glider pilots use "side window pitch strings" for AoA measurement
Agreed, and some jet pilots have more sophisticated AoA indicators to look at. But the aircraft mentioned don't. Propellor wash would upset a piece of wool stuck to the windows.
The OP mentioned having tried to find the information in the POH for the required types. Critical AOA isn't mentioned in those documents because it's impractical for a pilot to measure the wing's AoA.
As we all know, that's why recognition of an impending stall is so important.
