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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

Aerodynamics II

Getting to the Point

“Teaching the Science, Inspiring the Art, Producing Aviation Candidates!”

more on stability
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 stability3
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

aircraft control surfaces
Aircraft Control Surfaces
  • Ailerons
    • Control roll about longitudinal axis
  • Elevator
    • Control pitch about lateral axis
  • Rudder
    • Control yaw about vertical axis
aircraft control surfaces6
Aircraft Control Surfaces
  • Ailerons
    • Move in opposite directions
    • Increase or decrease camber
      • Changes AoA
      • Produce differential lift
    • Adverse yaw
      • Result of differential induced drag
aircraft control surfaces7
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
aircraft control surfaces8
Aircraft Control Surfaces
  • Rudder
    • Creates sideward lift
    • Also more effective at high power due to slipstream
airplane turn
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
slips and skids
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
airplane turn11
Airplane Turn
  • The greater the angle of bank, the greater the load placed on the aircraft
load factor
Load Factor
  • G’s increase with bank angle
  • 60 degree turn yields 2Gs
  • Stall speed increases as the square root of the load factor
load factor13
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
load factor14
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

  • 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.
stall background
Stall: Background
  • Stall: significant decrease in lift
stall background17
Stall: Background
  • Boundary layer:
  • Separation
stall progression20
Stall: Progression

α = 4°

α = 11°

α = 24°

stall is turbulent a bad word
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.
aerodynamic surfaces vgs
Aerodynamic Surfaces - VGs



stall recognition recovery
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
  • Airplane must be stalled before a spin can occur
  • Occurs when one wing is less stalled than the other wing
spin development recovery
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