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ANGLE-of-ATTACK

• Proprietary Software Systems, Inc.• www.angle-of-attack.com• (952) 474-4154• 950 Iris Circle• Excelsior MN 55331

© copyrighted 1999

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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

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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

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Looping Maneuver

AOA=8Attitude = -90

AOA=8Attitude=0

AOA=8Attitude=+90

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AOA is referenced to:

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Zero LiftLine

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Most Elegant reference for AOA

• Orient 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.”

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Setting AOA

• Leave everything alone to fly a fixed AOA• Trim wheel controls AOA• Trim for AOA• Perceiving AOA is difficult

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Gauging AOA

• Three components to AOA1. 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

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AOA=pitch attitude + angle of incidence

- flight path angle

AOA

Attitude

Incidence

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Flying AOA from High Density Altitude Airports

TargetAirspeed

PitchAttitude

Angle ofIncidence

ClimbRatio

Angle ofClimb

Angle ofAttack

Flat land 76 KCAS 11.0 4.5 900 fpm@

76 KTAS

6.6 8.9

Leadville(wrong)

76 KCAS 11.0 4.5 475 fpm@

90 KTAS

3.0 12.5

Leadville(right)

76 KCAS 7.4 4.5 475 fpm@

90 KTAS

3.0 8.9

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Flying at different Gross Weights

• Stall 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

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Flying at different angles of bank

• Stall 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.

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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.

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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.

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Flying Approaches to Landings

• An 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

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Flying the best engine out glide or maximum endurance

Lift=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.

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Understanding Lift to Drag• L/D max is used in flight for:

maximum endurance for jet powered airplanesmaximum range for prop driven aircraftmaximum climb angle for jet powered aircraftmaximum power-off glide range for jet and prop aircraft

• L/D max occurs at one specific AOA

Induced drag

Para

site

dra

g

stal

l

DR

AG

Units AOA

Tota

l Dra

g

L/D

max

NormalCommand

ReverseCommand

816 4 212

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Angle-of-Attack vs. Coefficient of Lift

Angle from zero lift (AOA)

Coe

ffic

i en

t of

Lif

t

Critical AOA (stall)

Angle Warning AOA (stall warning)

Optimum Approach AOA

L/D max, best glide, max endurance, best range

Zero Lift (induced drag=0)

Revers

e Com

mand

Behind

the P

ower

Curve

Cruise

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AOA fidelity and accuracy

• AOA 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.

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AOA is the ultimate aerodynamic instrument

• AOA 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.

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Flying AOA for All Approaches

Best AOA for all Approaches.

Trim for this AOA.

AOA too low.Increase back pressureand trim if necessary.

AOA way too high!Lower the AOAand go around.

Use the throttle to control the rate of descent!

Middle yellowlight

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AOA is Instantaneousbut IAS Lags

• Before • Immediately after stick/yoke pull

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AOA Professional Display

Zerolift

BestL/D

Optimumapproach

Angleadvisory

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AOA Sport Display

Cruise BestL/D

Optimumapproach

Angleadvisory

CriticalAOA

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Thanks for your attention

Fly Safe with ANGLE-of-ATTACK

• Proprietary Software Systems, Inc.• www.angle-of-attack.com• Jim@angle-of-attack.com• (952) 474-4154• 950 Iris Circle• Excelsior MN 55331

© copyrighted 1999