant and the temperature increases.
(Refer to figures 021-E56, 021-E57 and 021-E58)
Compression stroke takes place after the induction stroke. Having completed the downward Induction stroke,
the piston now starts moving upwards from the BDC position, driven through the connecting rod by the inertia
of the crankshaft. By compressing the mixture into a smaller space, its pressure and temperature is increased. As
the mixture is compressed it is heated adiabatically, and also gains heat from the hot surroundings. The pressure
therefore rises to a higher value than that which would be expected from volumetric reduction alone. The
purpose of the compression stroke is to raise the temperature of the fuel-air mixture to a value at which the fuel
will readily ignite and burn efficiently.
In the ideal cycle, the ignition spark occurs at TDC. However, this does not take account of engine RPM,
mixture strength or manifold pressure. The first consideration is that of RPM. Although engine RPM changes,
flame rate for a given mixture strength is fairly constant at about 60 ft/sec (18 m/sec). If the ignition point
occurred at the same angular position regardless of other considerations, at low RPM the, expansion of the gas
would initially try and turn the engine backwards. Conversely, at high RPM, the gas expansion would develop
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SYSTEM,POWERPLANT&ELECTRICS
fully when the piston was further down the cylinder than the ideal and mechanical advantage would be lost. On
some high speed engines this less than ideal situation is important. In the second case, flame rate changes with
mixture strength. With rich mixtures, at slow running and high power, the flame is faster and ignition would
need to occur earlier. With weaker mixtures, flame rate is slower and the ignition point needs to occur later.
On some large engines the effect of the required corrections tend to cancel each other out -but they still have to
be taken into account. It is as well to note at this point that if ignition has to occur earlier it is said to be
advanced (that is: advanced away from TDC); however, if ignition has to occur later it is said to be retarded
(that is; retarded towards TDC). In summary, the maximum development of gas expansion has to occur just after
TDC when the piston is past the ineffective crank angle point and maximum leverage, therefore, is exerted on
the piston.
330-Compression ratio may be defined as the ratio of:
A) volume of a cylinder with piston at bottom dead centre
to that with the piston at top dead centre.
B)piston stroke to piston area.
C)swept volume to piston area.
D)mass of air in a cylinder with piston at bottom dead centre
to that with the piston at top dead centre.
331-The valve and ignition timings of the theoretical Otto cycle are modified in order to improve:
A)engine RPM.
B)compression ratio.
C)overall efficiency.
D)piston displacement.
For explanation refer to question #314.
332-A cylinder head temperature gauge measures:
A)the temperature of the hottest cylinder.
B)the temperature of all the cylinders and gives an average reading.
C)the temperature of the coolest cylinder.
D)the temperature of the two cylinders furthest away from each other divided by two.
The thermal efficiency of a piston engine is on the average around only 30%. It means that out of the entire
thermal
energy released during the combustion of the fuel air" Chargeonly 30% is used as mechanical work for driving
the piston during the power stroke. Heat energy leaves the combustion chamber during the exhaust stroke
through the exhaust manifold, but a major part is dissipated into the cylinder heads as heat. The temperature of
the cylinder heads can by often monitored by the pilot using the Cylinder Head Temperature (CHT) gauge. It
typically uses the principle of a thermocouple attached to the cylinder => the thermocouple produces voltage
proportional to the temperature and it is then indicated in the cockpit as temperature. Some relatively simple
aircraft may have only 1 CHT sensor installed in the engine -in this case it will be attached to the hottest
cylinder-typically this will be one of the cylinders in the rear part of the engine, away from the ram air intake (=
receives the lowest portion of the cooling ram air flow). On aircraft where the CHT sensor is attached to every
cylinder the gauge will indicate temperatures for each of these cylinders. The readouts will never be averaged
among two or more cylinders. The gauge might be a digital indicator showing the temperatures of all cylinders
or it can be a simple analog gauge with a switch button to select the specific cylinder the pilot wishes to
monitor.
333-In a four-stroke engine, when the piston is at BDC at the end of the power stroke the position of the
valves is: (inlet/outlet)
A)closed/closed
B)open/open
C)open/closed
D)closed/open
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SYSTEM,POWERPLANT&ELECTRICS
334-What is the approximate thermal efficiency of a four stroke engine?
A)80%
B)50%
C)30%
D)98%
For explanation refer to question 318.
335-What are modern piston aero-engines constructed from?
A)Pressed steel.
B)Stainless steel.
C)Dense alloys.
D)Lightweight alloys.
Piston engines used in aircraft must be as light as possible, but at the same time have no compromise in the
reliability of operation. Therefore, lightweight alloys are used in their construction -typically aluminum or
magnesium alloys as they are very light but still offer very good structural characteristics.
336-In a four-stroke piston engine, the only "driving" stroke is:
A)compression
B)intake
C)firing-expansion
D)exhaust
337-The five events of a four-stroke cycle engine in the order,: of their occurrence:
A)Intake, ignition, compression, power, exhaust.
B)Intake, power, compression, ignition, exhaust.
C)Intake, compression, ignition, power, exhaust.
D)Intake, ignition, power, compression, exhaust.
338-If the exhaust valve of a four-stroke cycle engine is Closed and the intake valve is just closing,
the piston is on the:
A)intake stroke.
B)power stroke.
C)exhaust stroke.
D)compression stroke.
For explanation refer to question #329.
339-The horsepower developed in the cylinders of a reciprocating engine is known as the:
A)shaft horsepower.
B)indicated horsepower.
C)brake horsepower.
D)thrust horsepower.
For explanation refer to question311.
340-On which stroke or strokes are both valves on a four-stroke cycle reciprocating engine cylinder open
during a part of the strokes?
A)Exhaust.
B)Intake.
C)Power and intake.
D)Exhaust and intake.
341-What does valve overlap promote?
A)Lower intake manifold pressure and temperature.
B)A back-flow of gases across the cylinder.
C)An overlap of the power and intake strokes.
D)Better scavenging and cooling characteristics.
342-At what speed must a crankshaft turnif each cylinder of a tour-stroke cycle engine is to be fired 800
times a minute?
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SYSTEM,POWERPLANT&ELECTRICS
A)200 RPM
B)800 RPM
C)1.600 RPM
D)3.200 RPM
343-Which of the following will decrease volumetric efficiency of a reciprocating engine?
A)High fuel octane rating.
B)Short intake pipes of large diameter.
C)Low carburettor air temperature.
D)High cylinder head temperature.
For explanation refer to question 321 .
344-Prior to starting the engine the manifold pressure gauge usually indicates approximately 29" Hg.
This is because the:
A)pointer on the gauge is stuck at the full-power indication.
B)throttle is in full-open position.
C)throttle is closed, trapping a high air pressure in the manifold.
D)pressure within the manifold is the same as atmospheric pressure .
For explanation refer to question 309.
345-Pre-ignition refers to the condition that may arise when:
A)the mixture is ignited before the piston has reached top dead centre.
B)the mixture is ignited by abnormal conditions within the cylinder before the spark occurs at the plug.
C)a rich mixture is ignited by the sparking plugs.
D)the sparking plug ignites the mixture too early.
Pre-ignition is caused by a red-hot glowing piece of carbon residue or a local overheated hot-spot within the
combustion chamber, which ignites the mixture prematurely (before the spark occurs at the plug). This improper
ignition timing has of course negative consequences on the engine operation => rough running, loss of power
and continued firing after the ignition is switched off -these are all indications of pre-ignition. Also, the higher
the RPM the worse the situation will become. If not corrected, detonation may result. It is, therefore essential
that the engine is maintained correctly and that the engine is operated within its MAP, RPM and cylinder head
temperature limitations
346-The vapour lock is:
A) the exhaust gases obstructions caused by an engine overheating .
B) a stoppage in a fuel feeding line caused by a fuel vapour bubble.
C) the effect of the water vapour bubbles in the induction manifold caused by the condensation.
D) the abnormal mixture enrichment caused by a greater gasoline vaporisation in the carburettor.
Vapour lock is a problem that mostly affects gasoline-fuelled internal combustion engines. It occurs when the
liquid fuel changes state from liquid to gas (fuel vapors) due to increased temperature while still in the fuel
delivery system and Subsequently collects as fuel vapour bubbles that get trapped in the fuel lines around fuel
line bends. This disrupts the operation of the fuel pump, resulting In a significant reduction of fuel flow into the
engine or completely blocking it (transient loss of power or complete engine stalling). Restarting the engine
from this condition may be difficult. Vapour lock can more easily occur in fuel system where the fuel is suction
fed into the engine (using a suction feed pump as opposed to a gravity feed fuel system) -conditions for
occurrence of a vapour lock are high fuel temperature, low fuel amount in the tanks, low ambient pressure and
high angles of attack of the aircraft. The fuel can vaporise due to being heated by the engine, by the local
climate or due to a lower boiling point at high altitude. In regions where higher volatility fuels are used during
the winter to improve the starting of the engine, the use of "winter" fuels during the summer can cause vapour
lock to occur more readily. When a vapour lock occurs it is indicated by a reduced fuel pressure indication and
auxiliary fuel pump must be switched on (if aircraft is equipped with it) -this should increase the fuel pressure
and force it through the fuel line areas affected by the vapour lock.
347-The conditions which can cause knocking are:
A) low manifold pressure and high fuel flow.
B) high manifold pressure and high revolutions per minute.
C) low manifold pressure and high revolutions per minute.
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SYSTEM,POWERPLANT&ELECTRICS
D) high manifold pressure and low revolutions per minute.
Detonation is an unstable combustion and is caused primarily by an engine overheat condition or by using a fuel
with lower octane rating than the engine manufacturer recommended. During a normal combustion process,
after ignition, the flame rate inside the cylinder is approximately 60 to 80 ft sec and progresses gradually inside
the cylinder away from the ignition source (spark plug). However, as the engine temperatures rise and go into an
overheat condition, the flame front speed increases until it is practically instantaneous and around 1.000 ft sec basically an explosion. This causes an abrupt' power loss and there is a distinctive knocking noise. We refer to
this situation as "detonation". It causes high cylinder temperatures, violent "explosions" of the air/fuel charge
instead of gradual burning, etc, If the condition is allowed to continue the engine could be severely damaged overheating of the combustion chamber, colapse of the piston, splitting of the valves, burning of the spark plug
electrodes, etc. The corrective action includes retarding the throttle and if possible increasing the engine cooling
(lowering the Cylinder Head Temps) = richer mixture; turn the carb-heat OFF; decreasing the rate of climb and
increasing the climb speed to get more ram air cooling, etc.
Detonation may be caused by many factors:
•use of gasoline with too low octane rating;
•engine overheat condition;
•too weak (lean) a mixture;
•excessive boost from the turbocharger;
•a high charge temperature due to inappropriate use of carburettor heat;
•incorrect timing (spark too advanced, igniting the charge too early during the compression stroke => increased
combustion pressure);-,. selection of high power at low RPM, with a constant speed propeller -engine (torque)
loading too high for RPM selected.
Octane rating is an indication of a fuel's anti-knock rating (resistance to detonation) -the higher the number, the
more resistant the fuel is to detonation. High-performance engines typically have higher compression ratios and
are therefore more prone to detonation, so they require higher octane fuel. Octane rating of a spark ignition
engine fuel is the detonation resistance (anti-knock rating) compared to a mixture of iso-Octane (2,2,4trimethylpentane, an isomer of octane) and n-Heptane. By definition, iso-octane is assigned an octane rating of
100, and heptane is assigned an octane rating of zero. n-Heptane (collectively known as paraffin) detonates
rapidly. Iso-Octanes displays very little tendency to detonate even at high temperatures. An 87-octane gasoline,
for example, possesses the same anti-knock rating of a mixture of 87% (by volume) iso-octane, and 13% (by
volume) n-Heptane. This does not mean, however, that the gasoline actually contains these hydrocarbons in
these actual proportions. It simply means that it has the same detonation resistance properties as the described
'standard' defined mixture.
348-The octane rating of a fuel characterizes the:
A)the anti-knock capability.
B)fuel volatility.
C)quantity of heat generated by its combustion.
D)fuel electrical conductivity.
For explanation refer to question 347.
349-Vapour lock is:
A)vaporizing of fuel prior to reaching the carburettor.
B)the formation of water vapour in a fuel system.
C)vaporizing of fuel in the carburettor.
D) the inability of a fuel to vaporize in the carburettor.
For explanation refer to question 346
350-The octane rating of a fuel and compression ratio of a piston engine have which of the following
relations?
A)The higher the octane rating is, the higher the possible compression ratio is.
B)The lower the octane rating is, the higher the possible compression ratio is.
C)The higher the octane rating is, the lower the possible compression ratio is.
D)Compression ratio is independent of the octane rating.
For explanation refer to question 347.
351-With a piston engine, when detonation is recognised, you:
A)increase manifold pressure and enrich the mixture.
B)reduce manifold pressure and lean the mixture.
C)reduce manifold pressure and enrich the mixture.
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D)increase manifold pressure and lean the mixture.
For explanation refer to question 347.
352-A piston engine may use a fuel of a different grade than the recommended:
A) provided that the grade is lower.
B) provided that the grade is lower.
C) never
D) provided that it is an aeronautical petrol.
When a differential fuel grade has to be used for a piston engine ,it is always the next HIGHER octane rating
one. Lower octane rating should never be used because the engine would then be most likely Subject to
detonation inside the cylinders.
Octane rating is an indication of a fuel's anti-knock rating (resistance to detonation) -the higher the number, the
more resistant the fuel is to detonation. High-performance engines typically have higher compression ratios and
are therefore more prone to detonation, so they require higher octane fuel. Octane rating of a spark ignition
engine fuel is the detonation resistance (anti-knock rating) Compared to a mixture of Iso octane (2,2,4trimethylpentane, an isomer of octane) and n-Heptane. By definition, iso-octane is assigned an octane rating of
100, and heptane is assigned an octane rating of zero. n-Heptane (collectively known as paraffin) detonates
rapidly. Iso-Octenes displays very little tendency to detonate even at high temperatures. An 87-octane gasoline,
for example, possesses the same anti-knock rating of a mixture of 87% (by volume) iso-octane, and 13% (by
volume) n-Heptane. This does not mean, however, that the gasoline actually contains these hydrocarbons in
these actual proportions. It simply means that it has the same detonation resistance properties as the described
'standard' defined mixture.
353-Which one the fol1owing factors would be likely to increase the possibility of detonation occurring
within a piston engine?
A) Slightly retarding the ignition timing.
B) Using too lean a fuel/air mixture ratio.
C) The use of fuel with a high octane rating as compared to the use of one with a low octane rating.
D)Using an engine with a low compression ratio.
For explanation refer to question #347.
354-In addition to the fire hazard introduced, excessive priming should be avoided because:
A) the gasoline dilutes the oil and necessitates changing oil.
B) it drains the carburettor float chamber.
C) it fouls the spark plugs.
D) it washes the lubricant of cylinder walls.
Normally, fuel is sprayed into the choke tube of the carburettor where it is atomized and mixes with the intake
air ,evaporated in the hot induction manifold and is then in the
best form for immediate combustion delivered into the cylinders. When the engine is cold, the fuel does not
evaporate so readily and extra fuel is needed to produce enough vapour to get the engine started. The priming
system is used to provide additional fuel and a priming pump squirts
it into the choke tube, into the manifold or directly into the cylinders, depending upon the installation. The flight
manual will advise on the number of strokes required depending on the OAT. Clearly, the, colder the day, the
more fuel required. The pump can be manually or electrically selected and operated. Excessive priming can
cause not only a fire hazard, but it can also wash-off the ail film from the cylinder walls.
355-Vapor lock is the phenomenon by which:
A)abrupt and abnormal enrichment of the fuel/air mixture following an inappropriate use of carburettor heat.
B) burnt gas plugs forming and remaining in the exhaust manifold following an overheat and thereby disturbing
the
exhaust.
C)heat produces vapour bubbles in the fuel line.
D) water vapour plugs are formed in the intake fuel line following the condensation of water in fuel tanks which
have not been drained properly.
For explanation refer to question #346.
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357-If an engine detonates during climb-out, the normal corrective action would be to:
A)lean the mixture.
B)increase the rate of climb.
C)retard the throttle.
D)apply carburettor heat.
For explanation refer to question 347 .
357-On design purpose, the relationship between the fuel octane rating and the maximum
compression ratio of a piston engine is:
A)the maximum compression ratio is independent of the octane rating.
B)the lower the octane rating is, the higher the maximum compression ratio is.
C)the higher the octane rating is, the lower the maximum compression ratio is.
D)the higher the octane rating is, the higher the maximum compression ratio is.
For explanation refer to question 347.
358-The cylinder head and oil temperatures may exceed their normal operating ranges if:
A)a higher octane rating than specified for the engine is used.
B)a lower octane rating than specified for the engine is used.
C)the engine is operated at a higher than normal oil pressure.
D)the engine is operated at a too rich mixture.
For explanation refer to question 347
359-The function of the primer pump is to:
A)provide additional fuel for engine start.
B)serve as an alternate pump in case of engine driven pump
failure.
C)serve as main supply pump in a fuel injection system.
D)inject additional fuel during engine acceleration.
For explanation refer to question 354.
360-The octane rating of a fuel characterizes the:
A)fuel volatility.
B)resistance to detonation.
C)quantity of heat generated by its combustion.
D)fuel electrical conductivity.
For explanation refer to question 347.
361-The use of too low an octane fuel may cause:
A)higher manifold pressure.
B)detonation.
C)a cooling effect on cylinders.
D)vapour locking.
For explanation refer to question 347.
362-Which one of the following factors would be most likely to increase the possibility of detonation
occurring within a piston engine?
A)The use of a fuel with a high octane rating as compared to the use of one with a low octane rating.
B)High cylinder head temperature.
C)Using an engine with a low compression ratio.
D)Slightly retarding the ignition timing.
For explanation refer to question 347.
363-The fuel flow to a piston engine will vary with:
A)RPM and throttle position.
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B)RPM only.
C)RPM, throttle position and mixture setting.
D)RPM and mixture setting only.
The fuel flow of a piston engine will depend on various factors:
•RPM -the higher the engine RPM, the higher the speed of the intake air, hence more fuel is drawn in to
maintain the correct air/fuel mixture ratio.
•Throttle position -basically controls the engine RPM by allowing or restricting the amount of air through the
carburettor venturi -again directly affects the fuel flow.
•Mixture setting -when using rich mixture setting, the fuel flow will be higher (more fuel allowed in for a given
mass of air).
364-Detonation occurs due to:
A)use of too high an RPM with too low manifold pressure.
B)low cylinder temp and pressure.
C)excessive cylinder temp and pressure.
D)use of the wrong grade of oil.
For explanation refer to question 347 .
365-The difference between Avgas 100 and Avgas 100LL fuel respectively are:
1)colour
2)anti-knock value
A)1) same; 2) same
B)1) same; 2) different
C)1) different; 2) same
D)1) different; 2) different
There are 3 main types of AVGAS (Aviation Gasoline):
Avgas 100 LL -blue colour, low lead content, specific gravity 0.72, anti-knock rating 100/130
Avgas 100 -green colour, high lead content, specific gravity 0.72, anti-knock rating 100/130
Avgas 80 -red colour, low lead content, specific gravity 0.72, antiknock rating
366-The colour of 100 LL Avgas is:
A)green
B)red
C)purple
D)blue
For explanation refer to question 365 .
367-Which of the following conditions most likely lead to detonation?
A)Improper ignition timing.
B)Use of fuel with too low octane rating.
C)Improper valve grinding at overhaul.
D)Use of fuel with too high octane rating.
For explanation refer to question 347.
368-The auxiliary fuel pumps are:
A)mechanically driven by the engine and are connected in series with the main fuel booster pump.
B)mechanically driven by the engine and are connected in parallel with the main fuel booster pump.
C)electrically driven and are connected in parallel with the main fuel booster pump.
D)electrically driven and are connected in series with the main fuel booster pump.
On a simple fuel system the fuel is routed from the fuel tanks via a fuel selector valve to the fuel filter, where
any dirt is stopped by the filter screen. Fuel then continues through the fuel pumps into the carburettor. The
engine is typically equipped with the main fuel booster pump which is mechanically driven by the engine. Many
airplanes, especially those with a suction feed fuel system on low-wing aircraft (as opposed to gravity feed fuel
system on high-wing aircraft) are also equipped with an auxiliary fuel pump. This fuel pump is electrically
driven by the aircraft's main electrical system. The auxiliary pump is connected in parallel to the main booster
pump and serves as a backup in case of a failure of the main booster pump to ensure sufficient fuel supply to the
engine. It is also used in the critical phases of flight -such as takeoff and landing maneuvers to eliminate any risk
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associated with potential failure of the main engine driven pump. Auxiliary fuel pump may also be used to boost
the fuel pressure when a vapor lock condition occurs -as the fuel pressure is increased the vapour lock condition
is often eliminated in most cases. Another possible use of the auxiliary fuel pump is in emergency situation such as a low fuel condition or a rough running engine, when the exact cause is unknown (as a precaution to a
possible restriction in fuel flow the auxiliary fuel pump can be used).
369-The auxiliary fuel pumps installed on single-engine low-wing aeroplanes are typically used:
1)during takeoff
2)during cruise
3)during landing
4)in emergency situations
5)in case of a suspected vapour lock
6)in case of failure of the engine fuel pump
A)1,2,3,4,5,6
B)1, 3, 4, 5, 6
C)1,2,3,4,5
D)1,3,4,5
For explanation refer to question 368.
370-In which sections of the carburetor would icing most likely occur?
A)Main air bleed and main discharge nozzle.
B)Float chamber and fuel inlet filter.
C)Accelerator pump and main metering jet.
D)Venturi and the throttle valve.
(Refer to figures 021-E13 and 021-E12)
Carburettor icing is an icing condition which can affect any carburettor under certain atmospheric conditions. It
can occur with outside air temperatures as high as +30'C and in clear air ,given a relative humidity of 30% or
more, depending upon air temperature. Lowest temperature threshold for potential carb icing is approx. -5˚C
with a relatively low humidity (30%) up to -15 C with a relatively high humidity. The most critical free air
temperature is thought to be +13 C or so. Icing is more likely to occur at low power settings, such as descent
power, when the throttle butterfly is almost closed and creating a significant pressure/temperature drop. The
types of icing that may be encountered are the carburettor icing and the impact icing. Carburetors icing -There
are two elements to this type of icing: a)Adiabatic Cooling -air flowing through the venturi increases velocity,
decreases pressure and decreases temperature. The narrowest part of the venturi, narrowed still further by fuel
nozzles perhaps, is a place where ice can form. b)Fuel or Refrigerant Icing -when a fluid vaporizes it takes heat
from the surrounding medium and the temperature decreases. This will occur around the fuel nozzle and is
additive to the adiabatic cooling affect. Impact Icing -water droplets freeze on impact with the air intake, throttle
valve, and in any projection into the air intake system. Ice can build up very quickly indeed and at
temperatures of 0 C and below. Icing builds up in the venturi, around the fuel nozzles and butterfly valve and
gradually restricts all air flow into the engine. Rough running, jammed throttle (perhaps), low power and in an
extreme case, engine failure. The ice will typically form on the surfaces of the carburettor throat, further
restricting it. This may initially increase the venturi effect (causing higher pressure and temperature drop), but
eventually restricts airflow, perhaps even causing a complete blockage of the carburettor or even alter the flow
to such extent that the zone of low pressure is moved away from the fuel nozzle and complete engine stoppage
occurs. Icing may also cause jamming of the mechanical parts of the carburettor, such as the throttle butterfly
valve. The presence of cerb-ice can be identified by a drop in RPM on fixed-pitch prop aircraft, or by the
decrease in MAP on aircraft equipped with a constant-speed prop. To protect the carb from ice formations,
carburettor heat system is installed on most piston aircraft. It directs a hot air (heated up via the exhaust
manifold heat exchanger) into the carburettor. Note that when the carb-heat is initially applied, the RPM (or
MAP) initially drops a little bit further down (use of hot air lowers the density of the air intake and therefore
reduces engine power), then increases as the ice inside the carb is melted. Note: use of hot air (carb-heat) at
ambient temperatures of 0 C and below may in fact increase the carb-ice risk rather than cure the problem, by
raising the temperature of the incoming air to a critical level of around +13°.
371-With respect to a piston engined aircraft, ice in the carburetor:
A) will only form at OATs below the freezing point of fuel
0
B) will only form at OATs below +10 C
C) will only form at OATs below the freezing point of water
0
D) may form at OATs higher than +10 C
for explanation refer to question 370.
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372-In an engine equipped with a float-type carburetor, the low temperature that causes carburetor ice is
normally the result of:
A) compression of air at the carburetor venturi
B) low volatility of aviation fuel
C) vaporization of fuel and expansion of the air in the carburetor
D) freezing temperature of the air entering the carburetor
for explanation refer to question #370.
373-The first indication of carburetor icing during cruise, in aeroplanes equipped with constant speed
propellers, would most likely be a:
A) rough running engine followed by an increase in manifold pressure
B) decrease in manifold pressure
C) decrease in RPM
D) rough running engine followed by loss in RPM
for explanation refer to question 370.
374-Air flowing through a venturi of a carburettor causes:
A)a drop of pressure at the throat.
B)a reduction of air velocity at the throat.
C)a rise of pressure at the throat.
D)an increase in velocity and pressure.
375-In a normally aspirated piston engine carburetor icing can occur:
A)between 0°C and -10°C
B)at more than +10°C.
C)only at less than +10°G if there is visible moisture.
D)only above 5.000 ft.
For explanation refer to question 370.
376-Regarding carburettor ice, state the environmental caution areas most conducive for the formation
of this type of ice.
A)Temperature between +5°C and +18°C, visible moisture or relative humidity greater than 60%.
B)Temperature between -5°C and +18°C, visible moisture or relative humidity greater than 60%.
C)Temperature less than OOG, and clouds present.
D)Temperature between +5°C and +18°C and clouds present.
377-Carburettor icing can occur when the outside air temperature is between:
A)-15°C to +5°C.
B)O°C to +15°C.
C)+15°C to +30°C.
D)-5°C to +18°C.
For explanation refer to question 370.
378-In an aircraft equipped with a float-type carburettor and a constant-speed propeller, carburettor
Icing would probably first be detected by:
A)a drop in engine RPM.
B)detonation.
C)a drop in manifold pressure and engine RPM.
D)a drop in manifold pressure.
For explanation refer to question 370.
379-If the volume of air passing through a carburettor venturi is reduced, the pressure at the venturi
throat will:
A)decrease.
B)be equal to the pressure at the venturi inlet.
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SYSTEM,POWERPLANT&ELECTRICS
C)be equal to the pressure at the venturi outlet.
D)increase.
The quantity or mass of air flowing into the tube is the same as that flowing out of it. Therefore, the velocity of
the air as it passes through the venturi must increase in order to maintain constant mass flow. Bernoulli's
theorem states that the total energy of a fluid in motion is constant at all points, so an increase in velocity must
be matched by a decrease in pressure and consequently also a decrease in temperature. This is the basic
operating principle of a carburettor. Now .if you reduce the amount of airflow through the tube, the pressure
decrease at the venturi will be lower, because the velocity will not be so high. Therefore the correct answer to
this question is that the pressure will increase.
380-The amount' of fuel that flows through the carburettor is directly controlled by the:
A)throttle valve.
B)mixture control valve.
C)airflow through the carburettor venturi.
D)main metering jet.
381-The presence of carburettor ice in an airplane equipped with a fixed-pitch propeller can be verified
by applying carburettor heat and noting:
A)an increase in RPM and then a gradual decrease in RPM.
B) a decrease in RPM and then constant RPM.
C)an immediate increase in RPM with no further change in RPM.
D)a decrease in RPM, followed by an increase in RPM.
For explanation refer to question 370.
382-Icing of the carburettor can take place:
A)when the temperature drops below -5°C.
B)when the temperature drops and precipitation occurs.
C)when the temperature drops and sufficient moisture is present for sublimation.
D)when the temperature drops below O°C.
For explanation refer to question 370.
383-In an air-cooled engine:
A)the air cooler matrix is water cooled.
B)fins, baffles and deflectors increase the cylinder and head surface areas.
C)the header tank is placed above the system.
D)air is ducted through the oil cooler first.
Typical air-cooling system contains numerous baffles, fins and deflectors that guide the ram air airflow from the
intake around the hot parts of the engine. Heat from the engine is transferred to the cold air passing over it. The
cooling ram air lowers the Cylinder Head Temperatures (CHT). The more air passes over the engine the more
cooling effect. This air then exits through the bottom of the engine cowling on simple piston aircraft or through
a device called the "Cowl Flap on more complex aircraft. This device is typically manually controlled by the
pilot. It is basically a flap "valve" that controls the rate at which the air is allowed to pass through the flap
opening
and out of the engine compartment.
The cowl flap is set according to requirements that very much depend upon air speed. At slow speed, high
power, especially in hot climates, the flap will be substantially open and even more so during taxiing and ground
operations. Opening the cowl flap makes it easier for the cooling ram air to pass through the engine
compartment and therefore its speed increases, providing better cooling function. In the cruise at lower power
settings and at higher speeds, the flap will be substantially closed as the ram air is typically sufficient and
opening the cowl flaps would cause not only undesired drag but could also lead to over-cooling of the engine.
To improve the efficiency of the air cooling, heat dissipation is assisted by increasing the external surface area
of the cylinder heads and barrels using deep fins, though which the air can act upon. In order to avoid uneven
cooling of the cylinders the airflow must be across the engine, rather than along it. In the latter event the cooling
effect would be progressively reduced towards the rear of the engine. With in-line engines the cooling airflow is
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SYSTEM,POWERPLANT&ELECTRICS
introduced to one side of the engine and directed across the cylinders by means of baffle plates. In opposed
layouts the air is introduced into the cowling above the engine and baffles between the cylinders ensure that the
airflow passes downward through the cylinder cooling fins to the
lower part of the cowling. .
384-On an air-cooled reciprocating engine the cooling airflow is provided by:
A)supercharger outlet.
B)a temperature controlled by-pass valve.
C)ram air.
D)selection.
For explanation refer to question 384.
385-In liquid-cooled engines, the composition by volume of the coolant mixture is:
A)30% ethylene glycol and 70% water.
B)60% ethylene glycol and 40% water.
C)50% ethylene glycol and 50% water.
D)70% ethylene glycol and 30% water.
In a liquid-cooled engine an integral double water jacket is wrapped around the hotter parts of the engine,
through which the coolant is circulated under pressure. The liquid coolant is made up of 70% water and 30%
ethylene glycol together with a trace of inhibitors to combat any corrosion effects of the coolant. The system is
simple in outline. Fluid is stored in a header tank and a coolant pump circulates the fluid around the engine.
Return fluid is cooled by a radiator that includes a thermostatically controlled bypass valve set to a specific
temperature. Coolant pressures and temperatures are indicated on the flight deck. The system is pressurized by a
spring on a combined filler and vent cap (same as a car).
386-Cooling air for a reciprocating engine can be obtained by means of:
A)a super-charger.
B)ram air.
C)a turbo-charger.
D)a pneumatic system.
For explanation refer to question 383.
387-The main reason for opening the cowl flaps is to control the:
A)cabin temperature.
B)EGT (exhaust gas temperature).
C)oil temperature.
D)CHT (cylinder head temperature).
For explanation refer to question 383.
388-During ground operation of an engine, the cowl flaps should be in what position?
A)Closed to avoid excessive drag on takeoff.
B)Open to provide liquid coolant flow from the radiator
through the engine.
C)Closed.
D)Open.
For explanation refer to question 383.
389-The dry sump oil system for a piston engine incorporates an oil cooler that is fitted:
A)in the return line to the oil tank after the oil has passed through the scavenge pump.
B)between the oil tank and the pressure pump.
C)after the pressure pump but before the oil passes through the engine.
D)after the oil has passed through the engine and before it enters the sump.
(Refer to figures 021-E62 and 021-E63)
An oil cooler is a matrix which is usually air-cooled. and through which the oil flows. The cooler is located in a
duct through which the airflow is controlled by a shutter and this controls the temperature of the oil output. The
temperature of the oil is transmitted to the flight deck; although, the transmitter may well be located in the oil
tank or after the pressure pump. The shutter can be controlled manually or automatically. Most oil coolers
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SYSTEM,POWERPLANT&ELECTRICS
include a temperature or pressure controlled bypass facility or, a combination of both. On a dry sump system the
oil cooler is located between the scavenge pump and the oil tank (hot oil is cooled after passing through the
engine and before it goes back to the oil tank).
390-The reading on the oil pressure gauge is the:
A)pressure of the oil on the outlet side of the pressure pump.
B)difference between the pressure pump pressure and the scavenge pump pressure.
C)pressure in the oil tank reservoir.
D)pressure of the oil on the inlet side of the pressure pump.
(Refer to figures 021-E62 and 021-E63)
The oil pressure transmitter is typically located on the output side of the pressure pump. Oil temperature sensor
is typically located on the return line from the engine, after the oil cooler and before the oil is returned back into
the oil tank. The oil temperature sensor can also be located at the tank outlet (between the tank and the pressure
pump) on some installations instead after the oil cooler.
391-For internal cooling, reciprocating engines are especially dependent on:
A) a rich fuel/air mixture.
B) the circulation of lubricating oil.
C)a properly functioning thermostat.
D)a lean fuel/air mixture.
(Refer to figures 021-E62 and 021-E63)
There are several vital functions of the oil system in a piston engine: Lubrication -reduction of friction between
moving parts, by interposing a film of oil. Cooling -various internal parts of the engine by heat dissipation. Heat
is transferred from hot metal engine parts (by convection) to the cooler lubricating oil. Sealing -the combustion
chamber by filling the small space between piston rings and cylinder walls, thus preventing the flow of
combustion gases from combustion chamber to crankcase. Flushing -the engine by carrying sludge and residue
(mainly products of combustion) from the moving parts and depositing them in the oil filter. Corrosion
prevention -by protecting metal parts of the engine from oxidising agents (oxygen & water).
392-In very cold weather the pilot notices slightly higher than normal oil pressure on startup. This:
A) is abnormal and requires the engine to be shut down.
B) is acceptable provided it returns to normal after start up.
C) is abnormal, but does not require an engine shut down
D) indicates an incorrect oil type is being used and engine should be shut down immediately.
Viscosity is a measure of the resistance of a fluid which is being de formed by either shear stress or extensional
stress. In other words it is the tendency of a fluid to resist flow. In everyday terms (and for fluids only), viscosity
is "thickness". Thus, water is "thin," having i lower viscosity, while honey or oil is "thick" having a higher
viscosity. Water will flow a lot easier than honey or oil. The viscosity of the oil tends to decrease with
increasing temperature => hot oil is "thinner" flowing more easily, while the cold oil is "thick" restring flow and
flowing very slowly. An ideal lubricating oil would maintain a relatively constant viscosity over the whole range
of working temperatures of the engine, from cold, winter starting to hot, high temperature running. Because of
the fact that oil viscosity is determined by the oil temperature (cold oil has high viscosity -it is "thick" and
resists flow) it is common to see a slightly high oil pressure after starting the engine in cold environments. The
cold oil resists flow, hence higher oil pressure. As the engine warms up the oil gets warmer and viscosity is
lowered -oil becomes "thinner" and no longer resists flow, oil pressure returns to normal operating values.
393-Low oil pressure is sometimes the result of a:
A) too large oil pump.
S) restricted oil passage.
C)worn oil pump.
D)too small scavenger pump.
•Low oil pressure can be typically caused by low oil content or, failing oil pump. Another reason might be that
the pressure relief valve is stuck in the open position or is simply out of adjustment.
•High oil pressure could be caused by very cold oil or a sticking oil pressure relief valve. Danger of oil venting
overboard and oil leuse through broken pipes and joints.
•High oil temperature -possible gradual loss of contents (and the remaining small quantity of oil is absorbing the
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SYSTEM,POWERPLANT&ELECTRICS
engine heat => it will get hotter than normal quantity of oil), ineffective cooler, for example, stuck bypass or
cooling flap stuck shut, or prolonged flight at low speed in high ambient temperature conditions. A long slow
climb at high gross weights and power settings would be an example of this. In the first condition, the situation
would be resolve: ultimately by curing the leak (a bit unlikely) or shutting down the engine (highly likely). In
the second condition, reducing the climb rate and increasing the airspeed (increased airflow over the engine=˃
better cooling) should alleviate the problem.
•Oil leaks -oil quantity decreasing, then fluctuating oil pressure and increasing oil temperature; finally, complete
failure of the oil system, followed by bearing failures accompanied usually by engine vibration.
394-For a given type of oil, the oil viscosity depends on the:
A) oil temperature
B) outside pressure.
C)oil pressure.
D)quantity of oil.
For explanation refer to question #393.
396-The major task of the engine lubrication system is to:
A)cool the engine.
B)lubricate the engine bearings and running surfaces.
C)provide an oil mist in the crankcase.
D)provide heating for the fuel cooler.
For explanation refer to question 391.
396-The lubricating system of an air cooled piston engine is used to:
A)keep the engine warm.
B)reduce internal friction and provide cooling.
C)to operate the fuel control unit.
D)operate constant speed propellers.
For explanation refer to question 391.
397-The oil cooler in a dry sump lubrication system of a piston engine is fitted:
A)between the oil tank and the pressure pump.
B)after the pressure pump but before the pressure filter.
C)between the pressure filter and the crankshaft.
D)in the return line to the oil tank after the oil has passed through the scavenge pump.
For explanation refer to question 389.
398-If the ground wire between the magneto and the ignition switch becomes disconnected, the most
noticeable result will be that the engine:
A) will not operate at the left magneto.
B) cannot be shut down by turning the switch to the OFF position.
C)will not operate at the right magneto.
D)cannot be started with the switch in the ON position.
(Refer to figures 021-E59 and 021-E60)
Primary circuit of the mogneto -the primary coil and its controlling low (L T) tension circuit consists of 3 main
controlling elements as follows. The CAPACITOR stores electricity, in this case that induced in the primary coil
and reduces sparking across the contact breaker points; the CONTACT BREAKER POINTS are operated by an
engine driven cam and when opened collapses the primary field; an IGNITION SWITCH labeled ON -OFF:
when OFF is selected it earths any coil output by completing the primary circuit, therefore, no output to the
sparking plugs; when ON is selected, the switch is opened, the primary circuit is broken and the ignition system
is live. Remember: to inhibit a magnet operation and to prevent the spark from occurring the primary circuit
must be grounded. If the ground wire is broken then even with the ignition switch in OFF position the engine
will not stop running the magneto will continue to operate. Another important thing to remember for the exams
is that the rapid magnetic field changes (flux) around the primary coil in a magneto are accomplished by the
breaker points OPENING.
399-Ignition systems of piston engines are:
A) independent of the electrical system of the aeroplane
B) dependant on the battery.
C)dependant on the DC generator.
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SYSTEM,POWERPLANT&ELECTRICS
D)dependant on the AC generator.
(Refer to figures 021-E59 and 021-E60)
It is vital to efficient engine operation that a satisfactory production of a spark is provided to ignite the fuel/air
mixture in the cylinder. Ignition must occur at the correct time so that maximum pressure is achieved on top of
the piston as it passes TDC (Top Dead Center) and starts to move down again towards BDC (Bottom Dead
Center). There are two types of ignition systems: the one found in typical car engines which relies on the
electrical power supplied by the alternator/battery, and the magneto type which is used on aircraft engines. .
Aircraft piston engines use a device called a magneto to provide . electric power for the ignition -these are selfcontained "generators" of electrical power which are completely independent on the aircraft's electrical system.
Magnetos are driven directly by an engine gearbox -they are self contained generators using rotating permanent
magnets, completely independent on the aircraft's electricity system. Two magnetos are fitted to each engine in
order to provide not only better efficiency for the combustion process, but also to improve the reliability and to
provide redundancy. Each cylinder contains two spark plugs and each of these spark plugs receives power from
a different magneto. Two sparks provide two flame fronts within the cylinder. The two flame fronts decrease
the time needed for the complete fuel charge to start burning and there tore most of the fuel is already burning
at a lower temperature and pressure. As the combustion pressure rises within a single-plug cylinder, lower
octane portions of the fuel mixture far from the original flame front can explode lighting off another flame
front in a different part of the cylinder at a different . time. This leads to engine knock. Therefore two flame
fronts can help to decrease the octane requirement for any given engine and . situation.
400-The purpose of an ignition switch is to:
A) connect the battery to the magneto.
B) connect the secondary coil to the distributor.
C) control the primary circuit of the magneto.
D) connect the contact breaker and condenser in series with
the primary coil.
For explanation refer to question 398.
401-If an engine fails to stop with the magneto switch in OFF position, the cause may be:
A)excessive carbon formation in cylinder head.
B)switch wire grounded
C)defective condenser.
D)fouled spark plugs.
The function of the ignition switch is to permit or prohibit the operation of the magnetos of a piston engine.
When the ignition switch is placed in the OFF position the primary circuit of each magneto is grounded. In this
condition the magneto is unable to induce voltage that could be used by the sparks no matter how fast it is
rotated. However, when the ignition switch is turned to the ON position, the magneto circuit is no longer
grounded -it becomes live and now it is able to induce a spark if rotated with a sufficient speed. Therefore, with
reference to this question, answer B) is incorrect, because as mentioned above, when the magneto is grounded, it
is switched OFF and can not produce a spark. We therefore have only one more option left why the engine
might still be running and it is answer A). If there is excessive carbon formation inside the cylinder head it can
be glowing red-hot when you attempt to shut down the engine using an ignition switch. Even though there is no
longer a spark occurring from the magneto, it is this glowing carbon residue that keeps igniting the mixture
being sucked into the still running engine.
402-If, when the magneto selector switch is set to the OFF position, a piston engine continues to run
normally, the most probable cause is that:
A) there is a carbon deposit on the spark plugs electrodes.
B) the grounding wire of one of the magnetos is broken.
C)a wire from the magneto is in contact with a metallic part of the engine.
D) there are local hot points in the engine (probably due to overheating of the cylinder heads).
For explanation refer to question #398.
403-When is spark plug fouling most likely to occur?
A)In the climb if you have not adjusted the mixture.
B)Cruise power.
C)In the descent if you have not adjusted the mixture.
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SYSTEM,POWERPLANT&ELECTRICS
D)Maximum takeoff power.
Spark plug fouling is often caused by oily deposits forming on the spark plug electrodes -the result can be
evidenced by erratic idling RPM, engine rough running and failure to reach full power. One of the usual
causes is allowing the engine to idle for long periods thus permitting excessive oil seepage into the
combustion chamber. Also, the use of a fuel with standard lead content as opposed to that with low lead levels
(LL) will cause fouling of the sparking plugs(unless the "leaded" fuel is the type recommended by the engine
manufacturer). Another reason might be using a mixture excessively rich -this will result in lower combustion
temperatures, not burning all of the fuel content of the air/fuel mixture and subsequent oil/carbon deposits
forming on the spark plug electrodes. Sometimes it helps to run-up the engine to higher RPM and lean the
mixture to increase the combustion temp to
burn-off the deposits.
404-The ignition occurs in each cylinder of a four-stroke engine (TDC = Top Dead Centre):
A)behind TDC at each second crankshaft revolution.
B)before TDC at each crankshaft revolution.
C)behind TDC at each crankshaft revolution.
D) before TOC at each second crankshaft revolution.
405-Prolonged running at low RPM may have an adverse effect on the efficiency of the:
A)carburettor.
B)sparking plugs.
C)oil pump.
D) fuel filter.
406-An aircraft magneto is switched off by:
A)opening the primary circuit.
B)grounding the primary circuit.
C)opening the secondary circuit.
D) grounding the secondary circuit.
For explanation refer to 398.
407-The purpose of a distributor in an ignition system is to distribute:
A)secondary current to the sparking plugs.
B)primary current to the condenser
C)secondary current to the condenser.
D)primary current to the sparking plugs.
(Refer to figures 021-E59 and 021-E60)
The distributor device in the ignition system of a piston engine consists of a rotating arm which is gear-driven
from the magneto rater shaft at a speed that is half engine crankshaft speed. Spaced equidistantly around the
stator, or casing, of the distributor are a number of electrical contacts, one for each sparking plug. At the end of
till rotor arm is an electrical contact, supplied with high voltage from the secondary coil of the magneto
transformer. As the end of the rotor arm passes a stator contact the gap between the two is small, enough to
allow high-voltage current to flow from the magneto's secondary coil to sparking plug and the spark plug
produces a space The distributor is basically a mechanical spark distribution device distributing the energy to
the correct spark plug in the correct order
at any given moment.
408-Under normal running conditions a magneto draws primary current:
A) from the aircraft batteries via an inverter.
B) from the booster coil. .
C) directly from the aircraft batteries.
D) from a self-contained electromagnetic induction system
(Refer to figures 021-E59 and 021-E60)
A magneto is an AC generator which relies on Faraday's laws that when a conductor cuts or is cut by a
magnetic field, an electromotive force (emf voltage) is induced in the conductor. The magnitude of the emf is
dependent upon the strength of the field and the speed a which the magnetic field is cut. Further, suppose a coil
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SYSTEM,POWERPLANT&ELECTRICS
of a few but thick coils of wire is cut by the lines of force of a magnetic field. An. emf is induced which for the
sake of argument can be assumed to be say, 200 volts. If the field is varied, the emf will change; if the speed of
the coil moving through the field is varied, the emf will change. For illustrative purposes this coil will be called
the primary coil. Suppore now that around the coil of thick gauge wire a second coil of very: many turns of thin
wire are wrapped around the primary coil. Again for illustrative purposes, this second coil will be called the
secondary coil. As the magnetic field increases around the primary coil ii encompasses the secondary coil and as
the lines of magnetic force (flUX) change a voltage is induced in the secondary coil which is very much higher
than that of the primary due to the greater number of turns of the secondary coil. The output could be as high as
20,OO volts. The coils of a magneto then, are nothing more than a step-uc transformer. To intensify the
magnetic flux of the primary coil, the coils are wound around a laminated soft iron core; this will produce a
greater output. Basic production of a magnetic field" a rotating magnet (the most common type of magneto)
provides the initial flux and the coils are wound around a stationary armature. Maximum flux is obtained when
the poles are opposite the armature and the magnetic field encompasses the primary and secondary coils. To
further enhance the output of the coils, a switch is inserted into the primary foil and when it is closed the flux
increases but when it is opened, the flux collapses dramatically inducing an emf into the primary and secondary
coils. It is this system which forms the basis of an engine ignition system .
409-If the ground wire between the magnetos and the ignition switch becomes disconnected the most
noticeable results will be that:
A)the engine cannot be started with the ignition switch in the "ON" position.
B)a still operating engine will run down.
C)the engine cannot be shut down by turning the ignition switch to the "OFF" position.
D) the power developed by the engine will be strongly reduced.
For explanation refer to question 398.
410-The very rapid magnetic field changes(flux) around the primary coil in a magneto are accomplished
by the:
A) contact breaker points opening
B) Contact breaker points closing
C) Rotor turning past the position of maximum flux in the armature
D) Distributor arm aligning with one of the high tension segments
411-the most common type of magneto is the:
A) rotating magnet
B) rotating armature
C) impulse starter
D) high tension booster coil
412-if the ignition timing is advanced, the spark will occur:
A) nearer to TDC
B) further away from BDC
C) after the inlet valve opens
D) further away from TDC
413-a spark occurs when the:
A) contact breakers close
B) rotor arm is trailed
C) contact breakers are nearly closed
D) contact breakers open
414-Dual ignition provides a factor of reliability and:
A) saves wear caused by using one magneto constantly
B) provides more voltage
C) improves starting
D) improves combustion efficiency
for explanation refer to question 399.
415-Ignition systems of a running piston engine receive electrical energy from :
A) capacitors
B) batteries
C) generators
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SYSTEM,POWERPLANT&ELECTRICS
D) rotating permanent magnets
for explanation refer to question 399.
416-Once the engine has started, ignition systems of piston engines are:
A)dependent on the DC generator.
B)dependent on the battery.
C)independent of the electrical system of the aircraft.
D)dependent on the AC generator.
For explanation refer to question 399.
417-Spark plug fouling is more likely to happen if:
A)the engine runs at maximum continuous power for too long.
B)the aircraft descends without a mixture adjustment.
C)power is increased too abruptly.
D)the aircraft climbs without mixture adjustment.
418-With an aircraft fitted with a fixed pitch propeller, during flight at normal cruising speed, one
magneto fails completely" This will first cause:
A)loss of approximately 100 RPM.
B)an additional load on the other magneto.
C)excessive vibration.
D) the engine to overheat.
The correct functioning of the duplicated magneto ignition system is checked by means of a magneto drop
check. This is a check that each magneto ignition system functions correctly when its ignition switch is open (in
the ON position) and that it ceases to function when its ignition switch is closed (in the OFF position). With the
engine running at the RPM recommended in the operating manual (typically 1.500 -1.800), the magnetos are
individually switched OFF (one at a time) and the drop in RPM with the cylinders firing on one plug only (each)
is noted. This is a check both of the health of the individual magneto ignition systems and that the ignition
switches are operational. The RPM drop observed on a magneto drop check should typically be between 50 and
125 RPM. This procedure basically simulates a failure of one magneto during the flight.
419-The distributor of a magneto:
A)supplies primary current to the sparking plug.
B)supplies secondary current to the sparking plug.
C)supplies secondary current to the condenser.
D)acts as a step-up transformer.
For explanation refer to question 407.
420-If a magneto switch becomes "open circuit":
A)the switch will fail to stop the engine.
B)the engine will fail to start.
C)the point circuit will be connected in series with the condenser.
D)the engine will cut out when the other magneto is switched off.
For explanation refer to question 398.
421-What is the purpose of the distributor in the ignition system?
A)Close the contact breaker points.
B)Distribute primary current to the spark plugs.
C)Distribute secondary current to the spark plugs.
D)Distribute secondary current to the condenser.
For explanation refer to question 407.
422-The ignition system of a piston engine depends on:
A)the aircraft battery being fully charged.
B)a DC generator.
C)an AC generator.
D)nothing as it is independent of the aircraft electrical system.
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SYSTEM,POWERPLANT&ELECTRICS
For explanation refer to question 399.
423-In a 4-stroke engine when does Ignition occur?
nd
A)After TDG every 2 rotation of the crankshaft.
nd
B)Before TOG every 2 rotation of the crankshaft.
C)Before TDC every rotation of the crankshaft.
D)After TOC every rotation of the crankshaft .
424-The ignition is turned to the OFF position and the engine continues to run. The most likely
explanation is:
A)the ignition switch wire is broken.
B)the ignition switch wire is touching the airframe.
C)the magneto has malfunctioned.
D)the spark plugs are fouled and the engine is dieseling.
For explanation refer to 398.
425-What is the purpose of a condenser fitted to a magneto?
A)It provides the high voltage spark.
B)It prevents arcing and provides a sink for the collapsing primary current.
C)It ensures the spark discharge rate is correct.
D)It regulates the firing sequence.
426-In a 4-stroke engine, when does ignition occur in each cylinder?
nd
A)After TDC for starting and then before TDC every 2 rotation of the crankshaft.
nd
B)Before TDC for starting and then after TDC every 2 rotation of the crankshaft.
C)After TDC for starting and then before TDC every rotation of the crankshaft.
D)Before TDC for starting and then after TDC every rotation of the crankshaft.
427-The magnetos are switched off and the engine continues to run normally. The cause of this fault is:
A)a wire from the magneto coming in contact with the metal aircraft skin.
B)hotspots existing in cylinder.
C)carbon deposits on spark plug.
D)grounding wire from magneto being broken.
For explanation refer to question 398.
428-One reason for the dual ignition system on an aircraft engine is to provide for one of the following:
A)Improved engine performance.
B)Uniform heat distribution.
C)Balanced cylinder head pressure.
D)One ignition system serves as stand by in case the system in operation fails.
For explanation refer to question399.
429-In a four-stroke cycle aircraft engine, when does the ignition event take place?
A) After the piston reaches TDC on intake stroke.
B) Before the piston reaches TOC on compression stroke.
C)After the piston reaches TOC on power stroke.
D)After the piston reaches TDC on compression stroke.
430-If the ground wire of a magneto is disconnected at the ignition switch, the result will be:
A)The affected magneto will be isolated and the engine will run on the opposite magneto.
B)A decrease in magnetic lines of force.
C)The engine will stop running.
D)The engine will not stop running when the ignition switch is turned off
For explanation refer to question 398.
431-When performing a magneto ground check on an engine, correct operation is indicated by:
A)a decrease in manifold pressure .
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SYSTEM,POWERPLANT&ELECTRICS
B)an increase in RPM.
C)no drop in RPM.
D)a slight drop in RPM.
For explanation refer to question #418.
432-In a piston engine, the purpose of an altitude mixture control is :
A)enrich the mixture strength due to decreased air density at altitude.
B)weaken the mixture strength because of reduced exhaust back pressure at altitude.
C)prevent a weak cut when the throttle is opened rapidly at altitude.
D)correct for variations in the fuel lair ratio due to decreased air density at altitude.
Mixture ratio is the ratio of the mass of air and fuel entering the cylinder of a piston engine. Carburetors are
normally calibrated at sea level pressure, where the correct fuel/air mixture ratio is established with the mixture
control set in the FULL RICH position. However, as altitude increases, the density of air entering the carburetor
decreases, while the density of the fuel remains the same. This creates a progressively richer mixture, which can
result in engine roughness and, appreciable loss of power and obviously lower economy of the engine operation
(higher fuel bum than necessary). The roughness normally is due to spark plug fouling from excessive carbon
buildup on the plugs. Carbon buildup occurs because the excessively rich mixture lowers the temperature inside
the cylinder, inhibiting complete combustion of the fuel. This condition may occur during the pre-takeoff run-up
at high-elevation airports and during climbs or cruise flight at high altitudes. To maintain the correct fuel/air
mixture as the aircraft climbs the pilot must lean (weaken) the mixture using the mixture control and thus readjust the air/fuel ratio again to the optimum value. Leaning the mixture decreases fuel flow, which
compensates for the decreased air density at high altitude. During a descent from high altitude, the opposite is
true. The mixture must be enriched, or it may become too lean (weak) as the density of air increases during the
descent. An overly lean mixture causes detonation, which may result in rough engine operation, overheating,
and a loss of power.
433-The main purpose of the mixture control is to:
A)adjust the fuel flow to obtain the correct fuel/air ratio.
B)decrease the air supplied to the engine.
C)increase the oxygen supplied to the engine.
D)decrease the oxygen supplied to the engine.
For explanation refer to question 432.
434-When altitude increases without adjustment of the mixture ratio, the piston engine performance is
affected because of a:
A)decreasing of air density for a constant quantity of fuel.
B)constant air density for a bigger quantity of fuel.
C)increasing of air density for a smaller quantity of fuel.
D)decreasing of air density for a smaller quantity of fuel.
For explanation refer to question 432.
435-To adjust the mixture ratio of a piston engine when altitude increases, means to:
A)increase the mixture ratio.
B)decrease the amount of fuel in the mixture in order to compensate for the increasing air density.
C)increase the amount of fuel in the mixture to compensate for the decreasing air pressure and density.
D)decrease the fuel flow in order to compensate for the decreasing air density.
For explanation refer to question 432.
436-In a piston engine if the ratio of air to fuel is approximately 9:1, the mixture is:
A) weak.
B) rich.
C)too weak to support combustion.
D)normal.
437-An EGT (Exhaust Gas Temperature) indicator for a piston engine is used to:
A)control the carburettor inlet air flow.
B)control the cylinder head temperature.
C)assist the pilot to set the correct mixture.
D)control the fuel temperature.
438-An excessively rich mixture can be detected by:
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SYSTEM,POWERPLANT&ELECTRICS
A)black smoke from exhaust.
B)high cylinder head temperatures.
C)white smoke from exhaust.
D)a long purple flame from exhaust.
439-Which statement is true concerning the effect of the application of carburettor heat?
A)It reduces the density of air entering the carburettor, thus enriching the fuel/air mixture.
B)It reduces the volume of air entering the carburettor, thus enriching the fuel/air mixture.
C)It reduces the volume of air entering the carburettor, thus leaning the fuel/air mixture.
D)It reduces the density of air entering the carburettor ,thus leaning the fuel/air mixture.
Mixture ratio is the ratio of the mass of air and fuel entering the Cylinder of a piston engine. Carburettors are
normally calibrated at sea-level pressure, where the correct fuel-to-air mixture ratio is established with the
mixture control set in the FULL RICH position. However, as altitude increases, the density of air entering the
carburettor decreases, while the density of the fuel remains the same and without proper mixture setting
adjustment the mixture gets progressively richer =:> constant mass of fuel for the decreasing mass of air.
Application of carburettor heat has the same effect. When using carburettor heat a warm air is routed into the
engine intake manifold instead of the cold outside air -this of course reduces the density of the air and its mass
for a given volume -basically the same effect as increasing altitude => mixture will get richer (too much fuel
mass for the air mass) and the engine performance decreases due to the lower air density (RPM dr9Ps slightly).
440-From the cruise, with all the parameters correctly set, if the altitude is reduced, to maintain the
same mixture the fuel flow should:
A)decrease.
B)increase.
C)remain the same.
D)increase or decrease, depending on the engine type.
For explanation refer to question 432.
441-When applying carburettor heating:
A)a decrease in RPM results from the lean mixture.
B)the mixture becomes richer.
C)the mixture becomes leaner.
D) no change occurs in the mixture ratio.
For explanation refer to question 439.
442-Max. Exhaust Gas Temperature is theoretically associated with:
A)mixture ratio of 15:1.
B)cruising mixture setting.
C)full rich setting.
D)mixture ratio very close to idle cut-out.
D)mass of fuel and mass of air entering the carburettor.
443-Overheating of a piston engine is likely to result from an excessively:
A)rich mixture.
B)weak mixture.
C)low barometric pressure.
D)high barometric pressure.
444-The mixture control for a carburetor achieves its control by:
A)moving the butterfly valve through a separate linkageto the main throttle control.
B) varying the fuel supply to the main discharge tube.
C)altering the depression on the main discharge tube.
D)varying the air supply to the main discharge tube.
Piston engine carburettors are normally calibrated at sea-level pressure, where the correct fuel/air mixture
ratio is
established with the mixture control set in the FULL RICH position. However, as altitude increases, the
density of air entering the cerburettor decreases, while the density of the fuel remains the same. To maintain
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SYSTEM,POWERPLANT&ELECTRICS
the correct fuel/air mixture as the aircraft climbs the pilot must lean (weaken)the mixture using the mixture
control and thus re-adjust the air! fuel ratio again to the optimum value. Leaning the mixture decreases fuel
flow, which compensates for the decreased air density at high altitude.
The mixture control is always achieved by regulating the fuel supply to the main fuel jet. There are two ways
how to achieve this. One is needle-type mixture control, where a position of a needle is controlled by the
mixture lever from the cockpit -this needle restricts or opens-a small orifice in the carburettor through fuel is
allowed to flow into the main fuel jet. By restricting the fuel flow the mixture gets leaner, by opening the orifice
the mixture gets richer. By pulling the mixture lever to the fully lean position the needle fully closes the orifice,
completely restricting fuel flow and shutting down the engine. Second type of mixture control is an air-bleed
mixture control. In this case the mixture lever controls a position of a valve which allows or restricts air into the
float chamber of the carburettor .. thus controlling the pressure differential acting on the fuel inside the float
chamber. When the valve is fully open the air pressure exerted on the fuel in the float chamber is greatest providing a rich mixture. As the valve is gradually closed, air pressure inside the float chamber reduces and
mixture gets weaker. Fully closing the valve will reduce the air pressure in the float chamber to minimum, stop
the fuel flow into the venturi and shut down the engine.
445-For piston engines, mixture ratio is the ratio between the:
A)volume of fuel and volume of air entering the cylinder.
B)mass of fuel and mass of air entering the cylinder.
C)volume of fuel and volume of air entering the, carburettor.
D)mass of fuel and volume of air entering the carburettor.
For explanation refer to question #432.
446-Fuel/air ratio is the ratio between the:
A)volume of fuel and volume of air entering the cylinder.
B)volume of fuel and volume of air entering the carburettor.
C)mass of fuel and mass of air entering the cylinder.
For explanation refer to question 432.
447-Variations in mixture ratios for carburettors are achieved by the adjustment of:
A)fuel flow and airflow.
B)airflow.
C)fuel flow.
D)fuel flow, airflow and temperature.
For explanation refer to question 444.
448 A rich mixture setting has to be used during climb segments. This results in a:
A)significant reduction of power.
B)higher efficiency.
C)lower cylinder head temperature
D)higher torque.
449-For a piston engine, the ideal fuel/air mixture corresponding to a richness of 1 is obtained for a
weight ratio of:
A)1:9
B)1:10
C)1:12
D)1:15
450-When leaning the mixture for the most economic cruise; fuel flow, excessive leaning will cause:
A)high engine RPM.
B)low cylinder head and exhaust gas temperature.
C)high manifold pressure.
D)high cylinder head and exhaust gas temperature.
451-When the pilot moves the mixture lever of a piston engine towards a lean position the:
A)volume of air entering the carburettor is reduced.
B)amount of fuel entering the combustion chamber is increased
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SYSTEM,POWERPLANT&ELECTRICS
C)volume of air entering the carburettor is increased
D)amount of fuel entering the combustion chamber is reduced
452-The richness of a fuel/air mixture ratio is the:
A)mass of fuel relative to the volume of air.
B)volume of fuel relative to the volume of air.
C)volume of fuel relative to the mass of the volume of all'
D)real mixture ratio relative to the theoretical ratio.
453-(Refer to figure 021-18)
On the attached diagram showing the power output of a piston engine as a function of mixture richness,
best
economy is at the point marked :
A)1
B)2
C) 3
D)4
454-As altitude increases, if the mixture is not leaned:
A)the volume of air entering the carburettor remains constant and the fuel flow decreases.
B)the density of air entering the carburettor decreases and the fuel flow remains almost constant.
C)the volume of air entering the carburettor decreases and the fuel flow decreases.
D)the density of air entering the carburettor decreases: and the fuel flow increases.
For explanation refer to question 432 .
455-As altitude increases, the mixture ratio of a piston engine should be adjusted to:
A)reduce the fuel flow in order to compensate for the decreasing air density.
B)reduce the fuel flow in order to compensate for the increasing air density.
C)increase the fuel flow in order to compensate for the decreasing air pressure and density.
D)increase the mixture ratio.
For explanation refer to question #432.
456-The mixture controller of a carburettor:
A)alters the pressure drop at the main discharge nozzle.
B)moves the butterfly valve through a separate linkage to the main throttle control.
C)varies the fuel supply to the main discharge nozzle.
D)varies the air supply at the main discharge nozzle.
For explanation refer to question #444.
457-What may happen during a continuous climb with a mixture setting fully rich?
A)The engine will operate smoother even though fuel consumption is increased.
B)Increase of the power available
C)Fouling of spark plugs.
D) The engine will overheat.
458--Which statement is correct concerning the effect of the application of carburettor heat?
A) The density of the air entering the carburettor is reduced, thus enriching the fuel/air mixture.
B) The volume of air entering the carburettor is reduced, thus leaning the fuel/air mixture.
C) The density of the air entering the carburettor is reduced, thus leaning the fuel/air mixture.
D) The volume of air entering the carburettor is reduced, thus enriching the fuel/air mixture.
459-An air/fuel ratio of 10:1 would be considered as:
A)rich.
B)weak.
C)chemically correct.
D)critically solvent.
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460-A high cylinder head temperature indicates:
A)excessive lean mixture.
B)excessive rich mixture.
C)wrongly set pitch.
D)high oil pressure.
461-Using a rich mixture during climb will result in:
A)higher cylinder head temperature.
B)significant loss of power.
C)higher efficiency.
D)lower cylinder head temperature.
462-During a cruise, high cylinder head temperature (CHT) on a piston engine is generally associated
with:
A)mass ratio of 1:15.
B)cruise mixture setting
C)a weak mixture.
D) a rich mixture.
463-If the cylinder head temp increases and EGT increases this indicates:
A)the mixture is too rich.
B)the mixture is too lean.
C) the external barometric pressure has increased.
D) the external barometric pressure has decreased.
464-The carb heat is selected on, this results in:
A)a reduction in RPM as a result of leaner mixture.
B)no change in mixture.
C)mixture is now leaner but RPM is unchanged.
D)a reduction in RPM as the mixture is now richer.
For explanation refer question #439.
465-When controlling mixture you control:
A)fuel flow.
B)the amount of air entering the engine.
C)an increase in oxygen supplied.
D)a decrease in the oxygen supplied.
For explanation refer to question 444.
466-As altitude increases what does the mixture control do to the fuel flow?
A)Increases flow due to reduced air density.
B)Increases flow due to increased air density.
C) Reduces flow due to reduced air density.
D)Reduces flow due to increased air density.
Fore explanation refer to question 432.
467-In a modern carburetor, mixture is controlled via:
A)airflow.
B)airflow, fuel flow and temperature.
C)fuel flow.
D)airflow and fuel flow.
For explanation refer to question 444
468-On modern carburetors the mixture is controlled by:
A)varying the air, fuel flow and temperature.
B)varying the air and fuel flow.
C)varying the fuel flow only.
D)varying the air flow only.
For explanation refer to question 444
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469-Theoretically the maximum EGT is obtained with a mixture of:
A)cruise setting.
B)15:1.
C)8:1.
D)a mixture just above idle cut-off.
470-The best power mixture is that fuel/air ratio at which:
A)the most power can be obtained for any given throttle setting.
B)climbs or descents can be made without adjusting the mixture control.
C)cylinder head temperatures are the coolest.
D)a given power can be obtained with the highest manifold pressure or throttle setting.
471-When the pilot operates the mixture control, what is being accomplished?
A)He changes the air-to-fuel ratio.
B)He controls the amount of fuel bleed to the diffuser.
C)He controls the amount of air bleed to the combustion chamber. D)He controls the amount of fuel bleed to the
combustion chamber.
For explanation refer to question 432
472-Fixed pitch propellers are usually designed for maximum efficiency at:
A)idling.
B)cruising speed.
C)full throttle.
D)takeoff.
A fixed pitch propeller will only be efficient at one aircraft speed and the actual blade angle will be optimized to
the role of the aircraft. For maximum takeoff RPM to be achieved a fine pitch propeller is required. On the other
hand to have optimum cruise and range possibilities a coarse pitch option is desirable. Most single-engine
aircraft will have the fixed pitch propellers optimized for cruise -that means that the blade angle will be
relatively high => too high for the performance to be optimum during takeoff, but optimum for cruise performance. If the speed of aircraft with a fixed pitch prop increases, the AOA decreases. An increase of the prop
RPM will increase AOA.
473-What will happen to the geometrical pitch angle of a "constant speed propeller" if the manifold
pressure is increased?
A)It will increase and after a short time it will be the same again.
B)It will increase.
C)It will decrease so that the engine can increase.
D)It will remain the same.
(Refer to figures 021-E52, 021-E53, 021-E54 and D21-E55)
The RPM of a variable pitch propeller is typically controlled by RPM lever (Prop lever) and the Throttle
controls the power. The propeller pitch ((B) decreases (fines off) and the RPM increases if the RPM lever is
moved towards MAX RPM (typically forward). Converse the propeller pitch increases (coarsens off) and RPM
decreases the RPM lever is moved towards MIN (typically back). supposing that the aircraft is established in the
cruise and that the RPM lever is set to the recommended RPM and the throttle lever to cruise power Assume
now that the throttle lever (power setting • MAP or boost. is moved back slightly to reduce power. Engine
torque is reduce" propeller torque is too high and the RPM reduce. The CSU (constant Speed Unit) senses the
reduction in RPM (under-speed) an decreases propeller pitch. The propeller is now easier to turn (propeller
torque reduced) and the RPM are restored to the original setting.
Consider now what would happen if the throttle lever was to be pushed forward to increase power. Engine
torque increases and RPM rise slightly. The CSU senses the increase in RPM (over speed) and increases
propeller pitch to increase propeller torque The RPM is restored to original value or on-speed condition at the
slightly higher torque or MAP. However, in both conditions the TAS could have changed. If the TAS increases,
the AOA decreases an the blade angle will be in an overspeed condition. The CSU sense this and increases pitch
to restore the RPM. The range of propeller control in the above case is known as constant-speeding. When the
selected RPM is achieved the blade angle is correct, engine an, propeller torque are balanced and the pitch
change mechanism is hydraulically locked.
474-The slipstream effect of a propeller is most prominent at:
A)low airspeeds with high power setting.
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B)high airspeeds with low power setting.
C)high airspeeds with high power setting.
D)low airspeeds with low power setting.
(Refer to figure 021-E53)
Slipstream effect -the high-speed rotation of an airplane propeller gives a corkscrew or spiralling rotation to the
slipstream. At high propeller speeds and low forward speed (as in the takeoffs and approaches to power-on
stalls), this spiralling rotation is very compact and exerts a strong sideward force on the airplane's vertical tail
surface. When this spiralling slipstream strikes the vertical fin on the left, it causes a left turning moment about
the airplane's vertical axis. The more compact the spiral, the more prominent this force is. As the forward speed
increases, however, the spiral elongates and becomes less effective. The corkscrew flow of the slipstream also
causes a rolling moment around the longitudinal axis. Note that this roiling moment caused by the corkscrew
flow of the slipstream is to the right, while the rolling mOf1Jent caused by torque reaction is to the left. The
slipstream also provides more lift and positive control on the elevator and rudder.
475-The pitch angle of a constant-speed propeller:
A)increases with increasing true air speed.
B)only varies with engine RPM.
C)decreases with increasing true air speed.
D)is independent of the true air speed.
(Refer to figures 021-E52, 021-E53, 021-E54 and 021-E55)
Blade (pitch) angle ~ the blade has a chord, same as a wing ,and it moves in the plane of rotation as specified.
The angle between the chord and the plane of rotation is called the blade angle ((B).
Angle of Attack (AOA) -the blade is following a path through the air referred to as the helix -It Is determined by
the rotation of the prop itself + by the forward velocity of the aircraft. The AOA is defined as the angle between
the propeller chord and the actual path of the prop (this path determines the direction of the relative air -actual
propeller path equals the direction of the relative air). Bear in mind that the AOA will vary with RPM and
forward speed of the aircraft (TAS). Clearly any change in the relative airflow will alter the AOA. For example,
an increase in forward speed will reduce the AOA; an increase in RPM will increase the AOA and a change in
attitude will also effect the AOA. If the propeller has a fixed pitch only, TAS, RPM and attitude will affect AOA
and the helix angle or angle of advance. If the propeller is of the variable pitch type, the variable blade angle
will affect AOA and the angle of advance .As the speed increases (for example in a dive) while maintaining the
throttle constant, both the RPM and the AOA will change momentarily (initially) -AOA will decrease due to the
increased TAS and the RPM will increase due to the decreased prop torque (due to lower AOA). However, this
change occurs only momentarily -until the CSU (Constant Speed Unit) picks-up the RPM increase -it
immediately adjusts the blade pitch (coarser setting -increased pitch angle)to reduce the RPM to the original
value -as the blade pitch increases so does the AOA again to the original value –hence the outcome is no change
in either AOA nor the RPM and an increase in the pitch
angle of the blades.
476-On an aeroplane equipped with a constant speed propeller the RPM indicator enables:
A) selection of engine RPM.
B) control of power.
C)control of the propeller regulator and the display of propeller RPM.
D)on a twin-engine aeroplane, automatic engine synchronisation.
Cockpit instrumentation relating to the power output of a piston engine and the propeller RPM will vary by the
propeller design. Aeroplanes equipped with a fixed pitch propeller are typically only fitted with the RPM
indicator by which the power output of the engine as well as the propeller RPM are determined -both by the
RPM value. On aeroplanes equipped with a variable pitch (constant speed) propeller the engine power output is
indicated by the MAP gauge (Manifold Air Pressure) and the RPM gauge indicates the actual RPM of the
propeller. Therefore the RPM indicator can be used for adjusting the desired propeller RPM value (by moving
the prop control lever).
477-When in flight, a piston engine is stopped and the propeller blade pitch angle is near 90°, the
propeller is said to be:
A) at zero drag.
B)wind milling.
C)transparent.
D)feathered.
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An effective use of the power available on larger engines requires the blade angle (blade pitch) of the propeller
to be variable to allow greater flexibility over the speed range of the aircraft. In the increase direction, blade
angles change in ascending order: reverse, fine, coarse and feather. When selected, feather allows the blade to
increase (coarsen) until the blades are edge onto the airflow (approx . 90˚ pitch angle). Without this, the airflow
could drive the prop (wind milling). A wind milling engine produces enormous amounts of drag, apart from the
mechanical considerations of propeller overspeed and engine disintegration.
478-The main advantage of a constant speed propeller as compared to a fixed pitch propeller is a:
A)higher efficiency in almost all operating ranges.
B)constant efficiency in all operating ranges.
C)lower propeller blade stress.
D)higher efficiency in cruising range.
(Refer to figure 021-E45)
Propeller reticence = (Propeller Thrust x Axial speed) .(Resistance Torque x Rotational speed). The propeller
efficiency at a given pitch angle varies with forward speed .By varying the pitch continuously on a variable
pitch propeller through the speed range. a high efficiency can be maintained over a much wider range of
operating conditions. Typical prop efficiency is in the range of 8090%.
When comparing a fixed pitch prop with a variable pitch prop , they will have the same efficiency when
both operated at the design speed of the fixed pitch prop (at this speed the fixed pitch prop will have
maximum efficiency).However, as the speed increases or decreases above/below this speed, the variable
pitch propeller (after changing its pitch angle) will maintain its maximum efficiency, thus providing better
efficiency at these higher or lower speeds than the fixed pitch prop.
479-When increasing true airspeed with a constant engine RPM, the angle of attack of a fixed pitch
propeller:
A)stays constant.
B)increases.
C)reduces.
D)stays constant because it only varies with engine RPM.
(Refer to figures 021-E52, 021-E53, 021-E54 and 021-E55)
Blade (pitch) angle -the blade has a chord, same as awing, and it moves in the plane of rotation. The angle
between the chord and the plane of rotation is called the blade angle (B).
Angle of Attack (AOA) -the blade is following a path through the air referred to as the helix -it is determined
by the rotation of the prop itself + by the forward velocity of the aircraft. The AOA is defined as the angle
between the propeller chord and the actual path of the prop (this path determines the direction of the relative
air -actual propeller path equals the direction of the relative air). Bear in mind that the AOA will vary with
RPM and
forward speed of the aircraft
482-A propeller blade is twisted, so as to:
A)keep the local angle of attack constant along the blade.
B)avoid the appearance of sonic phenomena.
C)decrease the blade tangential velocity from the blade root
to the tip.
D) allow a higher mechanical stress.
480-The blade angle of a propeller is the angle between the:
A)reference chord line and the propeller plane of rotation.
B)reference chord line and the relative airflow.
C)reference chord line and the propeller axis of rotation.
D)plane of rotation and the relative airflow.
481-When TAS increases, the pitch angle of a constant speed propeller (RPM and MAP levers are not
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moved):
A) increases.
B) decreases.
C) stays constant.
D) first reduces and after a short time increases to its previous value.
For explanation refer to question #475.
482-For takeoff, the correct combination of propeller pitch W and propeller lever position (ii) at brake
release is:
A)(i) low; (ii) forward
B) (i) high; (ii) forward
C)(i) low; (ii) aft
D)(i) high; (ii) aft
If an aeroplane is equipped with a variable pitch propeller, the position to use for takeoff is a low-pitch setting
(fine pitch) = prop lever full forward. This will enable maximum possible RPM to be achieved. If the coarsepitch propeller setting was used with full takeoff power, there could be excessive torque between the engine and
the propeller.
483-The "constant speed propeller" has:
A)its best efficiency during climb.
B)only above and below the design point a better efficiency than the fixed propeller with the same design speed.
C)in general a worse efficiency than the fixed propeller.
D)only at the design speed a better efficiency than the fixed propeller.
For explanation refer to question 478.
484-A propeller blade is twisted in order to:
A)reduce the blade tangential velocity from root to tip.
B)avoid the appearance of sonic phenomena.
C)maintain a constant angle of attack along the blade.
D)allow an increased mechanical load.
485-The mechanism to change the propeller blade angle of a small piston engine aero plane in flight is
operated:
A) by aerodynamic forces.
B)hydraulically by hydraulic fluid.
C)hydraulically by engine oil.
D)manually by the pilot.
486-If TAS increases, assuming the manifold pressure and RPM levers are not moved, what will happen
to the pitch angle of a constant speed propeller?
A)Remains constant.
B)Decreases.
C)Increases.
D)Initially decreases and then returns to its precious value .
487-How does a feathering pump work when used in conjunction with double acting propeller control
units?
A)It operates from engine oil pressure.
B)It is an electrical device and can work when the engine has stopped.
C)It is a mechanical device driven by the engine.
D) It is a mechanical device driven by the wind milling propeller.
488-What happens to the angle of attack of a fixed pitch propeller as the aircraft accelerates down the
runway?
A)Increases.
B)Decreases.
C)Remains the same.
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D)Blade angle changes to compensate for forward speed.
For explanation refer to question 479.
489-What happens to the angle of attack of a variable pitch propeller with increasing TAS if the RPM
and throttle levers are not moved?
A)Blade angle remains constant to compensate for forward speed.
B)Increases.
C)Decreases.
D)Remains the same.
For explanation refer to question 473.
490-A fixed pitch propeller has wash-out from root to tip in order to?
A)Keep the local angle of attack constant along the blade length.
B)Keep the pitch angle constant along the blade length.
C)Keep the local angle of attack at its optimum value along the blade length.
D)Decrease the blade tangential speed from root to tip.
491-The correct combination of propeller pitch (i) and propeller lever position (ii) at brake release
point are:
A)(i) coarse; (ii) aft
B)(i) coarse; (ii) forward
C)(i) fine; (ii) forward
D)(i) fine; (ii) aft
For explanation refer to question 482.
492-Two of the forces acting on a propeller are ATM and CTM. Which one tends to turn the
propeller blade in which direction?
A)ATM to coarse, CTM to coarse.
B)CTM to fine, ATM to coarse.
C)CTM to coarse, ATM to fine.
D)ATM to fine, CTM to fine.
(Refer to figures 021-E52, 021-E53, 021-E54 and 021-E55)
Aerodynamic turning moment (ATM) is a vector force forward of the blade axis of rotation which tries to turn
the blade towards coarse pitch (increase blade angle). It is caused by the fact that the prop blade's center of
pressure is located substantially ahead of the blade's center of rotation. This force is used on some aircraft to
place the prop into the feather position if needed. ATM force is opposed by, and has less effect than centrifugal
turning moment (CTM). Centrifugal turning moment (CTM) -the mass of the propeller blade is behind its axis.
Therefore rotation causes a centrifugal turning moment which tends to turn the blade towards fine (decrease
blade angle). Counterweights are sometimes fitted counter or even reverse the effect.
493-The propeller blade angle is defined as the acute angle between the airfoil section chord line (at
the blade reference station) and which of the following?
A)The plane of rotation.
B)The relative wind.
C)The propeller thrust time.
D)The axis of blade rotation during pitch change.
For explanation refer to question 479 .
494-Concerning the twisting force acting on a propeller blade:
A)the centrifugal twisting force tends to increase the blade angle.
B)the centrifugal twisting force tends to decrease the blade angle.
C)the aerodynamic twisting force tends to decrease the blade angle.
D)the aerodynamic twisting force have no effect on the blade pitch.
For explanation refer to question 492. .
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SYSTEM,POWERPLANT&ELECTRICS
495-When engine power is increased, the constant-speed propeller tries to function so that it will:
A)maintain the RPM, decrease the blade angle.
B)increase the RPM, decrease the blade angle.
C)maintain the RPM, increase the blade angle.
D)increase the RPM, increase the blade angle.
For explanation refer to question 473.
496-For takeoff, a constant-speed propeller is normally set In the:
A)high pitch, high RPM position
B)low pitch, low RPM position.
C)high pitch, low RPM position.
D)low pitch, high RPM position.
For explanation refer to question 482 .
497-The angle of attack of a rotating propeller blade is measured between the blade chord or face
and which of the following?
A)The plane of blade rotation.
B)Full low-pitch blade angle.
C)The relative air stream.
D)The geometric pitch angle required producing the same thrust.
For explanation refer to question 479.
498-Which of the following is identified as the cambered of curved side of a propeller blade,
corresponding to the upper surface of a wing airfoil section?
A)Blade back.
B)Blade chord.
C)Blade leading edge.
D)Blade face.
(Refer to figure 021-E52)
The airplane propeller consists of two or more blades and a central hub to which the blades are attached. Each
blade of a propeller is essentially a rotating wing. As a result of their construction, the propeller blades act like
airfoils and produce forces that create the thrust to pull (or push) the airplane through the air. Just like a wing
with an asymmetrical profile the propeller has a curved side and a rather flat side. This is a common knowledge.
Now the tricky part comes -common sense would dictate that the curved side would be referred to as the prop
face, since this side is "facing" into the air as the aircraft travels forward, but it is quite the opposite. Therefore,
remember, that the propeller FACE is the flat side that you see in a single-engine aeroplane when you sit in the
cockpit and the prop BACK is the curved side, facing the direction of the flight
499-The primary purpose of a supercharger is to:
A) increase the velocity of the fuel/air mixture entering the cylinder
B) increase the mass of the charge entering the cylinder.
C) raise the temperature of the charge entering the cylin der.
D) improve engine scavenging and hence power output.
(Refer to figures 021-E08 and 021-E16)
increasing the weight of the air/fuel mixture charge beyond that possible by normal aspiration is known as
supercharging. It is achieved by forcing air into the induction system of the piston engine with some sort of air
pump, or compressor, instead of sucking it in with the pistons. The more air forced in, the higher the Manifold
Air Pressure (MAP) and therefore the greater the power output of the engine. We distinguish two types of these
devices -superchargers and turbochargers. In case of superchargers the compressor (centrifugal/radial) used for
compressing the intake air is driven by gears mechanically driven by the engine crankshaft (also known as the
internal type). In case of turbochargers the compressor is driven by a turbine (both on the same shaft where the
turbine RPM = compressor RPM), which is in tum driven by the exhaust gases from the engine (also known as
the external type). We further distinguish two methods how the MAP is increased: Altitude-boosting -on the
ground at sea level the power of the engine is almost the same (actually slightly lower) as if no turbocharger unit
was installed (just like a normally aspirated engine). However, as the aircraft climbs to higher altitude the
supercharger unit kicks-in and maintains the "sea level" manifold pressure all the way up to the critical altitude.
In this way the climb performance as well as the operational ceiling of the aircraft However, the maximum
power output of this super-charged engine is slightly lower than that of an equal engine that is normally
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SYSTEM,POWERPLANT&ELECTRICS
aspirated operated at SEA level conditions. The reason being that on the super-charged engine part of the engine
power is used to drive the compressor impeller. Ground-boosting -on an aircraft with a ground-boosting design
the turbocharger unit operates even at sea level. In this way the sea level MAP is increased, giving the engine
increased sea level power. Not only the climb performance and operational ceiling are improved, but the takeoff
performance as well. For an aircraft equipped with a supercharger the takeoff is made . with the throttle partially
closed in order to limit the MAP and to avoid over boosting of the engine. As the aircraft is climbing the throttle
must be gradually opened more and more to maintain the desired MAP. Eventually an altitude will be reached
where the throttle will be folly open and any altitude increase above this will result in MAP decrease and thus
the engine power output decrease. This is called the full throttle height. Because the speed of the supercharger
depends on the engine RPM the full throttle height will differ for each power setting. For example with
decreased RPM the full throttle height will be lower than with increased RPM. The full throttle height
corresponding to a specific power setting is referred to as the rated Altitude (or as critical altitude in case of a
turbo-charged engine).
500-The primary purpose of a supercharger is to:
A)increase quantity of fuel at metering jet.
B)maintain power at altitude.
C)provide leaner mixtures at altitudes below 5.000 ft.
D)provide a richer mixture at high altitudes.
For explanation refer to question #499.
501-The maximum horsepower output which can be obtained from an engine when it is operated at
specified RPM and manifold pressure conditions established as safe for continuous operation is termed:
A) critical power.
B) maximum power.
C)takeoff power.
D)rated power.
Rated Power -sometimes called the maximum continuous power for which the engine is certified, rated power
is used for specified occasions using specific RPM and MAP (Manifold Air Pressure): as climb power or as a
setting to be used in the event of failure of another engine. On some engines there may be a time limit for use
of this power setting, perhaps 30 minutes.
Takeoff Power -this is the maximum power that the engine can deliver and is used at takeoff. A typical time
limit is 5 minutes per flight or as specified in the flight .
502-What can be the consequence during a descent with a fully open throttle if the waste gate is seized?
A) The turbine blades will separate.
B) The power of the motor will decrease.
C) The turbine shaft will break.
D)The manifold air pressure (MAP) value may exceed the maximum allowed value.
(Refer to figures 021-E30 and 021-E08)
Because the pressure in the cylinders must not become too high to avoid air/fuel mixture detonation and
physical engine damage, the cylinder intake pressure must be controlled (by controlling the rotational speed of
the turbocharger). The control function is performed by a waste gate, which routes some of the exhaust flow
away from the exhaust turbine. The main function of a waste gate is to allow some of the exhaust gases to
bypass the turbine when the desired intake pressure is achieved. Waste gates are connected in parallel to the
turbocharger turbine -as the exhaust gas leaves the cylinders it is routed via a "Y-junction" -one arm of the
plumbing diverts the exhaust gases to the turbocharger turbine, whilst the other arm directs the gases to
atmosphere through a valve -a waste gate.
When the waste gate is fully closed all the exhaust gases flow through the turbine; when fully open most of the
exhaust gases bypass the turbine and are spilled to the atmosphere. Spring pressure opens the waste gate but it is
moved towards the closed position by hydraulic pressure against spring pressure. This operation is the basis on
which waste gate control is achieved. With engine stopped, the waste gate is fully opened by spring pressure but
when the engine is started, hydrate pressure starts to close off the gate to match the required conditions.
Supposing at low altitude and power setting, an increase in power was required and the throttle was opened.
Power, exhaust gas flow, turbine RPM and compressor RPM all increase and when the manifold pressure
(MAP) reaches the selected value, the waste gate will be opened a specific amount to prevent over boosting.
Assume now that the aircraft climbs. Air density reduces as does the MAP. The turbine controller closes off the
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SYSTEM,POWERPLANT&ELECTRICS
waste gate to allow the turbine to increase speed that increases the compressor speed, increasing mass flow and
restoring the MAP to the selected value. The throttle will be progressively opened by operation of the automatic
boost control. The aircraft will eventually reach the critical altitude, when the throttle will be fully open and the
waste gate will be fully shut. Any further climb will result in a loss of power and decreasing turbine speed.
If the waste gate controlling mechanisms fail and it seizes in the high altitude cruise position == closed position
it could pose a problem as the aeroplane descends. With the waste gate seized in the closed position all of the
exhaust gases are routed over the turbocharger turbine wheel ==> spinning the compressor at high speed and
providing a high degree of air intake boost. As the aeroplane descends into altitudes with higher air density the
MAP will be gradually increasing and may exceed the safe design value for the engine, causing mixture
detonation and/or physical engine damage If the waste gate seizes during the climb -for example in the half
closed position then any altitude increase above the altitude at which it seized will result in a decrease in MAP
because the turbocharger will not be able to achieve any higher boost than the value at which
the seizure occurred.
503-One of the advantages of a turbocharger is:
A) to make the power available less affected by altitude
B) an increased propulsive efficiency.
C)that there is no torsion at the crankshaft.
D)that there is no danger of detonation.
504-During climb with constant throttle and RPM lever setting (mixture being constant) the:
A)RPM decreases.
B)Manifold Air Pressure (MAP) decreases .
C)RPM increases.
D) Manifold Air Pressure (MAP) increases.
As the altitude is increased during a climb, air pressure falls and therefore its density reduces, efficiency and
power of a normally aspirated piston engine reduce. However, as altitude increases, the temperature of the air
reduces and this temperature decrease slightly increases the air density. This slight increase in density (due to
low temp) partially offsets the reduction due to the pressure reduction but the pressure reduction has the greatest
affect. Therefore, with an altitude increase, the MAP (Manifold Air Pressure) reduces and the engine power
reduces.
505-The power output of a normally aspirated piston engine increases with Increasing altitude at constant
Manifold Air Pressure (MAP) and RPM because of the:
A) lower friction losses.
B) lower losses during the gas change.
C)lower back pressure.
D)leaner mixture at higher altitudes.
For any given throttle setting the power output of normally aspirated piston engines reduces with decreasing
pressure and/or increasing temperature. The principal effect of increasing. the temperature is to cause the air to
expand(lower pressure), thereby reducing its density. Reduced air density means reduced air mass flow through
the engine at a given RPM and hence reduces its power output. Therefore ,when an aircraft is climbing a lower
air density at higher altitudes is experienced and unless the throttle is progressively opened the engine power
reduces.
However, another important aspect of a piston engine operation (if it is normally aspirated and not turbocharged)
is that the engine power increases with an increase in altitude provided the pilot maintains constant MAP
(Manifold Air Pressure). Constant MAP compensates for the decreased air density of the intake air charge.
Because the air is less dense at higher altitudes the scavenging of the exhaust gases improves == the exhaust
gases can be more easier expelled from the cylinders = they do not have to overcome the pressure of the outside
air so much. This increases the engine power output at a rate of approx 1% per 1.000 ft of altitude.
506-A turbo-charger impeller is driven by:
A)a connection through a gearbox connected to the crankshaft.
B) diversion of exhaust gases by the waste gate using energy that would otherwise have been wasted.
C) excess torque from the reduction gearbox.
D) a ram air turbine.
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(Refer to question 021-E30 and 021-EO8)
Increasing the weight of the air/fuel mixture charge beyond that possible by normal aspiration is known as
supercharging. It is achieved -by forcing air into the induction system of the piston engine with some sort of air
pump, or compressor, instead of sucking it in with the pistons. The more air forced in, the higher the manifold
pressure (MAP) and therefore the greater the power output of the engine. We distinguish two types of these
devices superchargers and turbochargers. In case of superchargers the compressor used for compressing the
intake air is driven by gears mechanically driven by the engine crankshaft (also known as the internal type). In
case of turbochargers the compressor is driven by a turbine, which is in turn driven by the exhaust gases from
the engine (also known as the external type).
Turbocharger is a piston engine power augmentation device -it uses the energy of the engine exhaust gas, a
resource which would otherwise be wasted (about a third of the fuel energy), to drive a turbine which in turn
drives a compressor (on a shared shaft). Centrifugal (radial) compressors are used in turbocharger units. The
turbine converts exhaust gas energy to rotational force, which is in turn used to drive the compressor. The
compressor draws in ambient air and pumps it in to the engine intake manifold at increased pressure, resulting
in a greater mass of air entering the cylinders on each intake stroke. This improves the engine's volumetric
efficiency by solving one of its cardinal limitations -a naturally aspirated. piston engine uses only the
downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder through the
intake valves. Because the pressure in the atmosphere is no more than 1 at (approximately 14.7 psi) and further
decreases with an increase in altitude, there ultimately will be a limit to the pressure difference across the
intake valves and thus the amount of airflow entering the combustion chamber. Because the turbocharger
compressor increases the pressure at the point where air is entering the cylinder, a greater mass of air (oxygen)
will be forced in as the inlet manifold pressure increases. The additional oxygen makes it possible to add more
fuel, increasing the power and torque output of the engine even at higher altitude. Since the turbocharger
compressor increases the pressure of the intake air it also increases its temperature, which is however an
unwanted side effect. Therefore some engines are fitted with inter-cooler units which cool the compressed air
as it leaves the turbocharger compressor and before it is supplied to the engine for combustion with the fuel.
By spinning at a relatively high speed, the compressor draws in a large volume of air and forces it into the
engine. As the turbocharger's output flow volume exceeds the engine's volumetric flow, air pressure in the
intake system begins to build. The speed at which the "turbinecompressor" assembly spins is proportional to
the pressure of the compressed air and total mass of air flow being fed into the engine. Because the pressure in
the cylinders must not become too high to avoid air/fuel mixture detonation and physical engine damage, the
cylinder intake pressure must be controlled (by controlling the rotational speed of the turbocharger). The
control function is performed by a waste gate, which routes some of the exhaust flow away from the exhaust
turbine. The main function of a waste gate is to allow some of the exhaust gases to bypass the turbine when the
desired intake pressure is achieved. Waste gates are connected in parollel to the turbocharger turbine -as the
exhaust gas leaves the cylinders it is routed via a "Yjunction" -one arm of the plumbing diverts the exhaust
gases to the turbocharger turbine, whilst the other arm directs the gases to atmosphere through a valve -a waste
gate.
507-One of the advantages of a turbocharger over a super charger is that:
A)there is no danger of knocking.
B)it has a better propulsive efficiency.
C)there is no torsion at the crankshaft.
D)it uses the exhaust gas energy which normally is lost.
508-The air in a piston engine turbo-supercharger centrifugal compressor:
A)enters the eye of the impeller and leaves at a tangent to the periphery.
B)enters via the diffuser and is fed to the impeller at the optimum angle of attack.
C)enters at the periphery and leaves via the eye of the impeller.
D)enters at a tangent to the rotor and leaves via the stator.
(Refer to figure 021-E16)
Increasing the weight of the air/fuel mixture charge beyond that possible by normal aspiration is known as
supercharging. It is achieved by forcing air into the induction system of the piston engine with some sort of air
pump, or compressor, instead of sucking it in with the pistons. The more air forced in, the higher the manifold
pressure (MAP) and therefore the greater the power output of the engine. We distinguish two types of these
devices -superchargers and turbochargers. In case of superchargers the compressor (centrifugal/radial) used for
compressing. the intake air is driven by gears . mechanically driven by the engine crankshaft (also known as the
internal type). In case of turbochargers the compressor is driven by a turbine, which is in turn driven by the
exhaust gases from the engine (also known as the external type). We further distinguish two methods how the
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MAP is increased: Altitude boosting -on the ground at sea level the power of the engine is the same as if no
turbocharger unit was installed (just like a normally aspirated engine). However, as the aircraft climbs to higher
altitude the turbocharger unit kicks-in and maintains the "sea level" manifold pressure all the way up to the
critical altitude. In this way the climb performance as well as the operational ceiling of the aircraft is greatly
improved. Ground-boosting -on an aircraft with a ground-boosting design the turbocharger unit operates even at
sea level. In this way the sea level MAP is increased, giving the engine increased sea level power. Not only the
climb performance and operational ceiling are improved, but the takeoff performance as well. The attached
figure illustrates a simple turbocharger unit where the exhaust gases drive a turbine connected to the
compressor. Note that at the front of the illustration you see the turbine unit, where the air is routed onto the
turbine at its periphery and is exhausted , at its center section in the compressor it is the other way around. •. The
compressor air intake is located at the eye of the impeller (its center section) and the air is then flung outwards
with a high level 'of kinetic energy and with an increase In pressure. Air then leaves the compressor at a tangent
to its periphery (at 90°). The principle of operation is the same on a supercharger units, where the compressor
drive force is provided by a mechanical gearing from the engine instead of the exhaust gases.
509-What would happen if the waste gate of a turbocharged engine seized in the descent?
A) Compressor will overspeed.
B) Turbine blades will fail.
C)MAP may exceed its maximum permitted value in the induction manifold.
D)RPM may exceed its maximum permitted value.
For explanation refer to question 502.
510-The kind of compressor normally used as a supercharger
A) a hybrid compressor
C) an axial compressor.
C)a radial compressor.
D)a piston compressor.
For explanation refer to question #508
511-A turbocharger consists of a:
A) turbine driving a compressor via a reduction gear.
B) compressor and turbine on individual shafts.
C)compressor driving a turbine via a reduction gear.
D)compressor and turbine mounted on a common shaft.
For explanation refer to question 499.
512-The conditions under which you obtain the highest engine power are:
A) warm and dry air at high pressure.
B) warm and humid air at low pressure.
C)cold and humid air at high pressure.
D)cold and dry air at high pressure.
For any given throttle setting the power output of normally aspirated piston engines reduces with decreasing
pressure; increasing temperature; increasing humidity. The principal effect of increasing the temperature is to
cause the air to expand (lower pressure), thereby reducing its density. Reduced air density means reduced air
mass flow through the engine at a given RPM and hence reduces its power output. Therefore, when an aircraft is
climbing a lower air density at higher altitudes is experienced and unless the throttle is progressively opened the
engine power reduces. Another factor affecting the engine performance is the humidity. Water vapour is lighter
than air, consequently air with high humidity is lighter than dry air. Therefore, as the water content of the air
increases, the air becomes less dense and based on the same principles described above the engine power output
decreases. The best engine performance is therefore achieved in cold, dry air at high pressure.
513-In a piston engine, turbocharger boost pressure may be monitored by:
A)both a CHT gauge and manifold pressure gauge.
B)a cylinder head temperature gauge (CHT), a manifold pressure gauge, and engine RPM readings.
C)a manifold pressure gauge only.
D)both engine RPM readings and a manifold pressure gauge.
As far as monitoring of the turbocharger operation the only indication of the boost pressure the pilot has is the
Manifold Pressure (MAP) gauge, indicating the current pressure in the engine intake manifold Cylinder head
temperature and the engine RPM, although affected by the boost pressure output of the turbocharger can not
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provide any consistent direct indication of this boost pressure -only the MAP gauge can.
514-A turbocharger system is normally driven by:
A)an electrically activated hydraulically powered clutch.
B)the exhaust system.
C)an electric motor.
D)a hydraulic motor.
For explanation refer to question 499.
515-During a climb in a standard atmosphere with constant Manifold Absolute Pressure (MAP) and
RPM indications and at a constant mixture setting, the power output of a piston engine: '
A) increases.
B) decreases.
C) stays constant.
D) only stays constant if the speed control lever is pushed forward.
For explanation refer to question 505.
516-On a normally aspirated aero-engine fitted with a fixed pitch propeller:
A)in level flight, manifold pressure will remain constant when the RPM is increased by opening the throttle.
B)the propeller angle of attack is constant at all indicated airspeeds.
C)in a descent at a fixed throttle setting manifold pressure will always remain constant.
D)manifold pressure decreases as the aircraft climbs at a fixed throttle setting.
In normally aspirated engines MAP (Manifold Pressure) decreases with increasing altitude. The power output of
such engines therefore reduces with increasing altitude at a rate of approximately 3,5% per 1000 feet
517-The power of a piston engine decreases during climb with a constant power lever setting, because of
the decreasing:
A)temperature.
B)air density.
C)engine temperature.
D)humidity.
For explanation refer to question 505.
518-A normally aspirated engine has:
A)a dual controller to maintain turbine speed.
B)no power augmentation devices.
C)a density controller.
D)a density controller and a rate controller.
A normally aspirated engine has no power augmentation
devices (not quipped with a supercharger or a turbocharger). This type of engine induces the fuel-air charge Into
the cylinder by creating a depression (a pressure lower than ambient at a lower-than-atmospheric pressure .
519-The air in a piston engine supercharger enters the centrifugal compressor at:
A)the periphery and leaves via the eye of the impeller of attack.
B)the diffuser and is fed to the impeller at the optimum angle
C) the eye of the impeller and leaves it almost at a tangent to the periphery.
D)a tangent to the rotor and leaves via the stator.
520-The most common type of integral supercharger is:
A)roots type
B)geared type
C)centrifugal type
D)veined type
521-The waste gate of a turbocharged engine seizes on the climb before critical altitude, the manifold
pressure would:
A)Initially increase but then decrease.
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SYSTEM,POWERPLANT&ELECTRICS
B)increase until critical altitude, then fall.
C)decrease.
D) remain constant.
For explanation refer to question 502.
522-The speed of a turbocharger is controlled by:
A)engine RPM.
B)propeller pitch and altitude.
C)altitude only.
D)waste gate position.
523 -In a turbocharger compressor:
A)the temperature increases and the pressure increases.
B)the temperature increases and the pressure remains
constant.
C)the temperature and pressure decrease.
D) the pressure increases and the temperature decreases.
524-With a super-charged engine, to maintain a rated boost with a decrease in RPM:
A) the waste gate must be opened
B) the waste gate must be closed.
C) the throttle valve must be opened.
D) the throttle valve must be closed.
For explanation refer to question 499.
525-The waste gate is moved to the open position by:
A)the oil outlet of the waste gate controller becoming blocked.
B) the oil inlet of the waste gate controller becoming blocked.
C)exhaust gas leakage.
D)the waste gate actuator spring.
526-Define a normally aspirated engine:
A)An engine that is supercharged.
B)An engine that is turbocharged.
C)An engine that is supercharged and turbocharged.
D)An engine that is neither supercharged or turbocharged.
For explanation refer to question #518.
527-At a constant throttle setting, the power of a piston engine reduces during a climb due to:
A)decreasing temperature.
B) increasing humidity.
C)decreasing density.
D)decreasing engine temperature.
For explanation refer to question 505
528-A normally aspirated piston engine aeroplane climbs at constant manifold pressure and RPM. The
power output:
A)decreases due to lower back pressure.
B)increases due to lower back pressure.
C)decreases because of the lean mixture being used at higher altitudes.
D)decreases due to lower frictional losses.
For explanation refer to question 505.
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529-A turbocharger is driven by:
A)exhaust gases.
B)an electric motor.
C)a pneumatic motor.
D)ram air.
For explanation refer to question499.
530-A turbocharger is usually fitted with:
A)an axial compressor.
B)a radial compressor.
C)a radial compressor driven by an auxiliary gearbox.
D)an axial compressor driven by an auxiliary gearbox.
For explanation refer to question 499.
531-A normally aspirated aircraft fitted with a variable pitch propeller climbing at constant throttle
setting:
A) the RPM will increase
B) the MAP will increase.
C)the RPM will decrease.
D)the MAP will decrease.
For explanation refer to question 505.
532-If a manifold pressure gauge consistently indicates atmospheric pressure, the cause is probably:
A)ice in the induction system.
B)too high a float level.
C)a leak in the gauge pressure-line.
D)the waste gate stuck in the closed position
533-If the turbocharger waste gate is completely closed:
A)none of the exhaust gases are directed through the turbine.
B)the manifold pressure will be lower than normal.
C)the turbo/supercharger is in the OFF position.
D)all the exhaust gases are directed through the turbine.
534-What is the purpose of a turbocharger system for a small reciprocating aircraft engine?
A)Compresses the air to hold the cabin pressure constant after the aircraft has reached its critical altitude.
B)Maintains constant air velocity in the intake manifold
C)Compresses air to maintain manifold pressure constant from sea level to the critical altitude of the engine.
D)Maintains variable air pressure to the carburetor venturi.
For explanation refer to question 499
535-An engine turbocharger is said to be "ground-boosted" when it:
A)maintains a manifold pressure above sea level conditions.
B)maintains sea level conditions with increasing altitude.
C)has a fixed waste gate setting.
D)has one rated altitude and one full throttle height.
For explanation refer to question 499.
536-As manifold pressure increases in a reciprocating engine the:
A) volume of air in the cylinder increases.
B)weight of the fue/fair charge decreases.
C)density of air in the cylinder increases.
D)volume of air in the cylinder decreases.
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537-During climbing flight using a turbocharged airplane, the manifold pressure will remain
approximately constant until:
A)an outside temperature of -18 °C is reached.
B)the waste gate is fully open and the turbine is operating at minimum speed.
C) the engine's critical altitude is reached.
D) an atmospheric pressure of 14,9 is reached.
For explanation refer to question 499.
538-what energy source is used to drive the turbines of turbocharged airplane?
A)Electrical system.
B)Ignition system.
C)Engine exhaust gases.
D)Mechanical engine compressor.
For explanation refer to question 506.
539-What regulates the speed of a turbocharger?
A)Turbine
B)Compressor
C)Waste gate
D)Throttle
540-A fan stage of a ducted fan turbine engine is driven by:
A)the high pressure compressor through reduction gearing.
B)airflow across it by the high pressure compressor.
C)high pressure turbine.
D)the low pressure turbine.
(Refer to figures 021-E70 and 021-E71)
On multi-spool turbofan engines, the spools are arranged concentricity with the HP turbine driving the HP
compressor, the LP turbine driving the LP compressor and a final (rearmost) turbine driving the front ducted fan
(on a triple Spool design). On most dual spool engines the front fan is driven by the LP turbine as the front fan is
part of the LP compressor section. Each spool rotates at a different speed -LP sections at a lower speed than HP
sections.
541-In an engine having a free turbine:
A)there is a mechanical connection between the power output shaft and the turbine.
B)there is no mechanical connection between the power output shaft and the turbine.
C)there is a mechanical connection between the compressor and the propeller shaft
D)air enters via compressor inlet on the turbine.
(Refer to figures 021-E70 and 021-E71)
On some turbo-prop and turbo-shaft layouts a free turbine rotor, independent of the HP or LP compressors, is
used to drive the propeller or rotor. This is called a "free turbine" or "power turbine" engine. The power output
(propeller) is mechanically connected only to this "free turbine" which rotates independently and is not
mechanically connected to the main engine. The free turbine is located downstream of the compressor-driving
turbines(s). As the airflow exits the combustion chamber it is directed onto the main engine turbines (these are
mechanically linked to the compressor and drive the compressor) -after passing through this turbine the airflow
continues onto a free turbine which is connected only to the propeller or rotor. This design allows for the free
turbine to rotate independently at separate speed from other turbine sections. Note: some JAA questions on this
topic can be very tricky you have to read the questions very carefully and realize what they are asking about. Of
course there has to be some sort of mechanical connection between the "free turbine" and the power output shaft
(e.g. the propeller shaft) => there must be a way to transmit the energy extracted by the turbine to the propeller the only way is through a shaft. However -this free turbine is not connected to the compressor shaft! There is
also no mechanical connection between the compressor-driving turbine and the power output shaft (to the
propeller)
542-Which part of the gas turbine engine limits the temperature?
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A)Combustion chamber .
B)Turbine.
C) Compressor.
D) Exhaust.
A turbine extracts energy from the gas stream to drive an associated compressor, auxiliary drives and, where
applicable, a propeller. Clearly, the greater the temperature achieved during combustion the greater the
expansion and the greater the energy transfer possible in the turbine. However, this is limited by the ability of
the nozzle guide vanes and turbine blades to withstand high temperatures. Turbines operate within a very hostile
environment and need to be constructed of materials that will withstand temperatures in the order of 1000 C
(850˚ C to 1700flC) and centrifugal loads, whilst white hot, of up to 50 tons per square inch. Therefore clearly
the primary reason for limiting the temperature of the gas flow in a turbine engine (Exhaust Gas Temperature EGT measured either after the HP turbine, or after the last stage of LP turbine) is to ensure the turbine maximum
operating temperatures are not exceeded.
543-In a free turbine engine:
A)its shaft may be connected to either a compressor or another turbine.
B) there is no mechanical connection between the compressor and the power output shaft.
C)the air enters the compressor via the input turbine.
D) the compressor and power output shaft are mechanically connected.
544-Both gas turbine and piston engines utilize a cycle of induction, compression, combustion and
exhaust. However in the gas turbine these processes are (i) and combustion occurs at (ii).
A)(i) continuous; (ii) constant pressure
B)(i) continuous; (ii) constant volume
C)(i) intermittent; (ii) constant pressure
D)(i) intermittent; (ii) constant volume
545-By-pass ratio in a turbine engine is the ratio of the:
A) speed of the combusted air to the speed of the by-pass air.
B)cold air mass flow to the hot air mass flow.
C) intake air pressure to the turbine delivery air pressure.
D) tertiary air mass flow to the primary air mass flow.
546-In a multi-spool turbofan engine, the fan is driven by:
A)the intermediate turbine.
B)the rearmost turbine.
C)the foremost turbine.
D) all three turbines since they are on a common shaft with the compressor.
547-In the airflow through a single-spool axial flow turbo-jet engine, the axial velocity of the air is
greatest:
A)as it leaves the turbine.
B)as it leaves the compressor.
C)within the combustion chamber.
D)on exit from the propelling nozzle.
(Refer to figures 021-E66 and 021-E67)
The greatest gas axial flow velocity is at the exit from the propelling nozzle. A propelling nozzle is bolted to the
downstream end of the 'engine exhaust section and straightener vanes are located within the unit to remove swirl
from the gas stream. The propelling nozzle can be either the standard convergent duct which increases the
velocity of the gas flow and lowers the temperature and pressure of a subsonic gas stream or a "con/di"
(convergant divergent) duct which does the same task for a supersonic gas flow. The gas stream enters the
exhaust unit at temperatures of approximately 550'C to 850'C, a velocity of approximately Mach 0,5 or 900 ft
per sec of a subsonic flow engine and a pressure higher than atmospheric. Heat insulation is provided between
the exhaust unit and the aircraft structure.
548-the thermal efficiency of a gas turbine engine will increase with a:
A)increase in humidity.
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B)increase in ambient air temperature.
C)decrease in ambient air pressure.
D)decrease in ambient air temperature.
(Refer to figures 021-E66 and 021-E67)
Thermal efficiency is defined as the ratio of the mechanical energy output of the engine to the heat energy
available in the fuel consumed. It increases as the turbine inlet temperature increases. The thermal efficiency of
a jet engine also increases with increased airspeed, due to ram effect at the compressor inlet. Under static sea
level conditions the thermal efficiency of a jet engine is 20% .. 25%, compared to 25% -30% for a piston engine.
However, the thermal efficiency of the piston engine decreases with increasing airspeed, becoming significantly
lower than that of the jet engine at higher airspeeds.
Effect of outside air temperature -as the temperature decreases, the mass flow through the engine increases
(higher air density) as does thrust and SHP (Shaft Horse Power). However, more power is required to drive
the compressor and a higher fuel flow is needed to maintain a selected RPM; otherwise, the RPM will fall.
Similarly as the air temperature increases, air mass flow, thrust or SHP will fall. The compressor will require
less power to drive it and fuel flow will be reduced to maintain the selected RPM. The fuel control system will
adjust fuel flow to ensure that limiting parameters are not exceeded at the extremes of temperature and, that up
to a specified ambient temperature, power is maintained. This latter situation is known as 'flat rated' and once
the limiting temperature is achieved, fuel flow and power reduces with any further increase in ambient
temperature. This ensures that turbine limiting temperatures, shaft speeds and internal pressures do not exceed
design limits. At high ambient temperatures, say in excess of 45˚ C (power loss of probably 20% plus), thrust
augmentation, for example water methanol injection, may be requited to restore the power loss.
549-The principles underlying the effects of jet propulsion are set out in:
st
A)Newton's 1 Law of Motion.
nd
B)Newton's 2 Law of Motion.
rd
C)Newton's 3 Law of Motion.
D)Faraday's conservation of energy precepts.
(Refer to figures 021-E66 and 021-E67)
All aircraft propulsion systems employ Newton's 3rd Law of Motion which states that for every force (or action)
there is an equal and opposite reaction. The amount of forward thrust created is proportional to the product ofthe
mass of air affected and the rearward acceleration imparted to it. In the case of propeller driven aircraft and
turbo-fans a large mass of air is given a relatively small rearward acceleration. In turbo-jets a much smaller mass
of air is subject to a much greater acceleration.
550-A gas turbine engine operates in accordance with the:
A)modified Brayton cycle.
B)modified Otto cycle.
C)Brayton cycle.
D)Otto cycle.
551-A free turbine is
A)directly connected to a specific axial flow compressor.
B)always found in centrifugal compressor engines.
C)connected to an LP compressor and then to the fan.
D)directly connected to a propeller or gearbox and to nothing else.
552-What does a diffuser in a gas turbine do?
A) Expands the air entering the combustion chamber.
B) Increases the total temperature of the air.
C)Increases the relative velocity of the air entering the combustion chamber.
D)Converts kinetic pressure into static pressure.
The diffuser section forms a divergent duct passage and its function is to prepare the air for entry into the
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combustion chamber at a low velocity, by converting some of its kinetic energy into pressure energy further
increasing static pressure .It utilizes Bernoulli's principle to decrease the velocity of the air as it exits the
compressor section to allow for its easier ignition -and, at the same time, continuing to increase the air pressure
and temperature before it enters the combustion chamber.
553-The disadvantages of axial flow compressors compared to centrifugal flow compressors are:
1)expensive to manufacture
2)limited airflow
3)greater vulnerability to foreign object damage
4)lower pressure ratio
The combination regrouping all the correct statements is:
A) 2,3
B) 1,2
C)1,3
D)2,4
(Refer to figures 021-E77, 021-E78 and 021-E79)
Axial flow compressors
•Better power/weight ratio on all but the smallest engines.
•Lower compression ratio per single compressor stage (as little as 1,2:1).
•Higher air mass flow per unit area and, on the larger units, length.
Therefore, by far the more powerful engine.
•Complex construction -more expensive to manufacture than centrifugal. Less rugged and more prone to foreign
object damage.
•Higher pressure ratios are possible and are typically 90% to95% efficient as compared with the centrifugal
compressor at75% to 80%. Also can provide power to higher altitudes.
Centrifugal compressors •Reasonably efficient for small applications (helicopter engines, APUs). •Simple
construction -easier and cheaper to manufacture. •Shorter in size, therefore occupy less space longitudinally
•Less susceptible to damage by ingestion of foreign objects. •Robust; less susceptible to stall and surge (lower
ensure rise); Used sometimes on helicopters where turbulence across intakes may cause a problem and APUs.
•Lower compression ratio (of the whole engine) when compared With an axial flow engine of similar power
output. •Higher compression ratio per single compressor stage (as much as 5:1). •Sometimes can be used as the
final stage compressor in a multi spool engine to reduce its overall length.
When comparing centrifugal and axial flow compressors of the same frontal diameter, the axial compressor will
be able to "consume" more air and will provide higher compression ratios than the centrifugal. Therefore when
we have a given mass flow through the compressor, the centrifugal compressor will need to have a larger frontal
area than the axial compressor. Even though the pressure ratio attainable by an axial compressor engine is as
high as 35:1 (while of the centrifugal compressor engines not more than about 12:1) the pressure ratio of the
individual stages is much higher in the centrifugal compressors (5:1) as opposed to a single stage of the axial
compressor (1,2:1). The high pressure ratio of an axial compressor engine is achieved by introducing many
compressor stages into axial compressor engine, On the contrary in a centrifugal compressor engine we can only
effectively use 2 stages (2 centrifugal compressors in sequence 3rd stage would be ineffective due to excessive
compressor speed and excessive centrifugal loading.
554-The diffuser in a centrifugal compressor is a device in which the:
A)velocity, pressure and temperature rise.
B)pressure rises at a constant velocity
C)pressure rises and velocity falls.
D) velocity rises and pressure falls.
555-What happens to pressure, temperature and velocity of the air in the diffuser of a centrifugal
compressor?
A)Velocity increase, pressure and temperature decrease.
B)Velocity crease.
C)Velocity, pressure and temperature increase.
D)Velocity, pressure and temperature decrease.
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556-In a gas turbine engine, compressor blades, which are not rigidly fixed in position when the engine is
stationary. take up a rigid position when the engine is running due to:
A)the resultant of aerodynamic and centrifugal forces.
B)oil pressure.
C)thermal expansion.
D)blade creep.
557-In a centrifugal compressor; air enters via the:
A) combustion chamber.
B)eye of the impeller.
C)variable IGV.
D) diffuser.
558-A gas turbine blade is usually of the:
A) Pelton wheel type.
B)impulse type.
C)reaction type.
D)impulse/reaction type.
(Refer to figures 021-E64 and 021-E65)
When employed in isolation both the impulse and reaction systems are inefficient and so most practical turbines
employ a combination of the two. In the impulse/reaction turbine, the blade root sections are predominantly of
impulse type bucket section, gradually changing to reaction type aerofoil section towards the tip. In the nozzle
guide vanes this change of cross section is reversed such that the greatest acceleration occurs close to the roots
of the vanes, whilst the greatest deflection in the direction of engine rotation occurs close to the tips. In the
rotors the changing cross section of the blades results in mainly impulse type energy extraction at the roots .
559-As the gas flows through the turbine:
A)pressure, velocity and temperature gradually decrease.
B)pressure, velocity and temperature increase.
C)pressure decreases, velocity increases and temperature increases.
D)pressure decreases, velocity decreases and temperature increases.
560-After air has passed through the compressor of a gas turbine engine the:
A) pressure will be the same as the inlet pressure.
B) velocity will be higher than the inlet velocity.
C) temperature will be higher than the inlet temperature
D) velocity will be the same as the inlet velocity.
(Refer to figures 021-E66 and 021-E67)
The purpose of the compressor is to increase the total energy of the air received from the inlet duct, compress it
and discharge it into the combustion chamber in the right quantity and at the required pressure. In the
compressor work is done upon the air to compress it adiabatically, and so the temperature of the air increases in
direct proportion to the pressure. The amount of air passing through the engine depends upon compressor RPM,
the atmospheric conditions at the engine inlet, such as the air pressure, density and temperature and the aircraft
speed. The pressure ratio of a compressor is the ratio of its outlet static pressure to its inlet static pressure
561-Engine temperature Limitations are usually imposed due to temperature limitations on the:
A) casing of the combustion chamber
B) compressor section.
C) turbine section.
D) jet pipe.
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562-For a subsonic airflow, in a divergent duct the:
A) pressure decreases, velocity increases and temperature increases.
B)pressure increases. velocity decreases and temperature increases.
C)pressure increases, velocity decreases and temperature decreases.
D) pressure decreases. velocity increases and temperature decreases
563-When a gas turbine engine is fitted with can-type combustion chambers:
A)each chamber is fitted with two igniters.
B)each chamber has its own igniter.
C)each chamber is fitted with one igniter and one glow plug,
D) a total of only two igniters are usually fitted since the chambers are inter-connected.
Can-type combustion chamber system is fitted to centrifugal compressor engines or to early axial flow engines.
The system consists of 6 to 14 individual combustion chambers located circumferentially in a circle. Each
chamber has an outer casing and an inner flame tube. The front of the casing, the "snout" has a housing for the
fuel burner. Older engines had a torch igniter inserted into one of the chambers and were used for starting only.
Current systems have two igniters per engine for starting purposes and the initial starting flame travels to the
other chambers via interconnecting tubes. The principal advantage of this type of combustion chamber is its
high resistance to distortion when heated. The main disadvantages fie in the amount of material needed for their
construction and their uneconomical use of the available space.
564-By comparison with an axial flow compressor, a centrifugal compressor is:
A)lighter and has a high power to weight ratio.
B)fuel efficient and has higher thermal efficiencies.
C)more efficient and with a higher compression ratio.
D)more robust and technologically less complicated.
For explanation refer to question #553.
565-by comparison with a single spool axial flow turbo-jet twin spool engine is:
A) is mechanically complicated and has an overall lower compression ratio with high turbine inlet temperatures
B) much less fuel efficient
C) heavier and has a lower power to weigh ratio
D) more flexible in operation less prone to surge and with higher compression ratios has better overall
performance
(Refer to figures 021-E77, 021-E78 and 021-E79)
Twin-spool compressors offer the following advantages over single spool systems:
•Because the spools are not physically connected each compressor section is able to operate at the RPM which
best match the prevailing air mass flow and pressure ratios thereby increasing overall efficiency and reducing
the danger of compressor stall and surge.
•Because the HP spool is required to handle only a small proportion of the total air flow, its diameter and mass
can be greatly reduced. The resulting low inertia enables it to react very quickly to throttle increases rapidly
accelerating to the required higher RPM, mass flow, and pressure ratio. This greatly reduces the probability of
compressor stall and surge during rapid throttle increases . Because only a small proportion of the air mass flow
passes through the HP spool, and the remainder passes at a much lower velocity around the outside, friction
losses are greatly reduced thereby improving the thermal and mechanical efficiency of the engine. •Because the
velocity of the by-pass air is more closely matched to that of the aircraft, propulsive efficiency is improved at
low to moderate speeds.
566-A divergent duct (diffuser) in the combustion chamber inlet and in the flame tube:
A) ensures the availability of cooling air.
S) increases air pressure only just prior to combustion.
C)increases inlet air velocity to a speed suitable for stable combustion.
D)reduces inlet air velocity to a speed suitable for stable combustion.
For explanation refer to question 552.
567-The function of the nozzle guide vanes is to:
st
A)ensure air velocity is at a maximum and the airflow direction is correct prior to entry to the 1 stage compressor blades.
B)increase the gas velocity (and therefore momentum) to as high a speed as possible and guide the stream at the
correct angle onto the turbine blades.
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C)guide the gas stream onto the turbine blades at the best angle possible only.
D)increase the velocity of the gas to the highest speed possible only.
(Refer to figures 021-E64 and 021-E65)
Nozzle Guide Vanes (NGV) convert pressure energy into kinetic energy and impart to the turbine gas at the
highest possible speed and at the correct angle. NGV gas exit velocity could be in the region of 2500 ft per sec
and bearing in mind the temperature of the gas at this point, the velocity is virtually sonic. The blades are
twisted towards the tip and this is to ensure that the gas load is spread equally along the length of the blade.
Compressor air bleeds provide internal cooling and allow higher temperatures to be accepted by the material .
568-What is the purpose of the turbine in a turbine engine?
A)Drive auxiliary devices.
B)Compress the air coming into the engine.
C)Exhaust burnt gases.
D)Drive the compressor using energy from the exhaust gases.
569-Each stage of an axial compressor is made up of:
A)a rotor and a stator.
B)a stator and a rotor.
C)two rotors followed by a stator.
D)two stators followed by a rotor.
570-What is the purpose of the FCOC (Fuel-Cooled Oil Cooler)?
A) To maintain the oil at the correct temperature.
B) To heat the fuel and cool the oil.
C)To heat the oil and cool the fuel.
D)To by-pass oil to the engine if the oil pressure filter becomes blocked.
571-The usual methods of starting civil aircraft engines are:
A)AVPIN or compressed air bottles.
B)electrical starter motor or AVPIN.
C)air starter motor or starter cartridge.
D)air starter motor or electrical starter motor.
There are two method to start a turbine engine. Electric motor starters are typically installed only on small
engines and APUs. In fact. it is desirable to have an electric motor starter on the APU so it can be started from
the aircraft battery. On larger engine the air starters are used. In these cases the electric motor would have to be
relatively large and heavy. Air starters are of comparatively lighter construction.
Electric starter is a high torque DC starter motor is coupled to the engine shaft when START is selected and the
motor winds the engine up at increasing RPM under the control of a 3-stage control unit. At some point fuel is
injected , the engine lights up and, at self sustaining speed, the starter motor de-energises and disengages If the
engine does not light up the starter motor will de-energise after 30 to 40 seconds.
. Air starter is basically a turbine wheel driven by air from a pneumatic manifold, pressurized by the APU, a
ground starter unit or bleed air from another running engine. When START is selected, an air control valve
opens which couples the pressurized air manifold to the motor. This turns the motor, which engages, via a
clutch, with the engine shaft. When the engine reaches self-sustaining speed, the air control valve is closed
automatically by a speed sensitive switch and the engine accelerates to idle power. If the original air supply
fails after the first engine had started, the air supply from the running engine can be utilised to start the
remaining engines; this is called a cross bleed start. The system is light economical to use and simple.
572-There are two types of oil system used on turbine engines:
A)total loss and pressure relief types.
B)total loss and full flow systems.
C)pressure relief and full flow systems.
D)none of the above.
(Refer to figures 021-E68 and 021-E69)
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SYSTEM,POWERPLANT&ELECTRICS
Pressure relief valve system -in this system the oil flow to the bearing chambers is controlled by maintaining a
constant pressure in the oil supply line. A spring-loaded pressure relief valve on the outlet side of the oil
pressure pump opens to return oil to the oil tank or to the suction side of the pump. The valve is set to begin
opening at a pressure corresponding to engine idling speed. The faster the engine (and, therefore, pump) speed
the more the relief valve opens to maintain constant supply pressure.
Full flow system -this system does not use a pressure relief valve, but instead feeds oil pressure pump output
direct to the oil supply line to the bearing chambers. Thus, the higher the engine (and pump) speed the greater
the quantity of oil supplied to the bearings. Because all the oil pumped is supplied to the bearings, with none
being spilled back by a pressure relief valve, pump sizes can be significantly smaller with this type of system.
Because of the higher pressures associated with the full flow system, pressure-limiting bypass valves are fitted
in conjunction with components such as coolers and filters, which could otherwise be damaged. Note: both the
pressure relief valve system and the full flow system are dry sump lubrication systems. Total loss system" oil is
dumped overboard after one circulation through the engine. For obvious reason it is only employed on some
very special applications and not in typical aircraft lubrication systems where oil recirculation must be
maintained
573-A pressure relief valve in an oil system that does not seat correctly would result in:
A)high oil pressure.
B)low oil pressure.
C)excessive oil consumption.
D)low oil temperature.
(Refer to figures 021-E68 and 021-E69)
On a pressure relief system the oil is passed from a pressure pump through a pressure filter element and then
into a spring-loaded pressure relief valve. This valve maintains a constant pressure of the oil that enters the
spray jets that deliver it into the individual engine sections. Any excess pressure is eliminated by routing portion
of the oil back into the tank. If the pressure relief valve does not seat properly it means that it remains partially
open, allowing more oil back into the tank than would be required. It means that the pressure of the all entering
the engine then it should be.
574-An aircraft flying in conditions of continuous heavy rain and high ambient temperatures may require
the precautionary use of:
A)engine intake anti-icing only.
B)airframe de-icing only.
C)engine igniters.
D)both engine intake anti-icing and airframe de-icing.
575-In a gas turbine engine lubrication system, the oil to fuel heat exchanger provides:
A)thermostatically controlled fuel heating by engine oil to prevent icing in the fuel filter.
B)fuel cooling to prevent vapour locking interrupting the fuel supply to the nozzles.
C)fuel heating as required whenever fuel filter clogging is detected.
D)oil cooling through thermal exchange with the fuel.
576-The accessory units driven by the accessory gearbox of a turbo-jet engine are the:
1)thrust reverser pneumatic motors
2)AC generator and its constant speed drive (CSD)
3)oil pumps
4)hydraulic pumps
5)high pressure fuel pumps
The combination regrouping all the correct statements is:
A) 2,3,4
B) 1,2,3,4,5
C) 2,3,4,5
D) 1,2,3,4
577-The oil system of a gas turbine engine may be fitted with magnetic plugs, or chip detectors. They:
A)provide warning of impending failure without having to remove the filters for inspection.
B)dispense with the requirement to fit an oil filter
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SYSTEM,POWERPLANT&ELECTRICS
C)monitor oil pressure and oil temperature.
D)are fitted in the pressure line upstream of the oil filter
578-The purpose of a chip detector in the oil system of an engine/gearbox is to indicate that:
A)the piston rings are worn.
B)there are metal particles in the oil.
C)the seals are worn.
D) the oil temperature is too high.
579-The purpose of magnetic chip detectors is to:
A)increase lubricating oil adhesion to main surfaces.
B)warn of impending failure.
C)remove large items of debris from the system.
D)perform the function of a micron filter.
580-The capacity of a scavenge pump in an oil system:
A)varies with fuel pressure.
B)is the same as the pressure pump.
C)is greater than the pressure pump in a wet sump system.
D)is greater than the pressure pump in a dry sump system.
(Refer to figures 021-E68 and 021-E69)
The output volume/pumping capacity of the scavenge pumps is typically larger than the volume of the pressure
pump. Scavenge pumps remove oil from the collector trays where it collects after having circulated through the
engine. Pressure pumps draw oil from the oil tank and pass it to the distribution system for delivery to internal
engine components. Typically there are several scavenge pumps located in the engine. The output of the
scavenge pumps is larger than that of the pressure pump in order to ensure the hot oil that has passed through the
engine is properly removed from the collector trays and routed into the oil cooler and back into the oil tank =>
in order for the engine sump to remain dry.
581-Viscosity of oil depends on:
A)oil pressure.
B)condition of engine.
C)oil temperature.
D) amount of oil in the sump.
Gas turbine lubricating oil is generally synthetic and must have the following properties:
•resist oxidation; particularly, in high temperature conditions.
•be sufficiently thin to allow engine starting down to minus 40°C.
•maintain a film of lubricant in high speed gear trains and plain bearings.
•must be resistant to chemical change caused by materials in the engine and must not damage engine materials.
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or extensional
stress. In other words, it is the tendency of a fluid to resist flow. In everyday terms (and for fluids only),
viscosity is "thickness". Thus, water is "thin", having a lower viscosity, while honey or oil is "thick" having a
higher viscosity. Water will flow a lot easier than honey or oil. The viscosity of the oil tends to decrease with
increasing temperature => hot oil is "thinner" flowing more easily, while the cold oil is "thick" resisting flow
and flowing very slowly. An ideal lubricating oil would maintain a relatively constant viscosity over the whole
range of working temperatures of the engine, from cold, winter starting to hot, high temperature running.
582-The oil pressure gauge measures oil pressure:
A)before the pressure pump.
B)after the pressure pump.
C)differential across the pressure pump.
D) in the tank.
(Refer to figures 021-E68, 021-E69 and 021-E14)
In a lubrication system the oil pressure is sensed on the output side of the pressure pump before the oil is
actually distributed into the engine sections.
583-The volume of the scavenge pump(s) in an engine lubrication system is greater than that of the
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SYSTEM,POWERPLANT&ELECTRICS
pressure /pump(s) in order to?
A) Prevent cavitation of the oil system feed-lines.
B)Ensure heat is dissipated more effectively.
C)Compensate for thermal expansion of the lubricating fluid.
D) Ensure that the engine sump remains dry.
584-What are the functions of FADEC?
1)engine limitation protection
2)automatic engine starting sequence
3)manual engine starting sequence
4)power management
A)1,2
B)4
C)1,4
D)1,2,3,4
585-In a gas turbine engine, the power changes are normally made by controlling the amount of:
A)air leaving the compressor by opening or closing of bleed valves.
B)fuel supplied.
C)air entering the compressor.
D)air entering the compressor and fuel entering the combustion chambers.
Turbine engines are generally simpler to operate in many ways than their piston engine counterparts,
however they require careful handling to get the best results. The amount of thrust a turbine engine produces
is directly proportional to its RPM => increased RPM produces more thrust and vice versa. In order to
increase the engine's RPM more fuel is supplied into the combustion chamber -this increases the temperature
of the gases and provides greater expansion on the turbines which in turn provide higher RPM for the
compressors and increase the mass flow through the engine. However. there are many limits that have to be
observed -including the maximum RPM to avoid damage due to excessive loading of the compressors and
the turbines as well as maximum temperature limits to avoid damage to the turbine sections .
586-On most gas turbine engines the takeoff power has a time limit of:
A)5 minutes only.
B)10 minutes.
C)15 minutes.
D)5 minutes unless an emergency exists which requires this power.
Turbine engines are generally simpler to operate in many ways than their piston engine counterparts,
however they require careful handling to get the best results. The amount of thrust a turbine engine produces
is directly proportional to its RPM => increased RPM produces more thrust and vice versa. In order to
increase the engine's RPM more fuel is injected into the combustion chamber this increases the temperature
of the gases and provides greater expansion on the turbines which in turn provide higher RPM for the
compressors and increase the mass flow through the engine. However, there are many limits that have to be
observed -including the maximum RPM to avoid damage due to excessive loading of the compressors and
the turbines as well as maximum temperature limits to avoid damage to the turbine sections. There are
several modes in which the turbine engines can be operated during a flight, depending on the thrust output:
Takeoff Thrust -during this mode the engine provides maximum thrust for which it has been designed. The
limiting factor for maximum available thrust in very cold environment will be the maximum pressure ratio
while in a hot environment it will be the maximum exhaust gas temperatures (EGT). Due to the fact that in
this mode the engines operate close to their design limits this mode is typically limited only for a period of 5
minutes. After this time the thrust has to be reduced in order not to cause damage to the engine. In case of a
dire emergency of course the pilot will be able to maintain this maximum thrust longer (however probably at
the cost of damaging the engine).
Maximum Climb Thrust -after takeoff. the pilots select the Max Climb Thrust mode. The engine RPM decrease
slightly (from the Max. Takeoff Thrust) and this mode can maintained all the way up to the cruising altitude.
As the aircraft climbs (and the outside air temperature drops) the engine RPM progressively increase. This
thrust setting can be used continuously (no time limit on use). Maximum Cruise Thrust -similar to the Max.
Climb Thrust, but slightly lower to prolong engine life (the less frequency the engine is operated close to its
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design limits the longer engine life).
Maximum Go-Around Thrust -similar mode as the Max. Takeoff Thrust, but slightly lower (maximum takeoff
thrust is not required on a go-around as the aircraft is already in flight). On some aircraft Max. Go-Around
Thrust = Max. Continuous Thrust.
Maximum Continuous Thrust -this thrust setting will provide the maximum possible thrust that can be
maintained on a continuous basis. It is the second highest thrust setting after Max. Takeoff Thrust. It is used
mostly in emergency situations -such as during an engine failure when the remaining engine must produce
maximum possible amount of thrust for a prolonged time until emergency landing can be made safely. This
thrust mode ensures maximum possible amount of thrust without a damaging effect on the engine. Aside from
emergencies it can be used for example in the following situations: a)Initial climb power under certain extreme
ambient conditions and/or high aircraft weight. b)If required to comply with an urgent air traffic request when
ordinary power settings are insufficient. c)On some aircraft, maximum continuous power is used for go around.
587-The engine pressure ratio (EPR) is the ratio of:
A)the total turbine inlet pressure to the total compressor inlet pressure.
B)total compressor outlet pressure to the total turbine outlet pressure.
C)total compressor inlet pressure to the total turbine outlet pressure.
D) the total turbine outlet pressure to the total compressor inlet pressure.
588-An engine pressure ratio (EPR) can be defined as the ratio of:
A) jet pipe total pressure to combustion chamber pressure.
B) jet pipe total pressure to compressor inlet total pressure.
C) combustion chamber pressure to compressor inlet total pressure.
D) compressor outlet pressure to compressor inlet total pressure.
589-An EPR gauge reading normally shows the ratio of:
A)compressor outlet pressure to compressor inlet pressure.
B)jet pipe pressure to compressor inlet pressure.
C) turbine inlet pressure to compressor outlet pressure.
D) compressor inlet pressure to turbine outlet pressure.
590-EPR is measured by the ratio of:
A) turbine pressure to combustion chamber inlet pressure.
B) high pressure compressor inlet pressure to exhaust pressure.
C) low pressure compressor inlet pressure to high pressure compressor outlet pressure.
D) exhaust pressure to low pressure compressor inlet pressure.
591-What is the effect of taking bleed air from a gas turbine engine?
A)Increase EPR, increase EGT.
B)Increase EPR. decrease EGT.
C)Decrease EPR, decrease EGT.
D)Decrease EPR, increase EGT.
592-Where are smoke detectors fitted?
A)Toilets.
B)Toilets and cargo compartments A.B.C.D.E
C)All cargo compartments.
D)Toilets and cargo compartments B, C, E.
(Refer to figure 021-E101)
EASA CS 25.854 -Lavatory fire protection
For aeroplanes with a passenger capacity of 20 or more:
(a) Each lavatory must be equipped with a smoke detector system or equivalent that provides a warning light in
the cockpit, or provides a warning light or audible warning in the passenger cabin that would be readily detected
by a cabin crew member; and
(b) Each lavatory must be equipped with a built-in fire extinguisher for each disposal receptacle for towels,
paper, or waste, located within the lavatory. The extinguisher must be designed to discharge automatically into
each disposal receptacle upon occurrence of a fire in that receptacle.
Refer to EASA CS 25.857 for the classification of cargo compartments and smoke detection requirements in
these.
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593-Smoke detectors fitted on transport aircraft are of the following type:
A)optical or ionization
B)chemical
C)electrical
D)magnetic
Most smoke detectors work on the principle of the reflective qualities of smoke. A continuously lit infra-red or
ordinary pilot lamp emitting light or radiation is located in a chamber. If smoke is present the light will reflect
off the smoke and an adjacent photo-diode detects the light and operates warning relays. Warning lights will
flash and some aircraft have warning horns wired into the system. Similar detectors are fitted in the toilet areas
are the warnings may be located on panels in the galley areas. A test facility is provided for each detector unit.
When operated, to TEST, a test lamp operates which simulates the presence of smoke in the chamber. The
detector may continue to give a warning, even after the smoke has cleared, until RESET is selected. There are 4
main types of smoke detectors:
•Photoelectric cells -detect the diffusion of a beam of light which occurs when the beam is interrupted by
smoke. The scattering of the light increases the conductance of the cell and its output is amplified to operate a
warning circuit.
•Alpha-particle detectors -are ionisation chambers which measure alpha radiation from radium. Alpha particles
are absorbed by smoke, which reduces the ionisation current of the device, to operate an alarm.
•Visual smoke detectors -are usually only fitted as alarm verification devices.
•Carbon-Monoxide detectors -found mainly in aircraft of American manufacture, these devices detect
concentrations of CO and activate a warning system.
594-An ion detector detects:
A)smoke and fire
B)smoke
C)overheat
D)light
For explanation refer to question #593.
595-Ion detectors are devices used in aircraft for systems protection .. They detect:
A)over-temperature
B)smoke
C)fire
D)over-temperature and fire
For explanation refer to question593.
596-Smoke detector systems are installed in the:
A)engine nacelles.
B)wheel wells.
C)upper cargo compartments (class E).
D)fuel tanks.
For explanation refer to question #592.
597-On what principle do smoke detectors work?
A)Resistance and capacitance.
B)Ionization and impedance.
C)Optical and ionisation.
D) Inductance and light diffraction .
For explanation refer to question 593.
598-The type of smoke detection system fitted to aircraft is:
A)optical and ionisation
B)chemical
C)electrical
D)magnetic
For explanation refer to question 593.
599-Regarding detection systems, ion detectors are used to detect:
A) smoke.
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B)over-temperature.
C)fire.
D)over-temperature and fire.
For explanation refer to question #593.
600-How do you test a gaseous smoke detector?
A)Use pressurized gas to test the sensor.
B)Use the test button.
C)Use a Lindburgh fire detector
D)Apply heat to the detector.
For explanation refer to question #593.
601-Aircraft toilets must be fitted with fire extinguishing and smoke-detection systems if the seatingcapacity is more than?
A)200
B)100
C)50
D)20
602-A fault protection circuit in a fire detection system will:
A)activate an alarm in the cockpit and in the landing gear bay for ground crew.
B)activate the fire detection system when the detection line is connected to ground.
C)automatically initiate APU shutdown and fire extinguisher striker activation in the event of fire.
D)inhibit the fire detector when the detection line is connected to ground.
603-The most common extinguishing agent used in gas turbine engine fire protection system is:
A)water
B)freon
C)CO2
D)powder
604-On a large transport multi-engined aircraft a fire detection system includes:
A)both a warning light and an alarm bell unique to each engine.
B)a single warning light but a separate alarm bell for each engine.
C)a single warning light and a single alarm bell.
D)a warning light for each engine and a single alarm bell common to all engines.
Fire detector signals activate warning lamps and/or captions on the flight deck and often audible warnings also.
Fire
warning lamps conventionally give a steady red indication .All detection systems include functional test circuits
and many are of a sophisticated type which monitor temperature trends in engine bays. There is one warning
lamp for each engine, but the warning bell will be activated by any fire detection circuit (common bell for both
engine and the APU). If the temperature rises in the appropriate area to the FIRE warning levels the following
indications are given in the cockpit:
•The fire bell sounds.
•Master FIRE WARNING lights illuminate.
•The associated engine fire warning switch illuminates.
•All related engine overheat alert indications illuminate.
After receipt of these warnings, the fire drill is carried out and this will close all fluid and air valves to and from
the engine, de-energise and uncouple the generator and, by turning the appropriate control, fire a 'squib' on the
fire bottle head, to direct fire extinguisher fluid into the engine. The APU is similar in operation but the APU is
shut down automatically and a fire warning hom sounds in an undercarriage wheel well in addition to the
cockpit (for ground operations of the APU). In both cases the warning remains illuminated until the fire wire
temperature drops below the onset value. The fire warning bell can be silenced manually by the pilot. In some
installations, the fire handle is locked until receipt of a fire warning which then unlocks the handle . The facility
can be overridden manually
605-Fire detection systems:
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SYSTEM,POWERPLANT&ELECTRICS
A)automatically fire the engine extinguishers.
B)can only use AC electricity,
C)are connected to the vital busbar.
D)can be tested from the flight deck.
606-The engine fire extinguisher system is activated:
A)after the engine has been shut down.
B)automatically when a fire warning is sensed.
C)by the pilot when required.
D)automatically after a time delay to allow the engine to stop.
607-An automatic toilet fire extinguisher is activated by:
A) odour detection.
B)CO2,
C)heat detection.
D)smoke detection.
608-The indication of the fire detection systems is performed by a:
A)gear warning.
B)warning bell.
C)warning light.
D)warning light and a warning bell (or aural alert).
609-A continuous loop detector system is a:
A)carbon dioxide warning system.
B)smoke detection system.
C)fire detection system.
D)fire fighting system.
610-The continuous loop system is used:
A)as a smoke detector.
B)as a fire detector.
C)as a carbon monoxide detector.
D)as a fire fighting system.
611-The most common fire extinguishant used in gas turbine engines is:
A)dry powder.
B)carbon dioxide.
C)water.
D)freon.
Power plants and APUs use fixed fire extinguishing installations consisting of pressurised extinguishant
containers, distribution piping and operating controls. The types of extinguish ant are usually toxic or semi-toxic
Freon compounds such as bromochlorodiflouromethane (BCF) and bromotrifouro-methane (BTM). .
612-The principle of operation of fire wire is:
A)positive coefficient of resistance, negative coefficient of capacitance.
B)positive coefficient of inductance, negative coefficient of impedance.
C)positive coefficient of capacitance, negative coefficient of resistance.
D)positive coefficient of impedance, negative coefficient of inductance.
613-The flight deck warning on activation of a fire detection system is:
A)an individual warning light and bell.
B)a common warning light and a common bell.
C)a warning light only.
D)an individual warning light and common warning bell.
For explanation refer to question 604.
614-Firewire detects a fire by:
A)detecting the smoke that is produced by the fire.
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B)detecting the heat caused by the fire.
C)detecting the flame produced by the fire.
D)all of the above.
615-What do you do if you encounter rain along your route of flight?
A)Anti-icing helps.
B)Wipers are sufficient even in heavy rain.
C)Alcohol in the anti-icing fluid helps.
D)Use rain repellent with the wipers in heavy rain.
616-The survival oxygen is:
A)the oxygen used for protection against smoke and carbon dioxide.
B)the oxygen supplied to a passenger who needs oxygen for pathological reasons.
C)the oxygen supplied to the airplane occupants in case of accidental depressurization.
D)a therapeutical oxygen specifically carried for certain passengers.
(Refer to figures 021-E98 and 021-E99)
Most civil transport aircraft are pressurized to maintain conditions inside the cabin equal to an altitude of
approximately 8000 feet, regardless of actual aircraft altitude above this figure. Under these conditions oxygen
is not normally needed for passengers and crew, but oxygen equipment is installed for emergency use in the
event of pressurization system failure or rapid decompression. Oxygen is typically carried as a gas or in a form
of chemical generators. Gaseous oxygen is carried in high pressure steel bottles. There are three types of system:
the continuous flow system, for crew and passengers; the diluter demand system ,for flight deck crew only;
portable oxygen sets to supplementother systems and these can also be used for therapeutic use and for cabin
crew to move around a depressurized aircraft. In today's modern transport category airplanes the flight crew
emergency oxygen system is gaseous (stored in a cylinder) and the passenger system is in the form of chemical
generators::: 2 separate systems.
PASSENGER oxygen system on a large transport aircraft is in most cases supplied from chemical generators
(survival oxygen) -a continuous flow oxygen system. The system is used after a cabin depressurisation via
automatically operated drop down masks, located above each seat. The system can be operated manually from
the flight deck.
SUPPLEMENTARY/SURVIVAL oxygen (built-in chemical generators) = supplied to the airplane occupants in
case of accidental depressurization.
FIRST AID oxygen (portable oxygen bottles) = provide some passengers with additional respiratory assistance
after an emergency descent following a depressurization or to deal with medical conditions of certain passengers
during normal flight (usually respiratory disorders).
617-The built-in passenger oxygen system can be activated by:
A)opening the oxygen-bottle valves.
B)switching the diluter demand regulator ON.
C)switching the passenger oxygen ON.
D)switching the diluter demand regulator and the passenger oxygen ON.
(Refer to figure 021-E22)
The oxygen system most commonly fitted in today's modern transport category airplanes for use by passengers
and cabin crew in case of accidental depressurization is in a form of chemical oxygen generators. It is a cheap,
light and effective way of providing passenger oxygen, which is produced from sodium and Iron powder. Quite
simply, the chemical reaction is triggered by pulling on a dropout mask after it has been presented by automatic
drop-out system (barometric ejection using an aneroid capsule that typically operates at 14 000 feet-releases the
mask to a half-hung position) or by manual operation from the flight deck -by selecting the "PAX Oxygen
System" to ON -this releases the masks, but the actual chemical reaction (flow of oxygen) can only be started by
the passengers by pulling on the mask.
Pulling on the mask triggers the electrical firing mechanism(in some models the firing circuit is initiated
mechanically) or electrical heater ,which Ignites a sodium chlorate and iron powder charge block. As the
temperature of the block rises, a chemical reaction creates a flow of low pressure oxygen through a
filter to the mask. Oxygen ,flow will normally be maintained for about 15 minutes and, despite the very high
temperatures generated, the oxygen Itself is at a comfortable temperature .A relief valve is fitted to relieve
excess pressure. The generator outside thermal paint changes colour after use to show that it needs replacing.
One generator will supply more than one mask (typically 4 masks).
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Chemical oxygen generators have a shelf/service life of ten years are of a relatively simple and light
construction(inexpensive to manufacture), and require no maintenance(unless it has been used). Also a risk of
explosion is lower than in gaseous systems as there is no oxygen stored under pressure in the chem. generators
and no leak can occur. Obvious disadvantages include: inability to control (modulate) the flow -once started, the
generator go for 15 minutes; non-reversible functioning (they can not be simply refilled -they have to be
replaced with new generators once used); poor autonomy (they can not be centrally operated the passenger has
to actually pull on the mask to get the generator running).
The passenger masks are supplied with a continuous flow of oxygen from the chemical generators. Once the
generator has been initiated, the flow of oxygen can not be regulated or stopped -the generator will only stop
after the chemicals are exhausted. The passenger is supplied a mixture of oxygen together with cabin air from
outside of the mask -therefore the masks will not protect the passenger from a smoke environment as the smoke
would be inhaled together with the oxygen flowing through the mask.
618-When quick donning masks are in use, the pilot is:
A)not able to do any radio communication.
B)only able to receive.
C)only able to transmit.
D)able to radiotelephone.
619-A passenger emergency mask is:
A)an on-demand type mask and in principle should not be used if there is smoke in the cabin.
B)a continuous flow mask and in principle should not be used if there is smoke in the cabin.
C)a continuous flow mask and must be used if there is smoke in the cabin.
D)an on-demand type mask and must be used if there is smoke in the cabin.
For explanation refer to question 617.
620-Smoke hoods protect:
A)full face and provide a continuous flow of oxygen.
B)mouth and nose and provide a continuous flow of oxygen.
C)full face and provide oxygen on demand.
D) mouth and nose and provide oxygen on demand.
(Refer to figure 021-E100)
The smoke hood or Protective Breathing Equipment (PBE) protects against fumes and smoke. It comprises a
single size hood which completely covers the head of the user, some models are also equipped with an
additional fire protection "apron" extending down over the chest. The PBE contains a small chemical oxygen
generator (typically located in the neck area of the PBE). Chemical reaction, once started by the user, provides a
constant flow of oxygen into the smoke hood -this chemical reaction is usually started by pulling a pin-latch
from the oxygen generator. Oxygen flow can be determined (checked by the wearer) by hearing a hissing sound
inside the hood. The oxygen flow typically lasts for about 12-15 minutes. After 12 minutes the chemical
reaction gradually starts to cease while providing an oxygen for another 3 minutes (total of 15 minutes of
oxygen availability to the wearer). One PBE unit must be located on the flight deck, one unit must be located
next to each required cabin duty member station and one must be located outside each accessible freight or
baggage compartment at which there is a fire extinguisher.
621-Emergency oxygen is provided by:
A)one system for both flight deck and cabin.
B)two independent systems, one for flight deck, one for cabin.
C)two systems each capable of supplying the flight deck and cabin.
D)three systems, one for the flight deck, one for the passengers and one for the cabin crew.
622-The passenger oxygen drop-down mask stowage doors are released:
A)by a lanyard operated by a barometric capsule .
B)mechanically.
C)electrically for chemical oxygen generators and pneumatically for gaseous systems.
D)manually by the cabin crew.
623-The passenger oxygen mask will supply:
A)cabin air and oxygen.
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B)100% oxygen.
C)cabin air and oxygen or 100% oxygen.
D)a mixture of oxygen and freon gas.
For explanation refer to question 617.
624-The chemical oxygen generator supplies oxygen for about:
A)5 minutes
B)30 minutes
C)2 hours
D)15 minutes
For explanation refer to question 617.
625-Protective breathing equipment:
A)protects crew against fumes and noxious gasses.
B)protects crew against accidental depressurization.
C)is not required on commercial flights.
D)is only available for cockpit crew.
For explanation refer to question 620.
626-In case of smoke in the cockpit, the crew oxygen regulator must be set to:
A)on demand
B)normal
C)emergency
D)100%
627-The excess cabin altitude alerting system must operate to warn the crew at:
A)8.000 ft
B)10.000 ft
C)13.000 ft
D)14.000 ft
EASA CS-25-841 Pressurised Cabins
(6) Warning indication at the pilot or flight engineer station to indicate when the safe or pre-set pressure
differential and cabin pressure attitude limits are exceeded. Appropriate warning markings on the cabin pressure
differential indicator meet the warning requirement for pressure differential limits and an aural or visual signal
(in addition to cabin altitude indicating means) meets the warning requirement for cabin pressure altitude limits
if it warns the flight crew when the cabin pressure altitude exceeds 3048 m (10000 ft)
628-A smoke mask is a:
A)mask with flow on request and covers the whole face.
B)continuous flow mask and covers only the nose and the mouth.
C)continuous flow mask and covers the whole face.
D)mask with flow on request and covers only the nose and the mouth.
629-To use passengers oxygen in case of severe cabin smoke is:
A)useless because the oxygen units do not operate under smoke conditions.
B)useless because the toxic cabin smoke is mixed with the breathing oxygen.
C)useless because breathing oxygen would explode under smoke conditions.
D)possible and recommended.
Passengers masks are not leak-proof. When you breath oxygen with the mask, you also breathe ambient air. It
becomes dangerous in case of severe smoke, because you inhale the smoke. There is often a big argument
among the students saying "But it is better to breather at least a mix of oxygen and the smoke". The masks will
NOT protect the PAX from smoke. There is no need to argue about this fact .Second thing -if you have smoke in
the cabin, you probably have a fire as well somewhere (or a fire about to start) in the cabin.
I'm sure that everybody knows the equation: Oxygen + Fire =. …. So do you really want to start a few dozen
chemical generators in the enclosed confined space of the fuselage (for absolutely no helpful reason at all -the
masks will NOT protect against smoke) and start pumping huge amounts of oxygen to support the fire ?
630-The purpose of the first aid oxygen is to:
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A)provide some passengers with additional respirator assistance after an emergency descent following a de
pressurization.
B)provide the cabin attendants with respiratory protection.
C)supply all the passengers in case of depressurization
D)provide the flight crew with respiratory assistance after depressurization.
For explanation refer to question 616.
631-The passenger oxygen mask will supply:
A)a mixture of oxygen and freon gas.
B)a mixture of cabin air and oxygen
C)100% oxygen.
D)a mixture of compressed air and oxygen or 100% oxygen.
For explanation refer to question 617.
632-In a pressurized transport aircraft, the protective breathing equipment:
A)gives medical assistance to certain passengers with respiratory disorders.
B)protects all the occupants against the effects of accidental depressurization.
C)protects the members of the crew against the effects of accidental depressurization.
D)protects the members of the crew against fumes and noxious gases.
For explanation refer to question 620.
633-A smoke hood is a device covering:
A)the whole head and with an oxygen flow only on demand.
B)the whole head and with a continuous oxygen flow.
C)only the nose and the mouth and with an oxygen/air mix.
D)only the nose and the mouth and with a continuous oxygen flow,
For explanation refer to question 620.
634-A diluter-demand type oxygen regulator:
A)supplies oxygen when the recipient inhales.
B)delivers a continuous supply of oxygen.
C)mixes oxygen and air in a passenger mask.
D)supplies oxygen only above FL150.
635-Oxygen supplied to the flight deck is:
A)gaseous, diluted with ambient air if required.
B)chemically generated and diluted with cabin air if required.
C)gaseous, diluted with cabin air if required.
D)chemically generated, diluted with ambient air if required.
636What is normally used as a leak detector in an aircraft oxygen system?
A)A form of non-oily soap solution.
B)A form of oil solution.
C)An oxygen-compatible lubricant.
D)Slow opening valves.
It is important that oil or any kind of grease does not come into direct contact with 100% oxygen as it would
produce a violent reaction. The most effective way of testing an oxygen installation for leaks is to use non-oily
soap solution -if oxygen is leaking, it will produce easily recognizable bubbles in the soap solution
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