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Instead of a single-fuselage cylinder, the D series melds two partial cylinders into a distinctive "double-bubble" shape. This adds to the lift and allows for longer, skinnier wings and a smaller tail, reducing drag.

The engines sit at the top rear of the fuselage, where they draw in slower-moving air that passes over the plane, using less fuel for the same amount of thrust—a technique known as boundary layer ingestion. To mitigate the engine stress this creates, the plane would travel about 10 percent slower than a 737; the researchers anticipate making up this time through quicker loading and unloading via the plane's second aisle.

(Illustration by Jeremy Cook)

Innovators: Mark Drela, Edward Greitzer, MIT; Jeremy Hollman, Aurora Flight Sciences; Wesley Lord, Pratt & Whitney

Boeing's 737 is the best-selling jet airliner in history: Today, it carries 29 percent of all U.S. domestic air traffic and is responsible for 25 percent of the industry's fuel use. A reinvention of this commercial workhorse, called the D series, could burn 70 percent less fuel, emit 75 percent less nitrogen oxide and dampen noise from takeoffs and landings. In short, it could transform air travel into a more environmentally benign practice.

Significant tweaks to the 737's basic tube-and-wing design add up "like compound interest" on the craft, says MIT aeronautics and astronautics professor Edward Greitzer. The MIT-led team, which includes two commercial partners, developed the D series in response to a $2.1 million NASA research program challenging engineers to design aircraft for 2035, by which time air travel is expected to have doubled. The team is one of only two in negotiations with NASA for Phase II funding. "How can the airline industry grow and, at worst, remain neutral in its impact on the environment?" asks project manager Ruben Del Rosario of NASA's Glenn Research Center. "We're trying to invest in technology that can decrease its impact."

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