Glad to see a NEW and HEALTHY RC BOARD!

Like to get some feedback on the process of "Dynamic" prop balancing. I'm using a DuBro High Point, balancing a 14" APC. I like the CA on the light side method. If I understand the dynamic method of balancing, the prop should not move from any point inwhich it is placed. My question is in interpreting a prop position of 10/2 o'clock or 2/8 o'clock from 12 o'clock starting point. Is this implying that there is a hub imbalance and if so, what would be the correction? Thanks!

Not sure what you mean when you say 10/2 o'clock, or exactly what you mean by taking your reference at the 12 o'clock position. When you say dynamic balancing, my analytic personality wants to think of somehow balancing the prop while it's on a moving engine?? I tend to think of what you are describing as static balancing. Be that as it may, it's really difficult to get it 100% right anyway. Some guys set the heavy side of the prop opposite the piston on a single cylinder engine. A perfectly balanced prop on a single cylinder engine seems a bit contradictory, althought that is what we do and for the most part it works out. Your thinking is correct on the way the prop should act on the balancer. It should not fall off either way no matter where it starts. Some props are just impossible to get where you want them. Even a spinner will booger up the works some times.
APC's are usually pretty good, but on the heavy side. Good flywheel effect on the engine though. Take care_Bob

I used to think it was a practical impossibility to get the prop to hold rock-steady in a magnetic balancer in any position you move it to, but after a winning pylon racer showed me how, now I can do it every time.

You are right about the heavy hub. Whatever angle a prop rotates to, that means the heavy part of the prop is at the six o'clock position. I use a dremel sanding drum to remove wood from the hub or blade root at that position. Just run a sight line straight down from the center of the prop shaft to the lowest point on the prop along that line, and sand off a bit of wood.

Make sure you ream or drill out your hub to fit the crankshaft BEFORE you try to balance the prop!

You will improve the efficiency of a wooden prop (Zinger, Topflite) significantly if you shape the tip to resemble the APC tip--that is a more or less parabolic arc from leading edge of prop to a point at the tip of the trailing edge. Also, you can reduce the thickness of the prop airfoil so as to get a very narrow featheredge at the TE, and a very tight radius round LE. This helps tremendously to reduce the drag of the prop, and boosts your rpms by at least a few hundred over an off-the-shelf prop.

All this can be done in half an hour using a dremel and/or drillpress sanding drum for the rough shaping, then hand-held or soft block fine grit for finishing. I usually finish with 3M sanding sponge (Home Depot) fine, then superfine, then 400 grit sandpaper. I remove 100% of the surface of the prop in this process, and end up with about half the weight of a stock prop. As long as you preserve the basic shape of the airfoil, all the wood you take off contributes to a more efficient (faster turning, more thrust, less noisy) prop.

You'll need at least a few coats of spray lacquer to seal the wood, and you can use this process to perfect your final balance. A light coat takes only a few minutes to dry. Your finished prop will be a thing of beauty, and your engine will love it even more than you do.

Thanks for the replies guys! You both have good points! Bob, the 10/2 o'clock reference was my way of describing the prop position on the high side. Sorry for the foggy description! When you referred to putting the heavy side of the prop opposite of the piston, does that mean the high tip (heavy) at 12 o'clock while the piston is at it's lowest point of travel? Majortom, have you done this procedure you described with an APC? Would you sand the back side of the APC proportionately in order to lighten it up?

Thanks again Guys!
Bruce

The procedure I describe above is strictly limited to wooden props, which are my usual preference for the .40-.60 sport flying I do. I use APC props on occasion, mostly when I want more noseweight than my wood props provide. The APC's are most everyone's favorite prop in my area, and deservedly so. The only thing I would do to dress up an APC or other synthetic material prop is to remove any flashing from the molding process, maybe round off the leading edge if it is not nicely rounded, and then balance it by spraying clear lacquer on the light blade. I do not strive for perfect balance with plastic as I do with wood, but try to come reasonably close. If I use a prop that is not perfectly balanced, then the heavy blade would be mounted 180 degrees opposite the piston, as you describe--piston at TDC, heavy blade at BDC.

Thanks Majortom! I'll give your suggestions a try. Maybe I should experiment with some 14-15" wooden props! Best Regards, Bruce

The other tip I would pass along is, in buying wood props, look for close grain running through the prop from front to back, not from LE to TE. There is a certain appeal in the appearance of grain running with the flat dimension of the prop; the visible contour lines of the grain are reminiscent of the old laminated props, which are pleasing to contemplate. But for better strength, look at the end of the blade for lines running the short way, the closer the better.