Guy Norris/SEATTLE

BOEING IS ON schedule to deliver large sub-assemblies for the first pre-production F-22 air-superiority fighter to its partner Lockheed Martin in September, amid rising confidence that the first flight will take place on time in late May 1997.

Boeing's two biggest sections of the F-22 are the large composite wing and the complex aft-fuselage assembly. "We're putting skins on the left-hand wing and will deliver the first shipset to Lockheed Martin in Marietta at the end of September," says Boeing F-22 operations senior programme manager, Bob Barnes.

Eleven shipsets will be delivered initially, nine for the aircraft being assembled under the $9.5 billion engineering and manufacturing development (EMD) contract, and a further two test units. Assembly of first production shipsets is expected to begin in 1997, even though EMD extends into 2002 under the revised time-scale.

Production of the wing skins, made from a toughened carbon-fibre composite called bismaleimide, has led to extensive use of newly developed manufacturing techniques, including numerically controlled precision drilling centres.

Three of these machines automatically drill holes in the exact location to the right depth and account for the effects of thermal expansion and other factors. The machines also eliminate "a tremendous amount of tooling and labour", says Barnes.

Composites account for around 28% of the F-22 by weight and include the "sine-wave" auxiliary spars inside the wing. The spars are made, by resin transfer moulding (RTM) in which, dry carbon-fibre laminates are laid up in a mould, into which resin is pumped.

"There are no defects, it's a completely robust process," comments Barnes. "The sizing of the spars is also very precise because of the pre-formed mould. This was a risky undertaking, but it was worth it," Barnes adds.

The company is also close to completion of the first centre-keel assembly, which forms the main part of the aft fuselage and is the backbone of the F-22. Attached to the predominantly titanium keel are highly loaded aft booms to which the horizontal and vertical stabilisers are attached.

Electron-beam welding is used to join the titanium boom castings, which are formed in two major sections before being manually spliced. For future weight saving,"we want to change it to a single piece which is all electron beam welded", says Barnes.

"At this point we have a good chance of making the first flight on time. From a cost stand point, we are slightly over but within 1%. We are also not overweight," stresses Barnes, saying that weight-saving measures taken after the critical design review in early 1995 have cut back around 300kg of total excess.

Pratt & Whitney has begun assembly of the first F119 flight-test engine for the F-22 and plans to deliver the initial shipset to Lockheed Martin in September.

Source: Flight International