Always balance your spinner. An unbalanced spinner can create small to large vibrations which can lead to serious problems with your model. For this piece, I am balancing the CARF P-51D composite spinner and aluminum backplate that came from CARF as an optional purchase. I have used this method of balancing spinners, to success, for many years. Some may like the method of adding weight to the spinner, but that always opens up the possibility of the weights eventually coming loose as well as the difficult task of figuring the amount of weight to add to begin with. The only common thing that comes to mind that we add weights to balance is automotive tires, and this takes a rather sophisticated machine to compute how much lead and where exactly to place it. This method (drilling the backplate) just seems easier and it’s used in balancing many reciprocating things such as engine crankshafts, flywheels and such on full scale aircraft and automobiles. I call it tried and true.
Balance your props independent of the spinner. Most spinners will require a larger/wider balancing setup than a prop. To handle the larger dimensions, take a scrap board, space and drill the holes to fit your balancer uprights. Get a 1/8-inch steel rod (rigid piano wire) about 12 to 18 inches long to handle the spinner. Or, get whatever rod to match your centering plugs. Add a level to make sure it’s going to be true. This is the High Point Balancer. Only seen one other guy with this brand in 30 years of RC! It is a very sensitive piece of equipment.
Make index marks on the backing plate and cone to be able to keep your balancing points consistent. Otherwise, you will be chasing your tail trying to balance. Yes, you can use a pencil or magic marker, but after a few flights you will lose those marks and have no idea how the cone and backplate were mated to balance. These marks are small but are permanent as I made them with a vibro-engraver. A little red paint touch-up and they become invisible.
Find the heavy point and mark it. Draw a line from there thru the center of the backing plate. Try to keep your lightening holes on this line. Drill-out only small amounts at a time, reassemble, and keep repeating till you get zero movement no matter where on the circle you place the spinner. Don’t drill the holes completely thru the backplate as this creates a jagged mess on the other side you need to smooth off, no need for that. When you prime, paint, and clear-coat a spinner like this one, you will likely have to remove quite a bit of spinner backplate to offset the paint buildup. Like figuring CG, it takes what it takes to balance out. Yes, this looks like a lot of drilling, but that’s what it took to balance in any position. This took about an hour to complete. But, it’s time well spent toward the success of your maiden and subsequent flights.
A hint on balancing. When the spinner moves slowly from a high point to a lower point, it means you are getting closer to a balance. So, make your next drill-out accordingly small. As the balance gets closer, the movement will become very slow from high to low, and your drill-outs should be very light. If you overdrill the heavy side and it becomes the light side, go to the opposite side and make a very small drill-out and test again. A light touch is best on the drill-outs.
One final note. Before you index the backplate to the cone and begin balancing, place the spinner on the engine just like it will be used at the proper point on compression stroke as you like to hand prop. Then mark the spinner and backplate with arrows or your favorite markings. You do this because if you randomly mark the backplate and cone on your shop table and then later assemble them on the engine shaft, odds are the index points will not match up! Without a match-up of index points, all the above described balancing will be for nothing. Yes, this can happen and been-there, done-that, thank you ma’am!
TEXT & PHOTOS BY LANE CRABTREE