Posted on 02/28/2023 8:42:22 AM PST by Paal Gulli
First reported here (twice), complete with video, when it happened last December at NAS JRB Fort Worth. The mishap was remarkable because the pilot ejected while the a/c was on the ground.
The news reports that followed all spoke to the engine as the cause -- which would seem to indicate that neither the pilot nor other aspects of the aircraft were under suspicion -- and DoD ordered engine manufacturer Pratt & Whitney to stop delivering new engines for the F-35B until the problem was sorted.
Last Friday, a news source that may not be quoted here for copyright reasons reported that P&W had identified the cause of the mishap as "a rare system phenomenon involving harmonic resonance" (in the engine). Not stated directly but P&W must have told DoD the problem is fixed because they have approved resuming engine deliveries. However, for reasons the story does not address (possibly waiting on a retrofit of "the fix" to all F-35Bs already in the field), the a/c are still grounded, which means the Marines won't be getting any new F-35Bs for the timebeing.
Harmonic resonance is the bane of mechanical engineers, and especially aircraft engines.
Not sure what that is. Could you hum a few bars?
The full accident report is still months away, but I wouldn't be surprised from watching the video that the "harmonic resonance" was first set up in the drive shaft powering the forward lift fan when the aircraft first hit the tarmac too hard.
Video of crash:
Spent 36 years in aviation maintenance and I’m familiar with Harmonic resonance but I’ve never heard of it in regards to an ejection event......I guess it’s possible.
Couple of wheel weights on the end of a a few turbine blades should do it.
I’m familiar with Harmonic resonance but I’ve never heard of it in regards to an ejection event......I guess it’s possible.
Counterfeit Engine Parts from China????
“Harmonic resonance is the bane of mechanical engineers, and especially aircraft engines.”
I’d add bridge/ structural engineers and provide an example of that bridge in the Pacific NW that shook itself to pieces back in the 1940s.
It is real.
Galloping Gertie. Tacoma Narrows bridge.
Although recently there was report it wasn’t really natural frequency issue.
Oh, I know it’s real, I just don’t think it had anything to do with the ejection...................
I used to experience harmonic resonance on a Dodge pickup. It would happen in the rear springs at about 50 mph. Leaf springs. I had to either speed up or slow down to get it to stop. Annoying.
Yes that would be interesting. I mean if they say it IS the engine. Perhaps the seat mechanisms are real weak!
Hard landing broke the front gear & aircraft started spinning. As soon as the spinning nearly stopped and aircraft was more level, the pilot punched-out.
Seemed like shutting down the engine was the problem at the time, which I don’t think would have anything to do with harmonic resonance.
Where I worked we were always vigilant about origin of manufacture of new aircraft parts were going use, and not just China either.....we actually had a list of countries that were banned from supplying parts.....even with all that occasionally parts from banned countries still made it to the production shop floor.....so I guess it’s possible.
Hey, at least they didn’t do the easy “pilot error” thing...
Just need a bigger flywheel. This baloney slicer from a Moto Guzzi should do the trick.
“I don’t think would have anything to do with harmonic resonance”
Me either, but that’s what aviation mishap investigations and Investigators are for.
The only thing I could think of would be a wire that got pinched when the aircraft bounced and shorted out switch like it had been intentionally ejected..............
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