The next time you're at a music festival and see a giant rainbow trout swishing around in the sky, there's just a chance you might not be intoxicated. It might be scientists testing an airship that moves like a fish.
The materials scientists from Switzerland call it the Airfish.
The 8-metre-long helium-filled prototype glides through air as a fish swims through water – by swishing its body and tail from side to side. As well as moving more gracefully than a conventional blimp, the Airfish is also much quieter and cleaner because it doesn't require the fume-belching engines and noisy propellers normally used for mid-air manoeuvres. As such, TV broadcasters might favour it for capturing aerial footage of music and sports events, the team suggests.
Christa Jordi and colleagues from EMPA, the Swiss federal laboratories for materials testing and research in Dübendorf, replaced traditional airship propellers with long artificial muscles strapped on each side of the blimp. The muscles are made from an acrylic polymer with carbon electrodes deposited on either side: when a high voltage is applied across the electrodes, establishing a strong electric field across the polymer, the electrodes are attracted to each other – physically compressing the material and forcing the Airfish to flex.
Alternate the voltages applied to each polymer muscle and the contractions will make the airship sway like a fish. Put some more membranes either side of its hinged tail, and it can swish it back and forth.
"We needed to mimic a fish that's a versatile swimmer, not one that's a specialist in fast acceleration or high manoeuvrability," says Jordi. "So we chose the rainbow trout because it is a bit of a generalist."
The team programmed software to control the power to each muscle and mimic the rhythm of the trout's motion, and ran it on a computer slung alongside lithium-polymer batteries in the gondola beneath the airship.
In tests (see video above) they found that the motion of the body and tail combined made the airship move forward at half a metre per second, with roughly half the speed supplied by each mechanism.
"That's a slow walking speed," says Jordi. "And it's interesting because you might think that all its speed comes from the undulating body – but we showed that's not the case by running the body and tail alone and then together."
She thinks the design's quiet operation has potential for stadia and at gig arenas; other applications could include surveillance or animal observations. But first they need to improve their flying trout's muscles, which currently wear out after a couple of months. They plan to try a hardier polymer made of silicone with silver electrodes instead.
Dan Speers, president of Mobile Airships in Brantford, Ontario – a Canadian supplier of blimps used to carry adverts or cameras at outdoor music events – is impressed with the design. "It is a very elegant-looking airship, with a great aerodynamic shape," he says. "Using a system that does not require gasoline is always a plus, as it cuts down on air and noise pollution."
Practically, however, the design faces many problems. "In an arena or stadium-like setting, there are other confounding factors that need to be addressed – such as wind currents," Speers says.