In February, NASA announced that it wanted to use its New Aviation Horizons program to revive the famed X-plane that did so much to advance post-war aviation. Now the agency has awarded a six-month US$2.9 million contract to Manassas, Virginia-based Aurora Flight Sciences to develop a scaled demonstration version of its Aurora D8 subsonic commercial airliner. Described as "changing the paradigm," the D8 is designed to significantly improve airliner performance by 2027.

According to Aurora, the D8 takes its inspiration from the famed Boeing 707 of 1958, which not only introduced the public to single-day world travel, but also used a tube-wing design that redefined passenger aircraft. The first commercially successful jetliner, its swept-back wings, in-wing fuel tanks, and pylon-mounted engines set the standard so that essentially, all modern commercial airliners are derivations of the 707.

Unfortunately, Aurora contends that the 707-based aircraft have reached the law of diminishing returns and are only improving in fuel efficiency at a rate of 1.5 percent per year. The D8 is designed to avoid this problem by recreating the 707's integrated design approach while drawing on Aurora's work on NASA's N+3 Program to produce advanced concepts for subsonic and supersonic commercial transport aircraft.

The resulting D8, named after its chief designer Mark Drela, takes a step forward in airliner design by taking a step backwards. Instead of a narrow fuselage, the D8 uses a "double bubble" fuselage made of two conjoined hulls similar to that on the old Boeing 377 Stratocruiser of the 1940s. Only in this case, the twin hulls have been laid on their side to make a very wide twin-aisle fuselage.

This design not only provides much more interior room than a 737-800, but it also allows the fuselage to act as an airfoil and provide extra lift. Along with composite materials, smaller, embedded high-bypass engines at the rear of the fuselage that improve thrust efficiency due to Boundary Layer Ingestion (BLI), the new fuselage saves weight by allowing for smaller wings and reduces drag by combining fuselage wake and engine thrust.

Aurora says that the D8 is designed to fly at Mach 0.764 (582 mph, 936 km/h) with 180 passengers over a range of 3,000 nm (3,500 mi, 5,500 km). The company also says the design has the potential to cut fuel burn by 71 percent, reduce noise by 60 EPNdB, and cut LTO NOx emissions by 87 percent compared to a best-in-class Boeing 737-800 narrow-body aircraft.

As part of the NASA contract, Aurora will build test components as the company develops a 1:2 scale demonstrator X-plane over the next three years. Aurora says that the D8 could enter commercial service by 2027.

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