Unusual flight

 
Published: Saturday 15 March 1997

Laws of physics explaining the mechanism that keeps an aircraft airborne fail to do so for insects. Reason: insect's wings, unlike an aircraft's, have a highly unsteady motion that cannot be explained by conventional laws of motion. They change direction and speed at a phenomenal rate. Charles P Ellington, a zoologist, and his colleagues at the University of Cambridge have provided the first clear evidence that an insect flies by an unconventional mechanism. To gain lift, air is driven downward by flapping the wings; vortices, cylinders of air that are caused to rotate by a puff of moving air, are formed around the downward-moving jets of air, and the leading-edge vortices are stabilised by a phenome non known as 'delayed stall', which allows the insect to generate enough lift to stay airborne (Nature, Vol 384, No 6610).

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