I was really lucky in my ASW-27 at 70% CG when I had a windshear induced stall while moving to flap L at ~300 above threshold. I lost 269' and was fortunate to recover over lower ground before having to dodge a topsoil pile in the neighboring gravel pit.
Applying headwind component = TAS - GS, examination of the recorded flight data reveals 3 windshears, each over a 2 second interval, of -17, +23, -28 kt (application of Pythagorean sum of squares of a triangle on the final shear yields 6 kt of apparent headwind giving -34 kt --
twice the recorded wind of 17 kt).
Recovery action was flaps negative and stick forward.
The usual stall practice at 3000 AGL with a 1 kt/second deceleration has little resemblance to a low level windshear stall.
More details on:
https://www.dropbox.com/sh/lq9osn15b...wuYvScXya?dl=0
The more usual course:
I watched one of those early ASW 20 fatal spins. It was from slow straight and level flight, not thermaling. The wing dropped sharply and the glider entered a conventional, nose-down spin. The recovery began almost
immediately (approx. 1/4 turn) but unfortunately there was not sufficient altitude (this began at approx. 300 ft AGL) and the pilot was killed when the glider impacted the ground slightly nose down (i.e., the recovery was almost
complete) but still sinking. Undocumented tail ballast was probably a factor... Pilot incapacitation due to dehydration may also have been a factor. The final blow, so to speak, was the lack of a headrest in this very early '20 and a battery pack behind the head that came loose. The pilot was an experienced, high-time competition pilot and instructor...
The usual tendency is that the pilot must have screwed up somehow. Perhaps the real lesson is to maintain adequate margins, but when and how do we know extra margin is needed?
Always adding speed to get through a shear of twice the wind can make for long landings.