Silent flight

The MIT concept of wires strung beneath the leading and trailing edges of the wing.
MIT Electric Aircraft Initiative

ENGINEERS AT the Massachusetts Institute of Technology (MIT) have recently tested a scale model of an aircraft that has no moving parts in the propulsion system.

Instead of the thrust generated by propellers or turbines for forward movement, the lightweight 5lb (2.2kg) glider with a 16ft (5m) wingspan uses what MIT engineers call “ionic wind” – a silent flow of energy produced aboard the aircraft itself that creates the thrust to propel the aircraft forward. No fuel is required and no noise is generated.

Steven Barrett, an associate professor of aeronautics and astronautics at MIT, began looking for ways to design a propulsion system with no moving parts back in 2010. He eventually settled on the concept of electroaerodynamic thrust, a physical principle that describes the energy produced when a current is passed between thin and thick electrodes. If enough voltage is applied, the air in between the electrodes can produce thrust.

According to the MIT, electroaerodynamic thrust was for years “a hobbyist’s project, and designs have for the most part been limited to small, desktop ‘lifters’ tethered to large voltage supplies that create just enough wind for a small craft to hover briefly in the air. It was largely assumed that it would be impossible to produce enough ionic wind to propel a larger aircraft over a sustained flight.”

However, through years of calculations Barratt believed there might be a way to make it work. The resulting design of what MIT calls an ‘ion plane’ involves thin wires strung beneath the leading edge of the wing that act as positively charged electrodes, while similarly arranged thicker wires along the trailing edge serve as negative electrodes.

An MIT statement explained lithium-polymer batteries, supplying 40,000v of electricity via a lightweight power converter, positively charge the wires on the leading and trailing edges. Once the wires are energised, they attract and strip away negatively charged electrons from the surrounding air molecules, like a giant magnet attracting iron filings.

The air molecules left behind are ionised and attracted to the negatively charged electrodes on the trailing edge. As the ions flow towards the negatively charged wires, each ion collides millions of times with other air molecules, creating energy and the thrust that propels the aircraft forward.

Ten test flights were conducted using the glider in MIT’s duPont Athletic Center, the largest indoor space the researchers could find. The scientists flew the glider for 198ft (60m) on its longest flight and, MIT said, “found the plane produced enough ionic thrust to sustain flight the entire time”.

Barrett said the type of propulsion MIT has researched could be put into unmanned systems initially, although any potential use of the technology in conjunction with conventional engines in a hybrid aircraft is much more distant.

He acknowledged: “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.”

However, he insisted: “This has potentially opened new and unexplored possibilities for aircraft which are quieter, mechanically simpler and do not emit combustion emissions.” An editorial in the scientific journal Nature, which published the results of Barrett’s study, noted scientists believed electroaerodynamic thrust was never going to be efficient enough to be useful.

However, it said: “Not only do the MIT researchers demonstrate the first flight of an aeroplane propelled in this way, but they also show that the efficiency will increase as the velocity of the aircraft increases, because the electrodes that act as the engine create such little aerodynamic drag.”

MIT said Barrett and his fellow researchers are working on producing more ionic wind with lower voltage and increasing thrust generated per unit area. Currently, flying the glider requires a large area of electrodes and MIT said Barrett would like to design an aircraft with no visible propulsion system or separate control surfaces such as rudders and elevators.