A Novel True Airspeed Indicator for Helicopters

A completely new approach is proposed for the accurate measurement and display of the true airspeed of helicopters in hover, low-speed and forward flight. Unlike conventional instruments, the proposed innovation will be characterized by high-frequency response and high sensitivity across the range of helicopter flight speeds. The proposed device will provide accurate speed indication both at low and at high airspeeds. The innovation items from the following significant advances made by AS&M in recent years: (a) the discovery of a direct coupling between airspeed and frequency of flow oscillations at the leading-edge stagnation region, and (b) the invention of constant voltage anemometry. A probe of specified geometry with closely-spaced, micro-thin multielement sensors will be used in conjunction with constant voltage anemometers to determine the true airspeed as well as the flow angularity. The frequency of the electrical output signals from the instrument will be related to the true airspeed of the helicopter. The one-time calibration of the airspeed indicator will be dependent on the probe geometry but independent of the installation (e.g., H-60).