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-   -   Question for Brian Cobb (http://www.rotaryforum.com/forum/showthread.php?t=47020)

Mike G 02-11-2017 05:42 AM

Question for Brian Cobb
 
Bryan
Where does this:
"3.0 IPS vibration (unairworthy by FAA standards) and a 0.5 IPS vibration (well within acceptable standards of airworthiness)."
come from?

If it's an FAA document I'd like to understand the context.
Mike G

bryancobb 02-11-2017 06:39 AM

Vibes
 
Quote:

Originally Posted by Mike G (Post 647910)
Bryan
Where does this:
"3.0 IPS vibration (unairworthy by FAA standards) and a 0.5 IPS vibration (well within acceptable standards of airworthiness)."
come from?

If it's an FAA document I'd like to understand the context.
Mike G

I have been diligently searching for that elusive document for us :)

I remember reading and seeing it SOMEWHERE...AND...It agrees with
manufacturer's limits in the Maintenance Manuals for helicopters I am familiar with.

I will post every tidbit of supporting data I can find to support my statements. Thanks.

Bryan

Jincamty 02-11-2017 12:35 PM

I had >3 IPS @ 2/rev up at the mast on a homebuilt helicopter and it's bloody scary.
Much like a car that is about to loose a tire at 100 mph.
I can see why there would be an upper limit from the authorities.

Cheers Cam

hillberg 02-11-2017 12:57 PM

The manufacture will determine the ips required in helicopter operations after maintenance - The Helicopter Directorate in Fort Worth will adopt general limits as a reference in Advisory Circulars ...AC 27-1A AC 29 2C ????

bryancobb 02-11-2017 05:56 PM

I didn`t have time to post the pics today but I looked up 8 different helicopters` Approved Maintenance Manuals and every one of them listed 0.2 IPS as the maximum to be accepted. All the instructions said something like keep at it until the maximum vibrations are under 0.2 IPS.

All polar charts had their outer (worst vibes) ring at 1.0 IPS.

Everything from the MD-600N to Bell 47 to Robinson R-66 and Enstrom. Haven`t yet found the UH-1 stuff but still looking.

HobbyCAD 02-11-2017 07:23 PM

What's the expected IPS of the CH-47 rear rotor?

Jincamty 02-11-2017 08:29 PM

This one got up to 400 IPS before destroying the transducer :-)

https://www.youtube.com/watch?v=roN2jvu-Jis

brett s 02-12-2017 10:32 AM

Every helicopter I've worked on had the acceptable limit set at 0.2 IPS, including CH-47's.

The older metal blades were a lot easier to track & balance on Chinooks than the composite ones they rolled out in the 80's. They also weren't nearly as tough & made less lift though.

HobbyCAD 02-12-2017 12:23 PM

Quote:

Originally Posted by brett s (Post 647942)
Every helicopter I've worked on had the acceptable limit set at 0.2 IPS, including CH-47's.

The older metal blades were a lot easier to track & balance on Chinooks than the composite ones they rolled out in the 80's. They also weren't nearly as tough & made less lift though.

My experience in Chinooks has been to sit as far forward possible, for the rear was always teeth chattering.

Jean Claude 02-13-2017 01:54 AM

Bryan,
Just observing the maintenance manual of the Robinson R22, it appears to me that the IPS requirement is only for 1/rev, since in hover. I see no IPS requirement in forward flight (2/rev).

http://img110.xooimage.com/files/b/9...re-519a4d2.png

http://rotorcorp.com/wp-content/uplo...ck_balance.pdf

bryancobb 02-13-2017 03:12 AM

Quote:

Originally Posted by Jean Claude (Post 647959)
Bryan,
Just observing the maintenance manual of the Robinson R22, it appears to me that the IPS requirement is only for 1/rev, since in hover. I see no IPS requirement in forward flight (2/rev).

Usually JC, the very next procedure in the Maintenance Manual is the forward flight T&B. Then after that you make one more fine adjustment in a hover to conclude.

bryancobb 02-13-2017 03:31 AM

http://i1271.photobucket.com/albums/...ps0zj855do.jpg

Jean Claude 02-13-2017 04:09 AM

Bryan, How much IPS max are required during the forward flight, here?

brett s 02-13-2017 05:24 AM

Quote:

Originally Posted by HobbyCAD (Post 647948)
My experience in Chinooks has been to sit as far forward possible, for the rear was always teeth chattering.

I don't remember any difference in vibration, but the noise level was worse in the back. Ever fly in one with all the soundproofing removed? It definitely makes a big difference!

I've got a fair amount of hearing loss + tinnitus as a reminder of my crewmember days...

As far as vibration in hover vs fwd flight goes - it can be a compromise for sure.

bryancobb 02-13-2017 07:55 AM

Quote:

Originally Posted by Jean Claude (Post 647968)
Bryan, How much IPS max are required during the forward flight, here?

In THIS case of the R-22, they are not specifying. They only say that as long as hover vibration is less than 0.2 IPS AND the forward flight tracking AT EVERY SPEED, is within 3/8", you are good to go.

On my Mini-500, I have hover IPS at 0.10 to o.18 IPS. Forward flight tracking has not been fine tuned but The DSS MicroBalancer shows it bouncing around from 0 to 0.25.


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