Butterflies are not merely beautiful. They use a complex pattern of rapid wing flapping and body deformation to execute impressive aerial acrobatics. This ability has not escaped the U.S. military, which is turning to these insects for ideas on how to create ever-smaller drone aircraft to execute reconnaissance, search-and-rescue and environmental monitoring missions. [View a slide show featuring different drones used by the U.S. military.]

The Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio is testing drones less than 60 centimeters long—roughly the wingspan of an Atlantic Puffin—with the hope they will be able to operate below rooftop levels in city streets.

Researchers at Johns Hopkins University in Baltimore, with help from the Air Force Office of Scientific Research and National Science Foundation funding, are now working on ways to shrink drones down to only a few centimeters. Using high-speed, high-resolution video techniques they have mathematically documented the trajectory and body conformation of painted lady butterflies.

The researchers captured the flight dynamics of the butterflies, which flap their wings about 25 times per second, using three high-speed video cameras. Each camera can record 3,000 one-megapixel images per second, compared with a standard video camera that shoots 24, 30 or 60 frames per second. Lead researcher Tiras Lin and his colleagues positioned the three cameras in a glass tank, released several butterflies and then snapped about 6,000 3-D images of the insects' flight maneuvers.

"We learned that changes in moment of inertia, which is a property associated with mass distribution, plays an important role in insect flight, just as arm and leg motion does for ice skaters and divers," Lin said in a press release. For his next project, Lin is setting his sights even smaller—on better understanding how fruit flies are land upside down on perches, which could suggest ways of improving the maneuverability of micro aerial vehicles, or MAVs.

The Defense Department is also funding mini drone work out in the field. In particular, AeroVironment, Inc. is developing hummingbird-like robots that weigh less than 20 grams. These Nano Air Vehicles (NAVs), as the company calls them, are 16 centimeters long, capable of climbing and descending vertically, flying sideways left and right, and flying forward and backward. They can also rotate clockwise and counter-clockwise under remote control while carrying a small video camera. Lockheed Martin, Charles Stark Draper Laboratory, Inc., and MicroPropulsion Corp. likewise have Defense Department contracts to develop NAVs.

Image courtesy of Will Kirk/Johns Hopkins University