While hybrid planes like the the 787 Dreamliner and SUGAR concept
Officially known as electrohydrodynamic thrust, this process utilizes a pair of electrodes—a negative terminal of aluminum and a positive copper terminal—to generate an electric charge between them and strip electrons from the ambient air molecules. These electrons are repelled by the copper terminal (aka the corona wire) and attracted to the negative electrode. As these electrons rush towards the aluminum terminal, they push other air molecules out of the way, which results in thrust. By varying the air gap between the terminals one can adjust the thrust output of the engine, which is limited only by the width of the aircraft. Even so, the thrust generated by an ionic engine could be many times more powerful than even the largest conventional jet engines.
According to a study recently published in the Proceedings of the Royal Society, MIT researchers assistant professor of aeronautics and astronautics Steven Barrett and grad student Kento Masuyama, have experimentally demonstrated that an ionic engine could produce up to 110 N/kW of thrust compared to the 2N/kW that jet engines generate. Surprisingly, the duo discovered that an ionic engine runs most efficiently at lower thrust levels.
"If you have a high-velocity jet, you leave in your wake a load of wasted kinetic energy," Barrett told the MIT press. "So you want as low-velocity a jet as you can, while still producing enough thrust." What's more, ionic engines are both silent and invisible on infrared since they done produce heat which makes them perfect for stealthy surveillance aircraft and ISR drones.
There's still quite a ways to go before these engines actually take to the sky. Engineers must first solve issues of thrust density (the amount of thrust generated per area unit) and the related problem of producing enough voltage to sufficiently power the system. However, Barrett believes that solutions to both issues are within the bounds of current technology.
[MIT]