On Friday, October 23, 2015 at 9:09:47 AM UTC-6, Jonathan St. Cloud wrote:
Didn't the SSA have a contest to develop a working AOA indicator for gliders? What ever happened to that project, has a practical AOA indicator ever been developed for gliders?

Not the SSA but OSTIV - I think. IIRC, several workable designs were proposed but none were adopted. Most involved some sort of external vane which was considered too fragile and complicated for gliders.

When discussing AoA instruments, it's important to make the distinction between simple stall warning systems and full AoA instruments. Stall warners just set off a flashing light and noise maker when the AoA exceeds a pre-set value. AoA instruments display the actual angle of attack throughout the whole operating envelope and are used to optimize performance. Stall warning can be added to an AoA instrument and the trigger point can be adjusted.

In recent years, NASA has developed several AoA systems that don't use vanes. Their "5-hole probe" not only measures AoA but yaw and stagnation pressure as well. For gliders we would only really need a 2-hole probe - essentially 2 pressure taps, one on the upper nose forward of the canopy and one on the lower. A vario-like instrument could measure the pressure differential between the ports and derive the AoA.

Of course the 5-hole probe could replace the yaw string with an instrument indication.