Should I use Props out of box? or All propellers need to be balanced before use?

Thanks</p>

I would not bother to balance anything smaller than 15inch diameter. thereafter it's probably a good idea. The smaller props just don't have enough material in them to be very far out of balance and 1 or 2 gram is not going to affect the rotating inertia significantly.

large props should be balanced because there the few grams becomes &gt;10grams which starts to be significant.

What I do is mount my props  with the heavier blade at the opposite side to the piston position. i.e. if the piston is down mount the heavier balde toward the top of its travel. If the piston is at tdc then mount the heavier blade down.

no material removal required so strength is unchanged

I balance every prop before I install it on an engine. I have engines from the 70's that still run and are on their original bearings. Even smaller props can be off balance. The only exceptions for me are props for .049 - .15 engines.

Any prop that goes into my prop box gets balanced. It only takes a couple of minutes so if it only helps an engine a little bit why not. On my smaller engines I use APC props, I have only found one size that is balanced right out of the mold, can never remember what size it is but as soon as it's on the balancer I know it. Some of them are really off! Fire up your plane with an out of balance prop then try one that has been balanced and see the difference in the vibration going into the air frame.

I was astounded at how out of balance stock props are from the store. Once you buy a prop balancer, you'll balance every prop after seeing how badly they need it.

There was a thread to this effect some time back and I think the conclusion was that it is down to your personal preference. I use MAS upto 15" so far and I have never balanced them. But then again, I dont have a balancer. In the thread I mentioned above, the forum memebers wer with and opposed to this idea in equal measure. I do try to cleanup the leading and trialing edge burrs to prevent finger injury, that's all

Ameyam

I used to belong to a Goldwing user group, and the forums on there were equally fanatical about tires, batteries, and motor oils. The mere mention of any of these subjects would spur nearly endless threads that all boiled down to one of several opinions.

1. It really doesn't matter, no matter what. "I ain't never done it, and I ain't never saw no diff'rentz. And I get 'long jes fine."
2. It matters to everybody because I can cite a very specific case where it mattered to me: therefore it must matter to everybody.
3. General rule of thumb of when and why.
4. It matters absolutely all the time, because "if we can save/improve 0.00000000001% performance, it must be achieved."


There are probably more.

I won't say what my philosphy is. But it fits with one of the opinion categories listed above.

It is such an easy thing to do it has always amazed me that I am the only person in my club who does it with all props.  Of course no one else uses after run oil either.  Maybe that's why none of their engines seem to last very long.

I agree 100%. I balance every single prop. Some right out of the box are way out of balance. I would not put the heavy side down or up an one poster mentioned. Why not take 5 minutes and balance the thing. It's not that hard.
Take for instance a crankshaft on a V-8 engine,or model engines,2 stroke or 4 stroke, If it's out of balance,watch what happens. The same with props.
A fine running engine requires every minutedetail, and that includes balancing a blade, crank, prop, flywheel,spinner, you name it. If it is not balanced, you will have problems and eventual failure of the engine because of it. That's my story and I'm stickin too it!

after run oil? why would anyone use afterrun oil? Modern synthetics lubricants are perfectly capable of neutralising the acidic products of combustion. Your fuel has oil so after running the motor, let it cool a few degressand turn the engine over a few turns to push some fuel and lube through it. The fuel evaporates leaving the oil behind to neutralise the acid. So why do you need afterun oil?

well prop balancing like so many other practices seems like a good idea at the time but is absolutely useless on a single piston engine.....


But if it provides a feeling of security then theres no harm. However there is no strong technical reason for balancing small light weight props.

I'dbe more concerend with sharp edges that reduce efficiency and slice skin.

Thanks for all the inputs.

this point interested me.
Why absolutely useless on a single piston engine.....?

a propeller is not a flywheel. It may have a small flywheel effect for smoothing the transition of the piston but its primary function is the conversion of heat energy into mechanical work. We want that propeller to be as light as possible, as stiff as possible and to have zero tip, leading and trailing losses as possible.
The quest to balance the propeller is lost in the inherant unbalanced nature of the engine itself. The unbalanced prop itself  and its losses smoothes the engines firing pulse. If it were a large heavy propeller where the flywheel effect is greater then its worthwhile time spent balancing the prop.

It makes not difference if the prop is out of balance by a few grams when you have a single thumping mass reciprocating inside a cylinder. The entire system needs to be balanced not just one component. For example, like the dynamic balancing of tyres on a wheel rim, means nothing if the shock absorber is no longer working.

want to reduce vibration to the airframe, fit a mass damper or a shocking absorbing engine mount, but personally I don't waste my time by balancing props.

Perhaps 30 year ago when injection moulding was still a black art and computer controled processes did not exist there was a large disparity between one prop to the next from the same mould. In Modern injection moulding, an entire batch of props will be within a few gram of balance and i have found that this holds true for the APC, Master Airscrew and Radio Active props I have used. I have a balancer because someone with 40 yrs experience in the hobby said I needed one. I bought one and have realised that manufacturing tolerances are tighter today than they were 30 yrs ago,

On large multi cyclinder engines there may be a benefit but a gram or two here and there on smaller engines (below 1cu.in ) it means nothing.

I have a prop balancer thay I will check larger props with 13" or over in size most of the time there really close and I don't bother with them too much, mainly sand the sharp plastic mold line off and a quick check to see if there close and on the engine they go.

No single cylinder engine can be balanced due to the design with one piston and rod. However, do you think adding an out of balance prop will make the engine run smoother??? It's just one of those common sense things. Some people do and some don't. My basic instructor thought removing the price tag off the prop was good enough. Our advanced instructor was a pattern pilot and he showed us the difference between balanced and not balanced with one of his panes and engines. From then on I balance.
Also being as I live in a very dry climate I don't use after run oil. If I lived in a humid place I would be running my engines dry to remove the alcohol and then using some type of after run oil, I like Marvel Mystery oil myself. I use it on rebuilds and engines I know will be under the bench for a long time. Little things like this will depend on other factors so it's up to the pilot/owner to decide things.

Vibration forces are normally small, but very persistant.
Their destructive force mainly comes from the frequency with which they repeat or rotate around a shaft.

IMO for the amount of effort it takes to balance a prop, there's no reason not to...
I balance all of my props....spray clear polyurethane on the light blade.

I check them all. Takes a few seconds with a pin. In the winter I use a proper balancer when I resupply the stock. I have also found some brands are much more consistant than others. XOAR wood has impressed me greatly (all have been balanced). APC is pretty good. ProZinger usually is but I've had a few doozers, but wood is subject to that.

Of a dozen props maybe 7 to 9 will be OK as is, three will need some work and one or two will need material removed and 10 minutes of futzing.

Yes balance your prop....

always balance your props ,no matter what size. also balance your lawn mower blade after you sharpen it too. just put the blade on a 3/8 ' bolt in a vise and the heavy blade will fall. sand or gring the heavy blade a little more......................done................RON

I guess that's why there is a counter balance un-necessarily machined into the crank shaft on single cylinder engines at a pointless expense, designed by engineers who had nothing better to do than waste time on the figuring as to how it should be shaped and weighted for (non?) optimum efficiency.
There is no engineering or design basis for your statement. True, a single cylinder engine has an inherent pulse generated vibration, but this is not a balance factor and is relatively well dampened in a well designed RC motor. Any unnecessary, avoidable high frequency vibration should be eliminated and prop balancing does just that.

Would anyone intentionally securely mount your plane on a palm sander or simlar device, turn it on and just vibrate the stuffing out of it? Sure, that may be a bit of an exaggeration...though not by much. That is just about what those who run wonky props are doing though. There is no reason not to eliminate as much avoidable vibration as possible since it does no good and only bad.

Excesive engine wear and fatigue aside, it also stresses glue joints, servo gears, solder joints-both electrical and structural, mechanical fasteners.....the list goes on and on. Just because you haven't experienced a failure that you could ascribe to vibration damage does not mean it's not there. It's cumulative and CAN be mitigated. Most everyone does in some fashion or other-wrapping receivers and bats in foam, stuffing a piece of foam in the rear fuse to keep rattling pushrods dampened or securing them in guides, etc. Why bother?

As someone said above, there are those who have made their minds up already to either discount balancing as anything worthwhile or to bow at the alter of the balancer and they probably won't be swayed one way or the other. Good for the latter, tough for the former.
Why not look into real scientific data before clinging to one or the other...or try this simple excercise: put a 1oz weight on a small hanging scale, like a fish scale($3.00 at Wally world), tie a short string to it and spin it around. Have someone shoot a bunch of pics of the scale with a decent camera on a fast shutter speed- one of the pics should show the measured weight on the scale. It'll be @ 12oz at 100-150 rpm. Interpolate that to 1gram @ 7,500-12,000 rpm. Or just look at any ceiling fan in anyone's home on high speed(@150rpm usually) Funny how a 1/2oz out of balance blade can cause a 12lb fan to swing around and oscillate that much.....how much do you think a 1/2gram would do at 8k+? No, you can't perfectly balance a prop at home, but you can get them a lot closer to balanced by doing something other than "removing the price tag" (LOL)

I'm just sayin'.......

Balance every prop you buy when you get it home from the store... it's quick and easy. This way you know that if it is in your prop box, it is balance. There are a few posts above that detail the specifics of why, and the ill effects of skipping prop balancing. Bottom line is that for the longevity of the airframe and electronic equipment you must ALWAYS balance the prop. I have bought more APCs than I care to think of, some were nearly balanced out of the package, and some have been extremely out of balance, and an out of balance prop is little more than a hazard on the nose of you plane.

PS. Sorry I took off like a raggedy ol' rocket on your post GB, I only got to the first line and lit up. I know you are a firm believer in balancing and have always seen good practice espoused by you.

I have recently starting balancing all of my props. Once you put one on a good prop balancer you'll be shocked how out of balance some of them are. It does make a significant difference, believe me.

Ray

Always balance.....takes 5 minutes for a smoother running plane. I have even found APC props out of balance NIB.

HI
YESbalance all propsairframe vibration will kill your radio equipment-ever put your hand on the side of a fuse with the engine running ?you might be amazed AT THE LEVEL OF VIBRATIONBEST REGARDS TONY