Design and Implementation of Amplitude-Varying Flight Strategy for Flapping Wing Aircraft.

Facing constantly varying airflow conditions, birds in nature adjust their flapping amplitude of wings to enhance flight efficiency. This behavior, termed variable amplitude flight, is mimicked by the our proposed flying robots, and a closed-loop control-based strategy is proposed for the motor . Firstly, a closed-loop model of wing flapping angle is built, considering the dynamic model of the motor and the dynamic characteristics of wing motion. Then, a controller is designed to achieve precise control of wing position. Building upon this, a variable amplitude flight strategy with gliding functionality is devised and its effectiveness is validated through numerical simulations. A solution is provided for the practical application of the variable amplitude flight strategy for various medium to large flapping-wing flying robots. This solution is based on a falcon-inspired flapping-wing aircraft platform, which is equipped with sensors to collect wing flap angles and a Falcon 2.0 flight control board to run the variable amplitude flight control algorithm. The equipped platform's total mass is increased by less than 30 g. As the results of the round experiments, within 0.2s the wings reach the specified glide angle, and variable-amplitude flight can be achieved with wings flapping at variable frequencies between 1~4 Hz. Additionally, ground turntable experiments demonstrate the proposed strategy can further improve the airflow utilization efficiency, with a 14.7% increase in the lift compared to traditional cyclic flapping methods. Flight tests show that the aircraft can achieve stable gliding within 0.5 seconds and can also perform amplitude-varying flight at frequencies of 2-3 Hz, fully validating the effectiveness of the proposed amplitude-varying flight strategy. The proposed amplitude-varying flight strategy enhances the degrees of freedom of the wing flapping motion in flapping wing aircraft, providing an effective solution for performance optimization and practical applications of flapping wing aircraft.