Transcript ANGLE-of-ATTACK

ANGLE-of-ATTACK
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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=8
Attitude=0
AOA=8
Attitude=+90
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AOA=8
Attitude = -90
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AOA is referenced to:
Zero Lift
Line
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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 CLSwV2
• 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
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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 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
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AOA=pitch attitude + angle of incidence
- flight path angle
Incidence
AOA
Attitude
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Flying AOA from High Density
Altitude Airports
Target
Airspeed
Pitch
Attitude
Angle of
Incidence
Climb
Ratio
Angle of
Climb
Angle of
Attack
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.
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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 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
Normal
Command
L/D max
Reverse
Command
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Units AOA
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Angle-of-Attack vs. Coefficient of Lift
Critical AOA (stall)
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)
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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 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!
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AOA is Instantaneous
but IAS Lags
• Before
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• Immediately after
stick/yoke pull
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AOA Professional Display
Zero
lift
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Best
L/D
Optimum
approach
Angle
advisory
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AOA Sport Display
Cruise
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Best
L/D
Optimum
approach
Angle
advisory
Critical
AOA
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Thanks for your attention
Fly Safe with
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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
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