Thread: Not understanding AoA indicators...
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Old 11-23-2014 | 12:14 AM
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Fluglehrer
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Joined: Apr 2010
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From: Pipers & RV-12
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There is a great deal of info out there for anyone who would like to learn more about the usefulness of AOA. Here are a few I like:

Angle of Attack by a pilot named Eddie Haskel. He has a good explanation of the usefulness of an AOA gauge from his personal experience in corporate aviation and as a USAF pilot Everybody Has an Angle (of Attack)
His website is a great source of info.

Another is Noel Kruse’s “Fly Better” books, especially his “Book One, Aerodynamics” (a free download from http://www.flybetter.co.uk/) He is excellent at making important connections, such as: “The angle of attack of the wing is caused by the angle of deflection of the elevator, independent of the airspeed. If we pull the stick back too far and deflect the elevator too far we will increase the angle of attack of the wing beyond the critical angle and stall it.” So even if you don’t have an AOA gauge, you do have a knowledge of what stick position will cause a stall. That stick/yoke position will cause a stall at any attitude and airspeed (well, if you’re fast enough above Va you will break your plane before you are able to pull back far enough to reach a stall).

Here is a NASA study on AOA effectiveness: http://www.scribd.com/doc/242221338/...-Effectiveness

JNB and Adlerdriver had a discussion about whether it would be worse to have high AOA in a level or descending turn. I think most military guys would say a descending turn is worse, and Adlerdriver says this is because you not only have to break the stall, you have to stop the sink. JNB, I think you also agree based on this quote of yours, which describes the problem of a descending high AOA turn well: “Again, when they get slow, they can get into a regime where they are not at an excessive pitch attitude, so not stalled or stalling, but where they are sinking and the AOA is way high due to the combination of slow speed, induced drag, etc.”
The T-38 had a large number of fatal final turn stalls, and the addition of the AOA gauge and especially the “AOA Indexer” at the top of the glare shield was intended to help stop this. Most of these accidents were high sink rate mishaps with high AOA. After the addition of AOA the USAF increased the speed of no-flap approaches and probably (my surmise based on memery from talking to graybeards when I was young) changed their way of flying final turns from tight, high sink rate, high AOA (probably .7 to .8) final turns to a more relaxed .6 AOA turn. Here is the study that put AOA into the T-38: http://www.google.com/url?sa=t&rct=j...80185997,d.cGE

I do remember my first night flight with another T-38 instructor as I was a 2nd Lt. Instead of an overhead he flew more of a sliceback to the runway, with .8 or higher AOA the whole turn and stroking burners during the rollout to final to kill the sink rate (VSI was pegged at 6000 fpm plus). Kept me awake.

Not sure if anyone already posted this link to the FAA recommendation for AOA:
http://www.faa.gov/other_visit/aviat.../InFO14010.pdf
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