It all Comes Down to a Bushing in the F-35 Joint Strike Fighter

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I’m not too sure how many people follow the F-35 Joint Strike Fighter program (I actually typically haven’t though I remember Deloitte competed for some aspect of that program when I was there back in 2003). I enjoy popping onto Aviation Week every now and again for blog fodder. This week’s visit did not disappoint. Apparently a fan blade incurred some damage during ground testing of the F135 engine built by Pratt & Whitney. Pratt & Whitney believe it all came down to a worn bushing. We should point out that the damage occurred at 2,455 cycles of a 2600 cycle durability test, or the equivalent of 8 years of in-service operation. The fix, according to Pratt & Whitney announced on a call on September 18 involves a snip of the blade tips, clipped off at their trailing edges to remove the areas susceptible to damage, according to the Aviation Week article.  Not a big deal according to the main article in the Aviation Week website.

But flip over to a blog post written on the same subject by the same author, where he goes on to say, This will not degrade the engine’s performance, the company stresses, and you will find some very interesting dialog in the comments section.

To wit, [Dangerous] wrote, “This will not degrade the engine’s performance, the company stresses.” This is incorrect, it certainly will degrade performance. This is pure spin control in the face of the GE-PW engine PR war which is in its final throes (for this year) with House-Senate conference upcoming. Sure this is “standard practice” to solve fan Aeromechanics issues but then why aren’t fans designed this way in the first place? Because clipping the tips kills fan efficiency, which increases fuel burn and thus impacts aircraft range. F-35 will see a range impact to this change, until or unless another root cause is identified, like those bushings, or the fan is redesigned again.

I have no idea if Dangerous is correct but the dialog over the engineering fix for this bushing makes for interesting learning and demonstrates the kind of educated discussion taking place in the aerospace blog world.

–Lisa Reisman

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