The flight testing campaign of the X-48C Blended Wing Body (BWB, aka Hybrid Wing Body) research aircraft kicked off on August 7, 2012, at NASA’s Dryden Flight Research Center. Eight months later the campaign has come to a close with the 30th and final flight carried out on April 12. NASA plans to use the data gathered over the campaign to aid in the design of future “green” airliners that are quieter and more fuel-efficient than conventional aircraft, while Boeing is touting the design's potential military applications.

Unlike flying wing designs such the Stealth Bomber that lack a definitive fuselage, BWB designs have separate wing structures that are smoothly blended into a flattened and airfoil-shaped body. The purpose of the recently-completed flight testing campaign was to establish base data relating to the lift, stall and spin characteristics of the BWB design that promises increased fuel economy and range due to the entire aircraft contributing to lift generation.

The manta ray-shaped X-48C began life as one of two 8.5 percent scale remotely piloted X-48B aircraft built by UK-based Cranfield Aerospace Ltd. from a design developed by Boeing Phantom Works working in cooperation with the NASA Langley Research Center. This resulted in a remote-controlled propeller-driven BWB model that was first flown in 1997.

In an effort to reduce the X-48B’s noise profile and study its low speed stability its wingtip winglets were moved inboard on either side of the engines – effectively turning them into twin tails – its fuselage was extended at the rear by about two feet (0.6 m), and its three 50-pound thrust jet engines were replaced with two 89-pound thrust engines. The result was the X-48C, which boasts the same 21-foot (6.4 m) wingspan and approximate 500 lb (227 kg) weight as the X-48B that made 92 flights between 2007 and 2010.

In the evolution from X-48B to X-48C, the aircraft’s flight control system software was also modified to account for the different handling qualities of the two models. The team says this enabled a stronger and safer prototype flight control system that is suitable for future full-scale commercial blended wing aircraft.

All of the campaign’s 30 flights were conducted at NASA’s Dryden Flight Research Center located at Edwards Air Force Base in California. Most flights of the X-48C lasted around 30 minutes and saw the aircraft reach speeds of up to 140 mph (225 km/h) and attain an altitude of about 10,000 feet.

"We have accomplished our goals of establishing a ground-to-flight database, and proving the low speed controllability of the concept throughout the flight envelope," said Fay Collier, manager of NASA's Environmentally Responsible Aviation project. "Very quiet and efficient, the hybrid wing body has shown promise for meeting all of NASA's environmental goals for future aircraft designs."

"Working closely with NASA, we have been privileged throughout X-48 flight-testing to explore and validate what we believe is a significant breakthrough in the science of flight – and it has been a tremendous success for Boeing," added Bob Liebeck, a Boeing Senior Technical Fellow and the company's BWB program manager.

While NASA believes a BWB design could be seen in future passenger aircraft 20 years from now, Boeing has its eyes on military applications such as aerial refueling and cargo missions. Both Boeing and NASA plan to continue to develop BWB technology with Boeing hoping to develop of a larger-scale, transonic BWB demonstrator in the future.

Sources: Boeing, NASA

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