Boeing X-48

Lore & Background

Boeing Phantom Works developed the blended wing body aircraft concept in cooperation with the NASA Langley Research Center. Earlier studies of a blended wing body design by Boeing had been dropped for passenger airliners after passengers disliked the theater-like configuration of the mock-up, but the concept was retained for military aircraft such as aerial refueling tankers. McDonnell Douglas had developed the blended wing concept in the late 1990s, and Boeing presented it during an annual Joint AIAA/ASME/SAE/ASEA Propulsion Conference in 2004. The McDonnell Douglas engineers believed their design had several advantages, but their concept, code named 'Project Redwood', found little favor at Boeing after their 1997 merger. The most difficult problem they solved was ensuring passengers a safe and fast escape in case of an accident, since emergency door locations were completely different from those in a conventional aircraft.

The X-48B had a 21 ft wingspan, weighed 392 lb, and was built from composite materials. It was powered by three small turbojet engines and was expected to fly at up to 120 kn and reach an altitude of 10,000 ft. The X-48B was an 8.5% scaled version of a conceptual 240 ft span design. Though passenger versions of the X-48B have been proposed, the design has a higher probability of first being used for a military transport. Wind tunnel testing on a 12 ft wide blended wing body model was completed in September 2005. During April and May 2006, NASA performed wind tunnel tests on X-48B Ship 1 at a facility shared by Langley and Old Dominion University. After wind tunnel testing, the vehicle was shipped to NASA's Dryden Flight Research Center at Edwards Air Force Base to serve as a backup to X-48B Ship 2 for flight testing. X-48B Ship 2 then conducted ground tests and taxi testing in preparation for flight. In November 2006, ground testing began at Dryden, to validate the aircraft's systems integrity, telemetry and communications links, flight-control software and taxi and takeoff characteristics.

The second X-48B was modified into the X-48C starting in 2010 for further flight tests. The X-48C had its vertical stabilizers moved inboard on either side of the engines, and its fuselage extended aft, both to reduce the aircraft's noise profile; it was to be powered by two JetCat turbines, each producing 80 lbf of thrust. The X-48C was instead modified to use two Advanced Micro Turbo (AMT) turbojet engines in 2012. Following flight testing of the X-48C in April 2013, Boeing and NASA announced future plans to develop a larger BWB demonstrator capable of transonic flight.

Reader's Guide

The X-48 program demonstrated the feasibility of flying a tailless blended wing body aircraft at low speeds. The X-48B first flew on July 20, 2007, reaching an altitude of 7,500 ft in a 31-minute flight. The remotely piloted aircraft was successfully stalled for the first time on September 4, 2008, with fixed leading edge slats, a forward center of gravity, and 23-degree angle of attack. Stall testing was repeated on September 11 with a NASA pilot at the console. On March 19, 2010, NASA and Boeing successfully completed the initial flight testing phase of the X-48B. Following the installation of a new flight computer in 2010, the X-48B began a new phase of flight tests to investigate controllability aspects in September 2010. The X-48C completed its 8-month flight test program with its 30th flight on April 9, 2013. The blended wing body concept offers advantages in structural, aerodynamic and operating efficiencies over conventional fuselage-and-wing designs, translating into greater range, fuel economy, reliability and life cycle savings, as well as lower manufacturing costs. These advantages are achieved at the expense of a multitude of disadvantages that make the concept impractical for airline use. Boeing and NASA planned to develop a larger BWB demonstrator, although no updates have been provided since 2013.