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Pratt & Whitney is investigating how a "handful" of fan blade tips damaged an F135 engine during a ground test simulating the Lockheed Martin F-35's engine performance at supersonic speeds.
The programme's latest technical issue comes amidst a heated debate between the White House and Congress about continuing to fund the F135's rival engine - the General Electric/Rolls-Royce F136.
Upon inspection, the errant parts were traced to several missing fan blade tips that somehow broke off. The parts were ingested into the compressor, which also sustained damaged in the first and second stages, P&W's expert says. The combustor and turbine stages escaped harm from the flying debris.
Pratt also says there should be no impact on F-35 flight testing, as the engine that failed has the "second-generation" IBR fan, which is lighter. The flight-test engines have the first-generation fan, which has already undergone durability testing, the company says. There is no halt to flight testing or engine ground testing, Pratt says.
Two other second-generation engines are on ground test and are being examined. The damaged engine should be repairable to retstart and complete qualification testing, the expert says. The fan will have to be replaced, but damage to the compressor blades is blendable and the rest of the turbomachinery looks undamaged.
this fan was built to replace the first generation fan (which cracked and failed)
Pratt: F135 Fan Fix Simple, Cheap.
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 "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.
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.
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'
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.
*included example of cropping*