A BIRD-LIKE, shape-shifting robot built to mimic the way the common swift alters its wing geometry during flight could slip in unnoticed among a flock of real birds.
Equipped with twin cameras that beam back three-dimensional video, it could allow people to fly virtually with real birds and gain a first glimpse of how the swift flies in its natural environment. 鈥淭hey are really agile and to study them you have really got to fly close to them 鈥� and look like them,鈥� says David Lentink of Wageningen University in the Netherlands. 鈥淪ome birds will attack any model aircraft that comes close,鈥� he adds.
In April, Lentink and his colleagues at Wageningen University and the Technical University of Delft, also in the Netherlands, analysed the swift鈥檚 (Nature, vol 446, p 1082). They observed swifts flying in wind tunnels and used high-speed video to work out how far the birds sweep back their wings at different airspeeds. This action allows the bird to ride wind currents and thermals efficiently and spend almost its entire life on the wing, only landing to breed. The researchers also measured how sweeping back one wing more than the other enables swifts to make their characteristic sharp turns.
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Now Lentink鈥檚 team is using these findings to create a robotic aircraft that looks and flies just like a swift. The propeller-driven RoboSwift, which is at an advanced design stage, has a 50-centimetre wingspan and weighs just 80 grams. It is scheduled to fly in public for the first time in March 2008 at MAV08, a micro air vehicle flight competition in Agra, India.
The US Defense Advanced Research Projects Agency (DARPA) is also involved in designing military aircraft with shape-shifting wings, but it is using expensive 鈥渟hape memory鈥� materials to allow a variety of wing shapes, so that a plane could both 鈥渓oiter鈥� for reconnaissance and 鈥渄ash鈥� to intercept a target (New 杏吧原创, 13 December 2003, p 28). The RoboSwift does not require this range of shapes and so can be made of cheaper carbon-fibre composite.
The last two-thirds of RoboSwift鈥檚 outer wing is divided into four long 鈥渇eathers鈥�, each of which is individually hinged but connected to the others. A lithium polymer battery drives a motor that controls each wing ensemble independently, allowing each one to sweep back anywhere between 5 and 50 degrees, depending on the airspeed.
Once flying in formation with real swifts, two cameras on each of RoboSwift鈥檚 wings will beam back 3D video to a virtual-reality headset. Anders Hedenstr枚m, a zoologist at Lund University in Sweden, is looking forward to this. 鈥淲e hope the stereo cameras will give us a close look at the swift鈥檚 wing dynamics. They may behave differently in the open air, outside the confines of the wind tunnel,鈥� he says.
