Air-speed/Wing-tip Speed Ratios of Insect Flight

Abstract

I HAVE made measurements of the wing movements of the tsetse-fly Glossina palpalis R-D. and other Glossina species in free flight, using a stroboscope and a large series of ‘Arditron’ flash photographs (duration about 1–2 microseconds). The wing-beat frequency for G. palpalis is 120 cycles per second; but investigation shows that the relative speeds of the ‘up’ and ‘down’ strokes are far higher. The times taken for the ‘up’ (return) stroke and for the ‘down’ stroke are approximately equal and have been estimated at 0.001 sec, whereas the time for the whole cycle is 0.008 sec. Two milliseconds are ‘wasted’ at the completion of the ‘down’ stroke and four milliseconds at the completion of the ‘up’ stroke. The wing-tips describe a distorted and flattened figure of eight, the axis of this ‘figure’ being set between angles varying between 30° and 80° to the horizontal axis of the insect. The angle is varied by the insect to regulate speed, and for turning, since it is apparently unable to change its wing-beat frequency. The maximum movement of the down stroke, measured along the arc, is 15.4 mm. and the up stroke is 20.3 mm.