Propeller Balancing

How important is it to balance a propeller across the blade? I can balance the propeller blade horizontally, but some propellers (Especially the APC props) are much heavier on one side and near impossible to balance across the blade. I was only able to get one propeller out of the three propellers that I had to balance across the blade and not think that I was sanding (Thinning) the blade too much. I had somewhat better luck with the Brodak wooden propeller. Any comments welcomed.

I find that most props are off at least a little with the chord. I take a little off the side of the hub until it is balanced (or at least very close). I have tossed out a few props that were way off. I use a wheel type balancer and find it's sensitive even down to that level. A perfectly (statically) balanced prop will rotate freely when touched with a finger and stop at random positions without joggling back and forth.

the other way to balance props ( instead of sanding) is to add a drop of CA to the back and smooth it out (i use my finger for this )....saves you weakening the prop.........

i do mine this way...seems to work REAL well

After watching a Windy video on prop balancing, I wondered why I would sand something away, paint it then sand and paint it again. Now, I remove the factory finish, paint it, then balance it by adding drops of paint to the backside of the light blade.

On APC's you will sometimes find the hole is drilled off center. If this is the case the prop will never balance. One effective solution is to drill the hub and install a bushing. The hub counterbore is perfectly centered. Use it to align your drill/mill/reamer for the OD of the bushing. Once you have the bushing installed, you can proceed with balancing.
This topic has been covered pretty thoroughly within the past year.
Derek Moran

Hi

Oh prop ballancing used to be a pain, chopping bits out, sanding and all. Now I just drill near the perimeter of the hub and insert lead wire in the holes. Far earier, quicker and no worried about aero asymetry. If you think this might weaken the hub, let me remind you that some manufacturers used to mould slots in the hub for ballancing. Use common sence, small holes and not too near the edge of the hub but far enough out to be effective.

I want to thank everyone for their suggestions. I will experiment with each of the suggestions from applying CA to drilling small holes in the hub and applying lead. I assume I could epoxy lead/silver solder in the hole vice pure lead. To answer one of the suggested ways to balance a prop, I did try filing off some of the hub, but the prop was still too heavy on that side. I did not check to see if the hole was centered or not. I will check. One of the questions that I asked and did not get any discussion on was : If the prop is balanced on the horizontal plane, is it critical to balance the prop perfectly across or along it's cord?

Here is an old tip.
If your prop is at 6 and twelve oclock at engine top dead center,
try rotating the prop one half turn so the blade that was at 6 oclock is now at 12 oclock.
Try this and see if the engine runs smoother.
Without an internal balancer it is impossible to balance a single cylinder engine at all speeds.
This is why all single cyl. engines in lawn equipment over 12 h,p.
have an internal balancer .
You may find that a tiny imbalance may actually help. I did say tiny.
Try it and see,
Don,t cost nuthing, won,t hurt nuthing.

The prop isn't really balanced until it is balanced both spanwise and chordwise. If the prop is heavy on one side of the chord it will affect your spanwise reading. You can tell the difference when running the engine. To paraphrase Zen and the Art of Motorcycle Maintenance: balancing prop require great peace of mind.
Derek

You are correct. Today I experimented with two props, one prop was balanced only on the horizontal plane and the other prop was balanced horizontially and along the cord. I had some vibration with the prop that was only balanced horizontally and almost no vibration on the prop balanced horizontally and along the cord. Thanks for the info.