Trailing anemometer for low airspeed calibration

A propeller-type trailing airspeed anemometer system is described for low airspeed (M not exceeding 0.2) calibration which has improved accuracy and is easy to implement as compared to most methods currently in use. The trailing anemometer system consists of the trailing anemometer itself, a deployment mechanism, and an operator's control box. The trailing anemometer is a small low-drag brass body provided with tail fins for self-alignment with the airstream. The rotational speed of a small six-bladed low-inertia propeller is sensed with a miniature self-generating tachometer inside the anemometer. A very satisfactory airspeed calibration can be made with this device in which true airspeed can be measured to within 1 knot. Results from flight calibration of an aircraft and trail-back characteristics of the anemometer and cable are included. The operating speed range of the designed cable-anemometer combination is 7 to 165 knots.