A seemingly simple change to airplane design can make a huge difference in fuel efficiency: add another engine. Yes, as counterintuitive as it sounds, NASA has figured out that by adding an engine to the rear of the plane the airflow of the plane itself can provide more thrust. Airplanes are notoriously bad for the environment and any efficiency in fuel consumption has a significant impact on emissions.

NASA’s idea is pretty straightforward: place a large turbofan engine on the rear of a plane, where it will collect the slow-moving air traveling along the plane’s body. This lets the wing-mounted turbofans be built smaller, which means less drag and a higher fuel efficiency.

That by itself would mean a minor improvement to fuel use, but NASA decided to go a step further. The engineers also added generators to the wing-mounted turbofans, and the electricity generated by these engines is used to power the tail-mounted one. This means that the rear turbofan that provides much of the plane’s thrust doesn’t require any fuel to operate.

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