Liftoff of A Motor-Driven Flapping Wing Rotorcraft with Mechanically Decoupled Wings

Flapping Wing Rotorcraft (FWR) combines flapping and rotating wing motion in one element. Such a hybrid design integrates the high-efficiency characteristics of the rotating wing and the high-lift feature of the flapping wing under low Reynolds number, providing a broader range of simultaneous lift and power efficiency optimization. Nevertheless, the flight performance of the current FWRs is limited by their complex transmission mechanisms. Such mechanical constraints not only induce coupled wing kinematics but also render tedious assembly work and fabrication imperfections. In order to fundamentally address the constraints, we propose a motor-driven FWR with mechanically decoupled wings. The wing of the proposed DFWR is directly actuated by two bi-directional rotating motors instead of using the crank rocker (or alike) transmission. The proposed DFWR flaps within 25Hz to 35Hz, with about 12.4 grams of system weight and 185mm wingspan. With the direct-drive principle, the wing kinematics can be modulated properly by real-time motor control. In particular, we tuned the flapping frequency, stroke amplitude, and mid-stroke angle of the proposed direct-drive FWR to attain its best lift performance. As a result, it can generate about 16 grams of maximum total lift. In order to validate the proposed design, free flight tests have been conducted. The proposed FWR demonstrates stable liftoff.