Balancing Props

[Brian Massey]

I hope this is the right forum! I just received the Top Flite magnetic prop balancer and at first glance am pleased. With the prop "suspended" in mid air with next to no drag,  the prop really does seem to rotate to the heavy spot. The instructions list several means of balancing: 1/ trim the heavy blade; 2/ Apply ca glue on the light blade or 3/ sand the underside of the heavy blade.

Which of these would be the "best"? If you trim, then one blade will be shorter, does that cause an issue? If you sand you could upset the airfoil, and on some props it could take a lot of ca to bring it to balance. If you sand or trim, is the exposed wood at any risk? I've never balanced props before and can just picture myself ruining a few during the learning curve.

Thanks for your thoughts and ideas.

Brian

[Bill Little]

Hi Brian,

Sanding or adding CA are the methods most guys I know use.  I like to use the sanding method, just go slow at first and get a feel for it.

If you are doing wood props, you need to seal them if you are using glow engines.  Actually just applying a fuel proof clear coat can balance a wood prop if it is not far out of balance.  Min Wax (not water based) clear is a good "fuel proofer" for props.  Many would take the wood prop and paint it to match the plane's color scheme in the past.  Not a bad idea and an easy way to help balance the prop while you are doing it.

On CF props, just sanding is fine, nothing extra to do is needed for fuel proofing.

Big Bear

[George]

Brian,

I have had the magnetic balancer and have been pleased with it, although it has its limitations with small props when the cone does not fit.

I tend to sand on the front of the blade, assuming that the rear maintains the pitch. Be sure to check that there are not tool marks on the prop where it may have missed a step in sanding at the factory.

One important thing to check for is that the hole is centered...not just on the axis of the blades but perpendicular to it also. That is, when the blades stay in place horizontally, move the blades to vertical and see if they fall to horizontal.

Good luck with your Magnetic Balancer...I think you'll like it.

George

[proparc]

Glad to see a "fundamental" thread in light of all the BOM stuff. I am a strong fan of the Dubro prop balancer. Yes its fancy-yes it’s pricey. But, I haven't found better. Big 4 strokes demand!!! that you balance your props very meticulously. Also, in light of the recently discovered "problems" of off-centered holes with the APC props-balancing is really becoming critical.

I can tell you first hand, that there is a big difference between the Saito 40A and the Saito 72FA in terms of balanced props. The big block, is much more sensitive to balance and, APC props with off-centered holes, had to chucked. I once trashed 2 in quick succession in one test stand session.