FLUG REVUE April 2005: JSF prototype construction advances

April 2005

F-35: MAJOR ASSEBLIES TAKE SHAPE

By Karl Schwarz

“OK, we're currently a few days behind schedule,” conceded Bob Elrod, who is responsible for the smooth development and build-up of production of the F-35 since August last year, during an interview with FLUG REVUE in Fort Worth at the beginning of February. Nothing serious, however, as “we are just starting on installing systems and are making good progress. And the system tests in the various test facilities are going according to plan.”

Only a few hundred metres away from his office, in the huge production hall, the first large-scale subassemblies of prototype F-35A-1 can be seen. While new improvements for simplifying maintenance are being discussed at a Kaizen event by the mock-up of the Joint Strike Fighter (JSF), technicians in a different area are working on the forward fuselage, which is fixed on its rotatable support. The cockpit floor has already been installed, and now it is the turn of the first wiring bundles to be fitted.

In another corner of the hall, the spar and rib structure of the wing, which measures around twelve metres by three end-to-end, is already standing on its side in its jig. It was completed in November 2004, and now awaits fitment of the carbon fibre composite skin. First of all the lower skin, manufactured by Vought in Milledgeville, Georgia, using a modern fibre placement machine, is attached and the holes required for the rivets are drilled. Following the detection and elimination of some minor programming errors dry runs, this is fully automated.

F-35 wing structure

While the lower skin is made up of two parts, the upper skin stretches from wingtip to wingtip. It was manufactured by ATK Composites (Alliant Techsystems) in Clearfield, Utah, using a 13 metre long, 4.2 metre wide and 2.4 metre high mould made of invar (steel containing a high proportion of nickel). Lockheed Martin tested the finished part for defects prior to assembly, using its patented laser UT scanner. For a precise fit, coatings of casing ply specially applied are milled to size.

It is not just at prime contractor Lockheed Martin that work on the first prototype is in full swing. Northrop Grumman has assembled the upper and lower halves of the central section of the fuselage in its factory in Palmdale, California, and begun work on the installation of hydraulic, fuel and electrical systems.

Meanwhile, at BAE Systems in Samlesbury, work on the left tail boom is nearing completion. As throughout, extreme accuracy was called for during the milling work on the structure, as the shape of the F-35 must match the design dimension precisely if the desired stealth characteristics are to be achieved. “We are speaking here of tolerances in the region of 0.2 millimetres – less than the thickness of a human hair,” explains BAE programme director Michael Christie. As well as the boom, BAE is also building the vertical fin and horizontal stabiliser. The former was worked on in January.

All the components are expected in Fort Worth in May so that final assembly can commence before the spring is over. This will be performed using a leading-edge Leica LR200 laser scanner, which is capable of determining the position of components to an accuracy of 0.02mm from a distance of 48m – and this is with sampling rates of 1,000 measurement points per second.

“Power on is planned for September, roll-out at the end of the year and the maiden flight here in Fort Worth in August 2006,” says Bob Elrod. Prototype A-1 is earmarked as a tool for aerodynamic testing, as its structure and the assembly methods used do not comply with the planned production standard.

“At the beginning we perhaps concentrated too much on maintainability and efficient production, which gave us a problem with the weight,” says Tom Burbage, joint head of F-35 management along with Elrod, looking back on a difficult year in which the STOVL Weight Attack Team was feverishly occupied with finding ways of shedding weight on the short take-off version of the F-35.

The problems and the resulting reorganisation of the programme, including slipping the first flights of the demonstrators and adjusting the production ramp-up, cost Lockheed Martin dearly. Whereas in the first year of the System Development and Demonstration (SDD) contract the company pocketed almost 95% of the potential bonus payments, by the beginning of 2004 this was down to less than 70 percent.

Despite this setback, Burbage is confident. “We now have a design that once again meets all the key performance parameters. The design of the USAF variant and the STOVL version is complete, and the aircraft carrier model will follow shortly. There are no changes to the unit costs.” On the other hand, Burbage adds, “We now have less commonality of parts in the structure. It is now more a matter of the same production processes, for example, for ribs of different thickness. But naturally all the systems are still identical.”

Some 400 design changes were necessary to cut 1225 kilograms from the F-35B STOVL version, which was almost ten percent overweight. The measures taken included:

A different structure in the centre fuselage area. The wing is now no longer superimposed on a lower structure but mounted as an integral unit with the full bulkheads. This design change will save 72.5kg.
A reduction in the weapons bay (including 46cm less length), which will no longer be able to hold large bombs. However, it will still be able to take eight 113kg small diameter bombs, 450kg JDAMs and the AMRAAMs.
A review of the entire electrical system: some individual devices have been discarded, one lithium ion battery is now 11.4kg lighter, and a less powerful starter/generator will save 53kg. Altogether almost 100kg can be saved in this area.

The engineers have coaxed out the equivalent of 270kg of weight through performance improvements in the propulsion system during the hover. Thus, the swivelling propulsive nozzle has been shortened by a few centimetres and the auxiliary air intake on the upper side of the fuselage has been aerodynamically optimised. Regulation of the offtake of engine bleed air to the roll control nozzles in the wing has also been modified. Whether the changes will bring the desired results will become clear in mid-2007 when the maiden flight of the first F-35B is scheduled to take place. Altogether the development phase provides for 15 flying prototypes and seven airframes for ground testing.

The first funds for the purchase of parts with long delivery lead times will be needed this year to build up to full production. Lot I, which will consist of five F-35A's for the USAF, will be ordered in fiscal year 2007.

“To fix the production plan, we need firm commitments from the international partners with regard to unit numbers and delivery schedules by December 2006,” Burbage explains. “This will require memoranda of understanding to be drawn up at governmental level. Discussions will begin this spring, as the subject is very complicated.”

The participation of industry in the partner countries will also play an important role. Most of the orders relating to the SDD phase have already been placed, and everyone who has joined the programme so far can expect good business on the biggest fighter programme of all time – as long as they remain competitive as regards cost, quality and delivery reliability. “The uppermost goal is an affordable aircraft, and in that area we are not making any compromises,” says Burbage.

From page 56 of FLUG REVUE 4/2005

Last updated 15 March 2005

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