An Ultrasonic Altitude-Velocity Sensor for Airplanes in the Vicinity of the Ground : I. Fundamental Characteristics

Abstract

This paper shows the possibility of an ultrasonic sensor which detects the altitude from the ground and the vertical velocity of an airplane in the vicinity of the ground. The principle of the present technique depends on the measurement of time in which the ultrasonic wave propagates the distance between the airplane and the ground, because the sonic velocity is approximately constant at the usual atmospheric temperature. Furthermore, by differentiating the altitude signal with respect to time, it is possible to detect the vertical velocity of the airplane, too. The fundamental performances of this sensor are investigated with some experiments carried out in our laboratory, and it is shown that the ultrasonic sensor will be useful in place of the radar altimeter, in particular at very low altitude. As an application of this sensor, the automatic control of a VTOL airplane in hovering flight is investigated by analog simulation studies.