Bird-inspired flexible tail improves aerodynamic performance of fixed-wing aerial robots.

The tail of a bird-or a bird-inspired aerial robot-is an aerodynamically effective structure that enhances efficiency, stability, and manoeuvrability through attitude control and morphing. Optimising the morphology and structure of the tail can further improve the flight performance of such flyers. Inspired by previous studies on bird tails, we designed and developed a flexible tail capable of deforming in a bird-like manner. We investigated the effect of tail flexibility on the flight performance of a bird-inspired aerial robot through wind tunnel experiments and computational fluid dynamic analyses. Our results demonstrate that passive morphing of a tail with appropriate flexibility can adjust the tail surface orientation to direct aerodynamic force forward via pressure at the leading edge, thereby improving the lift-to-drag ratio and overall flight efficiency of the aerial robot. The proposed design also enables tail weight reduction, contributing to improved stability and manoeuvrability. These findings highlight tail flexibility as a key design parameter for improving the performance of bird-inspired aerial robots.