RE: DJ77 (#4091)
DJ,
I believe industry practice is that the aircraft longitudinal axis (x-axis) is the reference for angle of attack (alpha), flight path angle (gamma) and pitch angle (theta). All angles are positive upwards. The relation between these angles is given by:
theta = gamma + alpha
From the ATSB Interim Report on the A330/QF72 accident:
For an A330, during all phases of flight, the typical operational range of AOA is +1
degree to +10 degrees. In cruise, a typical AOA is +2 degrees.
It may look strange that AoA depends on airspeed but probe litterature generally speak of "local AoA" and "corrected AoA". An important design stage for AoA probe installation is to find a place on the fuselage where the correction is quasi linear relative to airspeed. This is done experimentally in wind tunnel.
A calibration curve for the relation between vane angle and airplane AoA is established during flight tests. I assume that this calibration is used in the ADIRU to convert the alpha-vane output to AoA.
Stall warning AoA is normally not affected by airspeed or mach, but it is possible that the calculation algorithm applies a Mach-bias at high Mach.
regards,
HN39