All the airspeed systems below the rotor, such as those on the side of the Cobra, are at best a bad approximation of the airspeed during low speed cases. The calibrations of those systems is nearly random where it counts, mostly because the downwash contains strings of high speed tip vortex air that is easily at 40 to 60 knots of energy. If that vortex strikes any pressure sensor (a pitot, or a fancy pressure transducer) the results are chaiotic.. .. .The S-76 pitots, and the Sea Hawk's, are located in the nose so that the blade tip vortex sweeps above them at speeds above 30 knots or so. When we developed the S-76 system (I flew one prototype that had 10 pitots -it looked like a B-17!), we had to track the tip vortex pattern as it swept across the nose at 30 knots, across the pilot's door at 50 knots, across the upper doghouse at 80 knots and finally across the transmission/swashplate fairing at 120 knots. Since the FAA airspeed calibration must be accurate down to 30 knots in level flight, we chose the nose position for the type design.. .. .The sensors above the rotor are affected by inflow, but those are relatively predictable, and much smoother than the hash below the rotor. The first airspeed above the rotor was the S-61 bullhorn system, which uses a common pitot, but is quite accurate and reliable down to 30 knots. The rotating systems above the mast are as a class quite accurate, and also read the azimuth of the airspeed, a boon to weapons shooting.. .. .Comanche uses sensors in the blades to read the dynamic pressure continiously. A computer sorts out the phase and rpm effects, and leaves the airspeed data and azimuth as a very accurate result. The blade sensors are used on Comanche because all the other systems contribute too much radar return.