Lee Rannals for redOrbit.com — Your Universe Online
MIT researchers writing in the journal Proceedings of the Royal Society A say they found ionic wind thrusters may be a more efficient source of propulsion than conventional jet engines.
Ionic wind, or electrohydrodynamic thrust, was first identified in the 1960s. The phenomenon takes place when a current passes between two electrodes, creating a wind in the air between. If enough voltage is applied, the wind produces a thrust without the help of motors or fuel.
Past studies showed the concept of using ionic thrusters instead of jet propulsion for airplanes would be extremely inefficient. However, the MIT team’s findings found the opposite.
Researchers showed ionic wind produces 110 newtons of thrust per kilowatt, compared with a jet engine’s two newtons per kilowatt. They believe ionic wind may be used as a propulsion system for small, lightweight aircraft. Also, because the thrusters would be silent and invisible to infrared, they would be ideal for surveillance vehicles.
“You could imagine all sorts of military or security benefits to having a silent propulsion system with no infrared signature,” says Steven Barrett, an assistant professor of aeronautics and astronautics at MIT.
The ionic thruster consists of a very thin copper electrode, a thicker tube of aluminum, and the air gap in between. It has a lightweight frame that supports the wires, which connects to an electrical power source. Once voltage is applied, the field gradient strips away electrons in nearby air molecules. These ionized molecules are strongly repelled by the corona wire and strongly attracted to the collector. As the cloud of ions moves towards the collector it collides with surrounding neutral air molecules to create a thrust.
The team built a similarly simple setup, and hung the contraption under a suspended digital scale. They then applied tens of thousands of volts, creating enough current to draw power to an incandescent light bulb and altered the distance between the electrodes. According to Barrett, the device was most efficient at producing lower thrust.
“It´s kind of surprising, but if you have a high-velocity jet, you leave in your wake a load of wasted kinetic energy,” said Barrett. “So you want as low-velocity a jet as you can, while still producing enough thrust.” He adds an ionic wind is a good way to produce a low-velocity jet over a large area.
He said one obstacle to overcome is thrust density, which is the amount of thrust produced per given area. These thrusters depend on the wind produced between electrodes, meaning lifting a small aircraft and its electrical power supply would require a very large air gap. Barrett says these thrusters would cover the entire aircraft.
The researchers estimate a small aircraft would need hundreds or thousands of kilovolts to take off. Barrett says power might be supplied by lightweight solar panels or fuel cells.
“The voltages could get enormous,” he said. “But I think that´s a challenge that´s probably solvable.”
One team is preparing to complete a solar-powered flight across the US. The Solar Impulse team will be flying the HB-SIA zero-fuel airplane both day and night, solely on the power of the Sun. The aircraft will be making a coast-to-coast trip across the US, making several stops in key cities along the way.
The plane has a 208 feet wingspan, weighs nearly 3,600 pounds and relies solely on 12,000 solar cells for its power.