Optimal design of auto-rotating wings*

Autorotation is a passive flight mode in which lift is primarily created by the revolution of the flyer around itself. The aerodynamics of auto-rotating flyers is not well understood, and design rules derived in the context of fixed wings may not apply. Using carefully-controlled experiments, we study the aerodynamic performance of thin, quasi-rectangular auto-rotating wings. In this framework, we systematically look for the optimal dynamics by varying several parameters such as mass distribution, flexibility, shape, and winglet size. We use high-speed photography to extract flight characteristics such as flight duration, descent angle, and flight range, and develop reduced-order models to predict the behavior change. We find that a heterogenous redistribution of the wing mass, leading to spanwise tip flexibility and chordwise reduction in the wing’s moment of inertia, can result in improvement of aerodynamic performance. The design rules extracted from our investigation may contribute to the understanding of the settling dynamics of heterogeneous objects, shed light on the mechanism of seed dispersal, or help with the design of micro-air vehicles.