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

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  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 A

More on Stability

Aircraft Control Surfaces  Ailerons  Control roll about longitudinal axis  Elevator  Control pitch about lateral axis  Rudder  Control yaw about vertical axis  Ailerons  Control roll about longitudinal axis  Elevator  Control pitch about lateral axis  Rudder  Control yaw about vertical axis

Aircraft Control Surfaces  Ailerons  Move in opposite directions  Increase or decrease camber  Changes AoA  Produce differential lift  Adverse yaw  Result of differential induced drag  Ailerons  Move in opposite directions  Increase or decrease camber  Changes AoA  Produce differential lift  Adverse yaw  Result of differential induced drag

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  Elevator  Increases or decreases camber of horizontal stabilizer  Produces change in downward lift force  More effective at high power due to slipstream

Aircraft Control Surfaces  Rudder  Creates sideward lift  Also more effective at high power due to slipstream  Rudder  Creates sideward lift  Also more effective at high power due to slipstream

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  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  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 Turn  The greater the angle of bank, the greater the load placed on the aircraft

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

StallsStalls  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.  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: significant decrease in lift

Stall: Background  Boundary layer:  Separation  Boundary layer:  Separation

Stall: Progression

α = 24° α = 11°α = 4°

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.  Discussion on Monday about laminar versus turbulent boundary layers:  Laminar boundary layers separate easily.  Turbulent boundary layers separate later than laminar boundary layers.

Laminar v. Turbulent Laminar flow about a sphere

Laminar v. Turbulent Turbulent flow about a sphere

Aerodynamic Surfaces - VGs “laminar” “turbulent”

Aerodynamic Surfaces - VGs F-16 Speed Brakes

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  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  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

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

SpinsSpins

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  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  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