Performance and Control of Variable Pitch Proprotors for Multi-Scale Quadrotor Biplane Tail-sitters (QBiTs)

Hybrid air vehicles with VTOL capability and fixed wing efficiency continue to find application in the expanding aerospace landscape. One such concept, the quadrotor biplane tail-sitter, has a baseline configuration that is mechanically simple and utilizes a conventional quadcopter control scheme. The subject of this paper is the expansion of the baseline flight envelope through the implementation of independently controlled variable pitch mechanisms on each rotor. Hover data showed that power consumption increased as blade pitch (θ75) increased, climbing from 450 W to 880 W with a 20° increase in blade pitch. Additional hover data demonstrated that the operating motor efficiency decreased from 80% to 60%; when blade pitch is increased by 20°. Forward flight data measurements showed that the variable pitch mechanism successfully expanded the flight envelope. From 15° to 30° blade pitch, the minimum power required decreased from 520 W to 326 W, and the airspeed achieved increased from 6 m/s to 8.5 m/s. As a supplement to flight testing, preliminary efforts towards developing a mobile wind tunnel test stand to measure the impact of variable pitch and rotor-wing interactions are discussed.