Electrically driven wind may enable stealthy propulsion without heat or sound for small aircraft, researchers at MIT say.
When an electric current passes between two electrodes, one of which is thinner than the other, charged particles create movement in the air in-between. If enough voltage is applied, the wind that is generated can produce thrust without needing moving parts or fuel. This phenomenon, technically called electrohydrodynamic thrust, is known as “ionic wind,” and was first proposed in the 1920s. (Ionic wind thrusters differ from ion thrusters used in spacecraft, which blast out streams of electrically charged particles for propulsion.)
For years, hobbyists have posted how-to videos on building “ionocrafts,” lightweight assemblies made of balsa wood, aluminum foil and wire that can rise and hover. Despite such interest, ionic wind was long relegated to science-fair projects and basement experiments, due to the general belief that ionic thrusters were too inefficient to serve as a viable propulsion system, requiring enormous amounts of electricity to generate useful levels of thrust.
However, MIT scientists have found through experiments that ionic thrusters may actually be a far more efficient source of propulsion than conventional jet engines. Their findings suggest ionic wind can generate more than 50 times higher thrust per kilowatt than standard jet engines.
"Electrohydrodynamic thrust could be really efficient," says Steven Barrett, an aerospace engineer and atmospheric scientist who is also the director of MIT’s Laboratory for Aviation and the Environment.
The fact there are neither moving parts nor motors in these thrusters means they could propel small, light aircraft silently and without much of a heat signature, potentially making them ideal for spy planes.
"Its first applications could be in unmanned air vehicles, which could include lighter-than-air vehicles," Barrett says.
To investigate how efficient these thrusters are, the researchers built a simple version consisting of a few parts — a very thin copper electrode dubbed the emitter, a thicker cylindrical aluminum electrode known as the collector, an air gap in between, and a lightweight frame supporting the electrodes that also connected them to an electrical power source. When voltage was applied, electrons were stripped from nearby air molecules. These ionized molecules became strongly repelled by the emitter and attracted to the collector. As they flowed toward the collector, they collided with surrounding electrically neutral air molecules, creating wind.
The larger the gap between electrodes, the stronger the thrust produced. The scientists found these engines generally produce low amounts of thrust per given area, which means lifting up even a small aircraft would require a very large air gap. For a vehicle to use such propulsion, it would need to generate along its entire length and width, Barrett says.
"If it works, it would need a totally different aircraft and propulsion system configuration," he says.
One drawback is that very large voltages may be needed to lift up such aircraft. Small, lightweight balsa craft typically require several kilovolts, but even a tiny spy plane loaded with sensors and a power supply would need hundreds of thousands of kilovolts. Barrett thinks it is a solvable challenge, although he remains uncertain as to how exactly to tackle it.
Barrett and his colleague Kento Masuyama detailed their findings online April 3 in the journal Proceedings of the Royal Society A.
Top Image: Illustration of an aircraft propelled by ionic wind thrust. Credit: MIT.