July 30, 2007 The traditional airplane shape is well tried and tested, but manufacturers like Boeing are moving beyond the "tube with wings and a tail" design in the push to improve fuel economy and the environmental impact for the next generation of jets. Inspired by "flying wing" designs from earlier decades like 1988's B-2 Stealth bomber, the company has been collaborating with NASA to test the viability of a Blended Wing Body (BWB) aircraft, using a flat, wide body that tapers out to thin wing-tips and aims to strike an effective middle ground between the tube and flying wing designs. A BWB design allows the entire body of the plane to generate lift and reduces drag in comparison to a tube-shaped fuselage - both of which are key factors in reducing fuel usage. The BWB design also provides a much greater cargo and passenger capacity - making it particularly attractive to the military. After months of development, ground testing and wind-tunnel testing, Boeing flew its first BWB prototype last week with the 8.5 per cent scale, 500-pound X-48B aircraft reaching 7500 feet before a successful landing under remote control.
The innovative Boeing Blended Wing Body (BWB) research aircraft -- designated the X-48B -- flew for the first time last week at NASA's Dryden Flight Research Center at Edwards Air Force Base in California.
The 21-foot wingspan, 500-pound unmanned test vehicle took off for the first time at 8:42 a.m. Pacific Daylight Time on July 20 and climbed to an altitude of 7,500 feet before landing 31 minutes later.
The BWB aircraft is being evaluated for possible use in military and cargo applications, although Boeing is keeping a close eye on the results of the tests to see if the BWB design will eventually translate effectively into a passenger aircraft. The design's benefits include high-lift, low-drag efficient aerodynamics, reduced ground noise due to top-mounted engines, a greatly increased carrying capacity and improved structural weight.
"We've successfully passed another milestone in our work to explore and validate the structural, aerodynamic and operational efficiencies of the BWB concept," said Bob Liebeck, BWB program manager for Boeing Phantom Works, the company's advanced R&D unit. "We already have begun to compare actual flight-test data with the data generated earlier by our computer models and in the wind tunnel."
The X-48B flight test vehicle was developed by Boeing Phantom Works in cooperation with NASA and the U.S. Air Force Research Laboratory to gather detailed information about the stability and flight-control characteristics of the BWB design, especially during takeoffs and landings. Up to 25 flights are planned to gather data in these low-speed flight regimes. Following completion of low-speed flight testing, the X-48B likely will be used to test the BWB's low-noise characteristics, as well as BWB handling characteristics at transonic speeds.
Two X-48B research vehicles have been built. The vehicle that flew on July 20 is Ship 2, which also was used for ground and taxi testing. Ship 1, a duplicate of Ship 2, completed extensive wind tunnel testing in 2006 at the Old Dominion University NASA Langley Full-Scale Tunnel in Virginia. Ship 1 will be available for use as a backup during the flight test program.
Three turbojet engines enable the composite-skinned research vehicle to fly up to 10,000 feet and 120 knots in its low-speed configuration. Modifications would need to be made to the vehicle to enable it to fly at higher speeds. The unmanned aircraft is remotely piloted from a ground control station in which the pilot uses conventional aircraft controls and instrumentation while looking at a monitor fed by a forward-looking camera on the aircraft.
The Boeing BWB design resembles a flying wing, but differs in that the wing blends smoothly into a wide, flat, tailless fuselage. This fuselage blending helps to get additional lift with less drag compared to a circular fuselage. This translates to reduced fuel use at cruise conditions and because the engines mount high on the back of the aircraft, there is less noise inside and on the ground when it is in flight.
Disadvantages and design challenges of the BWB shape include less inherent flight stability than the tube design, less structural suitability for internal pressurization (it's easier to pressurize a tube than a wider, oval cross-section like the BWB's), a lack of passenger side windows, and a layout that moves passengers and cargo off the aircraft's centerline, which exaggerates the vertical motion felt when the plane rolls to turn.
While a commercial passenger application for the BWB concept is not in Boeing's current 20-year market outlook, the Advanced Systems organization of Boeing Integrated Defense Systems' (IDS) is closely monitoring the research based on the BWB's potential as a flexible, long-range, high-capacity military aircraft.
"The BWB concept holds tremendous promise for the future of military aviation as a multi-purpose military platform in 15 to 20 years," said Darryl Davis, Boeing IDS Advanced Systems vice president and general manager of Advanced Precision Engagement and Mobility Systems. "Its unique design attributes will result in less fuel burn and a greatly reduced noise footprint, which are important capabilities to offer our Air Force and mobility customers."
NASA's participation in the project is focused on fundamental, edge-of-the-envelope flight dynamics and structural concepts of the BWB. Along with hosting the X-48B flight test and research activities, NASA Dryden provided engineering and technical support - expertise garnered from years of operating cutting-edge unmanned air vehicles.
The two X-48B research vehicles were built by Cranfield Aerospace Ltd., in the United Kingdom, in accordance with Boeing requirements.