Propeller balancing, balancing and ultralight aircraft propeller, prop balancing your ultralight propeller.

Balancing your ultralight aircraft propeller.

Go from idle to full throttle and back hundreds if not thousands of times. Leave it out in the rain, hot sun, freezing cold.

Well one of the first signs that it is NOT feeling fine is that vibration  you may have noticed while flying. Or that you no longer notice because you have gotten use to it. An unbalanced and or out of pitch prop is a lot like a neglected wife - keep neglecting, and ignoring  her and sooner or later you will loose her!

An unbalanced prop can  shorten the life of your gearbox, and could effect your crankshaft.  It puts a strain on your airframe, and causes cracks in the frame and fittings. Vibration from a prop can loosen nuts and bolts literally shaking them off your ultralight.
Safety wiring prop bolts

A very sensitive prop balancer that checks both longitudinal and lateral balance can be constructed for less than $10 and a few hours of your time. The balancing is done by putting additional finish on  the light blade with a brush or spray gun. Of coarse, the balancing must be done in a closed room as the slightest breeze will move the prop on the balancer. This is not magic or rocket science.

Very true.  I know of an old guy who has been an A/P for about 50 years and specializes in old Piper singles who uses a lawnmower blade balancer bought
in a hardware store for $5.  It's a cone-shaped thingy that sits on top of a pointed pedestal.  He claims it works as well as any $500 mil spec machine. After watching him use it, I agree. 

There's no black art in maintaining props and doing your own thing is no problem if good common sense is used. Many of us have been programmed that if a certified repair station doesn't do the work, you'll end up falling out of the sky. Also IMO, spar varnish is nice, but doesn't last and has to be redone every few years.  Epoxy 2-part varnish by Polyfiber is much tougher and will last much longer.

A prop balancer can be as simple as this. The theory behind this balancer is that gravity will rotate the heavy side down. In this scenario the less friction the better.
I used a 5/16" steel rod centered in the fan with cone shaped bushings. This assembly rotates on a pair of leveled angled extruded aluminum.

Since a heavy blade will rotate down. The heavy blade is sanded or painted in the case of a finished propeller until the it will not rotate when left in any position. With 4 bladed fans, it is easier to balance 2 blades at a time. Number the blades 1 through 4 going clockwise. Balance 1&3, then 2&4.