I'm getting ready to take my new trainer out to the field this coming weekend (weather permitting), and the only thing I really overlooked was balancing the prop. I'm wondering how important this really is. I could get a balancer at the hobby shop but if I could save myself a 20 minute drive that would be dandy. What do you guys think?

-Patrick

It is very important. At the RPM's that typical model engines and motors (gas/fuel/electric) turn these props, it can vibrate to the point that can go as far as to destroy a model in a short period of time. Lesser vibrations can and do damage receivers, shake connections loose, break down batteries.. in short order too!

It only takes a few moments to balance a prop, and it is well worth it. Most modern props are pretty much in balance, and you will find that when you buy them, but occasionally you will run into one that is off balance.

Also, consider a landing that was less than perfect. When you 'hit the ground', the prop hits the ground too and it stalls the motor and, worse yet, chips the tip of one side of a two bladed prop. Ok.. now what happens? Well, that chunk of prop is now missing causing one side to be slightly heavier than the other... off balance... vibration time!! So, take it off, put it on the balance gig, then trim off the heavier side to balance it.... or replace it.

DS.

How big is the prop? If your prop is in the 5 - 9 inch range, forget it altogether (unless you are running a racing engine), if it is in the 9 - 10 - 11 inch diameter range with a sport engine, then balancing isn't very important but it can be an interesting exercise just for the fun of doing it. If is 12 - 13" then a balancing is a good idea but the world won't end if you forget to do it. If it is 14" or more, then you had better balance it.

Balancing is highly overrated. As long as you are not flying Extreme Speed planes, don't worry about it. I fly with prop sizes ranging from 9" to 22" (Mostly 11" - 14") and in over 40 years of flying I have balanced 3 props - and I only did those because a girlfriend bought me a Balancer for Xmas one year so I felt obligated to use it.

There ARE times when balancing is important - even critical, but flying you basic trainer or sport plane isn't one of them.

Thanks for the replies fellas. I think I'll skip the drive to the hobby shop and just make I have a spare prop on hand in case I smack one on the pavement.

A rotating mass that is out of balance will create vibration. Vibration over time will cause things to become loose. Do your self a favor and balance your propellors.

Out of the several props I have tried the master airscrew and topflight props where not really well balanced, but every APC I have tried was either dead on or very close. Now I just buy APC props and don't worry about.

In that case, you'd better throw away the piston in your engine.

Did you know that if you put an unbalanced prop on your engine with the heavy side opposite to the piston direction that you will actually REDUCE vibration?

The AMA did a series of tests on this 2 years ago, and their findings were that for a sport engine, balancing the prop (Except in extreme cases) was totally unnecessary.

I gotta agree with Minnflyer here. I also think prop balancing is over rated. If you have a balancer then it won't hurt to use it but don't not fly if you can't. I have used both balanced and unbalanced props on my G-90. The engine itself shakes so much the prop balancing had no effect

Minn... Thanks for the information.

Well, I stand corrected! I often wondered why, after a hard landing and chipping the tip off of one side of a prop, then flying again, that the plane never seemed to be any different. But, like most other 'sheep' in this hobby, we follow the suggestions given to us by the 'more experienced' pilots out there.

That means that I have thrown away several props that, otherwise would have been just fine. Go figure. Ah well, perhaps I ought to buy some APC stock

DS.

I'm not an expert in engine design but it was my understanding that two stroke engines are designed to counterbalance the piston stroke. If you are familiar with R/C helicopters why is that the most important thing to balance is the main rotor blades. These blades are nothing more than one big propellor.

I have to say i have found APC props to be very good props. and thay seem to perform much better to me. i just like the ugly props thay work great.

Balancing is much more important on a heli simply due to the SIZE of the rotor blades.

Something else to consider is that even an out-of-balance prop will only vibrate badly at a particular RPM. Have you ever driven a car with a tire that was out of balance? Ever notice how the car may shake at 60MPH, but not 55 and less, or 65 and over?

I agree that prop balancing is highly over-rated and I don't usually bother to check APC props because they are always very close.

But I once checked a 15" MA prop that was WAY off. Just for kicks (before throwing it away), I "balanced" it by trimming the end of the heavy blade. To get the prop to balance I had to cut off over 1/2"! The only thing that I can figure is that something went badly wrong when it was molded.

Based on this experience I think that it is worth checking non-APC props to make sure that they are at least reasonable.

In general APC are the best "factory" balanced props I buy. The worst would be master airscrew.

One of the reasons APC are so well balanced is that they have hardly anything out at the tips (Which is why the tips break off so easily) Personally, I avoid using them. I've tried them, and I'll use one now and them, but I just don't see anything special about them - combine that with the fact that they break at the drop of a hat, and I'm just not sold.

Now if you guys want to try a prop that will pull stumps, try a Graupner.

I don't think these things get nearly the publicity that they should. I use them almost exclusively on my 4-strokes. They cost a bit more, but (to me) they are worth every penny.

Also, they have some weight to them. This translates to a flywheel effect which will give you some increadably low idle speeds.

Try a 12 x 7 on a 70ish 4-stroke, or a 13.5 x 8 on a 90ish 4-stroke and you'll see what I mean.

If your LHS doesn't have them, you can get them here:

http://www.hobby-lobby.com/grprop.htm