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Floppy Wings = Efficient Flight
17 September 2009 (All day)
Next time you're on an airplane, check out the wings. Every bolt and rivet is flush with the surface, creating an extremely smooth shape. The wings of the desert locust are not nearly as sleek: They're covered with ridges and veins, and they twist and deform as they flap. But these features make the insect an efficient flier, albeit at lower speeds, according to a new study.
Biologists and engineers have long known that insect wings are more complex than just flat, rigid flapping plates. But most models of insect flight have treated them this way because scientists needed to simplify their calculations and lacked a detailed picture of how the wings actually work.
To produce a better model, biomechanicist Adrian Thomas of the University of Oxford in the United Kingdom and colleagues came up with a new way to capture wing-shape changes during flight. The team set up four high-speed video cameras around a desert locust (Schistocerca gregaria) and recorded its flapping. Each camera followed more than 100 dots marked on the bug's wings during each stroke. The researchers then used data on how those points moved to create a three-dimensional computer model of the locust. Simulations with the virtual insect closely matched experimental data on real locust wing air flow and forces.
With a validated model, Thomas's team members started erasing wing details. In one simulation, they smoothed out the virtual wings' ridges and camber--the curve from the front of the wing to the back. In a second, they removed the wing's ability to twist as it flaps, effectively making it flat and rigid. These two models were less-efficient fliers than real locusts: The curved, twisting wings of real bugs were about 10% more efficient in producing lift than the camberless wings, and they were 50% more efficient than the flat, rigid model.
In the models of the nontwisting wings, the air flow separates from the wings into vortices that create drag. Locusts avoid these vortices by keeping the angle between the wing and air flow constant. Conserving power by minimizing drag is crucial for desert locusts that sometimes must fly 300 kilometers at a time--orders of magnitude farther than small, battery-powered helicopters can, Thomas says. Engineers trying to design tiny aircrafts "drool" at the insect's endurance, he says.
Previous research has focused more on the forces insect wings produce, says biologist Douglas Altshuler of the University of California, Riverside. "Considering how wing shape affects power cost of flight is really valuable and a good way to focus future research."