Tailless control of a four-winged flapping-wing micro air vehicle with wing twist modulation.

This paper describes the tailless control system design of a flapping-wing micro air vehicle in a four-winged configuration, which can provide high control authority to be stable and agile in flight conditions from hovering to maneuvering flights. The tailless control system consists of variable flapping frequency and wing twist modulation. The variable flapping frequency creates rolling moments through differential vertical force from flapping mechanisms that can be independently driven on the left and right sides. The wing twist modulation changes wing tension, resulting in vertical and horizontal force variations during one flap cycle and generating pitching and yaw moments. We presume that the wing geometry and implementation method of wing-root actuation are related to the control authority of wing twist modulation. Then, the control system's performance is analyzed for various wing geometries and implementation methods, including wing length, leading-edge thickness, camber angle, and vein configuration. Furthermore, the cross-coupling effect is examined for the wing twist modulation, and a control surface interconnect is designed to compensate for the decrease of pitch control authority and adverse rolling moment. The refined wing and control mechanism demonstrated its high control authority without significant loss of vertical force and power efficiency. The flight experiments validated that the control system based on wing twist modulation is suitable for four-winged flapping-wing micro air vehicles, providing sufficient control moment and minimizing the cross-coupling effect.