Bird Flight Research

To: Birding Aus <>
Subject: Bird Flight Research
From: knightl <>
Date: Sat, 11 Dec 2004 13:22:08 +1000 0,5744,11654801%255E2702,00.html

Birds do it with spirals, scientists discover
Leigh Dayton, Science writer
December 11, 2004

BEES, bugs and butterflies do it, and now scientists know that birds do it, too.

"It" being the creation of a spiralling current of air to suck their wings up and generate lift.

According to a team of Dutch researchers, led by John Videler of Groningen and Leiden universities, birds use a specific part of their wing called the "hand-wing" in this "unconventional" way.

Previously, scientists believed birds kept aloft by using their wings as aerofoils, or arched structures, to force air to flow at different speeds above and below their wings.

But today, in the journal Science, Professor Videler and his colleagues report that the complex structure of bird wings allows them to combine both mechanisms in their aerial antics.

In a second article in Science, Ulrike Muller and David Lentink of Wageningen University in the Netherlands note that engineers applied the same phenomenon of spiralling air, or "leading-edge vortices", to design fighter jets.

In 1996 biologists discovered that insects generate lift by producing leading-edge vortices which they control by rapidly beating their wings.

Until now, researchers had no way of studying how air flows around the wings of flying birds. Professor Videler's group side-stepped this limitation by building a model of the wings of swifts -- extremely agile fliers that catch insects in flight.

Because air and water flow the same way in some conditions, they "flew" the wings in a water tunnel, discovering that the vortex spirals out from the top of the wing toward the tip. Like a tornado, the air pressure inside the vortex is low, sucking the wing upward.

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