Experimental Validation of an Aerodynamic Sensing Scheme for Post-Stall Aerodynamic Moment Characterization

A fixed-wing aircraft that is capable of low airspeed, high angle of attack flight can serve an expanded range of mission goals. A typical propeller-driven small unmanned aircraft can be equipped with an engine that provides greater thrust than airplane weight; in post-stall states, the aircraft then depends on propeller backwash over the tail for control moment generation. Due to this dependence on propeller wash and potentially negligible free-stream airspeed, conventional wind-vector measurements cannot adequately describe the aerodynamic forces and moments acting on the aircraft. This paper describes a distributed pressure sensing system for a small UAS, enabling in-flight estimates of pitch and yaw moments due to the tail surfaces. A wind tunnel test model was developed around an existing flight vehicle with a 1.8m wingspan. Embedded pressure measurements were taken across the tail surfaces at low-airspeed high-thrust conditions. Test data is used to develop a method of determining the in-flight aerodynamic pitch and yaw moments due to the tail surfaces on a fixed wing UAS. Through comparisons with torque transducer measurements, the pressure based measurements are shown to provide moment estimates within one standard deviation interval of transducer measurements at hover, thus are capable of providing accurate moment feedback for fixed wing UAS.