Prop Balancing Method

[Kafin Noe’man]

Hi, I’ve just got myself a Du-Bro Prop Balancer.



The instruction manual shows the A setup, meanwhile I’ve also seen some people doing the B setup (especially for the APC prop). I’ve tried both ways, and sometimes it gives the same result, sometimes it doesn’t. So, which one should I rely on?

Looking forward to hearing more from you!

[Peter in Fairfax, VA]

Kafin,

Setup A is preferred, when it fits.

In general, with any balancer, you average the settings, try the prop in all four orientations, etc.  I'm going to assume you did this already.

My balancer is the magnetic Top Flite.  Works pretty well.

best,

Peter

[spare_parts]

APC themselves say the hole in the front is not reliably centered. Therefore B is preferred.

[Colin McRae]

The A is intended for props.

I use B when balancing a spinner.

[Brett Buck]

APC themselves say the hole in the front is not reliably centered. Therefore B is preferred.

   Where is this stated? I have heard this repeatedly in various forums, but when we were at the APC factory, they said absolutely nothing about it, and neither do the instructions (such as they are), and there is no known factory source for the supposedly required "centering rings". Not that the idea is wrong, or that the drilled holes are sometimes off-center, but I have never heard or found any indication that they expect you to center your IC engine props using some other method than the existing hole.

     Brett

[Colin McRae]

DU-BRO also produced a good video showing how their prop balancer is intended to be set up and used. If interested, go to the DU-BRO website. The website also has lots of other videos on how to use a lot of their different products.

[Randy Ling]

On the APC website in the technical support section. There will s instructions about centering the prop on a motor shaft. It tells one to open up the center hole to clear the motor shaft and only let the prop adapter touch the shaft.

Randy

[Massimo Rimoldi]

   Where is this stated? .......

https://www.apcprop.com/technical-information/technical-support-advisories/

[Brett Buck]

https://www.apcprop.com/technical-information/technical-support-advisories/

  That was the same reference as before, but it is referring to electric, not conventional props. I haven't seem nor have I ever heard of any such "centering ring" for conventional APC props.


     Brett

[Howard Rush]

There’s a 3/8” diameter dent in APC props that’s fairly accurate. I drill out the prop to 3/8”, then put in a spacer to center the prop on the shaft. Only then do I balance the prop. I haven’t used APCs in awhile, but when I used them, the holes were badly off center.

[Dave Hull]

We are back to the same old issue:  That the molded counterbores in APC props are as accurate as their machined molds--which seem to be excellent--but that their only(?) post-molding operation of drilling the thru holes is often woefully inaccurate. I've purchased hundreds of their props and it is randomly evident in every size I can recall. Trying to balance some of these while still using the drilled hole can be futile.

So what they hope to convince you of is that this is planned, and part of their product. That the drilled holes were never intended to be used. The problem for us then is that the user must jig-align each prop to the molded-hole axis and rebore the hole and provide an accurate concentric bushing. Or, we should not expect to use the drive hub that comes with most engines but instead have one made that has a specific size pilot machined into it, as was done on the old K&B .40 engines such as the 8011. Or, we oversize the randomly drilled hole and use an accurate bushing for each installation thus making this a prop kit.

Since it is harder to rebore a hole to correct an incorrectly located hole, it would actually be better for them not to drill the hole at all. Of course, best of all would be to bring their post-mold drilling operation up the very high quality of the molded product and make all of this unnecessary.

And we've been in this situation for as long as I can recall--at least the last 15 years....

Dave

[Massimo Rimoldi]

  That was the same reference as before, but it is referring to electric, not conventional props. I haven't seem nor have I ever heard of any such "centering ring" for conventional APC props.


     Brett

If you read the balancing instructions you find that they apply to "all APC props".  Spacer rings are provided for electric propellers only but you can use aluminum tubing and/or fuel tubing and it is not specified that this does not apply to IC

Massimo

[spare_parts]

This issue existed before electric APC props. Many people thought APC were garbage because the hole was off center. I never had any issues even before the internet.

[Ken Culbertson]

This is slightly off subject but can an out of balance prop/spinner result in increased battery usage?

Ken

[Dave Hull]

Theoretically--yes. You are spinning around an offset from the body centroid (in the simplest case of a perfect prop with an offset hole) which increases the prop inertia. You are also causing vibration, which is energy being dumped into the structure. That assumes that your controller holds the rpm setpoint regardless of the increased load. There is also the likelihood that the aerodynamics of the prop are not as good resulting in minute losses there as well. (And although you are not closing a control loop around the airspeed and thrust[?] there is  effectively an "outer loop controller" which you, the pilot readjusts the controller until the airspeed/line tension criteria is met.) Since I can't think of any offsetting results, it seems to me that these losses combine to increase battery drain. There is also the miniscule additional loses of the armature support due to higher and varying loads in the bearings. My thought would be that the structural vibration would be the largest loss component.

Will you notice it? It would likely be lost in the noise of the measurement and all of the variable conditions from flight to flight  I think it would be unlikely unless it is way, way out of balance. Other things might break first....