A tool for examining hovering flight of insects and birds could allow researchers to study other matters pertaining to locomotion, Stephen Childress, a professor at New York Universitys Courant Institute of Mathematical Sciences, demonstrated at the American Association for the Advancement of Science (AAAS) annual meeting in St. Louis. The findings were part of a symposium, "How Insects Fly," which also included researchers from Cornell University and the California Institute of Technology.
Previous research in this area was conducted through observations of a small pteropod mollusk, or "sea butterfly," whose locomotion in water is similar to that of a butterflys flight. That revealed two modes of locomotion: in one, cilia mode, the organism swims forward much like a micro-organism, using waves of beating cilia, or hair-like structures; in another, flapping mode, the wings are extended and flapped back and forth in a symmetrical manner, propelling the body forward. These results showed that this particular organism was able to use both modes: one pertaining to the microorganisms, the other to the insects or birds. As the pteropods grew, observations by Childress with his colleague, Robert Dudley, a biologist at the University of California, Berkeley, showed that the wings enabled more rapid swimming. Extrapolating the data backwards to small size, it was found that wings ceased to be effective at a critical size, establishing a transition size for winged flight.
Building on this scholarship, Childress and his colleagues at the Courant Institutes Applied Mathematics Laboratory sought ways to study free flight in the laboratory. They first replicated the forward flight of the pteropod by driving a horizontal rigid blade in a vertical oscillation while immersed in fluid. The blade was mounted on a vertical shaft, free to rotate in either direction. The blade flapped horizontally according to Newtons law of motion. It was found that the transition seen in the pteropods occurred also with the flapping blade. The transition depends upon both the size of the blade and the frequency of flapping. The researchers were thus able to study the transition by varying the frequency instead of the size. Below a certain frequency the blade ceased to rotate.
James Devitt | EurekAlert!
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