A Counter-Propagating Laser Air Speed Sensor System for Aircraft

Abstract

This paper presents an investigation of the applicability of a counter-propagating laser air speed sensor (COPLASS) system to measure air flow velocity in the subsonic-totransonic aircraft flight regimes. The system uses the Doppler shift of an absorption line in the A-band of molecular oxygen near 760 nm, combined with an independent measurement of the static pressure, to determine the true air speed. The experimental arrangement allows for the possibility of fully analog signal-processing, while the size and weight of the system would be appropriate for most commercial aircraft or unmanned aerial vehicles flying today. Static pressure and velocity regimes were investigated in wind tunnel tests from static pressures of 20 to 150 kPa (altitude equivalent 40,000 feet to sub sea-level) and air speeds from 5 to 380 m/s. We conclude that COPLASS is a viable instrument for measuring true air speed in these aircraft flight regimes.