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.
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.