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The X-35A, built to validate propulsion and flying qualities for the Joint Strike Fighter, takes flight in October 2000. (Lockheed Martin)

Weight Watchers

How a team of engineers and a crash diet saved the Joint Strike Fighter.

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(Continued from page 5)

Performance had to be guarded, but the government also wanted to control cost. The F-35 started as the most expensive warplane in history—no one wanted the price tag to increase.

Military customers fretted that the airplane’s maintenance and logistics demands would increase due to the redesign. In response, SWAT included the impact on these parameters in its database of design changes. “We didn’t have those constraints,” Sheridan says. “But we definitely kept an eye on them…. [The JPO] had fear we were going to trash supportability.”

A major blow to the JSF manufacturing concept, leading to an increase in production costs, was the abandonment of “quick-mate joints.” The idea was to attach interlocking parts to individual components that would make the final assembly of the fuselage, wings, and engine easy, like snapping and soldering jigsaw puzzle pieces. But the interfaces drove the weight up by about 1,000 pounds, so a traditional, time-consuming joining system was adopted. All three F-35 variants lost their quick-mate joints to preserve production commonality.

The JSF team had earlier hatched a new idea to cut cost—use “cousin parts” instead of the sometimes heavier common ones. The concept was going to be applied to trim weight as well as cost.

A cousin part is manufactured using the same machine, but the computational design information is altered to produce a part unique to a variant. If a part is designed to handle certain stresses arising only during a carrier landing, it can be remade with the same tool for the conventional takeoff-and-landing variant, with only a minor cost increase. A commercially available part can be shaved to save room, offering, in some cases, a direct route for a hose rather than a circuitous one. Less hose equals less weight. Unique items cost more to manufacture and to replace, but the weight savings sometimes necessitated the higher cost.

Enewold says the production cost of F-35s has risen slightly due to implementations of SWAT plans. The effect on supportability cost is yet to be seen.

In October 2004, the Defense Acquisition Board signed off on more than 500 recommendations, officially making the STOVL weight loss attack team a success.

In eight months, the Lockheed engineers cut a total of 2,700 pounds from the F-35B. The effort also trimmed 1,300 pounds from the other variants. Comfortable with that legacy, SWAT faded, with accolades, into company history, but an estimated 20 ideas a week still turn up in the Weight Improvement Program office.

Design and assembly changes, mostly related to the SWAT recommendations, have cost about $4.8 billion—part of a $6.2 billion replanning to accommodate the additional design cycle required to make the improvements. The replanning forced an 18-month slip in F-35 deliveries. According to a 2006 Government Accountability Office report, since inception, the development costs of the JSF program have increased 84 percent and its timeline slipped by about five years. The STOVL’s final delivery deadline has been extended two years, to 2012.

When AA-1, the first CTOL F-35, rolled out of the assembly building on a gray, misty morning last February, it featured none of the SWAT-era optimizations. The weight of this F-35A is greater than what was originally projected, but not so high that the aircraft does not meet key performance parameters, Lockheed officials say. The margins would be very tight—they are not wide, even with the redesign—but it would have made it. Every F-35A that follows will be lighter.

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