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ANGLE-of-ATTACK Proprietary Software Systems, Inc. (952) 950 Iris Circle Excelsior MN © copyrighted 1999
Importance of AOA Fly by the numbers! Vs, Vx, Vy, VREF, Best Engine out Glide and Max Endurance Most of your Aircraft’s critical performance numbers are a function of AOA When you fly airspeed the airspeed actually was derived from AOA © copyrighted 1999
What is AOA Angle between the relative wind and the chord of the airfoil The Wright brothers flew AOA and their early aircraft were equipped with a reference stick and a piece of yarn © copyrighted 1999
Looping Maneuver AOA=8 Attitude=0 AOA=8 AOA=8 Attitude=+90© copyrighted 1999
AOA is referenced to: Zero Lift Line © copyrighted 1999
Most Elegant reference for AOAOrient the reference for AOA so that zero degrees AOA is where the wing creates no lift. L=1/2 CLSwV2 When the coefficient of lift is zero the wing creates no lift and induced drag is zero. The proper term for this reference is “angle from zero lift.” © copyrighted 1999
Setting AOA Leave everything alone to fly a fixed AOATrim wheel controls AOA Trim for AOA Perceiving AOA is difficult © copyrighted 1999
Gauging AOA Three components to AOA 1. Pitch attitude (angle of fuselage relative to the horizontal) 2. Angle of climb (angle of the flight path relative to the horizontal) 3. Angle of incidence (angle of wing relative to the fuselage) AOA =Pitch attitude + incidence - angle of climb Pitch attitude does not equal AOA © copyrighted 1999
AOA=pitch attitude + angle of incidence - flight path angle© copyrighted 1999
Flying AOA from High Density Altitude Airports© copyrighted 1999
Flying at different Gross WeightsStall speed varies with gross weight by the following formula: Vs2 = Vs1 W2/W1 If the stall speed at 2,000 # GW was 60 KCAS then the stall speed at 3,000# is 73 KCAS The stalling AOA (critical AOA) remains the same at all weights © copyrighted 1999
Flying at different angles of bankStall speed varies with bank angle by the following formula: Vs1 = Vs2 1/cos If the stall speed at zero degrees bank angle was 60 KCAS the stalling speed at 60 degrees bank is 85 KCAS The stalling AOA (critical AOA) is not affected by bank angle. © copyrighted 1999
Flying in turbulence Stall speed varies with turbulence by the following formula: Vs1 = Vs2 G If the stall speed at 1 “G” was 60 KCAS the stalling speed in a 2 “G” bump is 85 KCAS The stalling AOA (critical AOA) is not affected by turbulence. © copyrighted 1999
Cumulative Effect Stall speed increases due to weight, bank angle and turbulence are cumulative. If we were to encounter the heavier 3,000# weight, 60 degrees of bank, and the 2 “G” bump all at the same time, the stalling speed of 60 has now increased to 146 knots. The critical AOA is not affected. © copyrighted 1999
Flying Approaches to LandingsAn aircraft in the landing configuration will stall at the same AOA regardless of airspeed, fuel weight, payload, “G” loading, bank angle, and turbulence. If the critical AOA is constant during these different conditions then the optimum AOA for an approach is also constant. All approaches are flown at a fixed AOA. © copyrighted 1999
Flying the best engine out glide or maximum enduranceLift=V2CLA/2 and Drag= V2CDA/2 Lift/Drag=CL/CD The L/D ratio is not a function of airspeed or weight. A lightly loaded aircraft will have the same L/D as when heavier except that it will have a slower descent rate and a slower forward speed. Ignoring propeller effects, the best L/D occurs at a fixed AOA. © copyrighted 1999
Understanding Lift to DragL/D max is used in flight for: maximum endurance for jet powered airplanes maximum range for prop driven aircraft maximum climb angle for jet powered aircraft maximum power-off glide range for jet and prop aircraft L/D max occurs at one specific AOA Reverse Command Normal Command L/D max Total Drag stall Parasite drag DRAG Induced drag Units AOA 16 12 8 4 2 © copyrighted 1999
Angle-of-Attack vs. Coefficient of LiftCritical AOA (stall) Behind the Power Curve Reverse Command Coefficient of Lift Angle Warning AOA (stall warning) Optimum Approach AOA L/D max, best glide, max endurance, best range Cruise Zero Lift (induced drag=0) Angle from zero lift (AOA) © copyrighted 1999
AOA fidelity and accuracyAOA varies inversely as the square of the airspeed. Therefore, AOA fidelity increases with slower speeds and higher angles-of-attack. At maneuvering speeds and lower, AOA is it aerodynamically. © copyrighted 1999
AOA is the ultimate aerodynamic instrumentAOA is used to establish the best approach, best climb angles, maximum endurance, long range cruise, best glides and other flight maneuvers. You do not disregard airspeed altogether, but use the airspeed and angle-of-attack to supplement one another. © copyrighted 1999
Flying AOA for All ApproachesBest AOA for all Approaches. Trim for this AOA. AOA too low. Increase back pressure and trim if necessary. AOA way too high! Lower the AOA and go around. Middle yellow light Use the throttle to control the rate of descent! © copyrighted 1999
AOA is Instantaneous but IAS LagsBefore Immediately after stick/yoke pull © copyrighted 1999
AOA Professional DisplayZero lift Best L/D Optimum approach Angle advisory © copyrighted 1999
AOA Sport Display Optimum approach Angle advisory Critical Best AOAL/D Cruise © copyrighted 1999
Thanks for your attention Fly Safe with ANGLE-of-ATTACKProprietary Software Systems, Inc. (952) 950 Iris Circle Excelsior MN © copyrighted 1999
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