Inspired by bats and birds, the wings of a new type of unmanned Micro Air Vehicle can respond to air currents and change shape during flight

It flies like a bird, it was inspired by a bat and it could in every sense take off: a new British unmanned Micro Air Vehicle (MAV) can skim over the waves, splash down and take off and change wingshape in responses to the forces it encounters.

Drones have been used by the military for years. But scientists based at Imperial College and Southampton University have pioneered a new approach. They are testing a new MAV with better aerodynamic properties, which can fly long distances and will be more economical to run.

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The unique wing design has built-in electroactive polymers that make the wings stiffen and relax in response to an applied voltage to make performance even better. It means that, like a gannet, a kestrel or a horseshoe bat, it can flex and change shape during flight.

The new science of biomimetics has already produced a range of materials and technologies imitated from nature. This is a fruitful approach for flight, said David Hambling, author of a new book, Swarm Troopers: How Small Drones will Conquer the World.

“There are no biological forebears for an airliner with a sixty-metre wingspan that flies at 500 miles an hour, but a drone with a one-metre wingspan that flies at 30 miles an hour is in exactly the same flying regime as many birds,” he said.

Flapping wing drones or ornithopters may have the edge over aircraft-like designs, and there are drone projects that mimic the way birds find and ride thermals to gain height. Other researchers have developed drones that can perch on branches or wires with the feet based on the talons of a hawk.

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But the same biomimetic approach means a drone could be mistaken for a bird, even by other birds: US military Raven drones were reportedly knocked out of the sky by hawks. In any case, rather than biomimicry, Rafael Palacios of Imperial College’s department of aeronautics and one of the researchers behind the new bat-winged MAV, prefers the word bioinspiration.

“What we find is that bat wings (and this applies to all bats) have three key characteristics,” he said. These are flapping motions for propulsion as in birds; membrane structures, as in sails, which naturally change shape in the wind; and pretensioning through an integrated skeleton, and this last was the one that delivered all the amazing detail.

“We focused on this last one and looked for an engineering solution that would offer the same behaviour – but without trying to replicate a wing skeleton with mechanical parts, which would be a non-starter.”

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To do all this, the scientists started with a mathematical model, and built their bat software simulation from scratch. “We had to make sure it could model not only the wings themselves but also the aerodynamic flows around them and the effect of the electric field generated across them,” Palacios said.

He and his research colleague Bharath Ganapathisubramani, of the University of Southampton’s aerodynamics and flight mechanics department, tested a half-metre prototype first in a wind tunnel and then over the water. So far, there have been only tests, but the new batwing designs could be flying in the real world in as little as five years.

“We’ve successfully demonstrated the fundamental feasibility of MAVs incorporating wings that respond to their environment, just like those of the bats that have fuelled our thinking,” Ganapathisubramani said.

“We’ve also shown in laboratory trials that active wings can dramatically alter the performance. The combined computational and experimental approach that characterised the project is unique in the field of bio-inspired MAV design.”