Unlike turbine-powered planes, the aircraft does not depend on fossil fuels to fly and it is completely silent, unlike propeller planes.

“This is the first-ever sustained flight of a plane with no moving parts in the propulsion system,” said Steven Barrett, associate professor of aeronautics and astronautics at MIT. “This has potentially opened new and unexplored possibilities for aircraft which are quieter, mechanically simpler, and do not emit combustion emissions.”

He expects that in the near-term, such ion-wind propulsion systems could be used to fly less noisy drones. Further out, he envisions ion propulsion paired with more conventional combustion systems to create more fuel-efficient, hybrid passenger planes and other large aircraft.

Ionic wind, also known as electro-aerodynamic thrust, is a physical principle that was first identified in the 1920s and describes a wind, or thrust, that can be produced when a current is passed between a thin and a thick electrode. If enough voltage is applied, the air between the electrodes can produce enough thrust to propel a small aircraft.

The team’s final design resembles a large, lightweight glider. The aircraft, which weighs about 2.25kg and has a 5-metre 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, whose output is 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 energised, 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 ionised 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, 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 60 metres (the maximum distance within the gym) and found it produced enough ionic thrust to sustain flight the entire time. They repeated the flight 10 times, with similar performance.

“This was the simplest possible plane we could design that could prove the concept that an ion plane could fly,” Barrett said. “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.”

Barrett’s team is working on increasing the efficiency of their design, to produce more ionic wind with a lower 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 said. “Going from the basic principle to something that actually flies was a long journey of characterising the physics, then coming up with the design and making it work. Now the possibilities for this kind of propulsion system are viable.”

Unlike turbine-powered planes, the aircraft does not depend on fossil fuels to fly and it is completely silent, unlike propeller planes.

“This is the first-ever sustained flight of a plane with no moving parts in the propulsion system,” said Steven Barrett, associate professor of aeronautics and astronautics at MIT. “This has potentially opened new and unexplored possibilities for aircraft which are quieter, mechanically simpler, and do not emit combustion emissions.”

He expects that in the near-term, such ion-wind propulsion systems could be used to fly less noisy drones. Further out, he envisions ion propulsion paired with more conventional combustion systems to create more fuel-efficient, hybrid passenger planes and other large aircraft.

Ionic wind, also known as electro-aerodynamic thrust, is a physical principle that was first identified in the 1920s and describes a wind, or thrust, that can be produced when a current is passed between a thin and a thick electrode. If enough voltage is applied, the air between the electrodes can produce enough thrust to propel a small aircraft.

The team’s final design resembles a large, lightweight glider. The aircraft, which weighs about 2.25kg and has a 5-metre 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, whose output is 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 energised, 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 ionised 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, 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 60 metres (the maximum distance within the gym) and found it produced enough ionic thrust to sustain flight the entire time. They repeated the flight 10 times, with similar performance.

“This was the simplest possible plane we could design that could prove the concept that an ion plane could fly,” Barrett said. “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.”

Barrett’s team is working on increasing the efficiency of their design, to produce more ionic wind with a lower 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 said. “Going from the basic principle to something that actually flies was a long journey of characterising the physics, then coming up with the design and making it work. Now the possibilities for this kind of propulsion system are viable.”