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Design Notes: 787-9 lays the 787-10 foundation

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787-9_Rendering_560.jpg
With two and a half years to go before ZB021, the first production 787-9, is handed over to  Air New Zealand at the end of 2013, Boeing is advancing forward on detailed design of the larger 250 to 290-seat Dreamliner, while it appears to be quietly laying the foundation for the third variant, the yet unlaunched 787-10. 

Up Weight Paves The Way
First, Boeing has again increased the maximum take-off weight of the 787-9, though it's not entirely clear that the increase to 553,000lbs is driven entirely by regaining payload range capability due to an increase in airframe empty weight. Rather, one industry official indicates that the MTOW figure is be identical for the conceptual stretched 787-10. The increase actually appears to build a design bridge to the 787-10.

The same MTOW figures are indicative of structural similarity of the "simple stretch" -10, which hopes to fly 300 passengers a range of 6,900 to 7,000nm. If nothing else, the precedent for identical MTOW figures in Boeing stretches is found in the 777-200ER and 777-300, each with the basic takeoff roll weight capability of 582,000lbs.

While the 787-9 is starting to show signs of readiness for the -10, it still appears the larger jet is still "a long ways away" with hints of no earlier than 2015 and no later than 2017 starting to come in focus. 

A Question Of Fuel
Quietly tucked into the changing MTOW of the 787-9 is a further 44gal reduction in the aircraft's fuel capacity. While not a very significant reduction when compared to the overall 33,384gal capacity, the amount now sits 144gal below the 787-8. This is a small figure, but 787-9 is set to deliver a 500nm range improvement over the -8 with more structure and payload flying on a wing with an identical wing planform as the -8. In a February 2010 interview, vice president of airplane programs, Pat Shanahan offered these thoughts on the optimized design flying farther on less fuel with more payload and structure:
That's beauty of engineering, we're not going to extend the length, add the same planform and decrease the range. So, the team, through understanding the performance of the -8, optimizing the configuration, they found a way to get the range and the extra payload.
The Cart Before The Horse
All this talk of the 787-9 and -10 is - first - entirely dependent on the 787-8 and its final certified configuration establishing a transparent baseline to work from. That final configuration, said Spirit AeroSystems CEO Jeff Turner in his company's earnings call last week, will make the process of designing for the -9 considerably easier: 
I would say specific to the dash-9, as the dash-8 matures and nears certification, the dash-9 is a derivative off of that dash-8. So the more solid the dash-8 configuration is and becomes, the more straightforward the dash-9 derivative is. And that one is progressing very well.
Side-of-Body and Concept D
Before it was dismantled and relocated in pieces to the Boeing Boneyard in Everett, ZY997, the 787 static test airframe underwent a series of static tests with an updated side-of-body reinforcement modification designed for the larger -9 believed to be dubbed "Concept D". It is believed that Boeing is focusing particular attention on the side-of-body join, further refining this terribly troublesome area for both weight and further growth.

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Fuselage Length & Program Cost
The phrase "simple stretch" tends to be a terrible misnomer, but is intended to convey the idea that an airframe's modifications are generally limited to the fuselage and leverage capabilities already built into the smaller model, rather than optimize the airframe for equal payload and range performance. The 787-9 is made up of two 10ft stretches of Sections 43 and 46, placing all the structural growth into the center fuselage which is integrated in Charleston, already equipped with tooling for second model.

Industry officials say that design of the -10 is slightly smaller today than it was in 2007, but may still require a stretch of not just the 43 and 46 sections, but the 47 as well. The 2007 design stretched Sections 41, 43, 46 and 47. As the program seeks a low-cost investment to take on the Airbus A330-300, capital costs for tooling will undoubtedly be an important factor in keeping the investment low, stretching as few sections as possible is central to this say company sources. 

One potentially less obvious challenge is stretching the center fuselage so it still fits into the Dreamlifter. A 2008 diagram of the then-Global Aeronautica facility illustrated three types of centre fuselages on the pulse assembly line. Placing the full stretch in the center fuselage (preventing its air transport), could potentially make Charleston the base for the 787-10, saving tooling costs at Spirit and the nearby aft-fuselage fabrication facility.

Open Door For New Doors?
Saab North America, seeking to establish a presence in the US, identified the 787's doors as a possible opportunity to expand its supplier relationship with Boeing. Saab already supplies the cargo doors on the 787, while Toulouse-based Latecoere supplies the Czech-built passenger doors. Latecoere recently signed a long-term supplier agreement with Boeing, but the doors have been a source of trouble these last few years, requiring significant rework after delivery. Latecoere doesn't specify a variant in their announcement, but nor does Saab indicate on which model it hopes to expand its presence.

Renderings Credit Boeing

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