Gentlemen start your engines - F135 that is... (fixed)

spazsinbad · by **spazsinbad** » 19 Sep 2009, 01:31

Pratt: F135 Fan Fix Simple, Cheap Posted by Graham Warwick at 9/18/2009

Pratt & Whitney says it's standard industry practice - clip the tip of a blade to remove the piece that's susceptible to damage. And that's what the manufacturer plans to do with the fan blades on its F135 engine for the F-35, after a piece of the tip of a first-stage fan blade broke off during durability testing.

Pratt says the "potential cause" of the piece breaking off was an aerodynamic disturbance caused by a worn bushing ahead of the fan. The bushing is a cylindrical metal part used to seat, or locate, a component in the fan inlet case. Tear-down of the engine revealed all the bushings were severely degraded and some were missing.

That's not as bad as it might sound, because the blade damage occurred 2,455 cycles into a 2,600-cycle durability test of the initial service release (ISR) engine for production F-35As. That's the equivalent of eight years of in-service operation, Pratt says. When the tip broke off, the engine was 5 hours into a supersonic high-cycle fatigue test designed to deliberately excite blade vibration.

Pratt says the "minor modification" to be made immediately to all ISR engines will be to clip the corner off the tip of the fan blade at its trailing edge, removing the piece that broke off and "alleviating the potential" for it to fail. This will not degrade the engine's performance, the company stresses.

Engines for flight-test F135s are not affected, although the bushings are the same, because they have a "first-generation" fan that has already passed the required durability testing. The ISR engine has a "second generation" fan with lighter integrally bladed rotors. The bushings will be inspected periodically for wear until a new design is developed under the F135 component improvement program.

Source: http://www.aviationweek.com/aw/blogs/de ... d=blogDest

That_Engine_Guy · by **That_Engine_Guy** » 19 Sep 2009, 04:00

Yes; that sums up fan blade repairs...

Even FOD damage is 'removed' when blending. Ask any 'engine guy' :cool:

5 hours into a supersonic run!?! :shock:

WOW!
I doubt any 'installed' F135 will EVER do that; think of the fuel consumption! :twisted:

Keep 'em flyin' :thumb:

TEG

cobzz · by **cobzz** » 19 Sep 2009, 07:23

PW says the fix will have no negative impact on performance, however the comments on that page seem in indicate otherwise. Can anyone care to comment?

dwightlooi · by **dwightlooi** » 19 Sep 2009, 07:41

That_Engine_Guy wrote:Yes; that sums up fan blade repairs...

Even FOD damage is 'removed' when blending. Ask any 'engine guy'

5 hours into a supersonic run!?! WOW!
I doubt any 'installed' F135 will EVER do that; think of the fuel consumption!

Keep 'em flyin'
TEG

Not just 5 hours into a supersonic run, 5 hours into a supersonic run at a specific airflow rate where the vibrations are at their worst.

That_Engine_Guy · by **That_Engine_Guy** » 20 Sep 2009, 00:16

cobzz wrote:PW says the fix will have no negative impact on performance, however the comments on that page seem in indicate otherwise. Can anyone care to comment?

I agree with PW, and as I said just above, 'cropping' or 'tip-radius blends' are accomplished on a regular basis on ANY gas turbine engine when the tips or corners are damaged. (GE, RR, PW, CFM, etc...) Anyone not familiar with jet engine field repairs may think otherwise, but there isn't a performance issue here.

In the F100 series engine over 30 inches of blade leading and trailing edges may be removed by 'blending' before the fan is considered 'beyond limits' :shock:

In the example of a "hollow long chord fan blade" below you will see at the lower RH corner a small black line where our 'crack' is located. We will 'blend' or 'crop' the blade at it's tip using a constant radius.

The lower photo now shows our 'cropped' blade, the chord of the blade does not change, nor does the width, height, or tip clearances. The blade is still the same distance from the stators as it was before as well.

(Thanks to Paolo for putting his blade photos on the internet :cheers:

)

So any performance issues by doing this to a stage is almost non-existent; as you can clearly see very little material is removed from the blade, and all dimensions/twists/clearances are maintained while loosing a small fraction of surface area.

Like I said, ask any 'engine guy' about blade blending, it's a VERY common repair for FOD nicks and dents.

PW will address this in newer fans, don't worry about that. The bushing in question will be improved, as will the strength of the blades in the area 'cropped'. If any of us get to see the F135s in the field, I doubt many will see a 'cropped' first stage fan blade. If we do and the fans ever reach their first heavy maintenance, the improvements will be installed at that time.

NO production F135 will EVER operate in supersonic flight for 5 hours while experiencing 'maximum airflow'. Remember these are worse-case scenarios specifically designed to find weaknesses in the engine prior to them entering full scale production. There was no blade liberation, no catastrophic failure, no production delay, and no re-design of the fan as a whole.

This is simply good testing on PW's part and a good fix for a minor problem that 'could' arise 'if' a worse-case situation occurred during a 'maximum performance' request from the pilot after the engine was a few 'years' old.

Simply acknowledging the issue exists is clear proof that PW has the situation well in hand. (IE, not hiding anything)

Keep 'em flyin' :thumb:

TEG

Corsair1963 · by **Corsair1963** » 20 Sep 2009, 02:01

Not to ask a dumb question. Yet, why would they need to test the F135 at Supersonic Speeds for such a extended period of time??? (i.e. over 5 Hours)

That_Engine_Guy · by **That_Engine_Guy** » 20 Sep 2009, 02:28

Corsair1963 wrote:Not to ask a dumb question. Yet, why would they need to test the F135 at Supersonic Speeds for such a extended period of time??? (i.e. over 5 Hours)

Accelerated mission testing "life cycle" testing.

Put 8-12 YEARS of use and abuse "stress" on an engine in just a few months. (Just to make sure!)

Example:

Pratt & Whitney's F119 Engine Successfully Completes Accelerated Mission Test, Advances Toward ISR Approval

EAST HARTFORD, Conn., JUNE 18, 2001 -- Pratt & Whitney successfully completed accelerated mission testing (AMT) of the F119-PW-100 propulsion system selected to power Lockheed Martin’s F/A-22 Raptor aircraft, further readying the engine for initial service release (ISR) approval and operational deployment.

The AMT, performed at the Air Force’s Arnold Engineering Development Center, simulated six to eight years of operational mission usage of the F/A-22 weapons system. The test included a total of 4,330 total accumulated cycles (TAC) and 834 hours of engine operation at sea level and simulated altitude conditions. Altitude testing, which included 400 simulated high mach number TAC cycles at high inlet pressure conditions, demonstrated engine performance and operability throughout the F/A-22’s anticipated flight envelope. In addition, the engine performed extensive high cycle fatigue testing to demonstrate the long-term durability of the F119 propulsion system hardware. It is currently being shipped to Pratt & Whitney’s Middletown, Conn., facility for disassembly and analytical condition inspection.

"The AMT not only demonstrated the F119 engine’s performance, reliability, and durability," said Tom Farmer, Vice President of F119/F/A-22 Engine Programs, Pratt & Whitney. "It also shows the expected low cost of operation of the engine through its ruggedness. This parallels the exceptional capabilities being demonstrated during the ongoing F/A-22 flight test evaluation program at Edwards Air Force Base. This engine is setting a new standard for readiness and performance, and we are proud to be a part of an exceptional Air Force and Lockheed Martin team."

To date, the F/A-22 flight test aircraft have accumulated more than 520 flights and 1,160 aircraft flight hours.

Pratt & Whitney, a United Technologies company (NYSE:UTX), is a world leader in the design, manufacture and service of aircraft engines, space propulsion systems and industrial gas turbines.

Right now the F135 is getting it's AMT for ISR approval.

What I gather from the "cropping" article is that the F135 was in the middle of "extensive high cycle fatigue testing to demonstrate the long-term durability of the propulsion system hardware" portion of the AMT. PW's fix to get the current ISR motor's durability to 'pass' was to crop the blades to eliminate the spot that cracks. Future full rate production engines will have the issues reworked so that there isn't a problem in the future.

The AMTs are done at Arnold AFB.
REF: http://www.arnold.af.mil/library/factsh ... p?id=13893
(Note F100-PW-229 being tested!)

Keep 'em flyin' :thumb:

TEG
(Edit - hit the wrong button, wasn't ready to post!?! :doh:

)

spazsinbad · by **spazsinbad** » 21 Sep 2009, 21:30

Pratt Finds Probable Cause Of F135 Failure By Graham Warwick Sep 21, 2009

http://www.aviationweek.com/aw/generic/ ... line=Pratt Finds Probable Cause Of F135 Failure

Pratt & Whitney says the “probable cause” of fan-blade damage during ground testing of the F135 engine for the F-35 Joint Strike Fighter was a worn bushing — a part in the fan inlet case — causing an aerodynamic disturbance that led to a piece of the tip of a first-stage fan blade breaking off.

A “minor modification” will be incorporated immediately in all initial service release (ISR) production engines “with little or no impact on cost and schedule,” the company said during a teleconference Sept. 18. The blade tips will be clipped off at their trailing edges to remove the area susceptible to damage, a solution Pratt describes as “standard industry practice” (Aerospace DAILY, Sept. 15).

Blade damage occurred 2,455 cycles into a 2,600-cycle durability test — at the equivalent of eight years of in-service operation — and 5 hours into an 11-hour supersonic high-cycle fatigue test designed to excite vibration of the fan blades via throttle transients. Tear-down of the engine revealed all of the bushings were degraded.

The ISR engine for production F-35s has lighter “second-generation” integrally bladed rotors in the two-stage fan. F135s powering flight-test aircraft have a first-generation fan that has already passed durability testing, Pratt says. The F-35 Joint Program Office and Lockheed Martin have previously said no effect to flight testing was expected.