1
ANGLE-of-ATTACK
• Proprietary Software Systems, Inc.• www.angle-of-attack.com• (952) 474-4154• 950 Iris Circle• Excelsior MN 55331
© copyrighted 1999
2
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
3
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
4
Looping Maneuver
AOA=8Attitude = -90
AOA=8Attitude=0
AOA=8Attitude=+90
© copyrighted 1999
5
AOA is referenced to:
© copyrighted 1999
Zero LiftLine
6
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.”
© copyrighted 1999
7
Setting AOA
• Leave everything alone to fly a fixed AOA• Trim wheel controls AOA• Trim for AOA• Perceiving AOA is difficult
© copyrighted 1999
8
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
© copyrighted 1999
9
AOA=pitch attitude + angle of incidence
- flight path angle
AOA
Attitude
Incidence
© copyrighted 1999
10
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
© copyrighted 1999
11
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
© copyrighted 1999
12
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.
© copyrighted 1999
13
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
14
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
15
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
16
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.
© copyrighted 1999
17
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
© copyrighted 1999
18
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
© copyrighted 1999
19
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.
© copyrighted 1999
20
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.
© copyrighted 1999
21
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
© copyrighted 1999
22
AOA is Instantaneousbut IAS Lags
• Before • Immediately after stick/yoke pull
© copyrighted 1999
23
AOA Professional Display
Zerolift
BestL/D
Optimumapproach
Angleadvisory
© copyrighted 1999
24
AOA Sport Display
Cruise BestL/D
Optimumapproach
Angleadvisory
CriticalAOA
© copyrighted 1999
25
Thanks for your attention
Fly Safe with ANGLE-of-ATTACK
• Proprietary Software Systems, Inc.• www.angle-of-attack.com• [email protected]• (952) 474-4154• 950 Iris Circle• Excelsior MN 55331
© copyrighted 1999