Balancing props - where to add tape?

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Balancing props - where to add tape?

Postby hogster » Wed May 21, 2014 9:47 pm

Hi all :)

I'm just in the process of balancing the supposedly "factory-balanced" T-Motor V2 props that came with my CarbonCore Cortex. None of them were perfectly balanced, and two of the top 15" props (and so far one of the bottom 16" props) needed a small length of solder attached on one side of the mounting hole (evidently the mounting hole was drilled slightly off-centre, so positioning the prop vertically on my prop balancer it would start to rotate towards the heavy side)! :shock:

So my question when balancing propellers is where do you add the tape on the lighter side of the propeller? Roughly where the CofG of that side of the blade should reside? At the tip? At the root? Simple mechanics says if you add it at the tip you need to add less weight, and less if you add it at the root – but which will produce a correctly balanced blade?

Many thanks for any input, I've got the popcorn out :D

David
Last edited by hogster on Wed May 21, 2014 10:20 pm, edited 1 time in total.
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Re: Balancing props - where to add tape?

Postby SuperSharpShooter » Wed May 21, 2014 10:06 pm

I have previously put tape on the underside of mine to balance them, but lately I've been using a small amount of nail polish closer to the tip instead. Don't know if it's any better, but since it doesn't have sharp edges like tape I think it should work better.
-Glenn
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Re: Balancing props - where to add tape?

Postby hogster » Wed May 21, 2014 10:20 pm

Hi Glenn,

Thanks for the quick response! I too am adding tape to the underside, and currently to roughly the mid point between root and tip. Nail polish will certainly be smoother, but I like the remove-ability of tape ;)

Maybe it doesn't actually matter whether you add a small amount to the tip or a large amount to the middle ... although something in me tells me there is a difference!

Cheers :) David

PS. Just had to add a length of solder to the second 16" prop :|
Edit: ... and the third prop!
Last edited by hogster on Wed May 21, 2014 10:28 pm, edited 1 time in total.
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Re: Balancing props - where to add tape?

Postby SuperSharpShooter » Wed May 21, 2014 10:25 pm

The nail polish can also easily be scraped off with a fingernail or bank card, but use whatever works for you :)
-Glenn
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Re: Balancing props - where to add tape?

Postby hogster » Wed May 21, 2014 10:30 pm

Ah ok, I thought it was more permanent than that!

Right, that's all my props balanced, according to the balancer (DuBro Tru Spin) ... lets see if it makes any difference to my ACC noise (tomorrow if it doesn't rain)!

David
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Re: Balancing props - where to add tape?

Postby Max » Wed May 21, 2014 11:02 pm

I prefer to only add weight at the hub (the hole is often off center anyway like you say), but if that's not enough, then I start with thin shiny Scotch tape at the tip of the prop (underside). You definitely need way less weight that way, and I haven't read anything that says it matters otherwise. It can take longer to balance a prop when starting at the hub -- sometimes I use some "dummy" weight (tape) on the prop tips first to get an idea of how much it will need overall, then try just balancing the hub if it seems doable. Most instructions I've seen recommend doing the blades first, which is definitely quicker and easier, but can also lead to extra weight and unnecessary tape on the blades.

That's disappointing about those props, though not the first time I've heard that. In fact the whole MR prop market is a bit disappointing. Another big issue is matching CW and CCW thrust, even with the most expensive ones. :-|

-Max
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Re: Balancing props - where to add tape?

Postby bluuu » Thu May 22, 2014 1:02 am

you can use sandpaper (400 for the first and 800-1000 for finish)
Of course you must polish bottom side.
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Re: Balancing props - where to add tape?

Postby Max » Thu May 22, 2014 5:48 am

I know people recommend it so I guess it works for some, but I never had any luck with sanding. I just end up with a rougher surface and a bunch of dust, with no significant weight change. Sanding the tip weakens it, and sanding towards the middle will remove more material than necessary. If only a little weight change is needed, then balancing at the hub is better anyway (not changing airfoil). I dunno, sanding never seemed to work out for me.

2¢,
-Max
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Re: Balancing props - where to add tape?

Postby Kisssys » Thu May 22, 2014 1:45 pm

When I use to balance large blades on 60 size helicopters I would want to keep the center of mass of each blade exactly the same. I would take the blade off and hold it at a 45 degree angle on a razor blade until I found the balance point and drew a line. I would rotate it 90 degrees and do the same thing and drew a line. Where lines cross was the center of mass. I would do both blades and then add weight to the lightest blade to draw it's center of mass to match the heavier blade. The perfect center of mass would be straight down the blade from the mounting hole.

Kinda hard to do on a mult-rotor.
Steve
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