theory of flight

1. Theory of Flight
6.05 Lift and Drag
References:
Transport Canada Study and Reference Guide Glider Pilot
FTGU pages 91-98

2. Review
1. Name the 4 forces acting on an aircraft.
2. What are Newton’s 3 laws?
3. Is an aircraft considered to be in a state of
equilibrium when it is on the ground.

3. 6.05 Lift & Drag
• MTPs:
– Bernoulli’s Principle- how lift is created
– Airfoil terms
– Angle of attack versus lift
– Angle of Incidence
– Types of airfoils
– Types of Drag
– Wingtip Vortices
– Streamlining

4. Bernoulli’s Principle
• Bernoulli’s Principle
– An increase in the speed of a fluid occurs
simultaneously with a decrease in pressure or
a decrease in the fluid's potential energy.

5. Bernoulli’s Principle
Speed Pressure
Speed Pressure

6. Bernoulli’s Principle
– Airfoils are shaped in a way to manipulate air
pressure based on Bernoulli’s principle.
– Air moves faster over the upper surface of the wing,
decreasing pressure (or increasing suction)
– Air moves slower over the lower surface of the wing
and creates a higher pressure, or pushing force.

7. Airfoil Terms
Terms related to airfoils
• Relative Airflow
• Angle of Attack
• Centre of Pressure

8. Relative Airflow
– The direction of the airflow with respect to the wing.
– It is created by the movement of the airplane as well as the
movement of air.
– Relative airflow is usually opposite to the flight path.
– Relative airflow itself is not related to lift

9. Angle of Attack
–The angle at which the airfoil meets the
relative airflow

10. Centre of Pressure
• Is the average of the pressure on an airfoil
– Sum of the distributed pressures on the airfoil acting
through a single straight line
• Moves forward on an airfoil as the angle of attack is
increased

11. Centre of Pressure

12. A of A versus Lift
• Now we know how we get lift but how much can we get?
• One factor affecting lift is Angle of Attack
– As the angle of attack increases, what happens to lift?
– BUT… As the angle of attack increases, what
happens to drag?
Lift Increases
Drag Increases

13. A of A versus Lift
Angle of
Attack
Lift/
Drag

14. Angle of Incidence
– The angle of incidence is the angle between
the mean aerodynamic chord of the wing and
the longitudinal axis of the aircraft
– The angle of incidence impacts forward
visibility, take-off and landing characteristics,
and drag in level flight

15. Types of Airfoils
• Airfoil
A two-dimensional surface designed to obtain a reaction from
the air through which it moves.
The shape of an airfoil will affect how air flows over the wing
Airfoil – 2D vs. Wing – 3D

16. Types of Airfoils
• What are some functions
of airfoils?
– Create lift
– Create thrust
– Attachment point for the
control surfaces (including
flaps, slots, slats, etc)
– House fuel tanks and
instrument components
–Stability

17. Confirmation Check

18. Confirmation
1. Label where the high pressure and low pressure are:
2. Fill in the blanks
__________________: The angle at which the airfoil meets the
relative airflow
__________________: airflow with respect to the wing
__________________:the average of the pressure on an airfoil

19. Confirmation
3. Lift acts 90o to the ________________.
4. Bernoulli’s principle states that:
An ____________ (increase/decrease) in the speed of a fluid occurs
simultaneously with a _____________________
(increase/decrease) in pressure or a _______________
(increase/decrease) in the fluid's potential energy
5. As lift increases, drag _______________.

20. Drag
– Is the resistance an airplane experiences in
moving forward through the air

21. Types of Drag
There are 2 main types of Drag:
1. Parasite Drag– This drag is further broken
down
– Form drag
– Skin Friction
2. Induced Drag

22. Parasite Drag
Drag of all those parts the airplane which
DO NOT contribute to lift
– This drag is hard to eliminate but it can be
minimized
• Form drag is caused by the shape of the
aircraft
– Landing gear
– Antennas
– Struts
– Wing tip fuel tanks

23. Parasite Drag
• Skin Friction
– The tendency of air
flowing over the body
to cling to its surface
– What causes it to
resist motion?
• Ice on the wings
• Dirt build up

24. Induced Drag
– Caused by those parts of an airplane which
are active in producing lift
– Cannot be eliminated
Lift Drag

25. Induced Drag
• Induced drag can be reduced with a high
aspect ratio

26. Wing Tip Vortices
• Over the top of the wing the
airflow goes inward
• Under the bottom of the wing
the airflow moves outward
Due to the
pressure changes
This creates a swirling motion off the wing tip called a vortex

27. Streamlining
• The less drag you have…
– Flying a glider: the further you can
fly
– Flying an airplane: the less fuel you
use
• Therefore streamlining is important
– A design device by which a body is
shaped to minimize drag

28. Confirmation
1. Fill in the diagram
2. Is it possible to eliminate induced drag? Why
or why not?

29. Wingtip Vortices