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Giant-Scale Tips: HOW TO BALANCE A LARGE SPINNER

Giant-Scale Tips: HOW TO BALANCE A LARGE SPINNER

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.

1

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.

2

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.

3

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

 

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12 Comments

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  1. I meant to say in the last paragraph, … place the spinner AND PROP on the engine … . The prop is the key item here as the prop needs to be in a good position from 12 to 2 O’Clock just before compression to make a hand start. It is possible to put the spinner/backplate and prop on the engine only to find the two arrows will not meet, if you do not pre-assemble and mark them. One more thing I did later, on the CARF P-51 composite spinner cone, I ended up removing a quarter-sized slug of what appeared to be Epoxy inside the cone. Apparently CARF pre-balanced the cone and added the epoxy counterweight. Best to remove that before balancing the spinner and backplate as one mass.

  2. Thank you. I can comment on the Aero Works P51 where excessive vibration was sourced to the spinner. Once balanced the problem was solved.

  3. With total respect for the article’s Author I disagree.

    The small drills on the backplate have nothing to do with the spinner’s balance…in this way you are working on the backplate only!!

    Let me explain…..and sorry for my English.

    My experience came from my work on a big spinner (6,2 x 11.4″) for my 1:8 scale Convair XFY-1 Pogo.

    On my model I use electric motors and two 18 x 8” 3-blades contra-rotating wood propellers.

    The balancing process is very tedious since I’ve started to balance the SINGLE parts: backplate, propellers and fiberglass spinner.

    My backplate is an alluminium piece custom-made on a lathe machine…..it’s almost perfectly balanced but I’m looking for perfection so I have added a little touch of paint on the lighter side and now it’s perfect.

    Same as above for the three-blades wood propellers.

    Of course it’s important to cut-out the holes for the propeller’s blades and paint the spinner too.
    Next, with the spinner mounted on the backplate, use the balancing setup (mine is almost identical to the one in the article) to find the lighter part of the spinner.
    Add one or more strips of American Tape INSIDE of the spinner at the proper position.
    No need for epoxy resin, lead or paint……the American Tape is a perfect solution.

    With the spinner almost perfect-balanced do the final balancing with ALL the assembled parts.
    In a “perfect world” everything should be balanced……but in the real-world expect some little inaccuracy.
    Without a dynamic vibration analyzer/balancer we can’t do any better.

    Ettore

    1. Yes, This is how I do it also, even the carbon backplates are nearly perfect, it’s the cone that is the worst part. I’m not sure what you mean by American tape though, I use CA glue and creep up on the right amount.

  4. Lane, I use a High Point from the late 70’s. Works even on 30″ props. Thanks for the instructions on spinners…off to the shop to balance.

  5. This is exactly how I balance my spinners including using a level and wood mounting stand to extend the balance points; and it works great. Dubro makes a similar balancer. They also sell separately an extra long rod that will easily handle a 5″ or larger spinner. Was going to comment about indexing the cone and backplate with the prop and spinner on the motor, until I read your last paragraph. Thanks for posting.

  6. Actually, the Dubro is the same design and works great on large props, allowing them to be extended beyong the edge of the work bench so the prop can be checked from any point in its rotation. Great product.

  7. Unless your parts are really awful you will find the balancing to be extremely good in actual practice. However you must be very careful with the balanced parts. The main starting point is to always assemble all your parts on the engine and set the prop in the correct position you will want it to be when you are finished. This will eliminate any clearance problems before your start the project. If you overdo the drilling of the holes you can fill with solder and start over. If you do be sure to brad the solder in the holes so it will not come out.

  8. I have used the same method on spinners with mixed result. If you balance the back plate first, then you can assume any imbalance is in the cone. Adjusting the backplate to compensate for the cone will give you static balance, but not dynamic. May be better to separately balance the backplate and then balance the cone; doing so by adding weight, such as a drop of epoxy, to the cone at its mid point ie half way between the base of the cone and its tip. Haven’t tried this method yet, but after mixed results on base plate adjustment, have to wonder if it has any merrit.

    1. Of course it is worth spending the money on a quality cone to start with. I have found True Turn cones to be fairly well balanced from the get go.

  9. I usually buy TruTurn spinners when I can. Found them to be balanced when you get them. Golfers use a lead tape to balance their golf clubs. It has a very strong adhesive and is very thin. I use it to balance prop hubs. It does not take much. This way you can leave the finish on the prop blades alone. I think you could probably use it for spinners on the inside of the cone. I have not tried it myself yet.

  10. I have used dabs of hot glue. Problem is, seems to peel up rather easily. But great idea of the golfers lead tape! I will peel up the hot glue, weigh it, and add back the same weight of thin lead tape.

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