GUY NORRIS / LOS ANGELES
Boeing is performing critical cost and performance studies on the blended wing body (BWB) design which could assure the future of the project as a passenger transport.
At stake is the true benefit of the commonality approach in Boeing's plan to develop five or six BWB derivatives seating between 180 and 570 passengers. This was identified by the company's Phantom Works, which is leading the studies, when it conceived a concept for laterally "stretching" or "shrinking" the aircraft to a variety of sizes by adding or subtracting the centre-body bay (Flight International, 30 October - 5 November 2001).
Under the scheme, wing area and span automatically increase or decrease with passenger capacity, while outer wing panels, nose sections and most passenger bays are common.
The passenger cabin of the BWB-450, seating around 480 passengers, for example, shares up to 97% commonality with the BWB-250, seating around 260, in terms of identical seats, crew rest areas, lavatories, galleys, ceilings, floors and other fixtures. However, by using the same wing, "the BWB-250 would be about 4,100kg (9,000lb) heavier than it needs to be", says BWB programme manager Bob Liebeck. "If we change the skin gauge to be optimum we're down to 3,000lb extra weight. Is it worth it for the sake of commonality?" he says, adding that calculations of the BWB-250 showed an approximate 8% weight penalty.
Boeing's goal includes a common part number for the outer wing, cockpit and many internal sections. This, with the unusual "big wing" and integrated fuselage shape of the BWB, contributes to an estimated 30% fewer parts compared with a conventional aircraft.
Boeing says distinct to each aircraft variant is the transition section aft of the nose, the aft centre-body and engines. Nose gear and outer main gear are common, with a centre main gear of varying capacity added where required.
Boeing has also revealed estimated comparative performance figures for the BWB against conventional aircraft such as the Airbus A380. Compared with the A380-700, Boeing claims the 480-seat BWB-450 will provide 32% lower fuel burn per seat on ranges up to 16,100km (8,700nm).
Empty weight is 19% lower, while maximum take-off weight is estimated to be around 18% lower. Total sea-level static thrust would also be around 19% lower, due largely to the use of three engines on the original BWB versus the A380's four. All later BWB concepts are twins.
Source: Flight International
