Purely electric aircraft are still in their relative infancy. Hybrid aircraft, however? They're closer than you think. Airbus, Rolls-Royce and Siemens are partnering on a hybrid electric aircraft prototype, the E-Fan X, that will prove the mixture of conventional and electric engines will work. The demonstrator will modify a BAe 146 by replacing one of its gas turbine engines with a 2MW electric motor, followed by a second if everything goes smoothly. It's currently slated to fly sometime in 2020.