I have always balanced my props by grinding off the tips until it was well balanced. I know that this can create a little uneven thrust between blades but with a 20 pound thrust engine we are talking less than a pound, probably just ounces of thrust difference between one blade and the other. Is that enough to cause problems in engine bearings ???

What do you guys do to balance props ??? I dont want to paint them, or something very difficult that might change with time.... Whats the easiest and best way ????

a bit off the topic.. sorry.

is there any way to balance the prop WITHOUT a prop balancer?

tks

Yes. Pay someone WITH a prop balancer to do it for you.

Dr.1

The easiest and best way to balance a prop is to spray clear poly-u on the front of the light blade. If it takes more than 2-3 coats, scrap the prop or take it back where you bought it. I'd NEVER grind the tip or sand blade to balance a prop.

Dr.1

i never understood why they dont get balanced at the factory they are made in. i am not ranting i was curious why they dont.

That's a lot of hand work that would raise the price of the prop considerably. Composite props are usually in balance due to the nature of the material and method of manufacturing. It takes only a few minutes to balance most wood props, and is a very satisfying (to me) part of the sport.

Dr.1

On APC and other similar props, I check the balance as soon as I remove the price tag and sticky stuff with alchohol. On the heavy side, I start by sanding the sharp trailing edge and leading edge off until I get it to balance roughly, then lightly sand the original light side trailing edge just to get the sharpness off the blade. Most of us choke the engine by hand and some props come out pretty sharp on the trailing edge and can cut your finger even when just pulling them through to prime. (Got scars to prove it.) I then finish the balancing by sanding the heavy side leading and trailing edges with 320 or 400 paper.

For smaller props, the best buy going is investing in a Top Flite magnetic balancer. You can balance a bunch of props and spinners with these things and they are only about $20.00. I have balanced up to a 26X10 wooden prop on one of these.

I agree with the light coat of clear something added to the light side of the wooden props. If you apply it very smoothly and evenly, you can actually create a smoother surface than the original. Some have enough clear on them that you can lightly sand them as above if they are not too much out of balance.

If you don't balance the rotating parts, you will pay for it in loss of rpms and excessive vibrations that can easily cost you your airplane. I can't believe anyone would procrastinate in purchasing an inexpensive prop balancer, if they only realized what it will end up costing them in the long run on equipment, running unbalanced.

Try this article.

http://www.findarticles.com/p/articl...09/ai_n9254549

Taking material off the tip, or trailing edge will move the balance problem from mechanical to aerodynamic, which both is not good.
Trailing edge correction can be done if the blades differ in width. Leading edge correction is bad yu-yu for above mentioned reason.
If the blades are the same in shape, then the options are either to thin the heavy blade, or apply extra thin coats of paint to the light blade. Rub in between when using spar varnish. For best balance, the prop should stop in any position on the balancer, without any bias towards one particular side.

I read the article, and the article said to sand off the TIP of the heavy blade, which is exactly what I have been doing.

Now can someone tell me why we should NOT sand off the tip ??? They say it makes it aerodynamically uneven, but the amount is negligable... Think about it, I have a 20 inch prop, and I take off less than 1/10 inch off the tip of one blade to balance it... The amount of lift that the shorter blade produces is a couple ounces at most [X(] Now how is it that an pulling force of a couple ounces is going to hurt the bearings ??? You all ever heard of P factor ? In climb and high angle of attack, the Right side of the prop pulls more than the left even on a perfectly balance propeller. Im just having a hard time buying that grinding the tip off the blade to balance the prop....

I have heard this from serveral sources though, so maybe there is something I am over looking ??? Thats why im asking Just remember, out of BALANCE gets amplified a thousand times at high RPM's, but the aerodynamic lift of the prop is in the 20 pound range at full RPM, so a couple ounces of uneven lift is just a couple ounces, even at full RPM... If there is a prop expert out there that could shed some light on this subject, that would be great So many different opinions out there of what to do, im drowning in conflicting information [sm=drowning.gif]

Hi Mudspike,
If you don't balance your props, I read a article about installing the heavy blade at bottom dead center (BDC) with the piston at top dead center(TDC). This is supposed to cancel out the difference. It sounds good for single cylinder engines. Of course you will need to determine which is the heavy blade.

Dave

Take that difference in ounces, grab the prop by the tips and apply that force in rapid alternating mode. Large props will generate a lot of torque this way. See what happens?
Does that look to you as balance? No way! The unbalance in a single cylinder engine is bad enough, without us adding to it.
Do not believe all that is written. A lot of it is plain ..., not worth the paper it is written on, or the bandwidth it spoils.
A good example is the single blade speed prop. It takes som very fancy shaping of the counterbalance mass, to get all oscillating torques balanced out for that record run, when everything must be just right.

I learned from a good friend to spray clear Laquer paint on the back side of the light blade until balance is achieved. I don't know if this is the best method but It seems to work pretty well.

What we are talking about removing on APC and Master Airscrew props is the very sharp edge that is left from the mold seams when they molded the prop. These are sometimes very dangerous and should alway be removed. Sorry if we weren't clear. I agree, we should never sand to remove material from tips or the main body. There is really nothing wrong with a light sanding that only removes some finish or excess paint or clear coat off of a prop. We can split hairs to the point here, that the novice will be afraid to balance a prop at all. I have had some props that were so bad, that I returned them to the manufacturer for replacement/refund, because of what you said. You can start by seeing where you are by checking the prop before you do anything. If one side drops like a rock, then start adding some weight with tape on the light side. If you feel too much is required, don't even go there, there would be too much work to balance the darned thing.

I have had some Master Airscrews that all it took was removing the painted on label and painted tip on the heavy side and the prop balanced perfectly. This can be done with either 400 paper or chemical paint remover. These props always seem to have allot of material on the edges that is ruff, but sharp, almost like a cerrated knife blade. I have had some APCs that balanced perfectly right out of the bag. Just cleaned up the sharp edges and kept track of material clean up as I went with the balancer.

Hope we didn't cloud the water too much about the "delicate art" (and opinions) concerning prop balancing. Many instruction manuals give pretty good direction on this. Like any hobby, there are many opinions, but the manufacturer's should be responsible enough to provide directions on how to best balance their product. Don't even start discussing how to balance a compostite prop!!!

Good luck with your new hobby!

Great article, thanks for the information. Just wish they had been a little more informative on hub balancing.

Go to aircraftinternational (dot) com they have a video on this very subject that is excellent. It is also on DOD.

AS specified on the video, don't forget to balance the hub!! You'll be surprised how much weight you need on one hub side to balance, when the tips are balanced.

Great Video and some good ideas as well. Thanks for the heads up. I have visited that site many times and totally missed that thread. Isn't it amazing, when we are looking for certain information that we often become oblivious to other information that we could use as well. Now I gotta go buy a new Dubro Large prop balancer to add to my shop. That one looks so much better than the one I am using now!

in the world of wooden model prop's a couple ounces is quite a lot of wood, I would hope one wouldn't need to remove much more than a gram or 2,,,

I had a Zinger 20 incher that needed a lot of sanding on 1 blade's trailing-edge, once balanced and on the motor I could tell that it didn't produce an even amount thrust, it produced what I would say were pulses of thrust, when I replaced it with another Zinger that was balanced with glue added to 1 tip I had a prop that produced a more even thrust of air,,,

measuring the first prop's blades did show a difference in the blade's widths, so the widest blade was producing more thrust than the other,,,

so now for balancing I will add clear poly, and or paint the tips and then add more paint to balance the light blade...

Jim

Hub balance first by letting the heavy blade come to a stop. Now if the blade is sitting exactly at 12 and 6 oclock you're all set to spray on your favorite paint or lacquer to the light blade.

If the prop isn't perfectly vertical you can clearly see which side of the hub is heavy. Now here is what I do. I take BB's and masking tape and tape the BB's to the light side of the hub. The nice part is you can see exactly how many BB's you need before you ever attach them. I then take a drill bit and drll very shallow holes that bury the BB's about three quarters of the diameter into the hub. Use a slightly undersized drill so you can tap the BB's into the holes. Once tapped in lock'em with then CA.

Rich

PlaneInsane- Now that's a good idea, beats gooping on an epoxy mixture like I do.

I've been called an idiot for doing it but I've screwed small screws into a prop hub and ca'd them in place to balance a prop hub before. I've never had one come out and if they did they would be captured by the spinner. Lot's of ways to skin a cat.

Another nice thing about the BB's is it gives you a standard. For instance I balanced a Fuchs 32x12 for a fella that was a 15 BB hub...yep, now that is one outta balance carbon prop. The funny thing is he bought two and the other prop was a zero BB hub. But on average I've noticed between 3 and 6 BB's usually does the job.

problem with most balancers i've seen is the way the prop is supposed to be centered with those stupid cones. all it takes is a slight imperfection on the very edge of the prop hub's hole for the cones to hold the prop way off center! when clamped right it is amazing how close to perfect balance APC props are...but put them on the cones and they suddenly need lead added to one side of the hub...


dave

That is a BIG problem ZAGNUT, I have done my best to have the cone hold the prop on correctly, but as you say a slight inperfection can mess throw your measurements way off [X(] How do you balance your props ZAGNUT ?? I have never seen anything but the cones available for prop balancing... And BTW, on my 20x10 APC prop, the hub is so thin that the cones will not hold the prop, they hit each other at the small ends before teh cones grip the prop [:@] What do you guys do ????