In addition to Bill's comments the calibrations process must consider the position of the flaps. Remember you are measuring the AOA of the airfoil, not just the airflow relative to the fuselage.

Wayne
http://www.soaridaho.com/Schreder
..
"bildan" wrote in message ...
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

If you want NASA quality data, the gold standard is the pitch vane
mounted on an air-data nose boom. There are a number of vendors who
sell these for UAV's which are about the right size for homebuilt
airplanes.
Here's an example: http://www.spaceagecontrol.com/Adpmain

Bill D