Prop balancing re: #7780

After reading the thread on prop balancers, My question is: How necessary is propeller balancing, really? I can see trying to salvage a grossly unbalanced prop, or a real compulsive competitor doing that, but isn't "good enough" satisfactory for 95% of most applications? Would the time be better spent building? (I will now don my Nomex jockey shorts)....INCOMING!!

Necessary? Perhaps not.

Worth doing, at least the weight balance portion? Absolutely.

Cy

Prop balancing is a good thing.....and a sport flyer will see the benefits. Smoother engine runs will yield much better engine runs.

There will be other, subtle advantages....things are less likely to loosen and fewer parts will be ejected.

Props (two blade, at least), balance quickly and you will feel rewarded by doing so.

See Ya

>After reading the thread on prop balancers, My question is:
>How necessary is propeller balancing, really? I can see
>trying to salvage a grossly unbalanced prop, or a real
>compulsive competitor doing that, but isn't "good enough"
>satisfactory for 95% of most applications? Would the time be
>better spent building? (I will now don my Nomex jockey
>shorts)....INCOMING!!

No, this is definitely not a "competitors only" deal. It's better than it used to be, but it's always worth checking the balance on any prop, for pretty much anybody. Vibration causes so many hard-to-diagnose problems it's worth $10 and 30 seconds of anyone's time to avoid it.

Repitching, changing pitch distribution, blunting LE, sharpneing LE, changing airfoil, etc. are probably not necessary. But I think balancing is.

If nothing else it makes you feel virtuous. I did get several APC 11 x 5's which were heavy on one side. You could visually see that the blade was thicker on that side. Usually APC's are pretty close.

Well, I avoided cluttering up the first thread, but now I can't resist. Never really thought store-bought props would ever be that far off in the first place. Never noticed a bad one and been flying since 1955. Then took a brand new Oriental with an FP40 to the VSC about 6 years ago. Really shook when I started it up- didn't do that on previous planes. Took off and my flying hand was vibrating. The lines had 8 to 10 sine waves dancing through them. Finally the engine quit and the nose was almost broken off! Fillets cracked, top block cracked and it was glass-coated. The prop, a Top-Flite "PowerPoint", was the culprit. It looked ok, but that thing must have had the hole drilled off-center. It wasn't able to be balanced. I now carry the cute little DuBro balancer in my flight box, just to make a cursory check if I'm ever forced to use a prop that I havn't balanced at home. For what it's worth, best regards,

OK, so here's something I've done on my McCoy .40 on my ringmaster, it can be a real paint shaker. Instead of balancing the prop I put the heavy side opposite the piston at top dead center, seems to work, but I have no proof other than my eyeball watching the nose shake, any opinions? Does this work, or do I just convince myself I'm seeing the end result I want? I've done this on my fp .40 in the past also, it also seemed to work on rc models at idle, but on my Sig Mustang, it runs smoother with a balanced prop and let it turn up like it wants to do.

And how balanced is balanced enough? I'm using a homemade magnetic balancer, and I've noticed you can have a prop "balanced" and then leave it on the stand overnight, and find that one blade still must be a little heavier than the other, I've marked the blade and repeated the experiment several times, so I no it's not something else like the central heat moving it. I figure if it takes several hours for the blade to move enough to see it, it's gotta be overkill, right?

I once watched Konstantin smooth out an engine/prop combination by wrapping a piece of plastic tape around the prop near the hub and progressively trimming it back until the vibration was reduced to his liking. To say I was mind boggled would be an understatemnet.

Best, Hoovie

LAST EDITED ON Feb-08-04 AT 01:29 PM (CDT)
 
Moving the heavy side opposite the piston is a trick used on Fox .35's for years. Not sure how much it affects the crankshaft bushing.
I use the Top Flite magnetic balancer.

>OK, so here's something I've done on my McCoy .40 on my
>ringmaster, it can be a real paint shaker. Instead of
>balancing the prop I put the heavy side opposite the piston
>at top dead center, seems to work, but I have no proof other
>than my eyeball watching the nose shake, any opinions?
>Does this work, or do I just convince myself I'm seeing the
>end result I want? I've done this on my fp .40 in the past
>also, it also seemed to work on rc models at idle, but on my
>Sig Mustang, it runs smoother with a balanced prop and let
>it turn up like it wants to do.

The heavy blade opposite works to some degree. Remember that our engines are not balanced as is, and even the counter balance on the crank shaft is a bandaid to help. That said, the counterbalance on the crankshaft is at least under the piston, so these two weights, even though they do not perfectly balance one another out, are still in line. The prop is not in line with the piston. It will tend to cause a different type of shake which is why they dynamically balance tires these days and the bubble balance is out.

>And how balanced is balanced enough?

If you get it "close" you should be fine. If it doesn't drop on its own, and immediately on a "friction free" balancer, then it should be good enough.