Investigations into helicopter pilot fatigue require that external wind forces be known in order to correlate the pilot's reaction and motions. To fully separate the forces and responses, the wind sensors must have a response time shorter than either the pilot or vehicle reaction times. This proposal describes an air velocity sensing technique which $ detects the vortices that are shed from a sm4all rod held in the airstream. The vortex shed frequency is directly proportional to the air velocity and with a small vortex rod size, vortex frequencies of several thousand per second are obtained. Since each vortex is an independent measure of the airspeed during its formation, response times of less than one millisecond can be obtain. The wind vectors will be separated into two components and each component measured. The vortices are detected using an ultrasonic im4aging technique. Instruments using this technique have been test flown on helicopters as airspeed and direction sensors. However, in those applications, response times were not critical. The same sensing technique has been used in automobile air intake sensors where response times of less than 10 milliseconds were measured. This lends promise that the airspeed sensor, combined with the fast processing of the automobile sensor will fulfill the requirements of this program.
