"National Post"
 August 16, 2001

 Scientists deploy Robofly to solve 'bumblebee paradox'

 Joseph Brean
 National Post

 A robotic fruit fly 100 times larger than a real one has helped solve the
 mystery of how flies fly, scientists say.

 The bumblebee paradox, which confounded scientists in 1930 when it was
 proven that flies' wings are too weak to get the bugs off the ground, was
 supposedly solved five years ago by Charles Ellington, a renowned Cambridge
 entomologist. But his theory was wrong, said insect flight expert James
 Birch, whose team in the department of integrative biology at University of
 California, Berkeley, found a better solution. It appears in the current
 issue of Nature.

 The team used data from the sensors on Robofly, a pair of fibreglass wings
 that flap in a tank of mineral oil to mimic how thick air feels to a fruit
 fly.

 The researchers demonstrated that a whirl of air like a "little tornado"
 sits on top of the wing. This whirl, called a vortex, creates a region of
 low pressure that sucks the fly upward.

 In theory, the vortex should quickly grow too strong for the wing and peel
 off, but it is held mysteriously stable on the wing, Dr. Birch said.

 As flies flap, their wings hit oncoming air at a high angle, 45 degrees
 compared with 10 degrees on most airplanes. The deflected air creates an
 upward force and a downwash of air.

 This downwash lowers the angle at which the next flap strikes oncoming air,
 diminishing the strength of the vortex and keeping it in place, Dr. Birch
 said. Without this stabilizing effect, Mr. Birch says, the vortex would fall
 away, the lift would be lost and the fly would plummet.

 The vortex is stabilized and the fly is kept aloft by this effect of the
 previous strokes, "the ghosts of vortices past," Dr. Birch said.

 Dr. Ellington's debunked theory had likened flies to such delta wing
 airplanes as the Concorde, which keep their vortex in place with air flowing
 along the wing.

 Robofly's 25-centimetre-long, fibreglass wings are powered by three motors
 that allowed Dr. Birch to accurately recreate the wing movements of a fruit
 fly.

 "We can create any kind of movement or kinematic pattern that you can think
 of," he said. "That's something that Charlie [Ellington] did not have, and
 really it's why we've been able to jump ahead."

 Dr. Birch is collaborating with engineers to make a "micro- mechanical
 flying insect" which could have applications for tiny flapping robots that
 could be used for search and rescue or espionage.

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