Aerodynamics II

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Aerodynamics II
Getting to the Point
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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
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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
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More on Stability
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Aircraft Control Surfaces

• Ailerons
• Control roll about longitudinal axis
• Elevator
• Control pitch about lateral axis
• Rudder
• Control yaw about vertical axis

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Aircraft Control Surfaces

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

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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

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Aircraft Control Surfaces

• Rudder
• Creates sideward lift
• Also more effective at high power due to
  slipstream

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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

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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

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Airplane Turn

• The greater the angle of bank, the greater the
  load placed on the aircraft

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Load Factor

• Gs increase with bank angle
• 60 degree turn yields 2Gs

• Stall speed increases as the square root of the
  load factor

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Load Factor

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

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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
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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.

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Stall Background

• Stall significant decrease in lift

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Stall Background

• Boundary layer
• Separation

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Stall Progression
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Stall Progression
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Stall Progression
a 11
a 4
a 24
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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.

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Laminar v. Turbulent
Laminar flow about a sphere
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Laminar v. Turbulent
Turbulent flow about a sphere
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Aerodynamic Surfaces - VGs
laminar
turbulent
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Aerodynamic Surfaces - VGs
F-16 Speed Brakes
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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

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Spins

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

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Spins
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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