Details remain to be sorted out, but the new Boeing twinjet is set for design freeze next year
Boeing says the 7E7 programme is "on track" for design freeze in July 2005, as high- and low-speed windtunnel tests enter their penultimate stages.
Recent refinements include a growth in the overall wingspan for the baseline 7E7-8 version at around 1.2m (4ft), to 60m, inclusive of the gently upturned and raked wingtips, says the 7E7 senior vice-president Mike Bair. "The high-speed lines for cruise performance are pretty much there, and looking really good," he says.
An overall aerodynamic efficiency improvement of almost 6% has been proved by the final configuration, which was chosen after "literally hundreds" of iterations generated by computational fluid dynamics were reviewed. The relatively large leap in efficiency is also partly due to the increased flexibility of the design through the use of composites. "The span is near that of the 777, but the wing is thinner and so is the wingbox, which is fine because composites allow you to do things that you could not with aluminium," says Bair.
Boeing is still refining the span for the short-range, cropped-wing 7E7-3, which is now put at around 50-52m. The -3's wing will also feature more prominent winglets rather than the upswept tips of the full-span wing on the baseline -8 and -9 stretch.
Distinctive look
The overall appearance will be "distinctive enough to meet the goal of having 99% of the public say 'hey, that's a 7E7'," Bair says. But the notable shark-fin vertical tail proposed looks set to be eliminated by aerodynamicists as they refine the configuration. "You'll see a less dramatic tail," says Bair, although the rudder may have a "hint of a reverse curve". The nose will have the distinctive conformal streamlining of the original impressions, says Bair, and the flightdeck will have a four-pane windshield, instead of the standard six-pane design. He adds, however: "We're not going to compromise efficiency just to make it look cool."
One of the most interesting external features about to make its first public appearance is the enlarged cabin windows, which will be around 30% bigger than current transparencies. "We're just trying to make sure we have enough room for wire runs between the frames, but the good thing about composites is that this allows us to have large windows without penalties."
The cabin length of the 7E7-9 is still under debate, as is the entry into service (EIS) target for the stretch, which is now sliding by two years, to 2012. "We could still do the stretch sooner," says Bair. "Air New Zealand can take its 7E7 options up as the stretch, and 2012 is the latest EIS date we have guaranteed them."
Stretch options are being evaluated to accommodate around 245 to 255 passengers. "All I can tell you is it definitely won't be 250," says Bair, who adds that the debate is being driven largely by differing requirements from a couple of Middle East carriers.
Progress on structures continues, with the amount of composites remaining stable while trade studies are completed. "We are a bit overweight, although less so than we were on the 777 at this point in the process," says Bair, who expects most of the final reductions to come from trimming weight on systems and structures. "We are roughly 50% composite now by weight. We don't have an actual target in terms of either weight or percent for composite, we're just doing what makes most sense," he adds.
The current production plan will see the 7E7's composite fuselage constructed from three or four major sections. Ongoing trade studies are evaluating whether to use aluminium for ribs in the otherwise composite wingbox. "At the moment it is cheaper to produce the ribs in aluminium, but we are working hard on that and expect that they'll end up being composite," says Bair.
Composites dominate the vertical and horizontal tails, the wingboxes for which Boeing now plans to assemble as a single co-cured piece using technology perfected by partner Alenia. Another trade study is ongoing for the floor beams, which could be composite or aluminium. "The amount of aluminium we have in it is disappearing," adds Bair. "I think we're going to have more and more titanium, which saves weight, but adds some cost."
The first 7E7 is due to fly in the third quarter of 2007, and enter service a year later. Production levels will remain relatively low through 2009 to reduce exposure to risk from any significant structural or systems changes that may be required as a result of the flight-test programme, which is due to start in 2007.
Contracts for the conversion of three 747-400 outsize transports, which will be used to transfer 7E7 subassemblies from partner sites to the final assembly line in Everett, are due to be awarded at the end of August. "The modification doesn't have to be elegant and is essentially straightforward. It just has to work," says Bair, who says the first aircraft has to be available to start the assembly process in late 2006.
So far four airlines - Air New Zealand, All Nippon Airways, First Choice Airways and Blue Panorama - have announced commitments for 62 7E7s, and Boeing says it has taken deposits from around 24 airlines for over 200 aircraft. "All delivery positions through 2009 are committed, as is 80% of 2010," says Bair. No leasing companies are yet on board. Bair says: "We're looking a little light on customers in the USA. At some point the US carriers are going to wake up to the 7E7 and we're going to have to tell them that we don't have any aircraft available."
GUY NORRIS & MAX KINGSLEY-JONES
Source: Flight International
