Lesson Two: Theory of Flight II

Don’t read:
o “Mach Number”
o “The Radar Altimeter”
o “The Gyrosyn Compass”
o “Angle of Attack Indicator”
o “Mach Indicator”

Flight Performance Factors
o Conditions which can affect how the plane will perform.
o Some of these factors will require input on the pilot’s part to correct for
movement in an undesired direction.
o Torque
 Propeller generally rotates clockwise from the perspective of the pilot
looking out. Reaction to spinning prop is to turn the nose to the left
(counterclockwise).
 Compensated in design by giving plane slight right-turning
tendency; i.e. left wing higher AoI than right wing. Aileron trim
tabs also compensate for torque.
 On T/O, right rudder corrects left-nose tendency.
o Asymmetric Thrust
 Also called P-Factor, results in left-turning tendency as well.
 At high AoA and high power, descending blade of prop meets air at
higher AoA than ascending blade; results in yaw to the left.
 Only feelable at high AoA (i.e. climbing)
o Precession
 Spinning propeller of airplane acts like a gyroscope.
 Gyroscope obeys concept of rigidity in space – rotating gyro tends to stay
in same plane of rotation, resists motion from said plane
 Sudden decrease in pitch will cause airplane to yaw sharply left.
 Corrected with right rudder.
o Slipstream
 Air pushed back by rotating pro has corkscrew motion; causes increased
pressure one side of fin and less pressure on other side.
 Causes plane to yaw to the left, esp. as the throttle is opened on the
take-off roll.
 Corrected by offsetting fin in design; applying right rudder on T/O.

Pushers vs. Tractors
 Tractor props “pull” the airplane forward; located in front of
plane. Slipstream is most apparent with tractors, although since
tractors are located in the front they bite into the “clean” air.
 Pusher props “push” the airplane forward; located in rear of
plane. Slipstream not apparent with pushers, although they bite
into the “dirty” air already disrupted by the plane.
 Overall pushers have greater efficienciy.
o Climbing
 Elevators channel the energy given as thrust from the engines into
altitude.
 Caused by pulling back on the control column and pushing in the throttle.
 Control column back  Throttle in  Elevators up  Tail meets
air at lower angle of attack  Tail drops  Nose rises  Plane
climbs  Airspeed decreases as energy is channeled into moving
the plane up.
 Can’t climb forever
 At higher altitudes, air density decreases, less reactive forces on
wings, less lift.
 Less air goes into engines, so they lose power too.
 Eventually reaches altitude where plane’s climb is too shallow to
further increase altitude.
 Best rate of climb (Vy)
 Rate of climb where most altitude will be gained in least time
 Defined by an airspeed in the plane’s POH.
 Not affected by wind.
 Best angle of climb (Vx)
 Rate of climb where most altitude will be gained in least distance.
 Defined by an airspeed in the plane’s POH.
 Affected by wind.
o Gliding
 Force of thrust removed.
 Constant forward movement caused by equilibrium between lift, drag
and weight.
 Steeper glide angle, faster glide speed.
 Best glide speed for range (best L/D)
 Speed/angle at which to fly for the longest distance per altitude
drop
 Best glide speed for endurance (min sink)
 Speed/angle at which to fly for the longest time in air
o Turns
 Turn control column to right  plane rolls right  lift force directed to
inside of turn  pulls nose (and the whole of the plane) to the right
 Forces no longer in equilibrium, since not enough component of lift in the
vertical to counter weight; AoA must be increased to produce more lift,
otherwise nose will drop
 Centripetal force (force which turns plane towards inside of turn)
counters centrifugal force (apparent force which tends to force plane out
of turn, like how your body goes to the side when you turn sharply in a
car)
 The steeper the angle of bank (AoB) (at a given airspeed):
 The greater the rate of turn
 The less the radius of turn
 The higher the stalling speed
 The greater the loading (g-forces)
 **60o bank = 2g
 Turns too steep can cause structural damage to airplanes; so many planes
have limitations as to the max bank angle (the steepest turn I’ve been in
in a C-172 was a 60o turn)
 Read up on climbing and descending turns and load factors
 Skid: using too much rudder in direction of turn, causes tail to “lead”
turn.
 Slip: using too little rudder in direction of turn, causes nose to “fall” into
turn.
o Stall
 Occurs when the wing is no longer capable of producing sufficient lift to
counteract weight of plane.
 Occurs when AoA is increased to the point that laminar flow over the
wing no longer occurs; airflow separates from wing, becomes turbulent.
 Pressure differential between top and bottom gone.
 Point at which airflow pulls away from wing is called the separation point
 **An airplane will stall if the critical angle of attack is exceeded, no
matter the speed, altitude or attitude.
 Airspeed is a good indicator of when a stall is about to occur.
 Can also feel “bumpiness” of the plane (buffeting)
 An airplane loaded properly will stall at an indicated airspeed
somewhere near the stalling speed published in the PoH
 Factors:
 Weight
o Increase in weight = Requires increase in AoA to produce
enough lift  critical AoA will be reached at higher
airspeed



Centre of Gravity
o How a plane is loaded affects C of G; C of G to far aft will
cause nose-up tendency to be prevalent
o Rearward C of G = lower stalling speed, but worse stall
characteristics due to poorer longitudinal stability 
harder to recover.
 Turbulence
o Sudden upward gust can cause an abrupt increase in AoA
 Turns
o As AoB increases, less lift provided to counteract weight.
Hence the greater the AoB, the higher the stalling speed.
 Flaps
o Deploying flaps will increase lift, hence decreasing the
stalling speed.
 Snow/Frost/Ice/Dirt
o Contaminants on wing disrupt airflow, causing a decrease
in lift.
o Can also cause separation point to occur much farther
forward on wing than normal (i.e. more turbulent flow)
o Read the rest of this section
Stall warning devices
 Many light airplanes fitted with a warning device, like a stall horn
when insufficient airflow passes over the top of the wing.
 Best prevention of stalls is pilot experience.
o Which is why you need to practice stalls when you learn to
fly.
Stall recovery
 Decrease AoA.
 Increase power to accelerate plane, if possible.
o Spins
 Defined as autorotation which develops from a lopsided, aggravated stall.
 Occurs when one wing stalls before the other.
 Drag on downgoing wing abruptly increases AoA, further exacerbates
spin condition.
 Nose drops, autorotation sets in.


Incipient stage  Developed stage  Recovery
Recovery
 Neutralize ailerons.
 Power idle.
 Control column forward to decrease AoA.
 Ease out of dive when rotation stops.
 Forward and vertical speeds are comparatively low in a spin.
o Spiral Dive
 Not caused by a stall; just an aggravated, uncontrolled steep descending
turn with excessively nose-down attitude.
 Attitude less nose down than spin, although speed and loading increases
much faster in a spiral dive.
 Recovery
 Close throttle and level wings as cleanly as possible.
 Ease out of dive, in a straight manner.
 Once airspeed has settled, use throttle to maintain altitude.

Airspeed Limits
o VNE – Never Exceed Speed
 Higher air speed may result in structural failure/flutter/loss of control
o VNO – Maximum Structural Cruise/Normal Operating Limit speed
 Maximum safe speed at which the airplane should be operated in the
normal category.
 Try not to exceed anyway; a sudden gust can send you way past the V NE
as this point.
o VA – Maneuvering Speed
 Maximum speed at which flight controls can be fully deflected without
damage to the airplane structure.
 Used for abrupt maneuvers, or when flying in rough air/turbulence.
o VFE—Maximum Flaps Extended Speed
 Max speed at which airplane may be flown with flaps lowered.

Flight Instruments
o Pitot-Static Instruments
 Instruments which are connected to the pitot-static system
 Pitot pressure source: usually located near front of plane, typically on the
LE of wings where it is clear of slipstream, or directly on nose of glider. It
is a dynamic pressure source, using the incoming airflow combined with
the ambient atmospheric pressure to take readings.

Static pressure source: located near the side of an airplane, away from
incoming air. Reads in ambient atmospheric pressure.
 The airspeed indicator (ASI) uses both the pitot and the static sources.
The altimeter and the vertical speed indicator (VSI) use just the static
source.
 Issues
 P-S system susceptible to accumulation of dirt, water and ice.
 Completely blocked pitot source will have pressure trapped in the
ASI; it will read like an altimeter.
 Partially blocked pitot source, ASI will read 0.
 Partially blocked static source: alti., ASI and VSI will under-read in
climb, then lag to catch up as the plane levels off. In descent, ASI
will over-read, VSI will indicate less than true rate of descent, alt.
will over read.
 Since static source located on one side of plane, slipping in that
direction can cause misreadings in that direction.
o The Altimeter
 Special form of aneroid barometer (barometer without liquid) which
measures static pressure of the atmosphere.
 Diagram of altimeter.
 Since the pressure in the atmosphere decreases pseudo-uniformly with
height, the pressure can be seen as a measure of altitude.
 Under standard conditions of 15oC, the pressure at sea level is 29.92
inches of Mercury.
 Decrease in pressure sensed by altimeter = increase in height.
 Read up on how altimeters work.
 Errors
 Pressure Error
o Heights which airplanes are required to fly for air nav are
indicated altitudes above sea level; done so by calibrating
by using altimeter settings.
o Obtained from ATCs and flight service stations.
o Important to use most updated altimeter settings,
otherwise this happens:
What you thought: 6000’
Reality: 5400’
29.80’’
6000’ indicated altitude
4800’ mountain
29.20’’


o **From high to low – watch out below.
o Every 0.10’’ Hg change ~ 100’ altitude difference
o Altimeter Setting Region
 When set on barometric scale, altimeter shows
indicated altitude above sea level (ASL)
 Set to alt. setting of nearest ATC or FSS; when
you’ve landed at an airport, your altimeter will
read the altitude above sea level (field elevation)
o Standard Pressure Region
 Over trans-oceanic flights and/or flying above
18000’ MSL; set alt. setting to 29.92’’ Hg
 Pressure altitude is the height above sea level
corresponding to a setting of standard air
conditions.
 Altitude at which airplane is flying with respect to
pressure altitude called flight level
Temperature Error
o Altimeter calibrated to indicate true altitude, based on
standard atmospheric temperature profiles. When the
temp. is way far off the standard, the values shown on the
alt. get thrown off
o In cold conditions, true altitude will be lower than
indicated altitude (you’ll think you’re higher than you
actually are)
o Density altitude: barometric pressure and temperature
both affect air density; defined as pressure altitude
corrected for temperature
 Important when considering T/O performance
 Density altitude = pressure altitude + 100*(actual
temperature – standard temperature)
 Temp. of standard air is 15oC at sea level.
 Lapse rate of 2oC/1000’ of altitude
 For every 1oC difference from standard air, there is
a 100’ difference between true altitude and
indicated altitude.
Mountain Effect Error
o Mountain waves (atmospheric gravity waves flowing over
a mountain ridge) can force an airplane up/down a lot
faster than one might expect; given that the pressure
decrease associated with a fast flowing mountain wave (by
Bernoulli’s Principle) might trick the altimeter into thinking
that you’re higher than you actually are.
 Altitude Definitions:
 Indicated altitude: what you see on the altimeter
 Pressure altitude: reading on the altimeter at 29.92’’
 Density altitude: pressure altitude corrected for temperature
 True altitude: exact height above MSL
 Absolute altitude: actual height above earth’s surface (altimeter
set to field level pressure [AGL])
o The Airspeed Indicator
 Units of knots and miles per hour
 To get airspeed, takes difference in pressure between the pitot and static
systems.
 Diagram.
 Reading on dial called indicated air speed
 Read up on how the ASI works.
 Markings
 Red: VNE
 Yellow: Beginning of yellow marks VNO
 Green: Normal operating range
 White: Upper limit VFE, lower limit power-off stalling speed with
flaps and gears down (VSO)
 Errors
 Density error: deviations from standard atmospheric densities as
explained previously.
o Can calibrate by adding 2% to IAS for every 1000’ of
pressure altitude.
 Position error: eddies that form as the air passes over wings and
struts disrupts pitot pressure source
 Lag error: mechanical error due to friction (IAS lags behind what it
should actually read)
 Icing error: ice formation, blocking of pitot and/or static sources.
(Previously mentioned)
 Read about pitot heat
 Water error: similar to icing error
 Definitions
 Indicated airspeed (IAS): What you read on the ASI, uncorrected
for errors.

Calibration airspeed (CAS): IAS corrected for instrument error and
installation error. Performance data in POH typically written in
CAS.
 Equivalent airspeed (EAS): CAS corrected for compressibility factor
(applicable only at high speeds)
 True airspeed (TAS): CAS/EAS airspeed corrected or indicator
error due to density and temperature.
o Vertical Speed Indicator (VSI)
 Measured in ft./min., shows rate at which plane is ascending or
descending.
 Diagram
 Operates on principle of change in barometric pressure (similar to
altimeter).
 Read up on how a VSI works
 Errors
 Change in altitude must occur before VSI can indicate such a
change; often takes a second or two before it shows a climb or
descent.
 Can lead to “chasing the VSI” for inexperienced pilots
o Gyro Instruments
 Useful for VFR navigation purposes.
 A gyroscope is a rotor rotating at high speed in a universal mounting
(gimbal) so its axle can be pointed in any direction.
 Very complicated classical mechanics description, if you know
your vectors and calculus feel free to look at this in more detail.
 Two fundamental characteristics for applications in aviation:
gyroscopic inertia (rigidity in space) and precession
 Gyroscopic inertia is the tendency of any rotating body to
maintain its plane of rotation, if left undisturbed.
o So if the rotor is already spinning, if you flip the gyroscope
around, the rotor will still spin in that same plane (won’t
change orientation)
 Precession is the tendency of a rotating body, when a force is
applied perpendicular to its plane of rotation, to turn in direction
of its rotation 90o to its axis and follow a new plane of rotation
parallel to applied force.
 Power sources for gyro instruments:
o Engine Driven Vacuum System
 Typically heading indicator and attitude indicator
 Suction allows for the gyros to spin


o Venturi Driven Vacuums System
 Uses Venturi tubes instead of an engine-driven
vacuum pump; typically found on older airplanes
o Electrical
 Typically turn coordinator/turn and slip
 Usually used on most airplanes with a vacuum
system for safeguard
 Care for gyros
o Excessively crazy maneuvers to prevent tumbling
(gyroscope spinning out of plane, can damage bearings)
o Avoid abrupt brakes and other high g-loads
o Keep them clean
Heading Indicator (HI)
 Typically engine-driven vacuum powered
 Tells you heading of the airplane
 Not of its own accord north-seeking; you must set it to match that
of the compass within your cockpit
o Compass affected by many errors associated with
magnetism and acceleration issues; using HI removes such
issues (until you need to reset it)
o HI responds instantly without lag or oscillating, unlike
compass.
 Errors
o Precession error
 Earth rotates beneath plane, which causes an
apparent “drift” or precession of the plane with
respect to the Earth. Must reset HI every 15 min.
 Do so by holding airplane steady, straight
and level, then take steady compass reading
and set HI as such.
o Reliance on mercury vacuum to operate
o Tumbling can throw HI off
Attitude indicator (AI)
 Also called artificial horizon
 Means of reference when natural horizon can’t been seen (clouds,
mountains, rain, etc.)
 Shows orientation of plane with respect to the Earth
 Blue = Sky, Brown = Earth
 Limitations
o Requires vacuum, 4’’ Hg


o Can tumble if not caged prior to aerobatics.
o Precession errors
 Accelerating causes horizontal bar to move down
indicating climb; opposite for deceleration
 In a skidding turn, gyro precesses toward inside of
turn; after returning to straight-and-level flight, AI
will still indicate turn in direction of skid
Turn and Slip Indicator
 Also called turn and bank or needle and ball
 Ball indicates amount of bank in the turn, while needle indicates
direction of turn
 Ball controlled by gravity and centrifugal force, while needle
controlled by gyroscopic precession.
 In straight and level flight, both ball and needle are centered.
 In a correctly banked turn (coordinated turn), the needle indicates
rate and direction of turn, ball is centered.
 If one wing is low, the needle will be straight, while the ball will
roll towards the low wing.
 Skidding right: needle right, ball left (to fix, step on the ball)
 Slipping right: needle right, ball right (to fix, step on the ball)
Turn Co-Ordinator
 Most planes you’ll be flying (C-152/C-172) use this instead of the
turn and slip
 Same principle, except instead of a needle you have a plane
diagram indicating direction and rate of turn.
 Reacts to both roll and yaw, as opposed to the TaS indicator
reacting to roll only.
 Can be used to keep wings level in straight flight if the AI has
failed (relies on electrical system)