GUY NORRIS / LOS ANGELES
747 derivative is designed to accommodate largest subassemblies of proposed aircraft
Boeing is refining a specially designed 747-400 outsize transport concept for a third and final windtunnel test phase as part of efforts to develop an air-based parts delivery system for the proposed 7E7.
The 747 derivative has undergone two major windtunnel tests and a third is planned for December. Configured with an extended upper fuselage lobe, the modified aircraft is designed to accommodate the largest subassemblies for the 7E7, and to be able to load them without the need for a hingeing nose door. Rising aft from around the Section 41 break line, the extended upper fuselage line will increase the interior height by up to 3m (10ft) as far back as the middle of Section 46, when it will taper into the Section 48 tail section. This is also revised, with a 747SP-style extended fin 0.6m taller than that of the standard 747-400.
The rudder will be extended downwards, says Boeing, which also studied an extended SP-style horizontal stabiliser as well as end-plates similar to those used on the Space Shuttle carrier aircraft. Windtunnel tests showed none of these modifications were required when lateral stability was augmented with a large dorsal fin and "strongback" reinforcement beam extending forward from the leading edge of the fin.
The upper fuselage modification produces a wider constant cross-section that enables the 747 to accommodate the "full 7E7 cross-section", it adds. Design range will be similar to "747-400 capabilities, but the additional structural weight will reduce payload to between roughly 99,900kg [220,000lb] and 113,500kg", the company says.
"Although there is a large statement of work, the whole idea is to keep it simple with minimum change," says Boeing, which aims to modify up to three secondhand -400 airframes to support the proposed 7E7 assembly rate. The design includes up to two main-deck cargo doors in the aft fuselage, although the company is closing on a "probable" final configuration with one main door on the aft left side. This will be large enough to take sub-assemblies larger than the 31 x 4.5m 777 wingbox unit, which is the biggest single structure to arrive pre-assembled at Everett. Currently, this is barged from Seattle docks, where it is offloaded from ships arriving from Japan. Most other parts arrive by road or rail.
Boeing plans a relatively rapid modification and test phase for the aircraft beginning early next year, but says: "This is a tool built for the 7E7, and their fates are clearly linked." By adopting the air transport system pioneered by Airbus, Boeing is projecting possible savings of 20-40%, compared with current methods. "Transporting large pieces by air will allow us to dramatically reduce flow time," says 7E7 senior vice-president Mike Bair. Delivery times for the large, mostly composite subassemblies, will be cut from 30 days to just one day, says Boeing.
Source: Flight International
