LOW COST/LOW AIRSPEED SENSOR FOR HELICOPTER APPLICATIONS

Design features and results from wind tunnel and helicopter flight tests are reported for an innovative low airspeed sensor utilizing constant voltage anemometry. The flight tests were conducted on a Bell 412 helicopter with instrumentation for this purpose. The sensor was calibrated at the National Institute of Standards and Technology (NIST). The prototype sensor provided a fraction of a knot resolution at speeds as low as a knot. The output signal from the sensor electronics varied linearly with speed and is relatively immune to EMI and RFI. Changes in pressure, density, and temperature in the normal helicopter flight envelope had negligible impact on the probe performance. The probe weighs only a few ounces. A small enclosure used to house the sensor significantly reduced the influence of rotor downwash. The unique frequency domain output of the sensor allowed the remaining rotor down wash effects to be filtered out and eliminated. The cost of producing such a device is expected to be well below other similar flight instruments for low-airspeed measurements.