Broken Mould

Boeing has produced an all-composite, one-piece fuselage barrel section for its new 7E7. Is this the way ahead for aircraft construction?

There was no curtain raising, no dry ice, rock music or laser show. There was simply a large fuselage barrel sitting on its mobile tool fixture in a corner of Boeing's enormous Developmental Center, the site originally built to house its long-abandoned 2707 supersonic transport project.

This was early January, and the first time the world had seen any tangible part of the 7E7, Boeing's Dreamliner, and it was displayed to prove that the new-technology twinjet is anything but a dream. The representative Section 47, an aft fuselage barrel, is the first, all-composite one-piece development and test article and will be followed by at least five other similar large-scale test sections. The results are crucial to the 7E7's success as composites account for more than 50% of the new airliner by weight and are a fundamental "game changing" technologies at the core of the 7E7 concept.

"It's the largest piece of pressure-vessel carbon fibre made, and the first one like it in the world," says Walt Gillette, Boeing vice-president of engineering, manufacturing and partner alignment. Measuring 7m long, and just over 5.74m in diameter at the constant-section end, it was selected for its challenging curvature as the best single unit to begin proving the process.

Based on the same fibre-placement principle as Raytheon uses for its composite-fuselage Premier I and Hawker Horizon business jets, the 7E7 fuselage sections will be assembled from composite tape laid down on a massive mould by a computerised machine. The mould itself is mounted on a tool that rotates as the tape is applied. When completed, the structure is wrapped and placed in the autoclave for curing.

Process perfection

Once the process has been perfected and standardised, all members of the Boeing-led fuselage assembly team will use identical procedures and hardware, including giant autoclaves. The team includes Vought, which has formed a joint venture with Alenia called Global Aeronautica to handle fuselage assembly in Charleston, South Carolina. Vought will produce aft fuselage sections 47 and 48 in a purpose-built 7E7 site to be co-located with the integration site at Charleston International airport.

Work on building the two sites is to start early this year, with the first fuselage due to be transported by the Boeing 747 Large Cargo Freighter (LCF) in early 2007. The Vought sections will be joined at the Charleston site to the Alenia-built centre fuselage sections 44 and 46, with all major shipments to and from the integration site made using the LCF.

Kawasaki Heavy Industries (KHI) is also a fuselage team partner with responsibility for part of the forward section. For the first time on any Boeing, the Section 41 nose unit will be stretched aft to encompass a far larger part of the constant section, while Section 43 will make up the remainder of the forward body. "Alenia builds composite wings for the Eurofighter and Kawasaki builds Bullet Trains from carbon fibre, so by tying all these together and working equally, the team co-developed the necessary elements to do this," says Gillette.

The 7E7 cross-section, which lies between that of the smaller 767 and bigger 777, is not truly circular, unlike its larger sibling, but ovoid. Unlike former designs, in which the intersections between the ellipses would have been contoured out with aluminium, the all-composite construction permits the entire one-piece section to be completed without any additional strengthening or filleting. "It's 15-20% lighter than aluminium, doesn't fatigue and doesn't corrode, and will require a lot less maintenance over the life of the programme," says Gillette. Stringers are co-bonded into the structure in the autoclave and composite frames will run the length of the fuselage, as will composite floor beams and panels.

Composite challenge

Originally, Boeing intended assembling the structure in a conventional way, but using composite panels in place of metal alloy. However, Gillette says the team instead "took the challenge of understanding the properties of composites and decided to make the fuselage in one piece. It's what composites really want." Gillette adds that the tests are "not really about the technical viability of the material. The challenge was to understand a manufacturing plan that allows you to build them at a commercial rate." The company made the commitment to go to a single-piece barrel in late 2003, thanks to the "instrumental" influence of Frank Statkus, the former Boeing Joint Strike Fighter programme vice-president and recently appointed vice-president of advanced technology, tools and processes. "We knew we would figure it out, the question was could we make it in time to meet the delivery schedule," Gillette adds.

The overall schedule calls for design freeze around late June for the firm configuration to be fixed and for assembly to start. In the meantime, design work on the 747LCF conversion is under way with the "first chainsaw hitting the aircraft at the end of the fourth quarter of 2005", says 7E7 vice-president Mike Bair. The first two 747-400s for conversion have been identified. "One is in the inventory and the second in China," says Bair. The final plan eventually involves three conversions, although only two are required to "get started", he adds.

Final 7E7 assembly will take place in Building 40-25 in the huge plant in Everett, Washington, a location that will be vacated by the second half of 2006 as the 777 transitions to a moving line in the adjacent 40-26 building. The assembly process for the 7E7 will be significantly shorter and simpler, however, largely because the large subassemblies will arrive at Everett already "pre-stuffed".

"It isn't very complicated, and the plan is not to have even a crane, other than maybe for the vertical tail," says Bair. Completion of the first aircraft is expected to be achieved in the second quarter of 2007, with first flight provisionally targeted for mid-2007 and deliveries starting around a year later.

Supercomputers

Digital definition is progressing on schedule, with several Cray supercomputers racking up over 650,000h of processing time on computational fluid dynamics (CFD) analysis. This process differentiates the 7E7 from the former models, which even during the digitally designed 777 programme ended up transitioning to conventional "drawings" that were gradually released to manufacturing. "This aircraft is being digitally defined, and we will go straight from digital definition right to building the aircraft," says chief project engineer Tom Cogan. Definition, formerly measured in percentages of design-release drawings, is therefore more closely defined in terms of gigabytes of design definition in the Enovia system data manager. "We have about 3Gbytes of the aircraft defined," he says.

Thanks to the massive computer power thrown at the CFD analysis, the aerodynamic design process is considerably shortened. "We tested between 50 and 60 wings on the 767, and on this we will come in at about 12 wings," says Cogan, who adds that from a performance perspective, "we aimed for 0.85 Mach and hit it right on the Mach number first time in the transonic windtunnel tests". The test effort is roughly two-thirds of the way through a planned 15,000h of windtunnel tests.

Another major effort, which began in December, is a weight-saving campaign aimed at paring manufacturer's empty weight back to target. Initially at least 3% adrift, it had reduced to 2.5% above target by mid-January and was "trending downwards", says Cogan, although he adds: "We still have a lot of progress to make towards our weight target, which is probably better than where the 777 was at this stage."

Systems and propulsion are also well advanced, with most contracts awarded . Given the "more-electric" design, it is perhaps not surprising that one of the areas of prime focus is on the development and test of the power-generation system. The 7E7 systems chief engineer Mike Sinnett says: "There has been a shift in the focus for all the teams to think about power, and power stability. That's a difference in some ways to previous programmes. We've all had to learn to be power engineers in some ways. In the past it was a stovepipe approach, with each looking after their own areas - but this way it is forcing a much broader view of the entire aircraft."

Dream power

With access to four 250kVA generators (two per engine) and two auxiliary power unit (APU) 225kVA generators, the 7E7 will have more available on-board electrical power than most airborne early warning and control aircraft, and will produce enough kilowatts to light a small town.

Tests of the generators and a wide array of other elements of this critical system (including the APU) will be taking place at a laboratory set up by Hamilton Sundstrand at Rockford, Illinois, while aircraft-level validation of the generators will take place in Seattle. Additional power system tests will also connect these labs with others in California and Connecticut.

The concept of giving more responsibility for individual and even multiple component and system tests to suppliers and "participants" is another key aspect of the 7E7. "With the 777 we did all of that integration at almost all levels, and now we're trying to concentrate on a higher level of integration responsibility," says Sinnett.

"The biggest difference is we're linking together different labs around Boeing and around the world. We're still running the SIL [systems integration lab] in Seattle for the flight simulators, all avionics, the flight-control system and the Iron Bird," Sinnett adds.

Pack leader

Boeing is also working with General Electric and Rolls-Royce on the GEnx and Trent 1000 engines as they move towards firm configuration, and with Goodrich on the nacelle. Design freeze for the nacelle and pylon is expected in April, says propulsion systems engineer Ron Hinderberger, who adds this necessarily is "ahead of the pack".

The design of the Hamilton Sundstrand APU, which does not have a load compressor as it is not required to supply bleed air for engine starting, is also being finalised, as is the configuration of the inlet and exhaust. "The inlet is tucked near the vertical stabiliser and rudder, and will look like a 777. To keep ramp noise to a minimum, we're ducting the exhaust totally aft and up, so that's driven us back to a more conical tail that looks more like a 767. We're looking at either a long exhaust muffler or a combined tail cone/exhaust chamber. There are some really meaty trade studies going on," says Hinderberger.

Boeing 7E7 and Airbus A350 performance
	7E7-8	A350-800	7E7-9	A350-900
Weights (t)
Max take-off	218	242	227	242
Max landing	TBA	182	TBA	189
Max zero fuel	TBA	170	TBA	177
Max fuel (litres)	TBA	139,100	TBA	139,100
Engine thrust (lb)	70,000	72,000	70,000	72,000
Performance
Range (km)	15,700	15,900	15,400	13,900
Pax (three-class)	223	245	259	285
Service entry*	H2 2008	H1 2010	**H2 2012	H2 2010
List price ($m) ***	125	153.5	TBA	170.5

Note *H = half **could be accelerated to late 2010. ***2004 delivery conditions TBA = to be announced

Source: Flight International