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Old 01-10-2015, 21:21   #1
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Dynamic balance for a folding prop?

Hi, I've got a slight propeller vibration issue at higher RPMs. It's more at the annoyance level than the nasty, and at cruising revs it not a problem, but I'd like to sort it out if I can.

Has anyone ever had a prop dynamically balanced, and did it help?

Our local prop guys can do a weight balance, and check the pitch, but don't have the gear to do a dynamic one.

The vibration is definitely from the stern, and the engine seems nicely aligned.



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Old 02-10-2015, 08:36   #2
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Re: Dynamic balance for a folding prop?

You don't say which prop you have, but on our Volvo 3 blade folder, there is a specific order the blades need to be installed on the hub. The blades are sold in matched sets and have numbers stamped into them that corresponds to numbers in the hub.

Did you by any chance remove your prop lately and may have the blades in the wrong order?

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Old 02-10-2015, 13:54   #3
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Re: Dynamic balance for a folding prop?

g'Day Ben,

If the static balance on your prop is good, I'd be looking for some other source for the vibration. Have you checked the shaft for straightness? Strut bearing clearance? Any dings on the blades? Are the blade stops all even? (This latter factor could indeed alter dynamic balance, and wouldn't show up on a static check.) Is the bored socket in the hub truly on center (ie, any runout in the hub)?

Lots of possibilities...

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Old 02-10-2015, 14:37   #4
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Re: Dynamic balance for a folding prop?

Go to a modern prop shop and they can balance it to a gnat's ass with electronic equipment. They show you your props vibe frequency on a computer screen.
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Old 02-10-2015, 14:42   #5
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Re: Dynamic balance for a folding prop?

Quote:
Originally Posted by Snowpetrel View Post
Hi, I've got a slight propeller vibration issue at higher RPMs. It's more at the annoyance level than the nasty, and at cruising revs it not a problem, but I'd like to sort it out if I can.

Has anyone ever had a prop dynamically balanced, and did it help?

Our local prop guys can do a weight balance, and check the pitch, but don't have the gear to do a dynamic one.

The vibration is definitely from the stern, and the engine seems nicely aligned.



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Are you sure the vibration is not from your Cutlass bearing? Our prop shook badly until I changed the bearing. Also, make sure the shaft is not bent
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Old 02-10-2015, 16:07   #6
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Re: Dynamic balance for a folding prop?

Thanks for the thoughts. Just some more info, New shaft, New bearing. New engine install (well actually second-hand engine, but a lot newer than the old bukh.

The prop came with the engine and is a locally made stainless steel variant of the martec eliptics. That is it's a non geared folder. It works well and is nicely matched to the engine/gearbox combo.

The manufacturer also built my shaft, checked it for straightness and cleaned up the prop, but I'm not sure if they rebalanced it, or even checked the static balance.

So maybe my first move is to pull off the blades and weigh them and carefully measure them. Maybe they are slightly out. I guess if it's all perfect then a dynamic balance might be needed?

I'm happy enough, with how it runs for now but I'd like to improve things over time. I might recheck alignments, and dive on the prop and mskesure one blade isn't covered in barnacles!


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Old 02-10-2015, 17:14   #7
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Re: Dynamic balance for a folding prop?

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Go to a modern prop shop and they can balance it to a gnat's ass with electronic equipment. They show you your props vibe frequency on a computer screen.
I suspect that you have not been to Tasmania lately... the OP said that the prop shop that he has access to can't do dynamic balancing.

Tassie ain't the end of the world, but if y ou go to the top of Mt Wellington you can see it in the distance!

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Old 02-10-2015, 17:25   #8
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Re: Dynamic balance for a folding prop?

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Originally Posted by Jim Cate View Post
I suspect that you have not been to Tasmania lately... the OP said that the prop shop that he has access to can't do dynamic balancing.

Tassie ain't the end of the world, but if y ou go to the top of Mt Wellington you can see it in the distance!

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Not even something like FedX? dang that is remote.
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Old 02-10-2015, 17:44   #9
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Re: Dynamic balance for a folding prop?

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Not even something like FedX? dang that is remote.
Well, I can't speak for Ben, but I had a folding prop sent from the States to Hobart a few years ago. It took 21 days and cost nearly 400 bucks.

This might be a deterrent to some...

Jim
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Old 02-10-2015, 18:57   #10
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Re: Dynamic balance for a folding prop?

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Originally Posted by Jim Cate View Post
Well, I can't speak for Ben, but I had a folding prop sent from the States to Hobart a few years ago. It took 21 days and cost nearly 400 bucks.

This might be a deterrent to some...

Jim
Well I was thinking of the prop shop in Panama City, Panama, over near the canal. That might be going too far though.
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Old 03-10-2015, 00:19   #11
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Re: Dynamic balance for a folding prop?

Ha, yes I could probably source somewhere on the mainland that could do it, but it would take a few weeks to get there and back and probably cost a fair bit. If that's what it takes to get a real smooth drive train I'm happy to go that way, but it would be good to know how much better a dynamic balance is over a good static balance? Since the local, very experienced prop guys seemed happy with just the static test.

For all snowpetrel 1's faults she did have a very smooth drive train, and I've seen how even small vibration issues can do some pretty nasty long term damage and fatigue.

Anybody done a static balance of their own prop?

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Old 03-10-2015, 00:55   #12
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Re: Dynamic balance for a folding prop?

Ben, it is probably not relevant in your situation but I am faced with a similar sounding prop balance issue and once I had phoned around for a few quotes on balancing I decided the current prop will become my spare prop. It just seemed expensive compared to the residual value of my prop. But have a very old fixed blade prop which I would like to replace with a Kiwiprop if I can afford it, so my situation may not be all that relevant. Anyway, from less than perfect memory, there's a bloke here in Adelaide who can do dynamic balancing. I think the name is something like Eagle marine. If he can help you then I'm happy to help with the logistics if I can in any way. Matt


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Old 03-10-2015, 08:56   #13
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Re: Dynamic balance for a folding prop?

If there is any play in the retaining pin(s) that would create a vibration.
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Old 03-10-2015, 10:31   #14
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Re: Dynamic balance for a folding prop?

Hi Check that the prop key is not holding the prop slightly off on the shaft.
A few years ago I had this problem and a quick clean up of the key and a check with bearing blue and the problem was solved .
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Old 03-10-2015, 21:05   #15
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Re: Dynamic balance for a folding prop?

Thanks Matt, that's good to know that something can be done there. Might get some quotes, but as you say, it will probably cost more than the props worth...

It's an interesting prob.. It's grub screwed onto the shaft on a slight interference fit like a coupling. Seems to work fine on a bunch of boats here in Hobart. But if the hub is not bored perfect it will always have a wobble.

My guess thinking about it is that when I got the prop with the engine it was in bad shape, the PO had cleaned of the old paint buildup with a flap disk, and he scarred the blades a fair bit.
The manufacturer cleaned it up and polished the prop, but he may not have rebalanced it afterwards and he must have taken a bit of metal off.

So a proper balancing has got to be my first step. And I can do that without even pulling the prop off. I'll just take off the blades and carefully weigh them. If they are out I can grind a bit of the heavy blade. Until they have the same weight and centre of balance.

If it all goes pear shaped, or its the boss I'll just go with a new FOFold or similar sometime in the future. And keep the old prop and shaft as a spare.

Thanks for all the sugestions.

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