ORIGINAL: redcommander
I am curious to see the interest level in a sensor that can could measure true airspeed. The current technology (Pitot static) requires accurate measurement of static pressure (which can be extremely difficult at high altitudes). It also requires accurate air temperature measurements. Finally, a Pitot-static system is inaccurate below about 30 knots.
Does anyone know of any current projects that could benefit from a sensor (1.5" diam x 8"length) that could measure true airspeed (not pressure) and was accurate below 10 knots?
As I understand pitot-static systems, the main inaccuracy in sensing dynamic pressure difference has to do with the AOA at the inlet (cos(alpha)*freestream vector). At low speed, the AOA becomes large enough to cause a significant reduction in ram pressure (small angle approximation doesn't work anymore). One way to do it would be to use a traditional pitot-static system with AOA, pressure altitude and temperature sensors and process the input before displaying it. It's done this way using various methods on some full-scale airplanes. Of course all that equiment would add weight. Wouldn't want to use a windmill: far too draggy, and that's still "indicated" airspeed anyway.
Why would you want to measure the true airspeed of a model anyway? Are you thinking about a UAV or something high dollar like that? True airspeed is used to calculate ground speed and wind correction angle, but indicated (or calibrated) airspeed is what operating limitations and climb performance are based on.