# Theory of Flight 6.05 Lift and Drag References:

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

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. Answers: Lift, Weight, Thrust, Drag 2. A body persists its state of rest or of uniform motion will stay in motion unless acted on by an external unbalanced force. Force = mass x acceleration For every action, there is an equal and opposite reaction 3. No

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

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.

Bernoulli’s Principle
Speed Pressure Speed Pressure

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.

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

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

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

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

Centre of Pressure

A of A 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

A of A versus Lift Lift/ Drag Angle of Attack

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

Types of Airfoils Airfoil Airfoil – 2D vs. Wing – 3D
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

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

Confirmation Check

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

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 _______________.

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

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

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

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

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

Induced Drag Induced drag can be reduced with a high aspect ratio

Due to the pressure changes
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

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

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

Wingtip Vortices