Development and flight-test verification of two-dimensional rotational low-airspeed sensor for small helicopters

This paper describes the development and the verification of flight test results of a differential pressure-based, two-dimensional low-airspeed sensor designed for the navigation or disturbance detection in small helicopters. The compact and lightweight sensor is integrated with the main rotor of a small helicopter and comprises two probes at both arm ends, a differential pressure sensor, rotary encoder with one magnet and two sensors, microcomputer, a wireless data link, and battery. It measures the differential pressure between the total pressures captured by two total-pressure probes at each rotor angle, instead of using static pressure probes. Thus, the airspeed of the fuselage can be evaluated from the low speed. Flight tests were conducted employing a reference ultrasonic two-dimensional airspeed sensor for comparison. The results demonstrated that the magnitude error of the airspeed is less than 2 m/s for low-airspeed flights ( \(<\sim\) $<\sim$ 23 m/s) when utilizing Pitot-type probes. The error in wind angle approximated 30 \(^\circ\) ${}^{\circ }$ , and the delay was less than or equal to that observed with a global navigation satellite system sensor.