Double bubble aircraft design would use 70 percent less fuel

http://www.gizmag.com/mit-double-bubble-green-aircraft/15142/

The D double bubble design uses long, skinny wings, a small tail and - hence the name - replaces the traditional cylindrical fuselage with a two partial cylinders placed side-by-side. The engines sit at the rear of the fuselage rather than on the wing to make use of a technique called Boundary Layer Ingestion (BLI). This approach sees slower moving air from the wake of the fuselage enter the engines, resulting in less fuel consumption for the same amount of thrust. The downside is slower speeds and more stress on the engine.

The result is a plane that travels 10 percent slower than the Boeing 737 it is designed to replace, but according to lead designer of the D series Mark Drela, the longer flight times would be partially mitigated by the ability to load and unload the plane faster. Another advantage is that it could also be used with current airport infrastructure.