Controllability and Trajectory Controls of an Underactuated Flapping-Wing Aircraft Steered by Center of Gravity

This study presents a flapping-wing micro aerial vehicle designed for three-dimensional trajectory tracking. The design features center-of-gravity-based steering, three actuators, and omits a dedicated yaw actuator, time-varying wingbeat patterns, and high-frequency actuator switching. To investigate the dynamics of the proposed design, a modified nonlinear controllability framework was developed for theoretical analysis, and a series of flight experiments were conducted to validate the analytical results. The analysis indicates that, despite the absence of a dedicated yaw actuator, the yaw torque required for three-dimensional maneuvering arises from center-of-gravity shifts, asymmetric wing aerodynamics, and an intrinsic feedback mechanism that stabilizes the angle difference between vehicle's yaw angle and trajectory rotation angle. Furthermore, the yaw dynamics exhibit nonminimum phase behaviors in response to center-of-gravity movement. Based on these findings, a multi-tier control architecture is proposed to accommodate these unique dynamics for autonomous flight. Experimental results demonstrate that the proposed design can perform three-dimensional trajectory tracking, with attitude errors below 5° and altitude deviations within 10 cm in most cases.