Owl holds clue to cutting jet noise

The Times 4 March 1999 ...

The secrets of the silent swoop of the owl have been discovered by researchers who want to produce quieter aircraft. Scientists at Southampton University and NASA's Langley Research Center in Virginia found three key features on the wings of nature's stealth bomber.

Most important, down on the feathers on the upper surface kills noise above two kiloHertz. Second, most birds' wings have sharp, clean edges like those of an aircraft but the owl has a serrated edge, like a saw, on its primary feathers. This creates tiny, streamlined eddies as the wing moves.

The third feature that reduces noise is the trailing edge of the wings, likened to the fringe on a scarf. Without this, the airflow would create a sound like a flute. In fact, the owl is not silent but the major noise generated is very low frequency which is not heard by its prey. It is hoped that by understanding the owl, aircraft noise can be reduced.