Designers creating the F-35 Joint Strike Fighter plan to combine best-value production techniques and extensive polymer matrix composites.
Thick composite wings will help carry the physical load in the multifunction aircraft, which is targeted for a broad international market.
JSF designers begin on the outside with precise surfaces incorporating low-observable stealth characteristics. In the past, designers created interior structures first and worked later on exteriors.
The program uses more composites and less titanium than recent fighters, Tom Burbage said May 14 in Long Beach, Calif., to the Society for the Advancement of Material and Process Engineering. Burbage is executive vice president of Lockheed Martin Corp.'s aeronautics company in Fort Worth, Texas, and the JSF program's general manager.
Other partners are Northrop Grumman Corp.'s integrated systems sector in El Segundo, Calif., and Farnborough, England-based BAE Systems' programs organization.
Three JSF variations have similar frame structures: heavier for the U.S. Navy and lighter for the Air Force, Burbage said. The Marines get a third version.
Burbage projects 81 percent commonality ``with the same molds and the same tools.'' Machining instructions will vary.
Composites account for about 36 percent of the proposed structural weight. Of the total, graphite epoxy represents about 32 percent and fiberglass and graphite bismaleimide make up 2 percent each.
``I will not be ashamed if it goes down'' from 36 percent, Martin McLaughlin of Northrop Grumman, director of the JSF airframe integrated product team, said in a telephone interview from Fort Worth.
By comparison, composites make up about 30 percent of the structural weight of the Air Force's B-2 bomber, 26 percent of the Air Force's next-generation F-22 fighter and 18 percent of the Navy's upgraded F/A-18E/F.
The partners will use suppliers to produce close-tolerance composite components, McLaughlin said. ``When we marry [those parts] to the [aluminum] substructure, they must fit. They can't bend.''
In the monocoque construction, thick, heavy composite skins carry more of the total load than in other fighters, McLaughlin said.
Designers ``unitized the skins into bigger chunks and minimized the number of seams on the aircraft,'' he said. ``We believe we have hit the nail on the head with relatively wide frame spacing'' and hefty composite masses.
The interior frame uses one-half as much substructure as exists on the F-22. Extra systems fill available gaps.
``We have not done the final selection of materials and processes yet,'' McLaughlin said. ``We have nearly all key suppliers under long-term agreements, and they are participating in preliminary design'' using previously certified materials.
Hexcel Corp. will supply 12,000- and 6,000-filament versions of IM7 graphite fiber. Hexcel makes the intermediate-modulus polyacrylonitrile-based fiber in West Valley City, Utah, said Jon Stowell, international vice president of marketing with Hexcel's composites business unit.
Using Hexcel fibers, Cytec Industries Inc.'s engineered materials division will preimpregnate unidirectional tape and woven fabric in Greenville, Texas, using toughened 977-3 epoxy, and in Anaheim, Calif., using BMI 5250-4, McLaughlin said. A Wrexham, Wales, facility will support European needs.
Loctite Corp.'s aerospace unit in Bay Point, Calif., will supply rolls of SynCore syntactic film. The low-density material increases stiffness of wings, fuselage and engine nacelles, reduces the required number of stiffeners and cuts cost and weight, said John Hutcheon, Loctite Aerospace western area manager. Loctite Corp. reports within the technologies group of Germany's Henkel KGaA.
Initially, Lockheed Martin will assemble the forward fuselage and wing in Fort Worth and the control surfaces and edges in Palmdale, Calif.
Northrop Grumman will assemble the central fuselage in either El Segundo or Palmdale.
BAE Systems will assemble the aft fuselage and empennage in Samlesbury, England.
Foreign suppliers will get work. Burbage said Italy's composites capability could make it a second source downstream.
Lockheed triumphs in JSF competition
Beginning in 1996, teams led by Lockheed Martin and Boeing Co. waged a winner-take-all fight that concluded last summer with demonstration JSF flights.
In late October the Defense Department selected Lockheed Martin's concept, triggering a $19 billion system-development and demonstration phase that extends to 2012.
There is ``a popular misconception that we are ready for production,'' said McLaughlin. ``We were fortunate enough to be selected to proceed.''
Preliminary design work, now under way, emanates from the winning concept, but changes are contemplated. Unitized structures, fiber placement and laser positioning are key design goals.
The schedule calls for completion of detailed designs in 2003, initial flights in 2005, low-rate production in 2006 and operational capabilities in stages beginning in 2010-12.
The Air Force version takes off and lands from conventional runways. Basic cost: about $40 million.
The version for the Marines and Britain's navy and air force has a shaft-driven metal lifter fan and diverter nozzle permitting short takeoffs and vertical landings. Cost: nearly $50 million.
The Navy model has a stronger wing box and airframe to absorb stresses of catapult launches and carrier landings. Larger wing and tail surfaces and wingtip ailerons allow aircraft control at slower landing speeds. Cost: in the middle.
Burbage said the United States purchased few fighters during 1994-99, and its aging inventory is approaching the end of its life.
About 3,000 fighters are being produced for the United States and the United Kingdom. Volumes could double eventually with expanded international sales, although makers of the Eurofighter Typhoon and joint venture Saab-BAE's JAS-39 Gripen will compete for foreign sales.