F-35 JSF engines in critical tests as Congress deliberates

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Altitude testing of a pre-development General Electric/Rolls-Royce F136 alternative engine has been completed as Pratt & Whitney prepares for critical tests of its F135 primary engine for the Lockheed Martin F-35 Joint Strike Fighter.

The tests come as US Congress deliberates whether to overturn the Department of Defense's decision to cancel the F136 to save money. Testifying in late March, the US Air Force leadership said they would prefer to keep both engines, but that there was an issue of affordability.

The first system development and demonstration F136 is scheduled to run early in 2009, but the GE/R-R Fighter Engine Team has been using "pre-SDD" engines fitted with production-representative fan, augmentor and controls to conduct early conventional take-off and landing and short take-off and vertical landing testing.

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GE/R-R completed high-altitude afterburner testing of a pre-SDD F136 in late March at the USAF's Arnold Engineering Development Center in Tennessee. The tests included the common exhaust hardware for the F-35. A second pre-SDD engine is undergoing CTOL and STOVL testing at GE's outdoor site in Peebles, Ohio.

In April, P&W will test an instrumented F135 to confirm the root cause and verify the corrective action for the low-pressure turbine blade failure that affected two STOVL engines. The company believes the high-cycle fatigue failure results from vibration caused by interaction of the third-stage blades and vanes.

"We intend to demonstrate we can turn the phenomenon on, and prove we can turn it off," says Bill Gostic, F135 programme manager. The test will be repeated in September using an engine with redesigned third-stage blades and vanes, "to show the redesign turns it off", he says. The redesign uses two different vane spacings to disrupt the vibration.

P&W also hopes the April test will validate a "viable limited flight envelope" for the unmodified engine. This would allow Lockheed to begin STOVL testing with the first F-35B in September. Otherwise, STOVL testing will be delayed until December, after the redesigned engine has been installed, says Gostic. The F-35B is expected to begin CTOL-mode flight tests in June.