Abstract: A method for determining the horizontal airspeed of a helicopter in the high speed (v.sub.e >20 m/s) range. Pitch angle and the longitudinal control signals are recorded by sensors such as an inertial navigation system and a potentiometer connected to the pilot's control lever. Equivalent speed signals are calculated from the measured pitch angle and longitudinal control signals by means of calibration equations. These signals are then filtered and weighted. The horizontal airspeed is then derived from the sum of the weighted signals divided by the sum of weighting factors k.sub..theta. and k.sub..delta.x determined in accordance with the sensed pitch angle and longitudinal control signals. The horizontal velocity signal may be filtered, if necessary.

Abstract: A method is disclosed for determining the horizontal airspeed of helicopters in low speed ranges. At least three control functions, .theta..sub.o,i (collective pitch), .theta..sub.s,i (longitudinal control) and .theta..sub.c,i (lateral control) are measured. The magnitude of the horizontal airspeed, V.sub.H,i, is determined from its known relationship to .theta..sub.o,i. This magnitude is included in non-linear calibration equations .theta..sub.s (V.sub.H, .psi.) and .theta..sub.c (V.sub.H, .psi.) and control profiles .theta..sub.s (V.sub.H,i, .psi.) and .theta..sub.c (V.sub.H,i, .psi.) are derived therefrom. The measured values .theta..sub.s,i and .theta..sub.c,i are applied to the respective control profiles and corresponding phase pairs .psi..sub.s,1, .psi..sub.s,2 and .psi..sub.c,1, and .psi..sub.c,2 located. The pairs are compared and the incident flow angle .psi..sub.i is determined as the value common to the two pairs.