Now if GRT will just publish their algorithm for calculating AOA, we might get a head start on that.....
It is quite simple and based on pitch attitude, vertical speed and true airspeed.
Using vertical speed and true airspeed gives you an angle of decent. AHRS gives you pitch attitude.
Combine both and use a normal calibration flight to find differences in pitch angle and flight path angle for various airspeeds (i.e. fly close to a stall and also get a "neutral" point - usualy straight and level, high power setting). Assume the stall point is 15 degrees (or therabouts) and everything else kinda falls into place.
This works very well for the stabilized approach but is pretty useless for everything else (which is perhaps fine). It suffers a bit from lag issues if the input data doesn not change fast enough so dynamic performance is not as good as a real AOA.
Real AOA works in any attitude so you can use it in a steep, slow bank to tell you how you are doing. Granted, this can be faked as well using bank angle from the AHRS and well known changes in loading and stall speeds. It gets close - but perhaps not close enough.
Good to use as a gadget and fun to play with (we have a calculated mode as option in our EFIS's in addition to normal differential or relative AOA measurement modes).
I agree with Garmin's opinion that perhaps calculated AOA is not the best of ideas. Suppose it depends on how its used.
Rainier
CEO MGL Avionics
