Is the future of aviation electric?

Siemens, Rolls Royce and Airbus are to collaborate on a project to deliver a Bae146-sized hybrid electric plane by 2020.
The three manufacturers claim that the E-Fan-X could radically change the face of aviation with cleaner, quieter planes that would allow planes to fly closer to city centres and compete with rail transport for more journeys.
They aim to build a demonstration plane based on the four-engined BAe 146 jet in which an electric unit, powered by an on-board generator, would replace initially one, and eventually two of the existing turbojets.
Challenges to be overcome would include how to incorporate a two-tonne battery capable of powering the aircraft – which would presumably preclude any usable bellyhold cargo capacity for a plane in passenger configuration.
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