DRAGONFLY FLIGHT .1. GLIDING FLIGHT AND STEADY-STATE AERODYNAMIC FORCES

The free gliding flight of the dragonfly Sympetrum sanguineum was film ed in a large flight enclosure. Reconstruction of the glide paths show ed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonf ly were calculated. The maximum lift coefficient (C-L) recorded from t hese glides was 0.93; however, this is not necessarily the maximum pos sible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselffy Calo pteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15000 for the bodies. The maximum lift coeffici ents (C-L,C-max) were 1.07 for S, sanguineum and 1.15 for C. splendens , which are greater than those recorded for all other insects except t he locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted fo r flat plates. Dragonfly wings thus show exceptional steady-state aero dynamic properties in comparison with the wings of other insects. A re solved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be inc luded in models to predict the parasite drag on dragonflies at non-zer o body angles.