Riddle of Insect Flight Solved

SCIENTISTS have long wondered how insects, with their heavy bodies and flimsy wings, can remain airborne. These tiny creatures seem to defy conventional principles of aerodynamics. Now researchers at Cambridge University, England, have discovered how insects perform this seemingly impossible feat.

To study insect flight, the scientists tied a cotton thread around a hawkmoth and placed it in a wind tunnel. They pumped nontoxic smoke through the tunnel and noted the way the smoke moved as the moth flapped its wings. Next, they constructed a mechanical model 10 times bigger that moved its wings 100 times more slowly and watched the now readily discernible effects. They found that when the moth’s wing begins its downstroke, a vortex, or whirlpool of air, is created at the root of the wing. The resultant low pressure above the wing produces lift, drawing the insect upward. If the vortex died out, the moth would lose lift and plummet to the ground. Instead, the swirl of air travels along the wing’s leading edge to the wing tip, and the lift thus generated by the downstroke, equivalent to one and a half times the moth’s weight, allows the insect to fly with ease.

Aeronautical engineers already knew that delta-wing aircraft (so-called because the wing resembles the Greek letter Δ) produce vortices at their wingtips, which create lift. But now that they know how vortices provide lift for insects that flap their wings, they want to study how to exploit this phenomenon in the design of propellers and helicopters.