bildan wrote:
I've worked this problem for a number of years. Let me offer a few
simple points.

Any system of measuring AOA will need to be calibrated. It doesn't
really need to be linear since the major interest is in the region
near stall and Cl max. It just needs to give a variable output that
is related to AOA - and be very repeatable.

If the cockpit is in clean free air flow as with a pusher or
sailplane, an effective AOA indicator can be made with a simple string
taped to the side of the canopy. On sailplanes, these 'pitch strings'
tends to 'over-indicate' by about 2:1 which is fine as it increases
the resolution of the indicator. Stall, Cl max and L/D max can be
marked on the inside of the canopy with grease pencil. It helps to
put one on each side of the canopy as they tend to validate each
other.

If you like the pressure differential AOA probes, this is a good one.
http://www.cgmasi.com/aviation/index.html

It occurs to me that a differential system should be fairly simple to
build. Solid state pressure sensors have been around a long time. Since
AOA would be the ratio between the two sensors it should be simple to
make a comparator to voltage converter since actual pressures are
irrelevant as long as they are sufficient to be read. Airspeed would
also not be a factor. I suppose a purely mechanical system could also be
built by a mechanically inclined type. Pressure from each port would be
sent to opposing bellows in an indicator which would position a needle.

Dan, U.S. Air Force, retired