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Aerodynamics

Aerodynamics. This presentation is not designed as a substitute for adequate and competent flight instruction, knowledge of current federal air regulations or advisory circulars. Much information was obtained from the FAA-H-8083-25 advisory circular (Pilots Handbook of Aeronautical Knowledge).

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Aerodynamics

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  1. Aerodynamics • This presentation is not designed as a substitute for adequate and competent flight instruction, knowledge of current federal air regulations or advisory circulars. • Much information was obtained from the FAA-H-8083-25 advisory circular (Pilots Handbook of Aeronautical Knowledge)

  2. Aerodynamics “A branch of dynamics that deals with the motion of air and other gaseous fluids and with the forces acting on bodies in motion relative to such fluids.” Source: Merriam-Webster Online

  3. Forces of Flight

  4. Forces Of Flight • Lift • Weight • Thrust • Drag • Forces can be broken into vectors

  5. Forces In Flight • During straight and level un-accelerated flight • The forces are in equilibrium

  6. Definitions: Forces Of Flight

  7. Lift

  8. Lift • In addition to allowing the aircraft to fly, changing the force of lift on various parts of the aircraft allows the aircraft to be maneuvered in flight • We will review how lift is created first

  9. Physics Review • Newton’s laws summed up. • 1st - A body at rest tends to stay at rest and a body in motion will stay in motion unless acted on by a force. • 2nd – Force = Mass * Acceleration • 3rd – For every action there is an equal and opposite reaction

  10. Bernoulli’s Theory of Lift • Bernoulli’s principal summed up: • as the velocity of a fluid increase, its internal pressure decreases.

  11. Bernoulli's Theory

  12. Bernoulli’s Theory of Lift • Bernoulli’s principal The airfoil acts as part of the venturi accelerating the airflow over the top of the wing and lowering its pressure

  13. Pressure Distribution Causes Lift • Pressure moves from high to low • A boiler explosion is an example of this force

  14. Theory of Lift • The relatively high pressure below the wing wants to move to the low pressure above the wing • The pressure differences create the force of lift

  15. Lift

  16. Lift • Changing the basic shape of the airfoil allows for different flow patterns about the wing changing the amount of lift created • Changing the amount of lift created by various airfoils on the aircraft allows the pilot to maneuver the aircraft in-flight • The various flight controls allow us to do this • We will review terms before discussing maneuvering flight

  17. Terms

  18. Terms

  19. Chord Line • Chord Line : An imaginary line leading from the leading edge to the trailing edge of an airfoil

  20. Relative Wind • Relative wind: the airflow that is parallel and opposite the flight path • It is important to note that the relative wind relates to the direction of flight and not the pitch attitude of the aircraft • All of the airfoils at the left have the same pitch angle but they do not have the relative wind

  21. Angle Of Attack • Angle of attack: Referred to as “AOA”, is the angle made up between the chord line and the relative wind

  22. Angle Of Attack

  23. Forces On An Airfoil

  24. Forces On An Airfoil • If lift is produced we will have drag

  25. Changing The Amount of Lift Produced • In order to change the amount of lift, we must change the pressure distribution about the airfoil • Increased or decreased velocity or mass airflow over the top of the airfoil means a change in lift • We can change the velocity of the airflow over the wing in two ways • 1. We can increase the velocity by increasing the airspeed at which we are flying • 2. Change the AOA by using the flight controls

  26. AOA changes velocity and mass of airflow over the top of the wing Increasing AOA allows us to increase lift Decreasing AOA reduces lift Review Note: Angle of attack of the bottom airfoil produces lift.

  27. Review • Increasing the speed at which you are flying also creates increased velocity of airflow over the top of the wing creating more lift. • This being the case, when we accelerate lift would be increased. In level flight we don’t want this. Remember Lift must = Weight. So what do we do?

  28. Maintaining Level Flight • Accelerating or decelerating presents a slight problem if we want to maintain level flight. • During level flight we are producing lift nearly equal to weight (L=W) • If we change speed, we must change AOA so that L=W.

  29. Maintaining Level flight

  30. Stalls

  31. Airspeed and Stalls • In the previous slide you noted that we had to increase AOA as we slow to maintain lift • We can only increase AOA so much before we induce an aerodynamic stall • Though airspeed is often associated with a stall, a stall can happen at any airspeed and in any attitude if the critical AOA is exceeded

  32. Airspeed/Stall Connection

  33. Stalls • For a given airfoil, we can only increase AOA so much before we experience an aerodynamic stall Airfoil in normal flight Airfoil in stalled condition

  34. Stalls • A stall occurs when the AOA exceeds the critical AOA • At this point airflow can no longer stay attached to the top of the airfoil • High pressure is allowed to move on top of the airfoil reducing the pressure differential and thus reducing lift • Drag also increases

  35. Stalls Stall: beyond the critical AOA, High pressure air from below the wing is allowed to move on top of the wing. This reduces lift and creates drag. To recover from a stall, you must reduce the AOA and regain smooth airflow over the wings

  36. Stalls

  37. Stalls

  38. Stalls • Generally aircraft are designed to have the root stall first • This gives the pilot an indication that a full stall is imminent if nothing is done to correct the situation (Airframe buffeting) • This also allows for some aileron control during imminent stalls since the aileron portion on the wing is not yet stalled

  39. Stalls

  40. Stalls

  41. Airfoil Design • Airfoil design effects the flight characteristics • The airfoil used on a specific aircraft depends on what the aircraft is designed to do • Fighter • High speed transport • Training aircraft • …

  42. Spins

  43. Spins • Spin = Aggravated stall that results in autorotation • Prerequisites for a spin • Stall • Uncoordinated

  44. Spins

  45. Spins

  46. Spins • General exit strategy - PARE • Power- Idle • Ailerons – Neutral • Rudder – opposite the spin • Elevator – foreword • Refer to your POH for specific procedures

  47. Maneuvering Flight

  48. Maneuvering Flight • The flight controls allow pilots to maneuver the aircraft by changing the pressure distribution (and the amount of lift created) on various parts of the aircraft. • The primary flight controls do this by changing the AOA to change the lift created thereby allowing the aircraft to pitch bank and yaw

  49. Primary Flight Controls

  50. Primary Flight Controls • The Rudder Ailerons and Elevator all change the AOA to change lift and maneuver the aircraft. This could be the rudder ailerons or elevator. They all change AOA and thus the lift produced

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