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HomeAircraftHelicopterMain Discussion › Clutch balance ?
01-17-2009 10:42 AM  9 years agoPost 1
Mike Moore

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Canford Heath, Poole, Dorset UK

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I've been rebuilding my Raptor Titan and going through the routine of balancing. Everything was going well, but when I put the clutch on the high balancer found it to be way off.
I was giving this some thought and if I balanced the clutch when it was in use and the shoes started to expand, would this change of mass change the balance ?
I've read all I could find about clutch balancing, but didn't find anything regarding this. With everything else nicely balanced it seams a shame to have the clutch throw it all out.
I would be very grateful if anyone can help ?
Thanks,
Mike.

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01-17-2009 12:36 PM  9 years agoPost 2
maveric4

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england

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Mike Moore

I balance all my clutches because as you have found some of them are way off.

I did it the same as you would a fan or clutch bell. Just remove some material carefully by drilling small dimples. I dont know if these are hardened in some way but I suspect they are because I found drilling them was quite hard. Dont drill where the clutch shoes are attached to the main body as this is a thin part anyway to allow shoe to move out and you risk one of them breaking off. just drill either side where there is some good thickness.
I did not worry about the mass changing as the only part that moves is the shoe. If its the shoe thats heavy you can drill on the inside of that one but again go carefull
Hope that may have helped

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01-17-2009 12:49 PM  9 years agoPost 3
BarracudaHockey

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Jacksonville FL

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Balance the fan and clutch as one unit.

Andy
AMA 77227
http://www.jaxrc.com

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01-17-2009 12:53 PM  9 years agoPost 4
predatorman

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Falkland Islands

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Check the Gaps in the clutch shoe as well...just to make sure they are equal distance.

Mine was slightly out too on my Predator...as was the fan.

I use a file and gently remove material off the heavy side...just a swipe or two can be enough.

In short...balance everything...it worth making up a balancer for the rotor head assy too.

Quality takes........time!

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01-17-2009 01:55 PM  9 years agoPost 5
Mike Moore

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Canford Heath, Poole, Dorset UK

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BarracudaHockey - If I balance the fan and clutch as a unit, if I change either I will have to do it all over again. I think balance each item, them check them again as a unit, but thanks for your input.

I guess the main mass of the clutch is fixed and you're quite correct in pointing out predatorman that it's only the two arms I guess you'd call them that are actually changing rotational position during use. I agree that this means that the arms need to mirror each other as a starting point before balancing. It's then down to the quality of manufacture.

It's good to bounce ideas/info. Thanks guys.
Mike.

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01-17-2009 04:48 PM  9 years agoPost 6
maveric4

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england

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HEY predatorman

like You I balance everything. Just curious when you say everything weather you go as far as taking the auto unit apart and balancing both those. I have found I cant balance them as one and they need to be done seperately. Just curious

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01-17-2009 05:30 PM  9 years agoPost 7
predatorman

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Falkland Islands

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I have looked at the main gear before now and while its ever so slightly out of kilter I havent bothered messing with that too much.

I am going to replace one or two itmes in that area...and yes its worth taking the two main parts apart and checking them out.

Barracuda is right. The two itmes are attached and its possible that when joined the clutch can be not aligned...which can bring about a vibe problem...dont forget that part of the system is rotating at the engines actual RPM.

Quality takes........time!

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01-17-2009 06:30 PM  9 years agoPost 8
AirWolfRC

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42½ N, 83½ W

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You will find that the engine itself, even when best balanced, still has MUCH more vibration than the clutch could ever have.

I don't bother balancing clutches.
. . . . I make sure they're running true but that's all.

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01-17-2009 08:40 PM  9 years agoPost 9
maveric4

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england

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Yep agree with Barracuda point about balancing the two units as one.

I have not had a clutch or fan that has been perfect, exceptable maybe but I always balance anyway.

I first check the fan and mark heavy point, then the clutch and do the same. It is possible to assemble them with the heavy points at opposite sides and this tends to cut down on the amount of material to be removed. But I prefer to do them seperate and then check them again when assembled just to confirm.

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01-17-2009 11:08 PM  9 years agoPost 10
predatorman

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Falkland Islands

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I agree about the engine vibes of course, I know that with the gasser engines you can get them modded so they cut down on vibes.

The idea with the fan and clutch balance and running true is to cut down on the severe vibes that you will get.

Would love a Turbine

Quality takes........time!

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01-18-2009 12:51 AM  9 years agoPost 11
Yug

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UK. Herts

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Hi Mike, hope all's well.
This balancing issue raises some interesting questions, particularly when considering the engine crank, clutch alignment and so on. The latter being very relevant to the overall balance if one considers the 'imbalance' nature of the crank, conrod, piston, and effect of the virtual unbalance caused by the power stroke. Due to this, I have tended to balancing the fan on it's own as a starting point. Then I mount the clutch and dial it in for minimal runout of less than a thou given that the materials will be of uniform mass per volume, while it's also worth remembering that the shoes can throw things off if static. However, if you consider how accurately the engine is aligned, then any offsets will dramatically effect this due to the shoes. Hence, after mounting the fan accurately, I then concentrate on the clutch mounting with minimal runout both axially and longitudinally.
I hate engine bearing changes cos of the hassle this involves but needs must.

Vegetable rights and Peace

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01-18-2009 01:25 AM  9 years agoPost 12
GMPheli

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W. Bridgewater, MA USA

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Yes, and if we used heim cranks it would save tons of time and agravation!

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01-18-2009 02:13 AM  9 years agoPost 13
predatorman

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Falkland Islands

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Just how good are the modded engines then? I personally cant be bothered sending a motor to get sorted out...would rather have this done if buying another gasser. Which is unlikely.

Quality takes........time!

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01-19-2009 02:47 PM  9 years agoPost 14
Mike Moore

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Canford Heath, Poole, Dorset UK

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maveric4 - I like your thinking.
Yug - Yeah good thanks.
I've been getting really into balancing at the moment. This includes the engine, but that's another subject on it's own. I each component is well balanced and then the items as a unit, what more can you do ? Leaving out the engine balance for now, all the other items can only lead to a far smoother running heli, which in turn makes for less viration and hence wear and tear.
Mike.

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01-19-2009 03:45 PM  9 years agoPost 15
AirWolfRC

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How much does the engine vibrate ?

take off the back plate and look at the crank counterweight.
. . . . That much imbalance is how much the engine vibrates . . . .

You think your clutch is anywhere near that ?
. . . . do you still think the clutch matters ?

Now . . . . true . . . . the clutch is at the other end of the engine, unsupported, so it does matter some, but not that much.

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01-19-2009 08:33 PM  9 years agoPost 16
alfred

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Australia, New South Wales, Mid North Coast

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Interesting

So if one shoe has a slightly larger gap then the other (lets' say 0.2mm) then we can assume that this side will be heavier as the shoe is further out from the centre.
So you now remove material to balance it.
Once the clutch engages in the clutch bell, let's assume that both shoes are now equal distance from the centre, the previous balanced clutch is now "unbalanced". LOL

We can't even guaranty that both shoes are the exact distance away as most clutch liners are rather soft. If one has just slightly more spring then the other shoe, it might just engage but not press as far outwards as the other shoe...it's unbalanced again

The one thing that nobody worries about appears to be the Hex starter adapters on most of our helies.
These are just about never a press fit to the shaft.
They use most of the time 2 grub screws which are about 45 degrees to each other.
When you tighten up the grub screws, you are forcing the adapter against "one" side of the shaft. It often also causes the adapter to be at an angle compared to the shaft.
Now the adapter spins at engine speed. So how much vibration is it causing?

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01-19-2009 09:05 PM  9 years agoPost 17
midwestpilot

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Crystal Lake, IL

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edited
edited... miss read above...

In life there is no spacebar!

Rich Erikson AMA 6175

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01-19-2009 09:12 PM  9 years agoPost 18
Mike Moore

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Canford Heath, Poole, Dorset UK

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Not quite. Let me try to explain. If you stand up and stick out both your arms and begin to rotate you are balanced, well to a degree, assuming here for arguments sake that each arm is the same weight and distance from your body. While continuing to rotate you then pull one arm in towards your body, the arm that is still sticking out now throws you off balance. This is the simplest explaination I could think of to try to explain. I hope you can see what I mean now ?
My clutch arm gaps were equal before balancing began, but there was more weight on one arm than the other, therefore throwing it out of balance. I then removed weight from the heavier arm until the clutch was balanced. How ever if the two clutch arms move out during rotation different amounts, the this would throw the clutch off balance again. The amount clutch arms move is not a great deal so the balance would still be reasonable good. Far better than stock anyway.
Starter shaft grub screws are balanced out by the recesses on the shaft to some degree.
With all measurments we have to decide what is an acceptable tolerance to work to. I'm sure you'd agree ?
Mike.

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01-20-2009 05:55 AM  9 years agoPost 19
alfred

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Australia, New South Wales, Mid North Coast

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The amount clutch arms move is not a great deal so the balance would still be reasonable good. Far better than stock anyway.
That is pure theory on your part, not easy to prove.
That doesn't mean that you are wrong, it's just that you are hoping it to be within a reasonable limit.
The only one I could say would come close to your theory would be the MA clutch/liner combo, as the clutch liner is extremely hard and once run in i.e dead round, it's hardness would assure that the shoes if properly designed will move equal distance to a high tolerance.
Starter shaft grub screws are balanced out by the recesses on the shaft to some degree.
Please re-read..I wasn't talking about the weight of the grub screws.
I was refering to the adapter being pushed off centre when tightening the screws.
As the adapters are solid steel, the off centre weight is higher.
All my MA helies use the "Flexi starter" which eliminates the hex adapter completely.

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01-20-2009 09:54 AM  9 years agoPost 20
Mike Moore

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Canford Heath, Poole, Dorset UK

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To get within a 'reasonable limit' is the aim.
As for the starter shaft I can only speak from my experience. The adaptor on my titan for example has a hole to match the shaft diameter. The grub screws are tightened down onto flats on the shaft and they don't push the adaptor off centre. Well actually it does, but only a very small amount, the tolerance between the adaptor hole and shaft diameter which is very small. A photo would help here I think ?
Anyway, as I said the aim is to get within an acceptable tolerance. There is no such thing as perfect. We all set our own level of acceptability.
Mike.

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