Fruit Flies Highlight Aerodynamics of Insect Flight

John Roach
for National Geographic News
April 23, 2003

To swat a fly can be a lesson in futility. The insect darts from each swipe with uncanny precision, altering its course to zip off in nearly the opposite direction.

Precisely how a fly achieves its aerial acrobatics is more than a curiosity of annoyance for Michael Dickinson, a bioengineer at the California Institute of Technology in Pasadena. Dickinson has built an entire research lab, not to mention professional career, seeking an answer to just how a fly's brain controls its muscles in precision flight.

"An interest in the brain led to an interest in flight and aerodynamics," said Dickinson. "I've spent a lot of time with folks in the lab trying to figure out the basic aerodynamics of insect flight."

Together with Steven Fry, a biologist at the University of Zurich in Switzerland, and Rosalyn Sayaman, a research assistant also at the California Institute of Technology, Dickinson determined how common fruit flies use their wings to make 90-degree turns at speeds faster than a blink of the human eye, let alone the swoosh of a swatter.

The researchers discovered that the mechanics of how flies execute such turns were contrary to what they initially believed.

To turn, a flying creature must generate enough twisting force, or torque, to offset two forces working against it—the inertia of its own body (think forward motion on a bicycle, once you stop pedaling) and the viscous friction of the air, which for small insects is thought to be like syrup.

Scientists had long assumed that the viscosity of the air, and not inertia, was the greater force for insects such as flies to overcome. Inertia, they believed, was primarily the bane of larger animals like birds.

"No one challenged the notion because there was no indication that it might be different," said Fry. "The results actually proved the opposite."

The research team found that fruit flies make subtle changes in the tilt of their wings relative to the ground and the size of each wing flap to generate the forces that allow them to turn. Flies then create an opposite twisting force with their wings to stop the inertia of the turn, preventing an out of control spin.

This finding, say the researchers, indicates that inertia, and not friction, is the greater force for the fruit fly to overcome in the turn.

Ron Fearing, an electrical engineer at the University of California at Berkeley who is developing a tiny robotic insect capable of autonomous flight, said that the research team has "shown a quite surprising result, in that very subtle changes in wing motion are responsible for rapid maneuvers."

The Fly Tests

Continued on Next Page >>





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