Usherwood, J. R.: Aerodynamics and energetics of animal flight based on propeller models

Recent work on flapping insect models has demonstrated the importance of a spiral ‘leading-edge vortex’ created by dynamic stall and maintained by some aspect of spanwise flow, for creating the lift required during flight (Ellington et al., 1996; Dickinson et al., 1999). This study uses propeller models to investigate further the forces acting on model and real animal wings in ‘propeller-like’ rotation (‘revolution’). The effects of camber, twist, and leading-edge characteristics are shown to be minor for model Manduca wings. Force coefficients are derived for wings of animals ranging from mayfly to quail. Some aspect of the aerodynamics of animal wings in revolution, presumably the leading-edge vortex, results in high lift and drag forces, and appears to be a robust phenomenon. A consistent relationship between vertical and horizontal forces, and the angle of attack, is described. This is independent from local flow conditions, and a new method for estimating power requirements is developed. The power requirements derived for hovering are higher than those previously predicted, but are considered upper estimates.