Comments on: F135 Damage ‘Significant’ Or Easy Fix?

By: Stephen

Stephen — Wed, 30 Sep 2009 01:54:04 +0000

“One would think that in 8 years of use that the military would surely take apart the engine to ensure there is no damage.“
There are periodic inspections of engines, from magnetic plug, oil contamination(worn parts) to a visual borescope inspection of the internals of an engine. As well as a visual(eyeballs down the intake) every time an engine is started.
All aviation engines have a time to overhaul limit, that includes military engines.

By: Roger

Roger — Wed, 30 Sep 2009 00:34:09 +0000

The worn bushing may have been on an variable inlet guide vane or flapper vane stem ahead of stage 1 fan blades. The worn bushing could cause abnormal vane rotation or displacement and induce a 1/rev excitation as noted in earlier post. Early HCF results. Odd thing is the loss of blade tip is likely high order vib mode again resulting in fatigue failure.

By: bob

bob — Mon, 21 Sep 2009 18:48:43 +0000

Not sure if any of you have visited the f135’s website, but it does clearly state that the engine went through 5 hours of testing at “supersonic conditions” and endured the equivalent of 8 years of use. One would think that in 8 years of use that the military would surely take apart the engine to ensure there is no damage. If you don’t consider that point, then buy a new vehicle a never give it an oil change or any other maintenance and see how long it lasts you.

By: Rhys F

Rhys F — Mon, 21 Sep 2009 08:38:25 +0000

so they’re talking about a worn bushing, and a blade failing, with additional fuss about older blade airfoils not being affected… they could easily be connected. The worn bushing allowing slop in the rotation which stresses the fan and causes it to weaken along stress lines in the new airfoil design as the fan wobbles back and forth with the slop from the worn bushing.

This scenario make sense to anyone else in explaining the inconsistancies in the various stories?

A fan hat falls apart by itself would be “significant” and require a whole new fan re-design, but a fan that fails because of a worn bearing or bushing is not significant since all it would need is a more durable bushing, which is easier to retrofit than designing a whole new fan assembly.

By: Curt

Curt — Mon, 21 Sep 2009 06:30:19 +0000

The Congressional Staffer and the P&W rep seem to be talking past each other. P&W says the potential cause is a worn bushing and the fix is relatively easy, while the Congressional Staffer says the damage to the engine was significant. They both could be right. And yes, the P&W rep is trying to put the company in the best light and I am sure the Congressional Staffer has reason to want the F136 to be funded. Doesn’t mean that they are not speaking the truth.

By: Steve

Steve — Sun, 20 Sep 2009 01:48:18 +0000

Well, the story doesn’t make a whole lot of sense. One one hand Pratt is talking about a bearing in the fan section of the engine. Yet the damage seems to have come from a piece of a blade that failed in HCF (high cycle fatigue) which could be due to a 1 per rev stress from sometining up stream, or due to HCF resulting from a tip rub. Pratt says that the engines that are flying have a different fan blade (older design) that is not affected by the same failure as this event. So, my take is that a redesign (possible weight reduction) may be involved with the failure. The bearing thing is confusing however.
But this is the kind of thing that flight test and endurance testing should find. Doesn’t mean that Pratt is hiding anything just is unfortunate timing. Much better to find problems at the front end of the program than at the beginning or well into production.

Steve

By: Stephen

Stephen — Sat, 19 Sep 2009 01:51:39 +0000

More likely that that the aide works for a representative that’s beholden to the competition.
Either straight up campaign funding or jobs for constituents.

By: tipover

tipover — Sat, 19 Sep 2009 01:21:36 +0000

So how much time in an engine shop does this “staffer” have? Must be 20–30 years (retired E-8 or E-9?) since he seems to know all about jet engine development problems and solutions.