GUY NORRIS / LOS ANGELES
Significant design breakthroughs mean that a far wider range of variants is possible than was previously thought
Boeing Phantom Works is studying a much wider range of potential blended wing body (BWB) family variants than previously planned following a number of significant design breakthroughs in the run-up to the construction of a low speed vehicle (LSV) sub-scale flying demonstrator.
"We're looking at a range roughly covering the 200-550 seat size, and our goal would be to have the same outer wing for all of them, and centrebody modules with the same cross-section," says BWB programme manager Bob Liebeck. "This is a change because when we started, stretching was not in the vocabulary, or so we thought at the time. Now it turns out the BWB is ideal for a family of airplanes as stretching takes place laterally, or spanwise."
The company's studies include two options for internal modules, one is a mid-size six-abreast configuration, and the other is a narrowbody five abreast arrangement. Each module would seat between 60 and 70, with flat panel seatback and wall panel displays in lieu of windows.
"These modules can be arranged in various combinations," says Liebeck, who says aerodynamic analysis has shown that common wing sections can be added to varying sizes of centrebody. "The aerodynamicists have been able to define an exceptional centrebody aerofoil shape that sort of 'shrink wraps' around the cabin," says Liebeck, who adds that the centrebody is an area-ruled surface.
This feature is now allowing Boeing to study much higher cruise speeds than first envisaged, at speeds up to Mach 0.95 compared with the M0.85 first identified. Within this speed range the M0.90 area is described as the "sweet spot for the concept" although the current assessments of the "value" of speed related to the marketing of the sonic cruiser could raise the target speed to around M0.93, adds Liebeck.
Liebeck says a passenger BWB version could enter service within "seven or eight" years of a launch decision if taken now, and that the development timescale will shorten as manufacturing technology improves. "The long pole in the tent is large-scale composite structures," he says, adding that development of the 200-250 passenger size variant could be spurred first through a military tanker variant being studied as a potential long-term contender for the US Air Force's KC-X competition.
Work is progressing on the delayed LSV which Boeing now hopes to fly at NASA's Dryden Flight Research Center at Edwards AFB, California in 2004, two years behind the original schedule. Delays to the definition of the 10.7m (35ft) span, unmanned vehicle, are related to unexpected weight growth and the removal of the BWB from NASA's Revcon (revolutionary concept) programme.
Powered by three 240lb (1.04kN) thrust Williams FJ44 turbofans, the LSV will have an all-up weight of 1,135kg (2,500lb) - some 450kg heavier than originally expected because of unforeseen range safety requirements and the need for redundant control systems. NASA is building the LSV to Boeing specifications as well as developing a duplicate set of flight control software.
Source: Flight International
