F136 Needs New Lug Nut; Testing Again By Xmas

The second engine for the Joint Strike Fighter needs a fancy lug nut redesigned and should be back up on the test stand by the end of the year, a GE spokesman says.

The program has been dogged by rumors that it faced a potentially significant redesign of its combustor but the real problem lies with a lug that attaches the diffuser to the combustor, GE spokesman Rick Kennedy said Tuesday morning.

"The actual combustor will not have to be redesigned," he said. The lug in question is about the size of a small fingernail. The company will know in a few days whether it can proceed with a temporary fix or should pursue a permanent redesign of the lug, Kennedy said. He also said the company was not sure whether the problem with the lug lay with its supplier or if it is a design problem: "We don’t know exactly yet. We think it’s a design issue." The company has not finished its highly detailed failure analysis yet.

Once the lug issue is resolved, GE/Rolls Royce expect to have three engines functioning "early in the new year," Kennedy said, including the one taken off the test stand in early October after the lug failed.

Kennedy rebuffed claims that the F136 is lagging far behind Pratt & Whitney in its testing program.  Critics say GE only has 52 hours of testing and has suffered four failures during SDD while Pratt's engine had undergone 700 hours of SDD testing with no failures at roughly the same point in the program.  "Our SDD test program is different from Pratt's...  We did all this pre-SDD testing," Kennedy said, while conceding that GE has "not run as many hours of testing as w would like in 2009."

The engine's fundamentals are all where the company wants to see them at this point, he said, saying thrust, heat and wear data are all looking good. He said the company has had to go slow at this phase in the program because "you have to put 2,000 sensors on the engine." Two of the four engine shutdowns occurred after testing sensors got sucked into the engine. One was the problem with bearing clearance that was resolved pretty quickly. And the fourth and most recent failure involved was the lug nut. "They are not design issues with the engine," he said, adding that reinstalling the 2,000 testing sensors delays testing by weeks.