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

2. 6.05 Lift & Drag Bernoulli’s Principle Lift Airfoil terms
Angle of Attack versus Lift
Angle of Incidence
Types of airfoils
Drag
Types of Drag
Wingtip Vortices
Streamlining

3. 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

4. Bernoulli’s Principle
Speed
Pressure
Speed
Pressure

5. 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 compared to the lower surface there by causing a difference in pressure
Decreased pressure on the upper surface and increased pressure on the lower surface

6. Lift
Lift is the force perpendicular to the relative airflow or relative wind

7. Airfoil Terms Relative Airflow Angle of Attack (AoA)
Centre of Pressure (CoP)

8. Relative Airflow
The direction of the air flowing with respect to the wing and in some causes the whole aircraft
Created by the movement of the aircraft as well as the movement of air (updrafts, downdrafts, turbulence)
Opposite to the flight path

9. Angle of Attack (AoA)
The angle between the chord line of the aerofoil and the relative airflow
Or, simply the angle at which the airfoil meets the relative airflow

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

11. Centre of Pressure

12. AoA versus Lift Lift Increases Drag Increases
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. AoA v. Lift
Lift / Drag
Angle of Attack

14. Angle of Incidence (AoI)
The angle between the mean aerodynamic chord of the wing and the longitudinal axis of the aircraft
The AoI impacts forward visibility, takeoff and landing characteristics, and drag in level flight

15. Types of Airfoils
An Airfoil is two-dimensional surface designed to obtain a reaction from the air through which it moves
The shape and design of an airfoil will affect how air flows over the wing

16. Types of Airfoils What are some functions of airfoils?
Create lift for flight
Create thrust, used in propeller and rotor designs
Attachment point for the control surfaces, flaps, slots, slats, external stores
House fuel tanks, instrument components, retractable landing gear
Added to effect stability

17. Drag Drag is the force parallel to the relative airflow
The resistance an aircraft experiences when moving through the air

18. Types of Drag There are 2 main types of drag
Parasite Drag which breaks down into
Form
Skin Friction
Interference
Induced Drag

19. Parasite Drag
Drag of all those parts of an aircraft which DO NOT contribute to lift
This drag increases the square of the speed so effort is taken to minimize its affect

20. Parasite Drag
Skin Friction is the tendency of air smoothly flowing over the aircraft’s surface. The air tending to cling to its surface and its resistance to the motion of the aircraft (increases with accumulation of ice, dirt, or any contamination)
Form drag is caused by the shape of the aircraft and attached components (Landing gear, Antennas, Struts)
Interference drag is how smooth the air can flow around the attachment points of the different components

21. Induced Drag
Is caused by those parts of an aircraft which are active in producing lift
Cannot be eliminated
Lift Drag

22. Induced Drag
Low aspect ratio – high induced drag and low parasite drag
High aspect ratio – low induced drag and high parasite drag

23. Due to the pressure changes
Wing Tip Vortices
Airflow over the top of the wing flows inward
Airflow under the bottom of the wing flows outward
Due to the pressure changes
This creates a swirling motion off the wing tip called a vortex, this is the induced drag

24. Wingtip Vortices

25. Streamlining
Streamlining is important and is a design by which a body is shaped to minimize drag
The less drag…
The futher and or faster you can fly
In a glider you can fly further
In an aeroplane you use less power so less fuel

26. Confirmation Check

27. Confirmation Check 1. Label where the high and low pressure areas are2.
________ is the angle at which the airfoil meets the relative airflow
________ is the angle at which the airfoil and fuselage are attached
________ is the average of the pressure on an airfoil

28. Confirmation Check 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 the drag ________
6. Label the diagram