there are finger balancers and magnetic ones top flight makes a pretty good one it suspends a rod that holds the prop between two magnets on a stand then you can check to see what blade is heaviest then you can lightly sand the blade to level them out .
what I have found is there is allot of difference between brands in balance the wood ones I have checked have been real close, allot of the plastic composite ones are way off

The three blade prop you saw was probably on an Alpha 40 or Alpha 60 trainer with the Evolution power system in it. The purpose is to slow the plane down for easier landings and to give it power but not too much speed while in the air. I personally didn't care for the ones on either of my trainers and I believe that the same can be achieved with the proper selection of a more common 2 blade prop.

3 blade props are "usually" used when you need more ground clearance for the prop. When going from a 2 blade to a 3 blade prop as a rule of thumb, you drop 1" in diameter.

There are several different balancers available. The simplest is the hand held one. It is an arbor, machined to points on both ends and has 2 cones that screw onto the arbor that center the prop and hold it in place. You just hold it between your thumb and finger lightly. The heavy blade will swing to the bottom. remove a little material from the heavy blade or add paint to the light blade until the prop no longer swings. It's easy to do and only takes a few minutes.

I keep one the hand balancers in my flight box, but also have a base mounted unit the has magnets to support the arbor for a more free motion. Either will get the job done satisfactorily. The base mounted units are a little more accurate.

Rod

I've always balanced my props whether they are 9" or 20".
I have found most plastic/composite props are not as unbalanced as wood props. Also to throw another wrench into this thread, if you have to enlarge the prop shaft hole in the prop use a prop reamer designed for the job or a bench press. Please don't use a hand held drill especially on a wood prop since the drill bit will follow the softer side of the hole. Which brings me to another complication: Off centered holes in the prop will drive you crazy trying to balance them.
Don't fly with them.
Oh BTW, don't trhow out your old broken props..they make good epoxy mixers and with the larger props 14" or better they make good paint stirrers.
Some 'old school' flyers at my field say to use wood props on trainers until your landings/taxiiing become alot smoother so you don't bend the prop shaft on your engine. I don't agree with this because I feel it would take more than an occasional ground strike to bend a shaft. Wood will take less stress to break and transfer less to the engine/airframe than plastic/composite props. Just my $.02
Another word of advice is to paint the tips of your props white or yellow so you can see the prop arch when running and will wear equally from each tip. I don't recommend painting one tip to balance as over time the paint will wear off and you'll be back to square one.
Always check your prop nut for tightness ,especially on wood props,before your flying session as wood will expand and contract more than plastic/composite props.
On four stroke engines if your engine backfires, recheck your prop nut. Chances are it came loose.
Always....always....always check your prop, spinner and prop nut whenever you even nick the ground. A flying prop without being attached to an engine can be extremely dangerous.
Do not ever.....ever....ever try to glue, attach or in any other way, repair a broken prop to fly.


Happy Flying


Tom

In reply to pghmike,

The 3 blade props are for better torque. But due to the fact that they have one blade more they are "heavier" for your engine. So If for example your engine is for 60-70size works well with 12X6 two blade and you use a good performance fuel with mixture containing Nitro 15%you can use a 10X6 or 11X6 or 12X4, 3 blade. If you use cheaper fuel then try not to stress your engne too much and use 10X6.
Now as far as ballancing your prop the first thing you should do is buying a prop-ballancer!! and a lot of sandpaper! Then try to sand the inner prop surface without destroying the leading edge. After you make it "lean" with sandng with proper sandpaper (it depends what prop you are sanding in order to choose the right sandpaper - if the prop is wood or plastic)and after the prop ballances on the prop ballancer you have a "perfect static ballance".

Cheers
Johnnie

Somewhere in cyberspace I came across a site that did some testing that seemed like it made sense anyway
they took wheels off of a plane and mounted it to a bench and using a well regulated power supply with a amp meter they tested prop balance by
measuring the current draw on the servos the more the prop was out of balance the more current the servos drew trying to hold center, the props that where in the best balance had the lowest amp draw so I guess prop balance does effect the plane to some degree can't see it being good for the servos to constantly be moving anymore then necessary to hold center there was also one on engine mounts http://www.centralhobbies.com/Engine...s/hydetxt.html

Way to go skiman762!!! You are right!!!!

We can lower the "vibes" but we can't eliminate them. Especially in glow or petrol or gaz engines. Damn the vibes are always there.![:@]
Cheers
Johnnie

Digital servos will probably be even more prone to excessive current draw, because of their higher resolution.

Rod