System Identification of a Free-Flying Quadrotor in a Wind Tunnel using Motion Capture Feedback

A system identification study was conducted on a quadrotor unmanned aerial system (UAS) that was free-flying inside the test section of the Naval Surface Warfare Center Carderock Division's Subsonic Wind Tunnel. Motion capture cameras installed in the wind tunnel provided position feedback information to the aircraft in real time, enabling autonomous flights. Longitudinal, lateral, heave, and yaw axis frequency sweeps were conducted at airspeeds up to 20 knots, in 5 knot increments. The extracted flight dynamics model showed excellent agreement in both the time and frequency domains across all airspeeds. Variation in the aircraft's stability derivatives, power usage, and trim information with airspeed was determined. This paper documents the test procedures, challenges with flying aircraft inside the wind tunnel, the controller model, and the system identification results. This free-flight wind tunnel testing methodology has wide applicability to assist with UAS flight control development, and represents a new opportunity in the way traditional wind tunnels can be utilized for UAS research, development, and testing.