Prop Balancing 101

[Dick Pacini]

The P40 is almost finished.  In preparation for flight, I opened up my new Dubro prop balancer.  It is well made and very sensitive.  Makes me cringe at the thought of the hacked up props I used to run back 36 years ago.

OK, so the balancer reveals a heavy blade.  There are several ways to adjust the prop;

Sand the tip of the heavy blade.
Sand the backside of the heavy blade.
Sand the front side of the heavy blade

Or

Paint on a drop or two of dope or varnish on the light blade.

I am reluctant to alter the shape of the blade by removing material.  A light brush stroke of varnish seems to be a better choice.

Gentlemen?

[FLOYD CARTER]

I think it is OK to sand the back side of a wood prop.  Varnish on the light side also fine, but will work if there is just a slight unbalance.

You should not sand the front of a prop, unless you just lightly sand the varnish and not the wood.

F.C.

[Steven Kientz]

I balance props by wiping a small amount of CA on the light blade. If you are a heavy handed sander and sand thru the finish then you'll have a moisture problem.

Steve

[Randy Powell]

I've used some props (notably Zingers) as basically prop kits. I've carved the front, back, tips to the shape I want then balanced. As long as you maintain the correct airfoil, not a big deal.

[Paul Taylor]

What if it is a APC or TT prop???

[Peter Nevai]

A thin smear of epoxy (on wood props only) allways worked for me. I does not have volatiles to evaporate.

[Steve Helmick]

What if it is a APC or TT prop???

Start with the flashing. Sometimes that's all you need on a TT. Seldom so lucky with an APC, but start there.
I prefer to sand the front face of the propeller. Part of the trick is getting a feel for the grade of sandpaper to start with...and then polish with 600. With FF wings, theory was that you wanted as smooth a bottom surface as you could get, and the top would be better a little rough, for turbulation. Same thing with props, IMO.

I don't know what the glop is they "finish" Zingers with, but it clogs up the sandpaper so much that I'd rather strip it all off to begin with...with paint remover.  Steve

[Chris Wilson]

I did read an article years ago that told you to glue solder into the hollowed out hub of a molded prop.

The author firstly placed blue tack or plasticine or similar into the recess, added or removed and placed it until satisfied, then weighed that with a fine scale and replaced it with the same weight of coiled solder super glued in place.

The same could be done with a solid hub by drilling out a small hole as the smallest amount of solder has great consequences to prop balance even though it is at the hub.

Cheers.

[Alan Resinger]

First off make sure that the blades are exactly the same length.  When sanding, or my choice scraping the back of a blade you may be altering the pitch.  Make sure and check after anything you do the the back side.  I use either a single edge razor blade or a cabinet scraper on the back side to keep it flat.  Undercamber blades require a different tack.  After gaining balance by sanding the front of the blade or scraping the back make sure that the prop will hold any position you put it in on the balancer.  Don't just place the blade in the horizontal position because it may balance there merely due to the hub of the prop being heavy on one side,  If that is the case you will have to take material off the heavy side of the hub.  3 Blade props are actually easier to balance than 2 bladers.  When balance is finally obtained spray a couple of light coats of urethane to protect the prop from moisture and fuel.

[Allan Perret]

First off make sure that the blades are exactly the same length. 

I've often wondered if this is really so important. 
I know we dont use them in stunt, but there is such a thing as a one bladed prop. 
If that works OK, why would say a 1/16" or 1/8" difference in blade lengths on a 2-blade prop really matter ?

Does anybody know what the event is that uses the 1 bladers, and how did that come about ? 
What is the advantage for that event if any ? 

[Ward Van Duzer]

One bladers used in speed events, and believe it or not, Rubber events!

W.

[Brett Buck]

One bladers used in speed events, and believe it or not, Rubber events!

    Not too surprising, both are trying to maximize the efficiency by running in clean air.

    Brett

[Steve Helmick]

The OT Rubber FF models fly pretty poorly with a single blader, because the nose oscillates with the thrust offset. Not very efficient, but you only had to make one blade, and it cut the chances of breaking the prop in half, a good thing. The speed models that use single blade props are interesting (at over 30,000 rpm these days), because the pitch adjustments are done by shimming the prop with tapered shims. Would be nice for stunt, except for that 30,000 rpm thing... Steve