bash@ihlpb.ATT.COM (Basham) (06/20/89)
From: bash@ihlpb.ATT.COM (Basham) >If someone would like to take the time to `draw' it for the newsgroup, >I'll gladly send a xerox of a diagram showing this. >M F Shafer |Ignore the reply-to address Based upon mu understanding I'll attempt to draw this. ____ pitch of aircraft | top = nose of aircraft. V ---> / <------------ direction of ---> / <------------ airflow travel ---> / <------------- ----------------------------------------------- <= this is the ground In the above "picture", the AOA is the angle between the pitch of the plane and the airflow (here about 45 degrees +/-). The MiG-29 that crashed in Paris was flying similiar to this . airflow (downward) --> / / / pitch of plane ---> / nose = top / direction of -> / / travel (up) / / / / ---------------------------------------------- <= this is the ground Here, the AOA is zero. This would be a plane in sustained climb. When an aircraft has been flying straight and level, the airflow meets the aircraft head on, like when you drive your car down the highway. Hold your hand out the window and feel the wind. When the aircraft changes it attitude (that is, changes pitch or bank) the direction of thrust changes also, but not the direction of travel. It takes a finite amount of time for the new direction of thrust to take effect. During this period the plane physically moves straight in the airflow, but at a funky pitch or bank. This is AOA. Once the new direction of the aircraft stablizes with the attitude of the aircraft, the AOA goes back to zero. Any climb, dive, or turn will result in an AOA change. In a climb or a dive, the movement of the plane will stabilize with the axis of the plane and AOA will return to zero (as stated above). However, a turn will create a constant AOA since the direction of the plane's movement will always be trying to catch the direction the plane's nose is pointing. Sustained high-G turns always result in high AOA since the nose is always rotating away from the direction of travel. Then there are moves like what the MiG-29 was doing. It was moving into the airflow, but the wings met the air at the AOA, resulting in reduced lift. My guess would be the pilot increased thrust to pull out of the maneouver without stalling and his right engine decided to malfunction. I hope this helps. If Mary (or anybody else) can add/correct anything, please do! Tom P.S. Emacs and 2400 baud sucks. --------------------------------------------------------------------- -- Tom Basham AT&T Bell Laboratories (312) 979-6336 att!ihlpb!bash "If you can't beat 'em, infiltrate bash@ihlpb.ATT.COM and destroy them from within." bash@cbnewsd.ATT.COM