Accomplished Insect Fliers

Abstract

The flight characteristics of dragonflies, and to a lesser extent hawk moths, have been summarized. Wing kinematics, aerodynamic force generation and flow-wing interactions are presented. It is clear that these insects generate and use unsteady separated flow structures to support flight. Prominent vortex-wing interactions are routinely documented in conjunction with significant force generation. The wing geometry and kinematics dictate optimal unsteady flow generation as long as the wingbeat frequencies are maintained within prescribed ranges. The dragonfly appears able to readily switch between the use of unsteady flows and the use of more conventional steady state aerodynamics. The latter is used for gliding, a major element of dragonfly territoriality defense as seen in patrolling. The hawk moth appears to use similar unsteady flow strategies but doesn’t exploit gliding. What we believe we have observed is (1) a mechanistic, self-correcting device for creating unsteady flows, (2) a set of devices for using these flows and (3) a set of principles for unsteady flow exploitation by other biological flight systems.