How a team of engineers and a crash diet saved the Joint Strike Fighter.
- By Joe Pappalardo
- Air & Space magazine, November 2006
(Page 7 of 8)
Still, he adds, the JPO needed to get some decision makers on the scene during the redesign to provide “sanity checks on trades” that were being suggested. A dozen colonels, majors, and upper-level civilian managers stayed in Fort Worth through 2004 to analyze solutions and sign off on program-level changes, something the usual retinue of about 20 JPO liaisons at Lockheed could not do.
Some half-dozen SWAT ideas were rejected, Enewold says. Lockheed engineers suggested reducing the maximum G forces the STOVL could pull, for example, but the JPO insisted it stay at 7 Gs. An attempt to remove some fire suppression generators was also nixed. “Even since then [SWAT], we’ve made some design changes that add a little weight,” he says.
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.