This fall,
several biologist colleagues of mine plan to build a
movie theater for houseflies. In fact, it's a miniature
IMAX theater—complete with a panoramic screen—inside
of which they'll place a tiny rotating cage, a downsized
version of the ones that astronauts use to simulate
tumbling in space. Some time next year, they'll strap a
fly into the cage and show it a movie.
A leisurely pastime for idle academics? Hardly. The
common housefly is an extremely maneuverable flyer, the
best of any species, insect or otherwise. What's more,
its flight control commands originate from only a few
hundred neurons in its brain, far less computational
might than you'd find in your toaster.
IMAGE: EYE OF SCIENCE/PHOTO RESEARCHERS INC.
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My colleagues in England—Holger Krapp and Simon
Laughlin at the University of Cambridge and Graham
Taylor and Richard Bomphrey at the University of
Oxford—and I want to know its secret. The fly-size
flight simulator will reproduce the inertial effects of
flight. The movie depicts panoramic scenes during
flight. By inserting electrodes into the fly's brain,
the biologists will be able to observe how its neurons
light up in response to these scenes. In a sense, we'll
see what the fly sees.
Our goal is to understand flight control from the
insect's perspective. What we have learned so far, and
what we expect the experiment to confirm, is that the
fly uses a flight control paradigm that is completely
different from that of a fighter jet. Whereas the F-35
Joint Strike Fighter, the most advanced fighter plane in
the world, takes a few measurements—airspeed, rate of
climb, rotations, and so on—and then plugs them into
complex equations, which it must solve in real time, the
fly relies on many measurements from a variety of
sensors but does relatively little computation.
And yet the fly can outmaneuver any human-built craft
at low speeds. Buzzing annoyingly across a room, a
housefly reaches speeds of up to 10 kilometers per hour
at twice the acceleration of gravity. When turning, it
is even more impressive: the fly can execute six full
turns per second, reaching its top angular speed in just
two-hundredths of a second. It can fly straight up,
down, or backward, and somersault to land upside down on
a ceiling. If it hits a window or a wall sideways, which
it often does, the fly will lose lift and begin to fall.
But its wings keep beating, and within a few
microseconds, the fly recovers its lift and can move off
in the opposite direction.
Discovering the fly's flight control scheme, I
believe, will have important lessons for the design of
micro air vehicles (MAVs), which attempt to approximate
insect flight, and for high-performance aircraft in
general.
Insect flight has been a
subject of academic interest for at least
half a century, but serious attempts to emulate it are
more recent. The field got a big boost in 1996, when the
U.S. Defense Advanced Research Projects Agency (DARPA),
in Arlington, Va., launched a three-year MAV program
with the goal of creating a flyer less than 15
centimeters long for military surveillance and
reconnaissance. A few fixed-wing designs were
successfully demonstrated, most notably the Black Widow,
from AeroVironment Inc., in Monrovia, Calif. The Black
Widow had a propeller, GPS navigation, and decent flight
control. Several rotary-type MAVs were also put forward.
But no one managed to get an insectlike flapping-wing
design off the ground.
Inspired by the DARPA program, I started my research
on MAVs in 1998 at Cranfield University, at the Royal
Military College of Science, in Shrivenham, England. My
main goal was to build a reconnaissance robot capable of
discreetly penetrating and maneuvering autonomously
within confined spaces, including buildings, stairwells,
and tunnels.
The military uses of such a vehicle are manifold. A
soldier mired in combat could take a few MAVs from his
backpack and throw them into the air to scout the
interiors of nearby buildings. Equipped with video
cameras, the tiny flyers could surreptitiously locate
hidden adversaries, downed comrades, or scared
civilians. MAVs could find equal application in bomb
detection and bomb deployment—the U.S. Air Force, for
one, is interested in using MAVs for precisely
delivering tiny bombs, to take out, say, a single
computer.