Posted in | Green Aviation

Researchers Use Ionic Wind to Power First-Ever Plane Without Any Moving Parts

From the time the first airplane took flight more than a century ago, nearly all aircraft in the sky have flown with the help of moving parts such as turbine blades, propellers, and fans, powered by fossil fuel combustion or by battery packs that produce a persistent, whining buzz.

A new MIT plane is propelled via ionic wind. Batteries in the fuselage (tan compartment in the front of the plane) supply voltage to electrodes (blue/white horizontal lines) strung along the length of the plane, generating a wind of ions that propels the plane forward. (Image credit: Christine Y. He)

Currently, engineers at MIT have developed and flown, for the first time, a plane with no moving parts. In the place of turbines or propellers, an “ionic wind” powers the light aircraft—a silent yet powerful flow of ions generated aboard the plane, and that produced adequate force to propel the plane over a steady, persistent flight.

In contrast to turbine-powered planes, the aircraft is not dependent on fossil fuels to fly. Moreover, the new design is totally silent, contrary to propeller-driven drones.

This is the first-ever sustained flight of a plane with no moving parts in the propulsion system. This has potentially opened new and unexplored possibilities for aircraft which are quieter, mechanically simpler, and do not emit combustion emissions.

Steven Barrett, Associate Professor of Aeronautics and Astronautics, MIT.

He anticipates that in the near future, ion wind propulsion systems such as this could be used to fly less noisy drones. In addition, he visualizes ion propulsion coupled with more traditional combustion systems to develop hybrid, more fuel-efficient passenger planes and other large aircraft.

Barrett and his colleagues at MIT have reported the outcomes in the journal Nature on November 21st, 2018.

Hobby crafts

According to Barrett, the inspiration for the team’s ion plane has arisen partly from the movie and television series Star Trek, which he watched enthusiastically as a kid. He was specifically attracted by the futuristic shuttlecrafts that smoothly skimmed through the air, with apparently no moving parts and barely any noise or exhaust.

This made me think, in the long-term future, planes shouldn’t have propellers and turbines. They should be more like the shuttles in ‘Star Trek,’ that have just a blue glow and silently glide.

Steven Barrett, Associate Professor of Aeronautics and Astronautics, MIT.

Nearly nine years earlier, Barrett began his hunt for techniques to design a propulsion system for planes that had no moving parts. He finally chanced upon “ionic wind,” also called electroaerodynamic thrust—a physical principle that was first discovered in the 1920s and depicts a wind, or thrust, that can be generated by passing a current between a thick and a thin electrode. Upon applying sufficient voltage, the air in between the electrodes can generate a force that would be adequate to propel a small aircraft.

For many years, electroaerodynamic thrust has generally been a hobbyist’s project, and designs have mostly been restricted to small, desktop “lifters” fastened to large voltage supplies that produce wind that is just enough for a small craft to fly briefly in the air. To a large extent, it was supposed that it would not be feasible to generate adequate ionic wind to propel a larger aircraft over a persistent flight.

It was a sleepless night in a hotel when I was jet-lagged, and I was thinking about this and started searching for ways it could be done,” Barrett recalled. “I did some back-of-the-envelope calculations and found that, yes, it might become a viable propulsion system,” he stated. “And it turned out it needed many years of work to get from that to a first test flight.”

Ions take flight

The final design developed by the researchers looks like a large, lightweight glider. The aircraft, weighing around 5 pounds and with a wingspan of 5 m, carries an array of thin wires, which are linked like horizontal fencing along and beneath the front end of the wing of the plane. The wires serve as positively charged electrodes, while thicker wires arranged in a similar way and running along the back end of the plane’s wing act as negative electrodes.

A stack of lithium-polymer batteries is provided in the fuselage of the plane. Barrett’s ion plane team included members of Professor David Perreault’s Power Electronics Research Group in the Research Laboratory of Electronics, who developed a power supply with the ability to convert the output of the batteries into a high enough voltage to propel the plane. In this way, the batteries supply an electricity of 40,000 V to positively charge the wires through a lightweight power converter.

As soon as the wires are energized, they attract and take away negatively charged electrons from the surrounding air molecules, similar to a giant magnet that attracts iron filings. The residual air molecules are newly ionized and are in turn attracted to the negatively charged electrodes at the back of the plane.

When the newly formed ion cloud flows toward the negatively charged wires, every ion collides with other air molecules millions of times, producing a force that propels the aircraft forward.

The group, which also included Lincoln Laboratory staff Thomas Sebastian and Mark Woolston, flew the plane as part of a number of test flights across the gymnasium in MIT’s duPont Athletic Center—the largest indoor space they could have to carry out their experiments. The researchers flew the plane for a distance of 60 m (the maximum distance within the gym) and found that the plane produced adequate ionic thrust to persist the flight the entire time. The flight was repeated for 10 times, with analogous performance.

This was the simplest possible plane we could design that could prove the concept that an ion plane could fly. 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.

Steven Barrett, Associate Professor of Aeronautics and Astronautics, MIT.

Franck Plouraboue, senior researcher at the Institute of Fluid Mechanics in Toulouse, France, stated that the innovative design is a “big step” toward demonstrating the possibility of ion wind propulsion. He notes that earlier, scientists were unable to fly anything heavier than a few grams.

The strength of the results are a direct proof that steady flight of a drone with ionic wind is sustainable,” stated Plouraboue, who was not involved in the research. “[Outside of drone applications], it is difficult to infer how much it could influence aircraft propulsion in the future. Nevertheless, this is not really a weakness but rather an opening for future progress, in a field which is now going to burst.”

Barrett’s group has been striving to improve the efficiency of its design, to generate more ionic wind using less voltage. The scientists also hope to enhance the design’s thrust density—the amount of thrust produced per unit area. For now, a large area of electrodes is required to fly the team’s lightweight plane, which essentially makes up the plane’s propulsion system. At the best, Barrett aims to design an aircraft with no visible propulsion system or separate controls surfaces like elevators and rudders.

It took a long time to get here. Going from the basic principle to something that actually flies was a long journey of characterizing the physics, then coming up with the design and making it work. Now the possibilities for this kind of propulsion system are viable.

Steven Barrett, Associate Professor of Aeronautics and Astronautics, MIT.

This study was supported, in part, by MIT Lincoln Laboratory Autonomous Systems Line, the Professor Amar G. Bose Research Grant, and the Singapore-MIT Alliance for Research and Technology (SMART). The study was also funded through the Charles Stark Draper and Leonardo career development chairs at MIT.

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