Second Failure Surprises Engineers

A cracked turbine blade in the Pratt & Whitney F135 turbofan destined for installation in the second F-35 joint strike fighter test aircraft has raised new concerns about the JSF program, though the manufacturer maintains a fix is in the works.

The Fort Worth (TX) Star-Telegram reports the crack was discovered Monday, following ground tests on the engine slated for installation in the first short-takeoff/vertical landing (STOVL) F-35B variant within the next month.

Pratt & Whitney believes the problem is due to unforeseen stress on the turbine compressor blades on the uprated STOVL variant of the engine. A similar problem was uncovered during tests on the same engine last year; after that failure, Pratt & Whitney went to work on redesigned turbine blades, slated to come online this summer.

In the meantime, the enginemaker implemented a series of tests to determine when the problem could reoccur. Engineers thought they had a handle on the problem... until Monday's failure.

"It's not a new issue. It's disappointing we didn't notice it until the part cracked," said Bill Gostic, vice president for F135 engine programs at Pratt & Whitney. Gostic added engineers think the problem is isolated to the STOVL variant (shown below), in which a drive shaft from the turbine is connected to a large, downward-facing ducted fan to provide vertical light on takeoff and landing. The drive shaft places additional stress to the blade disc, and the turbine blades.

On Friday, a senior official at Lockheed Martin, manufacturer of the F-35, told the Star-Telegram initial flight testing of the second F-35 shouldn't be delayed for long, based on discussions this week with Pratt & Whitney. First flight is targeted for late June.

"Our plan all along was to fly conventional first," said Dan Crowley, Lockheed's executive vice-president for the F-35. Initial testing of the aircraft's STOVL capabilities isn't scheduled until early next year -- by which time the blade fix should be in place.

"It’s the purpose of the development program to run these kinds of tests and find these problems," he added.

If such a blade failure occurred in flight, the results could be catastrophic. Of far greater concern to the F-35 program in the short term, however, are the ramifications of the failure at a time when lawmakers and Pentagon officials alike have the F-35 in their cost-cutting crosshairs.

The F-35 is the Pentagon's most expensive single weapons development project. Its estimated pricetag of at least $299 billion is almost twice that of the next priciest program.

If flight tests are delayed due to the blade failure, opponents could point to that lack of progress as justification for drastically scaling back the program. Adding to the turmoil is the likelihood one of the fiercest JSF proponents, Deputy Defense Secretary Robert England, will likely leave office by the time a new presidential administration takes office next January.

News of the problems also gives added ammunition to those calling for a second engine choice for the F-35. As ANN reported earlier this week, funding for development of the General Electric/Rolls Royce F136 was stricken from President Bush's fiscal year 2009 budget plan, the third year in a row the Bush administration has pushed to axe the project.

In each of the previous years, funding was restored in Congress.

FMI: www.pw.utc.com, www.lockheed.com