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Theory of Flight

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

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Theory of Flight

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  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 • 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. 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 are 2. ________ 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

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