Retired F4
I dont know, how it was done, what input it used. Im no techician´and also technically very interested i never questioned the functioning of the AOA. It was there, it was always working, also with a iced up pitot tube (we only had one).
I don´t see the problem there, the information was present in the AF447 aircraft (Stall warning, FDR traces....), it was not displayed.
OK, since I posted my query I’ve found an example of an F4 operational manual on the ‘net.
Short answer is that it wasn’t done with any precision.
The AoA probe doesn’t give incidence in degrees, but an AoA ‘index’. Probe output goes from 0 to 30 arbitrary units for an AoA range of -10 to +40. UAS pages give stall at 27 units, stall warning (pedal shaker) at 21.3~22.3 depending on aileron droop. [But it is said that it may not be recognisable due to heavy buffet!]. There is no mention of any variation of stall or stall warning with Mach number. Values of AoA units are suggested for a range of flight cases, but so far as I can see these simply replace pitch by AoA units as memory items. The weight range for the F4 seems to be small enough for such a simple approach to work. For example the index for approach (19 units) is said to be “adequate” for all loadings and in fact is a simple reflection of approach at 1.3Vs or whatever being close to a unique AoA for all CGs. But the indicated AoA is only valid with gear down – with gear up the aircraft stalls 3 or 4 units earlier. Stall, it is said, is preceded by buffet starting at 12~14 units and stall will “usually be above 25 units” although the actual angle varies considerably with loading. With flaps and gear down the pedal shaker operates about 17 kts above stall and 9 kts before wing rock.
I haven’t found any mention of automatic indication of stall AoA, so presumably you had to set one or more of the ‘bugs’ appropriate to the flight state?
Overall, I have to say that my impression is one of a system that can be made to work well enough on an aircraft operated as military, but which would need some additional sophistication to meet the needs of civil operation, unless one accepts use of memory items for typical AoA in routine day to day operation. Nothing wrong in that, it is already used in pitch, and any indication of AoA would be better than none, but I don’t see it as an all embracing panacea I’m afraid.