The Relationship Between Dragonfly Wing Structure and Torsional Deformation

Abstract

The effect of wing corrugation on torsional deformation was investigated for dragonfly wings. Wing corrugation dramatically increases the warping rigidity, without significantly increasing the torsional rigidity. This behavior implies that the warping moment, which is proportional to the warping rigidity, has a larger resistance against the external moment than does the torsional moment by Saint-Venant's theory, which is proportional to the torsional rigidity. The larger warping rigidity means the wing can be thinner, provided the maximum deformation is restricted. Such a thinner, lighter wing is more suitable for beating flight because such wings have better aerodynamic performance and require lower inertial power.We measured the natural frequencies of the torsional deformation of four species of dragonflies. In all cases, the lowest natural frequency of the torsional deformation was over two times higher than the beating frequency. This means that resonance does not significantly increase the passive torsional deformation caused by the flapping motion. The natural frequencies of the torsional deformation of dragonflies are determined by the warping rigidity, which is increased by the wing corrugation. The corrugation prevents unusually large deformation induced by resonance of the wing.