Thridle Op Des,
The phenomenon to which you refer is a "superstall" (not to be confused with a deep stall situation) or "accelerated stall" and is described in the literature.
The driving factor is the aerofoil pitch rate and, as one would expect, it is seen more in the rotary side of the house. If the pitch rate exceeds a critical value (rusty memory seems to flash 70-plus deg/sec in the cortex), then a vortex arises which causes the flow to reattach and the alpha can go somewhat above "normal" values.
There was a very readable article on this subject in the RAeS Journal several years ago. If I recall correctly, the subject has been touched on in PPRuNe before and there may be a reference to the AeroSoc article ?
Last edited by john_tullamarine; 5th November 2005 at 22:26.