IT ONLY flew for 12 seconds – the same as the Wright brothers achieved with their maiden flight – but it marks another aeronautical milestone.
After nine years’ work, Steven Barrett at the Massachusetts Institute of Technology and his colleagues have flown a first-of-its-kind zero-emissions plane with no moving parts. The small, unpiloted plane flew for 55 metres in an indoor sports hall, steered by remote control.
Instead of propellers or jet engines, the plane uses electrodes on its wings to produce ions that push against the surrounding air. The team claims the plane is quieter and cleaner than any other powered aircraft.
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“It really wasn’t clear that it would work,” says Barrett. “Quite a few colleagues said it had less than 1 per cent chance.”
“It weighs just 2.45kg and produces more thrust per unit of power than a standard jet engine”
The idea of producing aircraft thrust via an electric field, known as electroaerodynamics, was first explored in the 1960s. Electrodes are used to create an electric discharge that produces electrically charged atoms or molecules in the air. An electric field then accelerates these ions towards the back of the plane. Collisions with air molecules produce a thrust force in the opposite direction, pushing the plane forwards.
But nobody could make this “ionic wind” work for a plane. “The physics of thrust had not been fully worked out,” says Barrett.
So the team used a computer to generate a design that hit the perfect balance between weight and power for flight. The resulting aircraft has a wingspan of 5 metres, weighs just 2.45 kilograms and produces more thrust per unit of power than a standard jet engine.
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There is a long way to go before such a plane could do anything useful, however. A bigger plane would need a larger power supply, making it too heavy to fly. The team optimised their design for lightness not speed: it only flies at 5 metres a second compared with 200 metres a second or more for most passenger jets (Nature, ).
With air travel continuing to increase, many people hope that electric planes will one day provide a better alternative to jet fuel (see “Clean green aviation”). Norway has been testing electric, two-seater planes and wants all short-haul flights leaving its airports to be electric by 2040.
In theory, electric aircraft have a lower carbon footprint than conventional planes. They also produce no air pollution during a flight. But the batteries needed to power them are so heavy that larger planes are currently unviable.
Electric planes won’t replace existing passenger jets without a battery breakthrough, says Lynnette Dray at University College London. She estimates it will be at least 30 years before batteries can get even a small passenger jet, such as a Boeing 737, into the air.
What’s more, switching to electric planes without tackling where their power comes from won’t cut emissions overall. Most electricity still comes from burning fossil fuels. “If all planes were electric today and powered from the US grid, their footprint would be worse,” says Barrett.
With their greater efficiency, electroaerodynamic planes could give electric flight the boost it needs. The team’s design pushes the limits of what is possible with today’s materials and electronic technology. But Barrett thinks that it could be made to fly faster and for longer in the future.
The prototype only produces thrust around its wings. Barrett wants to make every surface, including the aircraft’s body, propulsive. He thinks future planes might have two sets of wings – one in front of the other – with a flow of ions between them. You could also steer the plane by changing the shape of its electromagnetic field, he says.
The result would be a plane that was carried along inside a pocket of electrically charged wind. “The whole aircraft would move through the air in a slipstream,” he says.
Clean green aviation
Passenger planes that fly using electroaerodynamics are many years away. Here are three alternatives for greener flight.
Biofuel: Aircraft powered by jet fuel partly produced from biomass have lower carbon emissions. A few airports, including Los Angeles International, are already refuelling some planes with biofuel. However, growing enough biomass to power the world’s aircraft could cause environmental problems of its own.
Electric planes: Small electric planes are being developed for short flights. But it could be decades before batteries are both light and powerful enough to power larger aircraft.
Hybrid planes: Like hybrid cars, hybrid planes could use a mixture of fuel and electricity to make them greener. Airbus, Rolls-Royce and Siemens are collaborating on a hybrid plane that could use batteries during take-off, when fuel consumption is greatest.
This article appeared in print under the headline “Zero-emissions plane has lift-off”
