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

Aerodynamics IIAerodynamics IIGetting to the PointGetting to the Point

More on StabilityMore on StabilityLongitudinal

StabilityTendency 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 StabilityMore on StabilityEffect 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

More on StabilityMore on Stability

Aircraft Control SurfacesAircraft Control Surfaces

AileronsControl roll about

longitudinal axisElevator

Control pitch about lateral axis

RudderControl yaw about

vertical axis

Aircraft Control SurfacesAircraft Control SurfacesAilerons

Move in opposite directions

Increase or decrease camber Changes AoA Produce differential

liftAdverse yaw

Result of differential induced drag

Aircraft Control SurfacesAircraft Control Surfaces

ElevatorIncreases or

decreases camber of horizontal stabilizer

Produces change in downward lift force

More effective at high power due to slipstream

Aircraft Control SurfacesAircraft Control Surfaces

RudderCreates sideward

liftAlso more

effective at high power due to slipstream

Airplane TurnAirplane 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 SkidsSlips 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 TurnAirplane Turn

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

Load FactorLoad Factor

G’s increase with bank angle60 degree turn yields 2Gs

Stall speed increases as the square root of the load factor

Load FactorLoad 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 FactorLoad FactorLoad factor requirements

vary by aircraft missionB-2 vs. F-16

FAA certifies different categories of aircraft Normal: +3.8, -1.52 GUtility: +4.4, -1.76 GAerobatic: +6, -3 G

Extra 300S, +10, -10 G

StallsStallsOccurs 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: BackgroundStall: Background

Stall: significant decrease in lift

Stall: BackgroundStall: BackgroundBoundary layer:

Separation

Stall: ProgressionStall: Progression

Stall: ProgressionStall: Progression

Stall: ProgressionStall: Progression

α = 24°

α = 11°α = 4°

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 - VGsAerodynamic Surfaces - VGs“la

min

ar”

“turb

ulen

t”

Aerodynamic Surfaces - VGsAerodynamic Surfaces - VGs

F-16 Speed Brakes

Stall Recognition & RecoveryStall Recognition & RecoveryRecognize 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

SpinsSpinsAirplane must be stalled before a spin can occur

Occurs when one wing is less stalled than the other wing

SpinsSpins

Spin Development & RecoverySpin 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