ENGINEERS often look to the natural world for inspiration–and flight engineers, doubly so.
Mankind’s desire to soar like the birds directly inspired the Wright brothers’ solution to the problem of controlling a heavier-than-air flying machine, by suggesting the way to do so was to warp the shape of the craft’s wings.
More recently, designers of ornithopters (tiny, robotic flying machines lifted by flapping wings) have looked to insects for inspiration, and built systems of sensory feedback that can keep aloft designs which are essentially unstable.
It would be better, though, if those designs were not unstable in the first place, so that any on-board electronics (all of which contribute to a craft’s weight) could concentrate on the more useful task of piloting the thing to its destination, rather than merely keeping it in the air. And that, by looking at a rather different natural model, is what Leif Ristroph and Stephen Childress of New York University think they have done.
Their ornithopter, described in the J ournal of the Royal Society Interface, resembles not an insect, but a jellyfish. As Dr Ristroph and Dr Childress note in their paper, this is not the first time flight engineers have used an aquatic rather than an aerial model, for only waterborne creatures (squid, for example) use jet propulsion. T
heir device, rather than having a continuous bell as a real jellyfish does, relies on four leaf-shaped wings. But that is mainly to simplify the construction, for it means the wings can be rigid (they are made of Mylar films, stretched on tough carbon-fibre frames).
Each wing is 8cm long. The pointed ends of the leaves meet at the apex of what is basically a cone-shaped device, and the wings are held in place relative to one another by a flexible carbon-fibre ring that connects them. Opposite wings, pulled via carbon-fibre threads by a small electric motor, beat simultaneously and out of phase with the other pair of wings to provide lift.
Crucially, when perturbed from outside, this design does not crash to the floor. It needs no fancy controls to stop it tipping over. At the moment, for simplicity, it is powered through a wire that tethers it down. But it would be easy to fit it with a small battery and let it go.
Dr Ristroph and Dr Childress, then, seem to have solved an important problem in ornithopter design. And in doing so they have also shown that evolution, though clever, is not always as clever as human engineers–for as far as is known nature has neither now, nor at any time in the past, come up with the equivalent of aerial jellyfish.
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