anuthabubba
Posts: 226
Joined: 11/9/2007
From: Transylvania,
LA, USA
Status: offline
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Great thread! Found it while searching for info on newer prop designs. I have and use a High Point balancer I got after being inspired at a siminar by one of the leading pylon racing guys (if you read this, I apologize for forgetting your name) back at an AMA Nats in Lake Charles many years ('70s) ago. Don't remember everything that was said but still use this general info and other tips learned along the way for balancing my props/spinners. Wish I had bought a Prather Pitch Gage when they were available.
On removal of material for balancing, it is recommended to sand only the curved, front, side facing away from the plane side (for a tractor prop) of the heavy blade to prevent changing the pitch. The spray a coat on the light blade method mentioned earlier sounds good too. It is also recommended to use a pitch gage to ensure the blades have the same pitch and to make adjustments/changes. You can also remove up to half of the wood (depending on hole size) on the heavy side of a hub. This may sound extreme to some of you but I've been doing this for years without mishap on blades up to 16 inch diameter and rpms up to 12K+ on the smaller diameters. Just be sure to 'feather' in all cuts and don't leave any scratches/gouges in the wood. I use CA to reseal.
On molded props, like APC, it is difficult to remove material from the hub so I add weight (like Nat P. showed me) to the light side. Have also done this to larger wood props. Balance and mark the hub, drill the appropriate size hole on the light side and put a chosen screw in it. Rebalance. Change as indicated. Works great! Never had a mishap, screws never came out/props didn't break, with this method either.
Another aspect of prop preparation to be concerned with is tracking. Making sure both tips run in the same plane. I use a homemade device with a flat base that has a 90 degree shaft/bolt sticking up. Place the, drilled to fit the engine, prop on the vertical (can be shimmed to fit) shaft and measure the tip clearance. Sand the back of the hub to get the tip clearances equal. Might have to sand the front if it's way off.
To make the High Point balancer (can prolly do the Dubro too) work with larger diameter props (up to 16" so far) I made extensions for the legs out of brass tubing and piano wire. It all disassembles and packs back into the case. I just crimped the tubing to the piano wire with diagonal cutters at the bottom end. Solder if you want to.
Another concern is the mostly invisible rotating propeller arc. After trying several colors (dayglo red/orange/yellow, yellow, red, and white), I have concluded that white is easier for my eyes to see. I paint about an inch, front and back, of each prop tip white. Most of them I also put another 1/4" white stripe or two spaced at 1/4". Done with care after balancing, rebalancing shows little or no change. An extra coat can correct it. These white prop tips show up very well whether you are behind or in front of the engine.
These methods are presented here as descriptions of techniques I have used for many years without mishap. If you choose to do similar, you do so at your own risk. I am not a trained/degreed engineer and don't play one on TV but have an MSMD (monkey see monkey do) from the CBAWSDB (College of Been Around a While and Seen it Done Before).
At least this great thread gets back to the top so more guys can enjoy it. Flame away.
Terry in LP
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All Forums >> RC Airplanes >> Tips & Techniques >> RE: Spinner and backplate balancing....How To 
RE: Spinner and backplate balancing....How To - 
