Heavier than air flight is possible when lift from stationary or rotating wings overcomes the force of gravity, and thrust from a propeller or turbine blades overcomes the aerodynamic drag created as the aircraft moves through the air. The motion of the propeller or turbine blades that create thrust produces significant noise as they beat the air—noise that is annoying to those who live near busy airports or that can cause an otherwise stealthy drone to be detected.
A new MIT airplane is propelled via ionic wind. Batteries in the fuselage (tan compartment in front of plane) supply voltage to electrodes (blue/white horizontal lines) strung along the length of the plane, generating a wind of ions that propels the craft forward. (Image source: Christine Y. He/MIT)
No Moving Parts
A group of MIT engineers has now built and flown an airplane that has no moving parts. It replaces propellers or turbines with an “ionic wind”—a silent flow of ions that is produced aboard the plane. The wind can generate enough thrust to propel a small, lightweight experimental airplane model over a sustained and steady flight. The new design is completely silent.
“This is the first-ever sustained flight of a plane with no moving parts in the propulsion system,” says Steven Barrett, associate professor of aeronautics and astronautics at MIT, in an Institute news release. “This has potentially opened new and unexplored possibilities for aircraft which are quieter, mechanically simpler, and do not emit combustion emissions,” he added.
According to the MIT release, about nine years ago, Barrett started looking for ways to design a propulsion system for planes with no moving parts. He eventually came upon electro-aerodynamic thrust, known also as “ionic wind.” This physical principle was first discovered in the 1920s. It describes a thrust that is produced when a current is passed between a thin and a thick electrode. If enough voltage is applied, the air in between the electrodes can produce enough ionized air to create thrust to propel a small aircraft.
How It Works
According to a 2013 MIT news release, “A basic ionic thruster consists of three parts: a very thin copper electrode, called an emitter; a thicker tube of aluminum, known as a collector; and the air gap in between. A lightweight frame typically supports the wires, which connect to an electrical power source. As voltage is applied, the field gradient strips away electrons from nearby air molecules. These newly ionized molecules are strongly repelled by the corona wire, and strongly attracted to the collector. As this cloud of ions moves toward the collector, it collides with surrounding neutral air molecules, pushing them along and creating a wind, or thrust.”
Hobbyists have played around with electroaerodynamic thrust for years, but designs have been limited to small, desktop models that have been tethered to large voltage supplies. They can create just enough thrust for a small craft to hover briefly in the air. The energy required for untethered flight of larger aircraft was assumed to be impossible.
“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,” recalls Barrett. “I did some back-of-the-envelope calculations and found that, yes, it might become a viable propulsion system,” Barrett says. “And it turned out it needed many years of work to get from that to a first test flight.”
Power Is the Key
Building an ionic wind-powered flyer first required a portable power supply—something that has only recently been possible with the availability of inexpensive but powerful lithium ion batteries. The MIT 2018 release notes, “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.”
The final design of the aircraft resembles a large, lightweight glider. It weighs about 5 pounds and has a 5-meter wingspan. An array of thin wires, which are strung like horizontal fencing along and beneath the front end of the plane’s wing, act as positively charged electrodes. Similarly arranged thicker wires, running along the back end of the plane’s wing, serve as negative electrodes.
Up and Away
When the wires are energized, they attract and strip away negatively charged electrons from the surrounding air molecules. The air molecules that are left behind are newly ionized, and are attracted to the negatively charged electrodes at the back of the plane. Noted in the MIT release, “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 airplane flew in multiple test flights across the gymnasium in MIT’s duPont Athletic Center—the largest indoor space that the team could find to perform their experiments. The plane flew a distance of 60 meters (the maximum distance within the gym) and produced enough ionic thrust to sustain flight the entire time. The flight was repeated 10 times, with similar performance. A short video of the flight is available here.
Although these initial flights have been modest, they do prove the concept. Barrett expects that, “in the near-term, such ion wind propulsion systems could be used to fly less noisy drones.” He envisions a future with ion propulsion paired with more conventional combustion systems to create more fuel-efficient, hybrid passenger planes and other large aircraft.
Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.
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