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It’s a Bird, It’s a Plane, It’s a … Spy?
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Science 23 March 2012: Vol. 335 no. 6075 p. 1433 DOI: 10.1126/science.335.6075.1433 NEWS FOCUS It’s a Bird, It’s a Plane, It’s a … Spy? If a hummingbird follows you into a building, one of two things is going on: Either your perfume is too strong, or the world’s smallest spy plane is on your tail. In 2011, AeroVironment, a company founded by Paul MacCready, the inventor of the fi rst human-powered aircraft to cross the English Channel, unveiled a new crewless aircraft called the Nano Hummingbird. With a wingspan of 17 centimeters and a weight of 19 grams, the robot is hefty for a hummingbird. But it can hover in place and fl y in any direction (including backward) as fast as 18 kilometers per hour. It can fl y through doorways and can be steered by a remote pilot using only video from an onboard camera. All of these abilities met or exceeded the targets for a secondgeneration “nano air vehicle” funded by the U.S. Defense Advanced Research Projects Agency. Very small ornithopters like the Nano Hummingbird face different challenges from their larger kin. As a fl yer (animal or robot) gets smaller, fl ying becomes more and more like swimming. Less energy goes to lift and more to thrust. Instead of sculpted airfoils, the wings can and should be simple, rapidly beating membranes. For robots, miniaturization of components and power sources may impose the biggest constraint. A real hummingbird can fl y across the Gulf of Mexico without stopping; the Nano Hummingbird can go for only 11 minutes. The main role envisioned for nano air vehicles is military surveillance and reconnaissance. But they could also be used for civilian applications such as search and rescue or environmental monitoring (for example, inside crippled nuclear reactors). Miniature devices have taken off in the past decade. In 2002, the dragonfl y-like Mentor, developed at the University of Toronto and SRI International, demonstrated hovering fl ight. In 2006, the (also dragonfl y-like) DelFly, developed at Delft University of Technology in the Netherlands, added a camera and forward fl ight; later versions have shrunk to 3 grams and a 10-centimeter wingspan. Nano fl yers aren’t yet fi t for duty, however. “The Hummingbird is way cool. I can’t say enough good things about it,” says Ephrahim Garcia, an engineer at Cornell University. “But it has a limited endurance.” Eleven minutes is not much time to scan a building for insurgents or earthquake survivors. Even so, Garcia adds, “Everything doesn’t have to be practical. We can learn a lot about fl ow-structure interaction from these devices.” –D.M.  [ Last edited by tt.yao on 2012-3-23 at 21:46 ] |
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2012-03-23 21:41:12, 143.5 K
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