runway777
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This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 3:45 am

This may seem easy for a lot of you. but I have a question involving my PPL course.
Right now we are doing aerodynamics and such. What exactly is the Angle of Attack?
I think I know what it is, but i was just wondering if I could get some clarification, because I keep getting it mixed up with other things

Thanks
"kalli, be the best pilot you can be, who happens to be a girl" -Joe White
 
MDorBust
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 3:50 am

AoA is the angle at which the wing is moving through the air. The lower the AoA, the closer the wing is pointed directly into the airflow. The higher the AoA, the more the wing is pointed up/down from the airflow.
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runway777
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 3:53 am

OHhhhhh!! okay. i get it now, i was getting confused with the angle of incidenence or something. lol
thanks so much hunn
"kalli, be the best pilot you can be, who happens to be a girl" -Joe White
 
SlamClick
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 3:58 am

Quoting Runway777 (Reply 2):
angle of incidenence

Angle of incidence is set at the factory when the wing is bolted on. An airplane in a hangar or upside down in a cornfield has an angle of incidence.
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runway777
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 4:01 am

yes. i got that much.
thanks tho.

-kalli
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Starlionblue
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 6:25 am

AoA is also known as "alpha" right?
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FredT
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 6:49 am

Quoting Starlionblue (Reply 5):
AoA is also known as "alpha" right?

Yes, that's the symbol usually used to denote AoA. In daily speak, it is alpha, with sideslip angle being beta.
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N231YE
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 7:52 am

AoA (angle of attack) is the angle at which the airfoil's cord meets the relative airflow. In this diagram, "a" (or alpha) represents the AoA:


If the AoA exceeds critical, then the airfoil can no longer produce enough lift, and the wing stalls (usually around 15º for a clean wing):


Note: Coefficient of lift (C subL) increases with an increasing AoA until the wing begins to enter a stall.
 
pilotpip
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 9:28 am

Also remember that the AOA is the Angle of the wing chord to the RELATIVE wind. This is an important little thing. It's entirely possible to be in a nose-down attitude and exceed critical AOA as a result.
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Starlionblue
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 9:53 am

Quoting Pilotpip (Reply 8):
Also remember that the AOA is the Angle of the wing chord to the RELATIVE wind. This is an important little thing. It's entirely possible to be in a nose-down attitude and exceed critical AOA as a result.

Indeed. One thing I have had to explain to many aviation enthusiasts (non pilots) is that while stall is commonly associated with low speeds, it is quite possible to stall at high speed by exceeding critical AoA.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
787atPAE
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 11:43 am

It's interesting you think angle of attack seems easy to everybody. AOA can be a bear to deal with, with respect to calculations and the physics involved, both in simulation use and in a practical setting. Of the regular pitch axis terms (AOA, pitch angle, and flight path angle), the AOA is the most difficult to think of.

FPA and pitch angle are referenced to the local horizontal, whereas the AOA is referenced to a variable (the velocity vector) that is constantly changing.

Other than the space shuttle, I don't know of any vehicle that uses AOA as a target in the flight control system. Airplanes (and pilots) will use FPA (eg, -3 deg glideslope) and pitch angle (eg, +15 deg on climbout), but I've never heard of anybody trying for a 5 deg AOA.

You have begun a quest for knowledge in the realm of aerodynamics. There's a ton of interesting stuff out there. Aerodynamics always keeps me thinking. It's neat to see the theory work in real life. Good luck!!
 
pilotpip
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 12:33 pm

AOA is very difficult even for most pilots. I spent the better part of an hour trying to explain it to my first groundschool class.
DMI
 
Curmudgeon
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RE: This May Seem Easy For A Lot Of You

Tue Nov 14, 2006 8:44 pm

Quoting 787atPAE (Reply 10):
Other than the space shuttle, I don't know of any vehicle that uses AOA as a target in the flight control system. Airplanes (and pilots) will use FPA (eg, -3 deg glideslope) and pitch angle (eg, +15 deg on climbout), but I've never heard of anybody trying for a 5 deg AOA.

Some EFIS aircraft have the option of AoA display. The 737 display does show a target range for a 3 degree approach-the range is equivalent to Vref to Vref +20, which is the normal band of recomended approach speeds.

Since nobody I know was trained on AoA, the display is largely in the "gee whiz" category, but it could come in damn handy with an unreliable airspeed indicator.
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jetmech
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RE: This May Seem Easy For A Lot Of You

Wed Nov 15, 2006 7:05 am

Quoting Runway777 (Reply 2):
angle of incidenence or something. lol

I don't think it has been mentioned specifically so far, but the angle of incidence is the angle between the aircraft's longitudinal axis and the chord line of the wing. IIRC, this angle of incidence remains the same for all aircraft attitudes.

Quoting SlamClick (Reply 3):
Angle of incidence is set at the factory when the wing is bolted on. An airplane in a hangar or upside down in a cornfield has an angle of incidence.

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FredT
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RE: This May Seem Easy For A Lot Of You

Wed Nov 15, 2006 7:17 am

Quoting 787atPAE (Reply 10):
Other than the space shuttle, I don't know of any vehicle that uses AOA as a target in the flight control system. Airplanes (and pilots) will use FPA (eg, -3 deg glideslope) and pitch angle (eg, +15 deg on climbout), but I've never heard of anybody trying for a 5 deg AOA.

Plenty of aircraft have AoA indicators. When you have it, it is very convenient indeed! No need to flip through speedbooks to find the correct airspeed for the current weight. You just park the aircraft at the correct AoA for that segment of flight. Fighters commonly have it right up front, I could list quite a few. It has also appeared in a few bizjets I've seen, and I'd bet there are airliners out there with it as well. It is available rather cheaply for GA aircraft.

In the fighters, it is very common to use the AoA as one of the main targets. Carrier based aircraft have indicators right next to the HUD telling them if they are above, below or on thet righ AoA for the approach (even if it is often mistaken to be a fast/slow indicator). In the Saab 37, you fly different alpha approaches depending on whether you are aiming for a short runway landing or not. The F16 has an AoA bracket popping up in the HUD when you drop the undercarriage. Put the flight path marker in the bracket and you are between 11 and 13 (IIRC) degrees AoA.

Any aircraft with a HUD with a flight path marker also has an AoA indicator. The AoA is the difference between the nose reference and the flight path marker.

You can also use AoA instead of a speed indicator. You can use AoA to tell you just how much harder you can pull in a turn. The stall is at a fixed AoA, remember?

To me, as an aero engineer, it is amazing that there are aircraft which do not have AoA indicators right up under the eyes of the pilot. I'd rather be without an ASI myself.
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DeltaGuy
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RE: This May Seem Easy For A Lot Of You

Wed Nov 15, 2006 1:23 pm

Quoting FredT (Reply 14):
Any aircraft with a HUD with a flight path marker also has an AoA indicator. The AoA is the difference between the nose reference and the flight path marker.

Kinda like this- the little Alpha symbol with the 0.6 next to it, on the left side.

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HAWK21M
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RE: This May Seem Easy For A Lot Of You

Wed Nov 15, 2006 3:38 pm

To add.
The AOA is Variable while the AOI is normally fixed.
regds
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