Tumbling dynamics of passive flexible wings.

The influence of flexibility on the flight of autorotating winged seedpods is examined through an experimental investigation of tumbling rectangular paper strips freely falling in air. Our results suggest the existence of a critical length above which the wing bends. We develop a theoretical model that demonstrates that this buckling is prompted by inertial forces associated with the tumbling motion, and yields a buckling criterion consistent with that observed. We further develop a reduced model for the flight dynamics of flexible tumbling wings that illustrates the effect of aeroelastic coupling on flight characteristics and rationalizes experimentally observed variations in the wing's falling speed and range.