Boeing 787 Dreamliner - Mark Wagner [39]
A stepping-stone toward composites on the 787 was the Boeing-NASA ACEE program in 1975. Under this effort five 737-200s were fitted with an experimental composite horizontal stabilizer and placed into regular service in 1984. Composite NARMCO T300/5208 replaced standard aluminum in a co-cured, stiffened-skin structural box arrangement with I-section stiffener panels. The unit incorporated two titanium spar lugs bonded externally to a precured graphite-epoxy chord. Although one, a MarkAir-operated aircraft, crashed in bad weather in Alaska in 1990, all the others flew until retired. On inspection all the stabilizers were found to be in virtually perfect condition. Here the second test airframe, a Delta Express aircraft, taxies at Orlando International, Florida, in 1996. Mark Wagner
However, it was the FS-X, a Japanese fighter project, that helped both Mitsubishi and Fuji boost their composite wing structure and building experience. The FS-X was developed as a semi-indigenous replacement to the aging McDonnell Douglas F-4. The FS-X, which was later called the F-2, was led by Mitsubishi and based heavily on the General Dynamics (later Lockheed Martin) F-16 design but with several advancements, including use of co-cured composite structures in a larger wing. In this process, the wingbox and skin could be cured and bonded in a single process, a production breakthrough that would have massive implications for the 787 more than a decade later.
The 7J7 was meanwhile terminated by Boeing in 1987 amid airline concerns over propfan noise and other technical challenges, and the company refocused instead on further developments of the 737 and the 757 to counter the growing threat from the A320. But the legacy of the 7J7 lingered, and in some cases provided a technology bridge to the 777, which benefited from the early development work.
Experience gained on the 7J7 empennage, which represented the first significant use of a toughened-resin CFRP material, plus test results from an experimental Boeing-built, 767-size composite horizontal stabilizer, encouraged the company to go in this direction for the 777. The march of time also meant carbon fibers with improved strength and stiffness, such as Hercules IM7 and Toray T-800H, were now available as well as tougher matrix polymers.
In addition, Boeing had gained valuable experience with large-scale composite structure work under NASA’s 1989 Advanced Composites Technology (ACT) program, which aimed to improve the efficiency of composite structures and to reduce their manufacturing costs. The program aimed, very simply, to reduce air travel costs through the use of composite materials on commercial aircraft. Targets included a 20 percent cut in production costs and a 25 percent cut in weight compared to conventional aluminum structures.
Early on, Boeing’s research involvement was tied to the advanced composite fuselage side of the $130 million effort, while McDonnell Douglas focused on the wing. Long Beach, California–based Douglas Aircraft was interested in using the ACT-derived wing on several future projects, including a new-generation twinjet dubbed the MD-XX. However, Boeing assumed the wing work through the 1997 merger with McDonnell Douglas.
Buoyed by ACT and 7J7 work, Boeing homed in on a 777 design in the early 1990s that overall was 12 percent composite by weight. Most of this was in the tail, where the stabilizers (vertical and horizontal) were designed with composite main and auxiliary torque boxes. The main boxes were made from CFRP, with solid laminate front and rear spars, honeycomb sandwich ribs, and integrally stiffened laminate skin panels.
The main box spars and panels used a toughened-matrix CFRP material from Toray called T800H/3900-2, a direct forerunner of material that would later be featured on the