Jelly flight Scientists have built the first ever flying machine that is capable of stable hovering simply by flapping its wings, using a movement similar to that of a swimming jellyfish.
Planes work pretty well to transport humans large distances across the planet, says lead author Dr Leif Ristroph, an applied mathematician from New York University.
But scientists are still trying to find the best design for small-scale autonomous flying machines that can manoeuvre around small crowded spaces.
Such machines are in demand for surveillance, monitoring and search and rescue.
"Any time you want a pair of eyes where it's not practical to have a human go, you could possibly use one of these flyers," says Ristroph.
One approach has been to build flying machines with wings that flap like an insect.
But, says Ristroph, insects require their brain to keep them upright during flight, and so such ornithopters require an onboard computer to do the same.
Ristroph wanted to design a flying machine that used flapping wings but would stay upright without requiring an onboard computer.
The design he came up with involves four distinct wings that are hinged at the top.
A motor at the top opens and closes the wings together at a rate of 20 times a second.
"The basic thing you want to do when you are flying is generate lift upwards," says Ristroph.
"If you open and close an umbrella in principle that will squirt air downwards and that will generate an upwards force."
"Our design is basically something similar," says Ristroph, who carried out the research with colleague Dr Stephen Childress.
Ristroph didn't realise until after that he had made something that moved like a jellyfish.
Of course a jellyfish doesn't have to generate lift to stay in one place like a flying machine does, but it does move upwards by expanding its bell to draw water in and then contracting to squirt it out.
Ristroph and Childress also found that having flexible rather than rigid wings improved the lift.
Most importantly, the researchers found that when the flying machine was tilted, it quickly became upright again.
"It's got an intrinsic stability," says Ristroph. "It's a property that insect-like motion doesn't have."
Ristroph says he and Childress still don't understand why their creation is self stable.
"The centre of gravity location is very important but we're still in search of a good aerodynamic and mathematical model to explain this stability," says Ristroph.