Abstract:
This paper describes the design, development and flight testing of a small novel quadrotor convertiplane Unmanned Air Vehicle (UAV) which has four propellers driven by individual brushless DC motors mounted at the tip of tandem wings. The segment of the wing under the propeller downwash is tilted with the propeller to improve the hovering efficiency of the UAV. Tandem low and high wing design is chosen to mitigate the interference losses due to the influence of fore wing and propeller downwash on the aft wing and the propellers. The motor and propeller suitable for the design are chosen through systematic performance measurements carried out using a hover test stand and wind tunnel tests. The effect of tilting the wing segment below the rotor is studied by modifying the hover stand and including the wing in the setup. A PID controller is developed, first in simulation and then implemented on a PixHawk autopilot board to stabilize the prototype during hover. The performance of the controller is demonstrated through flight test of the prototype. For the current configuration and size, the current design, with the wing in propeller downwash tilting with the rotor, offers 50% higher power loading in hover in comparison to a conventional quad tiltrotor with no wing tilting. It is observed that the propeller looses 40% of its thrust due to the download penalty on the wing when no part of the wing is tilted with the propeller. The tilting of the wing portion equal to the radius of the propeller increases the power loading of the propeller making it nearly same as the isolated rotor. The current design is estimated to consume 50% less power during airplane mode in comparison to the quadrotor mode thereby establishing the advantage of the proposed convertiplane vehicle over regular quadrotor UAVs.