THEORY OF FLIGHT
PART 1
References: FTGU 29th Pages 3-23, Pilot’s Handbook of
Aeronautical Knowledge Chapters 1-3
REVIEW FROM LAST CLASS
1.
2.
What is the VFR weather minima for fixed
wing aircraft <1000’ AGL in uncontrolled
airspace?
You are on final approach and you receive a
flashing red light from the tower. What does it
mean and what do you do?
TOPICS TO BE COVERED
The fuselage and empennage
 Parts of the airplane
 Four forces acting on an aircraft
 How lift is created
 Boundary layer

THE AIRPLANE
WHAT IS AN AIRPLANE?
The Canadian Air Regulations defines an
aeroplane as:
 “A power driven, heavier-than-air aircraft,
deriving its lift in flight from aerodynamic
reactions on surfaces that remain fixed under
given conditions of flight”

DEFINITIONS



Aircraft: any machine capable of deriving support
in the atmosphere from the reactions of the air
Glider: heavier-than-air aircraft not equipped
with a motor, which derives its lift from
aerodynamic reactions on surfaces which remain
fixed under given conditions of flight
Airframe: Total structure of the aircraft including
fuel systems and fuel tanks but excluding
instrumentation and engines
CLASSIFICATION

Aircraft can be
classified according to:
Position and number
of wings
 Number of engines
 Configuration of the
undercarriage

PARTS OF AN AIRPLANE
PARTS OF AN AIRPLANE
Vertical Stabilizer
Rudder
Aileron
Flaps
Horizontal Stabilizer
Elevators
Wing Strut
Aileron
Propeller
Engine Cowl
Landing Gear
FUSELAGE
The fuselage is the main body of the aircraft
 Holds all passengers and cargo
 Almost all parts of the aircraft are attached to
the fuselage
 Three types of fuselage construction:
Truss type
Monocoque
Semi-monocoque

TRUSS TYPE (SGS 2-33A)



Longerons: 3-4 steel or
aluminum tubes that
make up the frame
(wood in antique
aircraft)
Strength is achieved by
welding tubes into
triangles called
“trusses”
Frame covered in fabric,
metal or composite
MONOCOQUE (KATANA)





Uses a stressed metal
skin to handle all loads
Example: pop can
Main construction
consists of round
formers to give shape
and bulkheads to seal
off and connect sections
Stringers run
lengthwise to hold
everything together
Very strong but heavy
due to the strength
requirement of the skin
SEMI-MONOCOQUE (AIRBUS 320)



Structure of formers,
bulkheads and
stringers to create a
frame
Frame is covered by a
stressed skin to take
some of the bending
stresses
Most common type of
fuselage construction
REVIEW
1.
What is an aeroplane according to the CARs?
2.
What are the main parts of an airplane?
3.
What are the three types of fuselage
construction?
WINGS


Create lift to carry
aircraft in the air
Two main types of
wing configuration
Monoplane – One
wing
 Biplane – Two wing

WING POSITIONING
Three positions for the
wing relative to the
fuselage:
 High-wing – Attached
on top
 Mid-wing – Attached
in the middle
 Low-wing – Attached
on the bottom

CONSTRUCTION OF THE WING
CONSTRUCTION OF THE WING
Chord – Imaginary
straight line from the
leading edge to the
trailing edge
 Struts – External
bracing that support
the wings, mainly
seen in high wing
aircraft

Struts
CONSTRUCTION OF EMPENNAGE
STABILATOR


One piece movable
surface that replaces
the elevator and
horizontal stabilizer
Stabilators have a
movable surface
called an anti-servo
tab which act as trim
tab to relieve control
surfaces
CANARD
In some aircraft, the
horizontal tail is
moved forward
 Seen in early aircraft
such as the Wright
Flyer and modern
aircraft such as the
Beech Starship and
fighter aircraft

Canard
REVIEW
1.
What surfaces make up the empennage?
2.
What are the main components of the wing?
3.
What is the chord?
PROPULSION SYSTEM




For smaller GA aircraft
the main parts of the
propulsion system are:
Engine: Provides
rotation for the
propeller
Propeller: Creates
thrust through rotation
Cowling: Covers the
engine and provides
cooling through air
ducts
LANDING GEAR
Absorbs shock of
landing
 Supports weight of
aircraft
 Allows the movement
of the aircraft on the
ground
 Can be either fixed or
retractable

TYPE OF LANDING GEAR
Conventional (Tail
dragger)
Tricycle (Nose wheel)
LANDING GEAR ADVANTAGES
Conventional
1.
2.
3.
4.
5.
6.
Less parasite drag
Cheaper to build and
maintain
Less damage if broken
Easier to handle on
ground
Less propeller damage on
rough strips due to
distance from ground
Less airframe damage
due to landing shock
absorption
Tricycle
1.
2.
3.
4.
5.
6.
Reduced nose-over
tendencies
Reduced ground
looping tendencies
Better ground
visibility
Better ground
manoeuvrability in
high wind conditions
Better crosswind
control
Easier to learn to land
REVIEW
1.
What are the two types of landing gear?
2.
What are some advantages/disadvantages of
those landing gear?
3.
What are the main components of the
propulsion system?
THE CONTROL SYSTEMS
AIRCRAFT CONTROLS
Aircraft can move around or in three axes
 In order to move, some type of control mechanism
must be in place
 Three main control surfaces:
Ailerons (roll)
Elevator (pitch)
Rudder (yaw)

AILERONS



Control surfaces
attached to the
outboard trailing edge
of the wing
Move in opposite
directions
When the control
column is moved to the
right, the left aileron
goes down (increasing
lift) and the right
aileron goes up
(decreasing lift), this
causes the plane to roll
to the right
Source: Pilot’s Handbook of Aeronautical
Knowledge
ELEVATORS AND STABILATORS
Hinged to the trailing
edge of the horizontal
stabilizer
 Move up or down
when the pilot pulls
the column back or
pushes forward
 Controls the pitching
motion of the airplane

Source: Pilot’s Handbook of Aeronautical
Knowledge
RUDDER



Attached to the
vertical stabilizer
and moves the
aircraft left and right
through a motion
called yaw
Controlled by the
rudder pedals at the
pilots feet
Causes the rudder to
deflect and a force is
created at the tail
Source: Pilot’s Handbook of Aeronautical
Knowledge
SECONDARY EFFECTS OF CONTROLS
Rudder

Yawing moment in
the direction of the
turn created by the
relative airflow
hitting the side of the
fuselage ahead of the c
of g
Ailerons

Rolling moment in the
direction of the turn
due to the outside
wing moving faster
through the air
creating more lift
TRIM TAB



Source: Pilot’s Handbook of
Aeronautical Knowledge
Helps eliminate
excess force on the
controls by the pilot
Acts as an small
elevator on the
control surface which
creates a force to
keep it in a constant
position
Moves in the
opposite direction
of the surface
REVIEW
1.
What are the three main control surfaces and
where are they located?
2.
How do ailerons roll the aircraft?
3.
If we wanted to hold a nose high attitude,
which direction would we want to the trim tab
to move?
FORCES ACTING ON AN
AIRPLANE IN FLIGHT
THE FOUR FORCES
1.
2.
3.
4.
Thrust – force exerted by engine and propeller(s)
which pushes air backward causing reaction, or
thrust, forward
Drag – resistance to forward motion directly opposed
to thrust
Lift – force upward which sustains airplane in flight
Weight – downward force due to gravity, directly
opposed to lift
THE FOUR FORCES
EQUILIBRIUM
When two forces are equal and opposite, they are
said to be in equilibrium
 When the forces are equal, the aircraft will
continue to move at a constant rate of speed

LIFT


Lift opposes weight through aerodynamic
reactions
Creation of lift can be explained through two
separate principles:
Newton’s Three Laws of Motion
 Bernoulli’s Principle

AIRFOILS
An airfoil is any
surface designed to
create lift
 Most suitable surface
for creating lift is a
curved or cambered
surface

CAMBER
Camber is the
curvature of the upper
and lower surfaces of
the wing
 Usually the upper
surface is more curved
than the lower surface

NEWTON’S THREE LAWS OF MOTION
1st law: An object in motion will stay in motion
and an object at rest will stay at rest unless acted
on by another force
 2nd law: Acceleration of an object is inversely
proportional to the mass of the object and
proportional to the force applied (ex. You trying
to push a school bus as opposed to a soccer ball)
 3rd law: Every action has an equal and opposite
reaction

BERNOULLI’S PRINCIPLE
Energy in a system must remain constant
 If we look at a venturi tube, the amount of air
entering in the tube must equal the air exiting
the tube (flow rate)

BERNOULLI’S PRINCIPLE
As the tube decreases in size the velocity of the
air must increase to maintain the same flow rate,
therefore kinetic energy increases
 This causes the pressure to drop and the energy
remains constant

HOW LIFT IS ACTUALLY CREATED


As the air flows over
the wing, it
accelerates as it
moves over the
cambered surface
(just like in a venturi
tube)
This causes the
pressure above the
wing to decrease,
creating a force that
sucks the wing into
the air
HOW LIFT IS ACTUALLY CREATED
On the underside of the
wing, the air is
deflected downwards
DOWNWASH which pushes up on the
wing
 Also, air flowing off the
top of the wing is
deflected downwards,
this contributes to lift
 This phenomenon is
called downwash and
is a result of Newton’s
Force acting on air
3rd law
Force acting on wing

RELATIVE AIRFLOW (RELATIVE WIND)




Direction of the airflow
with respect to the wing
Created by the motion
of the aircraft through
the air
Can also be created by
air moving around a
stationary object
When an aircraft is on
the take-off roll, the
aircraft will be
subjected to the relative
wind by it’s own motion
through the air and by
the wind
ANGLE OF ATTACK
Angle of attack – angle airfoil meets the relative
airflow
 As angle of attack increases, pressure (lift)
increases until the critical angle of attack
 Beyond this angle, they decrease

CENTER OF PRESSURE
If we consider the
pressure distribution
across the wing as a
single force, it will act
through a straight
line
 This is called the
centre of pressure

CENTER OF PRESSURE
As lift increases, the
center of pressure
moves forward until
the wing stalls
 Will always occur at
the critical angle of
attack
 The C of P then moves
backwards; this can
cause the aircraft to
become unstable

REVIEW
1.
What is Bernoulli’s Principle?
2.
What are Newton’s three laws of motion?
3.
How does a wing create lift?
WEIGHT
Weight is the downward force created on the
aircraft due to gravity
 All of the weight acts through a single point
called the centre of gravity

THRUST


Thrust is force that
moves the aircraft
forward through the
air
While there are many
ways of producing
thrust, all rely on the
principle of moving
air backwards to
create a reaction to
push the aircraft
forward
DRAG


Resistance to the motion of the aircraft through
the air
There are two main types of drag:
Parasite drag – Created by parts of the aircraft that
do not contribute to lift
 Induced drag – Created by parts of the aircraft that
contribute to lift

PARASITE DRAG
Form Drag: Drag created by the shape of the
aircraft. Can be reduced through streamlining
2.
Skin friction: Drag created by the roughness of
the skin, can be made worse through dirt and
ice accumulation
 Parasite drag increases as speed increases
 Interference drag: Drag created by two parts of
the aircraft that create eddies where they
intersect (such as the struts and wings)
1.
INDUCED DRAG




Created by parts of
the plane that create
lift
Cannot be completely
eliminated
Greater the lift,
greater the induced
drag
Reduces as speed
increases
REVIEW
1.
What do we call the point at which all weight
acts through?
2.
How is thrust generally produced?
3.
What are the two types of drag?
WING TIP VORTICES
Decreased pressure on top of wing causes air to
flow inward
 Higher pressure on lower surface of wing causes
air to flow outward and curl upward over wing
tip
 Two airflows meet and causes eddies that create
resistance on the wing

VORTEX GENERATORS
Small
airfoils placed along the
wing
When the air flows over them,
small vortices will be created, reenergizing the flow which
prevents the air from separating
and becoming turbulent
This helps increase lift and
decrease drag
VORTEX GENERATORS
LIFT AND DRAG CURVES
Lift and drag are dependant on several factors:
 Angle of attack and the shape of the airfoil – CL
and CD
 Wing area – S
 The square of the velocity – v2
 Density of the air – ρ
 Lift equation: L = ½ CL v2 ρ S
 Drag equation: D = ½ CD v2 ρ S

LIFT AND DRAG CURVES
BOUNDARY LAYER




The boundary layer is a thin sheet of air that
sticks to the wing
This occurs because air is viscous (or has a
resistance to flow)
The airflow slows down as it gets closer to the
surface as a result of friction between the air and
the surface
If we use a wing as an example, the airflow
would be smooth at the front of the wing, this is
called the laminar flow region
BOUNDARY LAYER
As the air continues to flow back, it slows down
due to friction and eventually becomes turbulent,
this is called the turbulent flow region
 The point at which it changes from laminar to
turbulent flow is called the transition point

Transition point
COUPLES
When two forces are opposite and parallel, but
not acting through the same point, a couple is
created
 This couple will cause rotation about a given axis
 An example of this would be drag acting opposite
and parallel above thrust, this would cause the
nose of the aircraft to rise

COUPLES

Weight ahead of Lift – Nose down
COUPLES

Lift ahead of Weight – Nose up
COUPLES

Thrust below Drag – Nose up
COUPLES

Drag below Thrust – Nose down
REVIEW
1.
What is aileron drag and what does it create?
2.
What factors affect lift and drag?
3.
Explain the concept of couples.
DESIGN OF THE WING
AIRFOIL DESIGN - CONVENTIONAL




Thick airfoil that allows
for better structure and
lower weight
Camber is maintain
further rearward which
increases lift and
reduces drag
Good stall
characteristics
Thickest part of the
wing is at 25% of the
chord
AIRFOIL DESIGN - LAMINAR



Designed for faster
aircraft because of the
reduced drag
Thinner than the
conventional airfoil
and the cambering is
almost symmetrical
Thickest part of the
airfoil is 50% of the
chord
PLANFORM
Shape of wing from above
 Wing shapes:





Rectangular
Tapered (from wing root to wing tip)
Elliptical
Delta
ASPECT RATIO
Wing span divided by chord
 A high aspect ratio wing will generate more lift
and less induced drag.

For example, a wing with a span of 24 ft and a chord
of 6 ft has an aspect ratio of 4, while a wing with a
span of 36 ft and a chord of 4 ft will have an aspect
ratio of 9, for an identical area of 144 square feet.
 High aspect ration wings are preferred for glider
construction, where high lift and low drag are critical

ANGLE OF INCIDENCE
 Angle
at which the wing is permanently
inclined to the horizontal axis
 Most airplanes have a small angle of
incidence to ensure a small angle of attack
and therefore a greater visibility during
Angle of Incidence
cruise
Longitudinal Axis
Longitudinal Axis
WING TIP DESIGN
Designed to reduce wing tip vortices and induced
drag
 Wing tip tanks



Increase range, distribute weight across wing
Wing tip plates

Same shape as airfoil but larger
Droop wing tips
 Winglets

WINGLETS
Mounted vertically on
the wingtips
 Small airfoil surfaces
 Break up the wingtip
vortices which flow
towards the upper
surface of the wing

WASH-IN/WASH-OUT
Reduces the tendency for the entire wing to stall
at the same time
 The wing is slightly twisted so that the wing root
has a different angle of incidence than the wing
tip, forcing one to stall first
 This allows for the pilot to have more control
during a stall

WING FENCES
Fins attached to the
upper surface of the
wing
 Control the movement
of air over the wing to
allow for better
handling at low speed
and improve stall
characteristics

SLATS AND SLOTS
Slat




Extra airfoil on the
leading edge of the wing,
usually near wing tips
At a high angle of
attack, the low pressure
on top of the wing pulls
the slat forward
At low angles of attack,
the pressure pushes the
slat back into the wing
Allows for more airflow
over the top of the wing
to increase lift
Slot





Passageway built into the
leading edge of the wing
Can be across entire length
of wing or just in front of
ailerons
Increases airflow over the
wing at high angles of
attack
Remains stationary
Both increase lateral
control
SLATS AND SLOTS
REVIEW
1.
What is wash-in/wash-out and why would we
have it on an airplane?
2.
What are wing fences?
3.
What’s the difference between a slat and a slot?
SPOILERS AND DIVEBRAKES
Spoilers and divebrakes are devices attached to
the upper and lower surfaces of the wing
respectively
 When extended into the airflow, they will
decrease lift and increase drag
 This allows for a steeper approach angle without
having to increase speed

SPOILERS AND DIVEBRAKES
FLAPS


High lift devices
attached to the
trailing edge of the
wing at the root
They will provide the
pilot with:
- Better take off
performance
- Steeper approach
angles
- Slower approach and
landing speeds
VORTEX GENERATORS
Small airfoils placed along the wing
 When the air flows over them, small vortices will
be created, re-energizing the flow which prevents
the air from separating and becoming turbulent
 This helps increase lift and decrease drag

VORTEX GENERATORS
REVIEW
1.
What do flaps do?
2.
What do spoilers and divebrakes allow the pilot
to do?
3.
What do vortex generators do?
MORE REVIEW
1.
What is camber?
2.
What are the four forces acting on an aircraft?
3.
What is equilibrium and when would an
aircraft be in equilibrium?
4.
What is the centre of pressure and how does it
move when the angle of attack is increased?
SUMMARY

Today we have covered:
Parts of the aircraft
 Forces of the aircraft
 How lift is created
 Boundary layer


Next class we will continue Theory of Flight