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HomeAircraftHelicopterMain Discussion › Ok guys, what are acceptable tolerances for main shaft, clutch, etc...
03-05-2008 02:05 AM  10 years agoPost 1
joeycoates

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Dallas, Texas

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I am working on my TRex 600n, the reason that I am working on it is because I have a wicked vibration, especially on spoolup and spooldown, but it is there even at flight RPM's. If I come out of a hard descent to a hover in idel up the skids are sometimes doing a dance (big time vibrating) and the little exhaust deflector is simply blur...

So, I have broken out the dial and am about to go over EVERYTHING. But first I need to know what is acceptable, and what is out of spec. For instance, I just dialed the main shaft (which is about three flights old with no ground contact) at about .0013. I would assume that this is good, but what about fan runout, clutch runout, whatever else that can be measured and/or balanced?

I balanced the blades for both normal balance and cg.
I balanced the head with the paddles on, it seemed good as it would stop at different point when spun on the high point balancer, but needless to say I am going to go over it again.
I balanced the tail on the high point, will check again.

So what specs should I shoot for, and what am I missing? I want to end up with siilllkky smooth when I am done.

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03-05-2008 04:54 AM  10 years agoPost 2
medfoch

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Bay Village, Ohio

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Sounds like a high frequency vibration...are you sure your engine is not running a little lean? a couple clicks can make all the difference. If you are sure you are not running lean the next thing to try is different head speeds. At certin RPM's my engines are not happy - 50-100 rpm more or less and everything is happy again...

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03-05-2008 05:16 AM  10 years agoPost 3
ez2bgman

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N'awlins, LA

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but what about fan runout, clutch runout, whatever else that can be measured and/or balanced?
For the fan hub/clutch assembly, I would shoot for at least .002" run out. When I assembled my new Xtreme 50, I didn't pay enough attention to my fan hub during assembly. Needless to say I had a terrible high speed vibration. I redid the the fan hub/clutch and got everything under .002". When I went flying this passed Sunday, everything was super smooth. There was no noticeable vibration anywhere in the heli.

A high speed vibration like you are describing is usually engine related. I would make every effort to ensure that the fan hub/clutch are as true as possible.

Gary
Hot Girlz in da gallery

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03-05-2008 05:18 AM  10 years agoPost 4
David Blain

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Mt. Dora, Florida (USA)

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You mentioned that you balanced the blades,Do you have a Hi-Point balancer? If so check the entire assembly? (though I fly Raptors) I have found things out of balance in the head, the flybar and then the blades! If all balances out try another set of blades or recheck the CG to confirm.......Check and recheck again.......
like medfoch said, recheck the mixture (once you've gone over the entire head again) and work it, add a couple of clicks at least you will have eliminated the head and blade issue....
Good luck and let us know what you find....

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03-05-2008 06:53 AM  10 years agoPost 5
joeycoates

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Dallas, Texas

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Well, I have just finished with the fan, clutch, main shaft, tail blades, tail shaft (that the rear pitch hub runs on), flybar, flybar weights, and paddles.

The fan was out of balance, I used a sanding disk on the back side of the fan to take a bit of material off to balance it. Using a Top Flight magnetic suspension balancer it will spin forever and when it stops it stops in different places. This is the absolute lowest resistence balancer that I know of. Should be good.

The tail blades and paddles are now balanced to within 1 grain (I used my scale for reloading since that is the most accurate scale I have ) and 1 grain is 0.06479891 grams so I think that they should be good to go.

The main shaft runout is .0013 and the tail shaft had no appreciable runout.

The flybar is exactly centered and the weights are even to .1mm so that should be good. I did find that one of my thrust bearings needs to be replaced and when I do that I am going to replace the feathering spindle as well, it has been through a few mishaps but checks good, I will replace it with a new one anyway.

The fan is within .0007 or so and I could not find a very good way to check the hub runout exept at the base next to the crankcase, no appreciable runout there.

The clutch where it bolts down (at the begining of the clutch shoe) is at .002 as well. The outermost part of the shoe is about the same.

I will do the main blades tomorrow, too late tonight.

I am using the Carbsmart si I would imagine that it will take care of the tuning, it is about right without it, not tool lean.

I will see what happens next time I go fly, hopefully it will be nice and smooth.

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