The first ever “solid state” plane, with no moving parts in its propulsion system, has successfully flown for a distance of 60 meters, proving that heavier-than-air flight is possible without jets or propellers.
The flight represents a breakthrough in “ionic wind” technology, which uses a powerful electric field to generate charged nitrogen ions, which are then expelled from the back of the aircraft, generating thrust.
Steven Barrett, an aeronautics professor at MIT and the lead author of the study published in the journal Nature, said the inspiration for the project came straight from the science fiction of his childhood. “I was a big fan of Star Trek, and at that point I thought that the future looked like it should be planes that fly silently, with no moving parts – and maybe have a blue glow. But certainly no propellers or turbines or anything like that. So I started looking into what physics might make flight with no moving parts possible, and came across a concept known as the ionic wind, with was first investigated in the 1920s.
“This didn’t make much progress in that time. It was looked at again in the 1950s, and researchers concluded that it couldn’t work for aeroplanes. But I started looking into this and went through a period of about five years, working with a series of graduate students to improve fundamental understanding of how you could produce ionic winds efficiently, and how that could be optimised.”
In the prototype plane, wires at the leading edge of the wing have 600 watts of electrical power pumped through them at 40,000 volts. This is enough to induce “electron cascades”, ultimately charging air molecules near the wire. Those charged molecules then flow along the electrical field towards a second wire at the back of the wing, bumping into neutral air molecules on the way, and imparting energy to them. Those neutral air molecules then stream out of the back of the plane, providing thrust.
The end result is a propulsion system that is entirely electrically powered, almost silent, and with a thrust-to-power ratio comparable to that achieved by conventional systems such as jet engines.
Prof Guy Gratton, an aerospace engineer and visiting professor at Cranfield University, said: “It’s clearly very early days: but the team at MIT have done something we never previously knew was possible in using accelerated ionised gas to propel an aircraft. Aeronautical engineers around the world are already trying hard to find ways to use electric propulsion, and this technology will offer something else that in the future may allow manned and unmanned aircraft to be more efficient, and non-polluting. In particular, the fact that they have already got this out of the laboratory, and flown a battery driven model aircraft – albeit so far on a very small and controlled scale – is very exciting.”
The successful flight of the plane – which has no name beyond the uninspiring “Version Two” – owes as much to the engineering prowess required to make it as thin and light as possible as it does to the propulsion method itself. The plane weighs just 2.45kg, but manages to fit in a five-metre wingspan, battery stack, and a high-voltage power converter.
In the immediate future, the MIT team hope to increase the range and speed of the plane, primarily by scaling up the size of the overall machine. Potential applications in the short term include unmanned drones, where silent flight may be beneficial, and high-altitude solar-powered flight, where the lack of moving parts could allow such a plane to soar for years on end, acting as a pseudo-satellite.
In the longer term, the ability to power flight purely through electricity opens up the possibility of carbon-neutral flight, which could lower the emissions of the aviation industry globally.
Barrett also noted that solid state propulsion tends to miniaturise well, and suggested that smaller drones than those currently possible with rotor-based flight could take-off using an ionic wind drive in the future. “Solid state things lend themselves to scaling down quite well,” he said, “creating extremely small flight vehicles that serve uses we can’t imagine.”