To: Shawn Coyle
I would be slightly happier with this state of affairs if we had a good low airspeed sensing / indicating system for helicopters, but sadly that is not the case.
I believe such a system was developed by a firm called J Tech. It was originally designed to be used in underwater operations to detect water currents. It worked just as well in air. It operated on the principle of vortex shedding with the vortex frequency being detected by an ultrasonic detector. The individual units were coupled to provide airspeed in four directions
Another system is employed on the Apache and the USCG HH-65 but I believe in the case of the Apache, it is used to detect wind direction with this information being fed into the main computer to calculate windage for the chain gun. On the HH-65 I believe it is used to detect wind direction to correct for drift when in a hover. At least that is what I believe to be the reason for the systems.
