Ions take flight

The team’s final design resembles a large, lightweight glider. The aircraft, which weighs about 5 pounds and has a 5-meter wingspan, carries an array of thin wires, which are strung like horizontal fencing along and beneath the front end of the plane’s wing. The wires act as positively charged electrodes, while similarly arranged thicker wires, running along the back end of the plane’s wing, serve as negative electrodes.

The fuselage of the plane holds a stack of lithium-polymer batteries. Barrett's ion plane team included members of Professor David Perreault’s Power Electronics Research Group in the Research Laboratory of Electronics, who designed a power supply that would convert the batteries’ output to a sufficiently high voltage to propel the plane. In this way, the batteries supply electricity at 40,000 volts to positively charge the wires via a lightweight power converter.

Once the wires are energized, they act to attract and strip away negatively charged electrons from the surrounding air molecules, like a giant magnet attracting iron filings. The air molecules that are left behind are newly ionized, and are in turn attracted to the negatively charged electrodes at the back of the plane.

As the newly formed cloud of ions flows toward the negatively charged wires, each ion collides millions of times with other air molecules, creating a thrust that propels the aircraft forward.

The team, which also included Lincoln Laboratory staff Thomas Sebastian and Mark Woolston, flew the plane in multiple test flights across the gymnasium in MIT’s duPont Athletic Center — the largest indoor space they could find to perform their experiments. The team flew the plane a distance of 60 meters (the maximum distance within the gym) and found the plane produced enough ionic thrust to sustain flight the entire time. They repeated the flight 10 times, with similar performance.



A general blueprint for an MIT plane propelled by ionic wind. The system may be used to propel small drones and even lightweight aircraft, as an alternative to fossil fuel propulsion. (Image: MIT Electric Aircraft Initiative, MIT)

“This was the simplest possible plane we could design that could prove the concept that an ion plane could fly,” Barrett says. “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 new design is a “big step” toward demonstrating the feasibility of ion wind propulsion, according to Franck Plouraboue, senior researcher at the Institute of Fluid Mechanics in Toulouse, France, who notes that researchers previously weren’t able 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,” says 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 team is working on increasing the efficiency of their design, to produce more ionic wind with less voltage. The researchers are also hoping to increase the design’s thrust density — the amount of thrust generated per unit area. Currently, flying the team’s lightweight plane requires a large area of electrodes, which essentially makes up the plane’s propulsion system. Ideally, Barrett would like to design an aircraft with no visible propulsion system or separate controls surfaces such as rudders and elevators.

“It took a long time to get here,” Barrett says. “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.”

This research 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 work was also funded through the Charles Stark Draper and Leonardo career development chairs at MIT.

 

 


Source: Jennifer Chu, MIT News. Top image: Courtesy of MIT. Reprinted with permission of MIT News.