UAV Flight Testing with an Airborne Sonic Anemometer, IMU and GPS

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This paper details a series of flight tests performed on an 11-foot wingspan UAV. Flight test objectives included calculation of the aerodynamic angles (angle of attack and sideslip angle), calculation of in-flight horizontal wind velocity, and characterization of aircraft dynamic modes. Important flight variables included rotation rates as measured by MEMS rate gyros, velocities relative to the ground as measured by GPS, and airspeed as measured by an airborne sonic anemometer. The aerodynamic angles were calculated using a vector analysis of the aircraft's orientation and velocity as determined from the rate gyros and GPS, respectively. These results were then compared to those calculated from the onboard sonic anemometer. Similarly, wind speeds were calculated by subtracting groundspeed as measured by the GPS from airspeed as measured by the airborne sonic anemometer. These results were then compared to windspeeds measured from a second, grounded sonic anemometer. Finally, the short period, roll, and Dutch roll modes were excited by appropriate flight maneuvers and compared to theoretical/empirical predictions. Trendwise, the rate gyro/GPS aerodynamic angles agreed with the sonic anemometer during straight and level passes. The calculations would be improved by better Euler angle estimates and better knowledge of ambient wind. The average wind velocity vector obtained from the onboard instrumentation was higher than the one measured from the ground station. The aerodynamic influence of the aircraft at the location of the sonic anemometer and measurement errors of the Euler angles might be the possible causes. The dynamic mode flight results matched the theoretical/empirical predictions, though they were significantly affected by atmospheric turbulence.