F35s grounded.

[b1beefer]

'Defence Specialist'?!

[barit1]

Rulebreaker:

As turbine failures are generally considered uncontainable this must be considered a serious event...

As has been discussed in the A380 QF32 case, it was the turbine disc failure (IPT in that case) that was uncontained, Turbine blade failures should be contained, at least in civil-certified engines. (I know of some exceptions in military engines, but cannot speak directly to the F135 engine requirement)

[SpazSinbad]

For 'barit1' comment on previous page: http://www.pprune.org/military-aircr...ml#post7710920

F-35s Grounded As Precaution After Crack Found in Engine Blade

"...Officials are shipping the engine and its associated hardware to Pratt & Whitney's engine facility in Middletown, Conn., to conduct more thorough evaluation and root cause analysis...."

[SpazSinbad]

A good 'history' of F135 engine problems here:

F-35 Grounded After New F-135 Engine Problems By Johan Boeder (Source: JSFNieuws.nl; published February 22, 2013)

F-35 Grounded After New F-135 Engine Problems

There is an apparent factual error here AFAIK:

"...Some facts about what happened
It was a F-135 engine with 700 hours, of which 409 flight hours. The aircraft was the F-35A test aircraft AF-2. The half-inch wide crack was found in a turbine blade of the low pressure turbine section...." Perhaps it is a DUTCH language thing but here is what was reported earlier:

Half-inch crack blamed for F-35 fighter jet grounding: sources - Yahoo! News : "...The engine blade crack that prompted the U.S. military to ground all 51 F-35 fighter jets was over half an inch long, according to three sources familiar with the matter..."

Jul 22, 2008 briefing by Pratt & Whitney on engine problems and fixes

http://www.defense-aerospace.com/dae...efing-2008.pdf (8Mb)

[SpazSinbad]

F-35 grounding sends pilots to simulators 25 Feb 2013
By Brian Everstine and Aaron Mehta - Staff writers

F-35 grounding sends pilots to simulators - Air Force News | News from Afghanistan & Iraq - Air Force Times

"...Matthew Bates, a spokesman for engine contractor Pratt & Whitney, said the damaged engine had arrived to a P&W facility on Sunday and that crews are working on inspecting the crack...."

[John Farley]

Does anybody know if the cracked blade was a rotor or stator blade?

[barit1]

The pdf linked in SpazSinbad's post explicitly points to the LPT rotor 3rd stage blade, calling it "mistuned" and vulnerable to high-cycle fatigue (HCF).

BTW, I'm very surprised to see this P&W pdf briefing appear "in the wild". The pages are marked "proprietary".

EDIT: Well gee, If I were only paying attention I would have noticed the P&W briefing is 5 years old. I can only guess that the current 2/2013 grounding is more of the same.

[Turbine D]

SpazSinbad,

Thanks for your post, very enlightening indeed relative to history and cause of early stage 3 blade problems.

It would be my guess the problem this time around will have a different cause. First of all, it happened on an Air Force F-35, rather than on a STOVL version intended for the Marines. In the 2007 time period, the 3rd stage turbine blade failure was associated with the behavior of the 3rd stage vane nozzle just ahead of the blade rotor. The cause was related to an unanticipated wake force function when in the STOVL mode. This caused vibratory stress levels in some of the 3rd stage blades that exceeded the single crystal material capability, notably, at #6 internal cooling crossover hole near the blade leading edge. Since crossover holes do produce a higher level of stress concentration, the failure (crack) started there. To resolve this issue, the #6 crossover hole was eliminated as well as the internal coating that had been used. Some changes to the 3rd stage vanes were also made.

Now there is a cracked 3rd stage blade discovered on the Air Force version of the engine which would seemingly have none of the causes related to the STOVL engine incidents. IMO, the cause of this crack will be different. Hopefully, we will learn what is discovered after the engine teardown and metallurgical examination of this new crack.

TD

[Lonewolf_50]

barit1: thank you for your incisive posts.
Courtney:

Does anyone here think we'll ever build the perfect engine that never fails, never catches fire, never gets upset? Is this the first engine that ever had a blade failure? Is this anything to do with the rest of the platform?

Come on. Wait and see before we judge. They have, after all, built a lot of good engines before, so probably know what they're doing. Above all, the engine isn't the biggest concern in the whole system.

All true.

The media and chattering classes and others thrive on drama, manufactured or otherwise. Turdine D, thanks for the distinction between B and A, which to many laymen watching the above mentioned drama would be obscure. I expect the engineers will figure it out.

[SpazSinbad]

99% Sure

Pratt rules out worst-case cause for F-35 blade crack: sources 26 Feb 2013 By Andrea Shalal-Esa

Pratt rules out worst-case cause for F-35 blade crack: sources - Yahoo! Finance

"WASHINGTON (Reuters) - Pratt & Whitney is 99 percent sure the fan blade problem that grounded the Pentagon's 51 new F-35 fighter jets was not caused by high-cycle fatigue, which could force a costly design change, according to two sources familiar with an investigation by the enginemaker.

Company engineers have concluded that a 0.6 inch-long crack found on a turbine blade in the engine of an F-35 jet at Eglin Air Force Base in Florida was almost certainly caused by lesser issues, such as high heat exposure or a manufacturing problem, that would be easier to solve, the sources said.

"They're 99 percent sure that it's not the worst-case scenario of high-cycle fatigue," said one of the sources.

Flights of the single-engine, single-seat F-35 fighter could resume as early as this week if the Pentagon accepts the findings of Pratt, a unit of United Technologies Corp (UTX), after additional tests to be done Wednesday, said one of the sources, who was not authorized to speak publicly....

...It was not immediately clear if the Pentagon would order a one-time inspection of all F135 engines built by Pratt for the new F-35 fighter, or whether the incident would result in a new recurring inspection requirement. Some inspections of the other 50 fighters already in use by the Pentagon were underway.

Pratt began detailed tests of the engine on Sunday evening at its Middletown, Connecticut facility after the blade assembly was removed from the Florida test plane and shipped north....

...The official, who was not authorized to speak publicly, said Pratt was expected to deliver a comprehensive analysis of the test results to Pentagon officials no later than Thursday evening.

Two sources familiar with the investigation said the fan blade tests would include a "destructive" test that would cut into the turbine blade to better understand how the crack developed.

Engineers believe the crack is either a "creep rupture along a grain boundary" that was caused by prolonged exposure to high heat, or that it was caused by an anomaly during the metal casting process, the sources said...."

[matkat]

To post number 14 the RR Trent 900 issue was not caused by turbine blade failure but as a consequence of the oil feed line in the IP/HP bearing house this in turn led to an oil fire which caused the turbine disc failure.


Barit1, sorry just saw your post and of course totally agree.

[Turbine D]

SpazSinbad,

It is always interesting, but adds to the confusion, when newspaper publications refer to fan blades, compressor blades and turbine blades interchangeably when they are not at all.

So, assuming the problem is with the 3rd stage turbine blade or any turbine blade and not a fan blade, finding the crack to be associated with a grain boundary would not be good as all the turbine blades are supposed to be a single crystal, having no grain boundaries. It is possible however, in a turbine blade containing complex internal passages (for air-cooling purposes) to have an isolated grain boundary form due to an undetected internal defect and stress concentrations that are associated with the defect. We will just have to wait and see what P&W finds in their examination. I kinda expect the finding will be isolated to this one blade and not widespread.

TD

[SpazSinbad]

Pentagon says no additional cracks found in F-35 engines Wed, 27th Feb 2013

Pentagon says no additional cracks found in F-35 engines - Finance News - London South East

"WASHINGTON, Feb 27 (Reuters) - The Pentagon on Wednesday said no additional cracks were found on F-35 fighter engines during inspections done after the Feb. 19 incident that has grounded the entire fighter fleet and halted operation of the engines on the ground...."

[LowObservable]

Good news for the program, as far as it goes.

However, it's too early to pop the bubbly and say "manufacturing only" because one of the things that we do, when it comes to things that are essential to the aircraft's ability to maintain a positive height AGL on demand, is make sure that they are all manufactured roughly the same way. So the root cause may not be design, but it still needs to be found and sorted out.

[SpazSinbad]

F-35 to return to flight after grounding immediately

F-35 to return to flight after grounding By AUSTIN WRIGHT | 28 Feb 2013

F-35 to return to flight after grounding - Austin Wright - POLITICO.com

"Lockheed Martin's F-35 Lightning II is returning to flight after its grounding last week over a crack discovered in an engine blade aboard an Air Force-model jet, POLITICO has learned.

The decision is effective immediately, said Joe DellaVedova, a spokesman for the Defense Department’s F-35 Joint Program Office. Pentagon officials were planning to issue a statement on the decision later Thursday evening...."

[SpazSinbad]

Pentagon says to resume F-35 flights 28 Feb 2013 by Andrea Shalal-Esa

Pentagon says to resume F-35 flights | Reuters

"(Reuters) - The Pentagon said on Thursday it would resume flights of its F-35 fighter jets, which were grounded a week ago after a crack was discovered in an engine of a test plane.

"F-35 flight operations have been cleared to resume," Pentagon spokeswoman Kyra Hawn said.

No additional cracks were found during inspections of engines in the rest of the F-35 fleet or in any spare engines, Hawn said.

Matthew Bates, a spokesman for Pratt & Whitney, which supplies the engines for the planes, said the Pentagon's F-35 program office had decided to lift a temporary suspension of flight operations after it conducted extensive tests on the affected engine part. The tests showed that a crack in a turbine blade stemmed from the "unique operating environment" in flight tests rather than a design flaw, he said.

Bates said Pratt had been working around the clock with Pentagon officials to determine the cause of the crack in the engine blade.

"The team has determined that root cause is sufficiently understood for the F-35 to safely resume flight," Bates said.

The engine in question had operated at high temperatures more than four times longer than a typical F-35 flight, which led to a separation of the "grain boundary" of this particular blade, he said...."

[SpazSinbad]

Engine Investigation Clears F-35 To Return To Flight 01 March 2013 By Guy Norris

Engine Investigation Clears F-35 To Return To Flight

"...The fleet was grounded on Feb. 21 following the discovery by borescope of a 0.6 inch crack in a third stage low pressure turbine (LPT) blade on U.S. Air Force test aircraft AF-2 at Edwards AFB, Calif.

Investigators were initially concerned the failure could have been a repeat of a high cycle fatigue problem which was uncovered with the LPT during engine testing in 2007 and 2008. However Pratt says “there is no evidence of high-cycle fatigue or low-cycle fatigue, and there is no evidence of fatigue progression on the turbine blade. We believe that a key factor for the blade crack stemmed from the unique operating environment in flight test.”

The manufacturer adds the engine “had operated more than four times longer in the high-temperature environment of the flight envelope than the typical F-35 duty cycle. The exposure in this high temperature part of the envelope led to a separation of the grain boundary on this single blade.” This type of separation failure is also known as a creep rupture. This occurs when deformation begins under constant load and high temperatures, and over time reaches a point where the blade material fails...."

Then an explanation about 'horizontal tail scorching testing' for this particular aircraft.

[barit1]

One must question the style of program management that takes engine hardware which hes been intentionally abused in development test, and is then installed in a single-engine tactical aircraft. Isn't this a needless risk to a high-visibility program?

OTOH, maybe the inspection cycle that "caught" the cracked blade was designed specifically to minimize this particular risk, and was perhaps even applied to this particular engine (or a like fleet). If so, I'll award partial credit for this precaution.

[SpazSinbad]

Not to worry...

Pentagon says to resume F-35 flights | Reuters By Andrea Shalal-Esa / Reuters 01 Mar 2013

"...The Navy order rescinding the flight ban, or so-called "red stripe," said that engine had experienced the most "hot engine time exposure" of all the engines in the developmental program. It said it would now require reports to monitor and limit similar damage after every 25 flight hours...."
______________

F-35 Engine Issue Isolated: Fleet Cleared for Flight 01 Mar 2013 Amy Butler

[JSFfan]

Ok, they have reduced the bore-scope inspection from 50hrs to 25hrs