The ion drive meets the drone, while a small plane is flying without moving parts

The MIT's Johnson inner lane probably will not go into the story in the same way as Kitty Hawk, but it was the scene of a first powered flight. A team of researchers managed to build the first aircraft powered by an ionic wind, a propulsion system requiring no moving parts. Although the flight took place with the help of a small drone, the researchers' calculations suggest that the efficiency of the design would simply double by building a bigger craft.

Ionic wind

In conventional aircraft, the air is pushed by moving parts, whether propellers or turbines in the reactors. But we have known for a long time that it is also possible to use electric fields to circulate the air.

The problem is that the air is mainly composed of uncharged molecules that do not respond to electric fields. But at sufficiently high voltages, it is possible to ionize the nitrogen and oxygen that make up our atmosphere, just as lightning does it all the time. The electrons that are released go faster, collide with other molecules, and also ionize some of them. If this happens in an electric field, all these ions will begin to move to the appropriate electrode. During the process, they will collide with neutral molecules and push them. The mass movement resulting from atmospheric molecules is called an ionic wind.

Calculations made several decades ago, however, suggested that it was not possible to generate a practical surge with an ionic wind. Given advances in batteries, electronics and materials, an MIT team decided the time may have come to revisit the issue.

To do this, you must make many compromises. For example, the lower the electric field strength of an ion wind drive, the more thrust you get for a given power. Of course, if you decrease the intensity of the field enough, nothing will ionize in the first place. Since the thrust per unit area is small, a larger thruster system makes sense – aside from the fact that it will increase drag and slow down the aircraft.

Nevertheless, after using different designs of thrusters, researchers have discovered that it should be possible to generate enough thrust to get something in the air: the limit of what is technologically possible with current materials and technology. Electronic power. "

Find a balance

The chosen design is based on a thin wire in which nitrogen and oxygen ionize. Behind, a thin bearing surface covered by the second electrode. This can both provide a little more lift and allow the generation of an electric field that accelerates the ionized molecules from the wire to the leaf.

But this design had to be integrated with the battery and electronics that makes it work, as well as at the wing and at the crate that have turned everything into an airplane. Some of these ingredients were not even available until the team was in charge of designing them.

"The weight constraints required the design and construction of a custom battery stack and a custom high-voltage power converter," the researchers write, "which increases the battery voltage to 40 kilovolts." To manipulate the body of the aircraft, they powered a computer algorithm with a list of their constraints and optimized them to allow a stable flight with a potential range limitation.

The resulting equipment consisted of a five-meter wing with a thin body containing the battery and electronic components suspended beneath it, before pulling into a tail. On either side of the body, a series of wire / airfoil ionizers was suspended at the wing (two rows back and forth, both in a four – to – one column). total of eight). Everything weighed just under 2.5 kg.

With a launching catapult based on bungee-ropes, the craft could fly about 10 meters when it's off. Launch the ionic wind, it could cover 60 meters and would often gain altitude if it were lit. The measurements showed that the thrusters collectively generated five newtons for each kilowatt of power, a result similar to that of jet engines. But because of many inefficiencies in the system, the overall efficiency was only about 2.5%, well below that of conventional aircraft.

Still, researchers have a huge list of potential improvements. The current design was limited by the decision to let him fly inside the MIT track. Allow larger wings and higher speed could achieve this efficiency up to 5% without modification of the underlying technology. They also plan to explore different ways to generate ions, designs of electrodes that reduce drag and / or are integrated into the wing, as well as better electronic power conversion systems, all of which could improve things.

Although the paper concludes with discussions of silent urban drones and environmental monitoring devices that could remain in the air indefinitely, it is possible that the technology will eventually become a curiosity. Nevertheless, since this has been made possible by developments having nothing to do with flying, it will be interesting to see what happens when people really focus on the development of this technology.

Nature, 2018. DOI: 10.1038 / s41586-018-0707-9 (About DOIs).