Hi!

The basic principle comes from this reference:

http://www.nar-associates.com/techni...LowCostAoA.pdf

In order to be accurate for any atmospheric pressure (altitude), you can't make a straight differential measurement of your dynamic pressures. You need a reference pressure.

The thing is relatively tricky as you need to calculate a ratio of pressures to get the AOA... And at low speed the dynamic pressure is low... And the difference between the 2 dynamic pressures is equally low. And you must compute an accurate ratio of these 2 low values...

That's why my system uses 2 $35 pressure gauges: They are internally compensated for temperature and other factors, and outputs a 14 bits signal, with a full range corresponding to a 250 km/h dynamic pressure.

That's the price to pay to be below 1% at 70 km/h... And in practice it works...

The pitch string is corresponding to the instrument... But the string is very sensitive to sideslip... Not the instrument... That makes the side string useful only for calibration, when you can concentrate on keeping the middle string absolutely straight...