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Short Shaft Balancing


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Be careful, precise, follow the book and be ready to cut cotter pins to achieve the finest balance. Should be able to get less the .02 ips, book says .08 but should be able to do better, if you can't, send it to Acro for check and balance. May take lots of starts, remember since they are maintenance starts and do not have to record them and ensure pilot knows he may be there awhile. Some machines(the Aces~sp) can do in three runs, a well worth tool.


If you tell us the strobe type of machine am sure some people will give you more hints than just from dozey old pilot.


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If I remember, the books allowes .8 ips as a limit. I allways shot for .2 which is basically the industry standard for everything. Then when you get good at it .05 is a nice target. I don't ever remember using the chart in the book, as I learned to strobe from Terry Mooney who taught add opposite the accelleromitter and write everything down on a generic ips chart in which I still use today.

You basically do a run and get your reading.

make a weight change .

and adjust accordingly knowing 120 degrees will be your only move lines

I would be curious and use the proper chart as a reference and see if it is working, but I found alot of charts are not very accurate.

I seen in the past, many apprentices and engineers hate strobing as they don't write things down don't understand whats realy going on as there relying to much on the charts and don't see whats happening.

But .... that my 2 bits ....so good luck with your project.

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What can Acro do to insp and balance the shaft? The insp I can see but balance?

We have a -02 shaft assy and from what I see ECL has removed the insp and maint info from the manual? We did a run out check for kicks and found it to be about .010 thou anybody have any numbers? should they not be in the book?

Why does Eurocopter always remove info from the IPC and the M and O when they bring out a new assy? They make the assy on condition if it has no specifed data to maintain it ,do they not?

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we also on a shaft we don't know.spin the shaft through all three bolt locations to see which one is the least ips.then start.we had acro look at several shafts that came on new A/C ,and sent them back to eurocopterthere is also a letter on what and where to put for sealant on the bolts.a bit of mastinox on the washer and bolt /nut keeps the twist out of the coupling.the shaft won't move back and forth effortlessly otherwise from my findings..the tech club is a great idea to join.as there is a ton of info to be found..

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Rule #1 Never, ever ever dissassemble the couplings from the shaft!!!

It's pretty rare that you should have to send a shaft back because it won't balance. If it's really rough on the first run (1 ips or more), dissassemble the coupling from the splined adapter and rotate 120 degrees. Check it again. If it's still rough, rotate the spilned adapter another 120 degrees and take another reading. From there, put it back to whatever position was the less vibration and start balancing. What has always worked for me was to only work on one move line at a time.

If you still can't balance it to .2 ips or less, you might have to take the shaft off and turn it end for end. The shaft being out of round should'nt be a big issue. That's what you'r balancing for!!!

The short shaft on one of my Astar is out of round at least 1/8" as you can see it when the A/C starts up and accelerates and yet, it always balances to .2 ips or less every time!


Rule #2 Be patient!!!!! It's a fairly long learning curve specially if you're a new engineer.


P.S. Just balanced our short shaft to .15ips 2 days ago in 3 runs with our new "MICROVIB 2"

Nice little toy!!!!!!!


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You'd be surprised at how bent some of those short shafts are. Specialy on the "B" series Astars where the shaft sits behind the engine instead of underneath it like the 'D' model. Some guys have a bad habit of leaning on it when doing maintenance. But like I said, if it balances, you're laughin!!!

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