Balancing 3 blade props

[James Mills]

Whats the best way to balance a 3 blade prop compared to a 2 blade (ie how do tell when it's balanced)?

James

[Bob Reeves]

Really not much difference, just have another blade to contend with. I use the Great Planes magnetic balancer and either take away weight from the heavy blade(s) or add weight to the lighter one(s).

[Ironbomb]

 have yet to balance a three blade prop, but it should not be much diffrent that the two blade prop to balance. I consider my props balanced when they will stay at any position I put the prop in and not move.

I also use the magnetic balancer from Great Planes. I polished my magnets on 6000 grit sandpaper and I polished one end of the balance shaft. That is the end I allow to contact the magnet. I also tried to balance the centering cones, that got a little touchy.

Also, the finger balancer will work on the magnetic stand also. Drill out the holes in one end of the base, so the rods can be slide thru to make the small balancer fit between the magnets.

I use the small finger type balancer on a propeller, and the longer balance rod and cone for spinners.

hope this helps, happy balancing

Greg

[Steve Helmick]

One thing that worries me (a little) is that the 'cones' (either TF's plastic ones, or Prather's aluminum ones) have to be concentric to the shaft, and we know there are tolerances on all things made by man.

The other, less obvious thing, is that if the hole in the prop is chamfered, and if it's not the same all the way around, or if there is a burr left at the edge of the hole, this will throw the cone on the balancing shaft off center.

I'd rather work off the hole, not the chamfers on the hole. A piece of thinwall 1/4" OD steel tubing might be a good substitute. The friction in the magnetic Top Flite balancer is almost not enough. Having the furnace duct vents open is sometimes a problem. Outdoors is out of the question.    Steve

[Ironbomb]

I never thought to check the cones for concentric. I can do that. I have a good dial indicator. I like the steel rod idea also. I do dress my props before balance, and have never had flash interfere with my balance. I remove it before hand. I do know that my balances are pretty good, cause the vibration is very minimal. The spring loaded needles rarly vibrate, even in the breeze of the propeller.

Thanks for tips Steve

here is a pic of a plastic spinner being balanced, a requirement of mine when I have to remove material to make room for an APC prop.

Greg 

[Bob Reeves]

Believe it's SIG that has spinners that are already cut for APC props.

[Steve Helmick]

Depending on the weight of the prop you're balancing, you may not be able to use a solid steel rod for a prop shaft. A short dowel pin could work, if you modified your TF Balancer as noted in a post above, allowing the uprights to be pulled closer together.

I'm not real sure what would be required of the end configuration, for the magnetic field to suspend the rod or tube and prop. But I know that some of the bigger APC props I use are pretty close to the limit of what my TF balancer will support, on the stock shaft with plastic cones.     Steve

[Ironbomb]

Dont know what it may have to do with it, but I have always put the prop in the center of the shaft when balancing. The biggest prop I have had on the balancer is a 12" APC. I think it handles the weight well. Bigger, I have never done, so I dont know. So heres this, if you dont already do it Steve, can the prop be put closer to the contact end of the magnet, to support the weight a bit easier? I dont know if it would affect the balance at all, could see with a prop already balanced. Just a thought.

 Also, I think some magnetic strength is lost when the plastic ["plate"?] is on the magnet.

my $.02   

Greg 

[Leester]

FYI: Great planes spinners work fine with APC props also. At least the ones I've used.

[Ironbomb]

I'll remember that Leester, thanks. I dont remember why That spinner was on the balancer. I think it was still too small for the 11x4 prop. It may have been an 1 3/4 spinner. That pic was taken a while ago. 

Greg

[Gene O'Keefe]

I do it same way as in the picture but then I also reverse it 180 degrees after either
prop or spinner is balanced & recheck & adjust if necessary. My brand of beer too !

Geno

[Ironbomb]

I do it same way as in the picture but then I also reverse it 180 degrees after either
prop or spinner is balanced & recheck & adjust if necessary. My brand of beer too !

Geno

I bumped you one for the beer Geno 

Greg