A center wing box design flaw has forced Boeing to redesign a critical section of the 787, program sources tell FlightBlogger, due to the potential for premature buckling in the structural spars.
Stiffeners will be affixed to restore structural integrity to the spars on the existing center wing boxes, which are manufactured by Fuji Heavy Industries in Japan.
When approached for comment, Boeing reiterated the statement it released yesterday regarding design changes:
“It is normal during the development of a new airplane to discover the need for design enhancements. We are working with our partners to address the need for design changes in some areas. While these changes are not good for final assembly because they are dealing with traveled work at this time, the design changes are not the sole pacing item.”
During the initial development phase of the center wing box, the structural spars were designed to the appropriate width to support the required structural loads.
The original design for the center wing box was changed when the weight of the Dreamliner began to increase. The structural spars, which are made of composite, were reduced in width as a weight saving measure.
Boeing and Fuji Heavy Industries manufactured composite test pieces to demonstrate the structural capabilities of the spars. Findings indicated that the composite spars were buckling prematurely compared to metal spars of the same width.
A source familiar with the situation tells FlightBlogger that Boeing became aware of the issue around the time of the July 8, 2007 roll out of Dreamliner One.
"Similar design changes happened in 777, but the difference is that 787 was so far away from weight target that many weight reduction ideas were adopted even though there was high risk due to lack to supporting test data or manufacturing experience," says a source familiar with the situation.
As a result, Boeing is incorporating an interim solution to the existing six center wing boxes under final assembly.
The stiffeners intended for the center wing box have already been delivered to the Boeing Factory in Everett and are being prepared for installation on the four airframes under assembly. Two additional center fuselage sections, which include the center wing box, are being prepared for final assembly at Global Aeronautica in Charleston, SC.
The center wing box is made from both traditional metals and composite. The new stiffeners will be composite and aluminum and matched to complementary areas of the structure.
FlightBlogger has been told that a redesigned center wing box will likely be ready for the first production aircraft, Airplane Seven, which is expected to be delivered to Japan’s All Nippon Airways in 2009.
The center wing box is the structural core of the aircraft representing an intersecting node between the wings, Section 43 on the forward end, Section 46 and main landing gear well at the rear, and Section 44 which caps the center wing box and completes the center fuselage section.
The first public indications of a wing box problem came from Boeing’s largest 787 customer, International Lease Finance Corporation chairman Steven Udvar-Hazy reportedly told a JPMorgan analyst earlier in the week that he does not expect the first delivery to occur until the third quarter of 2009 as a result of structural design changes that are needed to the center wing box, implying an additional six-month program delay.