Aerodynamics II Part 2 – stability, turns, stalls, turning tendencies, load factor,etc.
Aerodynamics II
description
Transcript of Aerodynamics II
“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