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R44 mast rocking NTSB recommendations


deerock
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They cover this at the Safety Course now. I believe it had something to do with a batch transmission mounts being made from a different grade of rubber (or something like that)?

:huh: :)

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They cover this at the Safety Course now. I believe it had something to do with a batch transmission mounts being made from a different grade of rubber (or something like that)?

:huh: :)

 

How I understand it, they would test each 44 when new and if they rocked more then they should they would put heavier duty mounts on it, if they didn't rock they would keep the stock mounts on it...

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How I understand it, they would test each 44 when new and if they rocked more then they should they would put heavier duty mounts on it, if they didn't rock they would keep the stock mounts on it...

So I've always wondered what happens at the 2200 hour overhaul and the mechanic replaces the trans and mounts....oops.

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Robinson seem to have had notice of this since at least 2007,if you have done the Robinson safety course it appears that they now tell you about the procedure to combat the problem, shame they have not bothered to notify all owners, I understand there has been 3 machines damaged due to this problem, no one killed or hurt.

There is a lot of info out there on other sites regarding mast chugging or rocking, with some first hand reports.

The following remarks are taken from the FAA Flight Test Report dated 20 December 2007:

It was confirmed during these flights that the oscillation can easily be induced in the one helicopter that was a new production aircraft which had been through all production flight test procedures and signed as satisfactory with 4.0 hours on the Hobbs.

The second helicopter was a factory machine used for research and development that had 511.6 hours on the Hobbs.

On this aircraft, the oscillations could not be replicated by the test pilots.

Both helicopters were ballasted at the maximum forward centre of gravity

 

There were minor differences in the two aircraft configurations that in the view of the pilots, would not invalidate the comparative test.

However, the R&D factory-aircraft that could not replicate the oscillation was fitted with stiffer vibration isolators on the front main transmission mounts.

In this aircraft “the subject vibration could not be induced by any manoeuvre”

 

In the ensuing post-flight meeting between the test pilots and Robinson personnel, it was agreed that the problem is associated with the main transmission vibration isolation mounts and that this oscillation was not hazardous, but did exceed the vibration criteria of 14 CFR27.251 (whatever that is).

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In the ensuing post-flight meeting between the test pilots and Robinson personnel, it was agreed that the problem is associated with the main transmission vibration isolation mounts and that this oscillation was not hazardous, but did exceed the vibration criteria of 14 CFR27.251 (whatever that is).

 

The entire section of faa 14 cfr27.251 reads as follows:

 

§ 27.251 Vibration.

 

Each part of the rotorcraft must be free from excessive vibration under each appropriate speed and power condition.

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The entire section of faa 14 cfr27.251 reads as follows:

 

§ 27.251 Vibration.

 

Each part of the rotorcraft must be free from excessive vibration under each appropriate speed and power condition.

 

Thanks for pointing that out, Helistar

If you read the first hand reports the vibes were somewhat greater than I would want in ANY helio I was flying or in.

If you were low time pilot could you cope? even people with a fair few hours have said they thought the machine was going to disintergrate.

I would have thought it was beholden on Robinson to diseminate the saefty information they had.

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My concern is that Robinson is aware of the issue and have installed the stiffer mounts on their test aircraft knowing it resolves the vibration issue. However this raises another concern, what if anything is known about possible metal fatigue resulting in the vibration being transferred to the surrounding metal structure around the mounts? It's a valid question and I'd be interested in knowing if any type of information is available in the way of actual knowledge or the possible requirement of additional inspection requirements being needed if the stiffer mounts are installed...

 

disclaimer: I'm in no way an expert in this area study and am simply expressing my concern and thoughts on the subject...

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  • 2 weeks later...

Is this in reference to the R-44 "bucking"? I actually did a research project on this in June. I wrote a paper regarding this issue, and possible solutions regarding it. It was for a propulsion plant (accident) investigation class. I'm glad that the NTSB has recommended these things, the pretty much scream what I wrote in my paper.

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