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Aerodynamics II

Aerodynamics II. Getting to the Point. More on Stability. Longitudinal Stability Tendency of aircraft to return to original pitch attitude CG set forward of center of lift To balance, horizontal stabilizer generates downward lift. Image courtesy FAA-H-8083-25A. More on Stability.

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Aerodynamics II

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  1. Aerodynamics II Getting to the Point “Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”

  2. More on Stability • Longitudinal Stability • Tendency of aircraft to return to original pitch attitude • CG set forward of center of lift • To balance, horizontal stabilizer generates downward lift Image courtesy FAA-H-8083-25A

  3. More on Stability • Effect of CG • Forward CG • Stronger tail load • Less efficient • Outside limits • May not be able to land aircraft properly • Aft CG • Lighter tail load • Decreases stability • Stall recovery difficult Image courtesy FAA-H-8083-25A

  4. More on Stability

  5. Aircraft Control Surfaces • Ailerons • Control roll about longitudinal axis • Elevator • Control pitch about lateral axis • Rudder • Control yaw about vertical axis

  6. Aircraft Control Surfaces • Ailerons • Move in opposite directions • Increase or decrease camber • Changes AoA • Produce differential lift • Adverse yaw • Result of differential induced drag

  7. Aircraft Control Surfaces • Elevator • Increases or decreases camber of horizontal stabilizer • Produces change in downward lift force • More effective at high power due to slipstream

  8. Aircraft Control Surfaces • Rudder • Creates sideward lift • Also more effective at high power due to slipstream

  9. Airplane Turn • The horizontal component of lift causes airplanes to turn • Bank angle controlled by ailerons • The rudder controls the yaw • Rudder used to “coordinate” turn

  10. Slips and Skids • Normal turn • Horizontal lift equal centrifugal force • Slipping turn • Horizontal lift greater than centrifugal force • Need more rudder • Skidding turn • Horizontal lift greater than centrifugal force • Need less rudder

  11. Airplane Turn • The greater the angle of bank, the greater the load placed on the aircraft

  12. Load Factor • G’s increase with bank angle • 60 degree turn yields 2Gs • Stall speed increases as the square root of the load factor

  13. Load Factor • Load Factor – the ratio of load supported by wings to aircraft weight • Airplane in unaccelerated flight has a load factor = 1. The airplane’s wings are supporting only the weight of the plane • Turning increases load factor (G’s) b/c you are accelerating around a corner

  14. Load Factor • Load factor requirements vary by aircraft mission • B-2 vs. F-16 • FAA certifies different categories of aircraft • Normal: +3.8, -1.52 G • Utility: +4.4, -1.76 G • Aerobatic: +6, -3 G Extra 300S, +10, -10 G

  15. Stalls • Occurs when critical angle of attack is exceeded • Can occur at any airspeed in any flight attitude! • 50 kts, straight-and-level, max. gross weight. • 45 kts, straight-and-level, light. • 70 kts, 60 degree banked turn. • etc.

  16. Stall: Background • Stall: significant decrease in lift

  17. Stall: Background • Boundary layer: • Separation

  18. Stall: Progression

  19. Stall: Progression

  20. Stall: Progression α = 4° α = 11° α = 24°

  21. Stall: Is “turbulent” a bad word? • Discussion on Monday about laminar versus turbulent boundary layers: • Laminar boundary layers separate easily. • Turbulent boundary layers separate later than laminar boundary layers.

  22. Aerodynamic Surfaces - VGs “laminar” “turbulent”

  23. Aerodynamic Surfaces - VGs F-16 Speed Brakes

  24. Stall Recognition & Recovery • Recognize a stall: • Low speed, high angle of attack • Ineffective controls due to low airflow over them • Stall horn • Buffeting caused by separated flow from wing • Recover from a stall: • Decrease angle of attack – increases airspeed and flow over wings • Smoothly apply power – minimizes altitude loss and increases airspeed • Adjust power as required – maintain coordinated flight

  25. Spins • Airplane must be stalled before a spin can occur • Occurs when one wing is less stalled than the other wing

  26. Spins

  27. Spin Development & Recovery • Spin development: • Incipient Spin – lasts 4-6 seconds in light aircraft, ~ 2 turns • Fully Developed Spin – airspeed, vertical speed and rate of rotation are stabilized, 500 ft loss per 3 second turn • Recovery – wings regain lift, recovery usually ¼ - ½ of a turn after anti-spin inputs are applied • Recover from a spin: • Move throttle to idle • Neutralize ailerons • Determine direction of rotation (reference turn coordinator) • Apply full rudder in opposite direction of rotation • Apply elevator to neutral position • As rotation stops, neutralize rudder. Otherwise, you may enter spin in opposite direction • Apply elevator to return to level flight • Remember PARE (power-idle, aileron – neutral, rudder – opposite, elevator - recover

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