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An Airplane With No Moving Parts

MIT researchers have used ion drive—until now a purely space-based system—to fly a model plane a short distance indoors

2 min read
Gif clip from video of the plane taking off.
Gif: Steven Barrett

MIT researchers have flown the first airplane that has no moving parts. The aircraft, packed with lithium-ion batteries, used an ion thruster to fly the 60 meters that were available in the indoor flight area.

“This was the simplest possible plane we could design that could prove the concept that an ion plane could fly,” said Steven Barrett, associate professor of aeronautics and astronautics at MIT. “It's still some way away from an aircraft that could perform a useful mission. It needs to be more efficient, fly for longer, and fly outside.”

The plane weighs a little over 2 kilograms (5 pounds), and its engine has a thrust-to-weight ratio roughly comparable to that of a jet engine. Its lithium-ion batteries put out about 500 watts.

Ion drive was first demonstrated 101 years ago by famed rocketeer Robert Goddard, and it’s now routinely used in space, for instance to reposition satellites. Space applications are natural because of the great thrust that can be generated while using a very small amount of propellant, always in short supply up in orbit. 

“For every kilogram [of propellant] you take up in space you have to have more propellant in the launch vehicle,” Barrett said, in a press conference run by the journal Nature, which today published the study. “So you use the propellant as efficiently as you can, throwing it behind you as fast as you can. In our application it’s sort of the opposite: You want a large volume of air, and the ion wind is a good way of achieving that objective.”

The researchers produce that wind by running 40,000 volts through a number of thin electrodes at the front of the plane’s 5-meter wingspan. That strips electrons off nitrogen molecules in the air, leaving behind positively charged ions. The ions then shoot toward a second electrode at the back; on the way, they collide with millions of air molecules, pushing them along as well—hence the large volume of air.

There’s a lot of electrodes sticking out, and one of the group’s next goals is to hide them away in the wing. While they’re at it, the researchers may want to lay on photovoltaic cells, which could recharge the batteries for use in high-flying applications where the plane functions like a relay station or a surveillance post. Such “pseudosatellites,” which would fly for extended periods on automatic pilot, could benefit from the great potential reliability of a system with no moving parts.

One more possibility cannot have escaped the notice of the military: Ion thrusters make no noise and are therefore stealthy, at least to the human ear. 

Don’t look for them in people-moving aircraft anytime soon. Barrett speaks of “a low number of decades, not in five years or anything like that.” 

People living near airports can hardly wait for the silence.

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We Need More Than Just Electric Vehicles

To decarbonize road transport we need to complement EVs with bikes, rail, city planning, and alternative energy

11 min read
A worker works on the frame of a car on an assembly line.

China has more EVs than any other country—but it also gets most of its electricity from coal.

VCG/Getty Images
Green

EVs have finally come of age. The total cost of purchasing and driving one—the cost of ownership—has fallen nearly to parity with a typical gasoline-fueled car. Scientists and engineers have extended the range of EVs by cramming ever more energy into their batteries, and vehicle-charging networks have expanded in many countries. In the United States, for example, there are more than 49,000 public charging stations, and it is now possible to drive an EV from New York to California using public charging networks.

With all this, consumers and policymakers alike are hopeful that society will soon greatly reduce its carbon emissions by replacing today’s cars with electric vehicles. Indeed, adopting electric vehicles will go a long way in helping to improve environmental outcomes. But EVs come with important weaknesses, and so people shouldn’t count on them alone to do the job, even for the transportation sector.

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