Fly like a Fly

The common housefly executes exquisitely precise and complex aerobatics with less computational might than an electric toaster

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.
By: Rafal Zbikowski, IEEE’s Spectrum Issue Nov 2005

The fly brain receives sensory inputs from about 80 000 sites on its body, so about 98 percent of the neurons are specialized, devoted to sensory processing. The remaining 2 percent take care of higher-level functions, such as flight control, recognizing predators, and the like. Of course, the fly has many tasks other than flying, so quite a few of its sensors aren’t related to flight, such as those for taste, smell, sound, temperature, and humidity.

The fly’s compound eyes are the key to its agile flight control. Each compound eye is composed of up to 6000 miniature hexagonal eyes, or ommatidia. Each ommatidium compares what it sees to what its closest neighbors see to determine the direction of the local velocity vector.
Studies suggest that the fly’s flight control commands originate from a few hundred neurons in its brain (out of the brain’s total of about 338 000 neurons). A neuron can be thought of as the brain’s smallest computational unit, each one like a switching transistor, with its binary on-off states. Obviously, then, flies are not executing millions of calculations to solve forbidding differential equations in midair. But they still must obey the same laws of physics as the F-35, so whatever they are doing must be functionally equivalent to solving those equations in real time.
Because of its panoramic vision, the fly sees in a sphere all around it. So to depict how the fly sees motion, you can map the local velocity vectors onto this sphere. The sphere at the far left shows what the fly sees when moving upward. The sphere at the left shows what the fly sees when it’s rolling. Flattening the spheres reveals that small sections of the global vector pattern can be identical [shaded gray], even when the fly’s motion is completely different.

The fly has a number of directions along which it prefers to fly [red arrows show examples of preferred rotation directions]. When it detects the global vector patterns representing these directions, its neurons sense the patterns more strongly. If the insect is not flying in a preferred direction, its response is more muted.
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.
Read the full article at IEEE’s SPECTRUM Online
or
visit IEEE’s SPECTRUM home page