okay I have tried for some time to master prop balancing and I am still not sure if I'm doing it correctly so I thought I'd post this thread with some pictures and how I do it and see if its correct......

1. In photo 1 this is how I start....
I try to balance the prop to where it will stay level if it doesn't I sand material from the blade that falls
I then flip the prop 180 degrees (as in picture 2) and make for sure it stays level that way as well (usually it does)....

Now here is where I'm not for sure I'm doing it right.....

2. In step 2 I place the prop at an angle as in photo 3, it should stay in that position if its perfectly balanced. but for example if it rotates to where the prop is level and the blue side is on the bottom then I sand the ENTIRE PROP on the blue side......
I then try again to see if it will stay in the angled position..... (sometimes you will sand one blade more than the other and have to go back to step one)

3. From the angled position I rotate the prop 90 degrees (as in pic 4 ) where it is at an angle with the red side facing primarily down, I then release the prop if it rotates to level wit the red side facing down I then remove material along the entire red side..... if it rotates to level and the blue side is facing down I then remove material from the entire blue side....

I keep doing this 3 step process over and over again until I get it to where no matter what angle I place the prop in it stays.....
I believe I am balancing the prop length wise and chord wise....
so I ask am I doing it correctly or is this wrong?
If so then how are you to properly balance props?

Here is picture 4 ( I didn't have a picture for it so I mirror pic 3 so you get the idea)
I hope its not to hard to follow if you don't understand just say so and I'll try to re-phrase....
Thanks!

I'm probably no expert for sure... but just take some off the heavy side like your doing... but there is another trick. You can take a drop of CA and spread it instead of sanding. Works for me. Also if you get it where it's "level" across. Then the force of imbalance is pretty much minimized. Think about it. How much centrifigal force could the Chord actually produce? But if you're really worried put a drop of glue on the heavy side at the center. What kind of prop is that? Is it painted?

no its an apc.... its photoshoped to add the colors so I could show what I was asking...

There is always debate about what side of the prop you should sand or remove material. I thought I would throw that question out in this discussion. I always either add or remove material from the back side of the prop.
Leo

Is there any prop LEFT after all that sanding? [sm=eek.gif]

Just kidding, and it's a good idea to learn how to properly balance a prop (seems you have), but I certainly don't go to those extremes. Once it's balanced level, I leave it alone. Never noticed any adverse affects from not doing more.
Dennis-

Dennis is correct (As usual), don't get too anal about it. Unless a prop has something seriously wrong with it, in most cases, they don't even need to be balanced.

So unless you're doing something out of the ordinary, like extreem speed, "close enough" is probably closer than you even need.

Totally agree with post #6 and #7. Instead of removing any material from the prop, try spraying a little clear lacquer on the light side. Spray just a bit at a time and wait for it to dry, then re-check the balance.

so basically if it balances level then flip it 180 degrees and it balances level again I'm good?
I've read up on it and I know you can't perfectly balance a single cylinder but I'm one of those "tinkerers" who like getting into every detail of the build and getting everything perfect.......
actually I just have alot of spare time and get bored......

Okay, now you're talking a whole new game.

If you really want to get anal, you don't touch the prop at all. You find the heavy blade, then mount it so it's directly opposite the cylinder head when the piston is at top dead center.

That way, the heavy blade helps offset some of the piston weight, thereby allowing for a better balanced engine.
Dennis-

All the documentation I have read stresses the following...

Never change the pitch, length, or chord of the propellor. If you have to sand to remove weight, sand the curved side of the prop to be flatter.

The static balance of the prop is one thing, but when spinning, the prop generates thrust. The thrust is a function of the airfoil shape, pitch, chord, and length. Having one side of the propellor (or one part of the propellor blade) generating more thrust than the other side can have a more damaging effect, and cause more vibration than having a statically unbalanced prop. An Ideal prop is both statically and dynamically balanced, but modellers do not have the resources to spend the $$$ required to get dynamic balancing eqpt.

Back to the prop.... The thrust of the prop is a function of length, chord, pitch, and airfoil. Changing the length, chord, and pitch of the prop all change the dynamic nature of the prop way more than the airfoil shape. So, to change the static balance of the prop and have the least impact on the dynamic balance, change the airfoil shape ... sand the curved side flatter.

gus

P.S. See http://www.bollyprops.com/propbal.html

Actually, if you are REALLY anal, you figure out how much out of balance the prop is, mount it as Dennis says, use a meter to measure the engine vibration (they exist, but I forget the name), and then test various amounts of "out of balance" until you get the smoothest running engine. Then you adjust all your props to that setting.



Have fun. Me, I usually just bolt them on and fly. But then again, I fly combat, so I can easily spend more time balancing a prop than I would flying it before it gets broken in a mid-air

Or, more accurately. the heavy side of the "Prop Disk".

If you think of a prop correctly, it does not have two sides, it has 360 degrees.

So think of it as a disk.

If you put a CD into your prop balancer (and it was perfectly balanced), it would stay in which ever position you put it in.

If a certain area always fell to the bottom, that side is heavy.

Same thing with a prop. If you cocked the prop below at a 45 * angle, and it leveled itself out, then side "D" is heavy.

If it always stopped with "E" at the bottom, Blade "A" is not heavy, area "E" is (or "F" is light)

So, to paraphrase Dennis, put the heavy "area" opposite the piston at TDC.

Sure Mike, I know. You just had to find a way to use that graphic.
Dennis-

You mean props HAVE to be balanced??
Somehow I asummed currently available commercial pros from a reputable manufacturer like Master Airscrew would be balanced when you buy them.
How important is checking for balance on a new prop?
I gues I will start paying more attention to those little details

Luis

Most people say that for small modern non-wood props (< 13") that the balancing is not necessary. An off-balance prop won't cause excessive vibration.

My opinion is that it is probably better to check the balance of the prop anyway, but to "pass" out-of-balance props unless they are way out.

Further, my (limited) experience is that Master Airscrew props in the 10,11, and 12 inch range (which is where I play), are typically inferior in balance, and performance than the equivalent APC props.

I found that switchin from an 11x6 MA prop to an 11x6 APC boosted the "feel" of my plane "drastically". It was a whole new plane.

For a 20% price increase to APC, It is worth the cost.

I am just an impressed APC user... no association to the company.

My understanding is a few-fold. APC props have a "modern" airfoil shape, is more efficient in the air. Less noisy. Further, the MA props have more weight near the tips of the props, where centrifigal forces are larger (centrifigal forces are related to the square of the distance from the hub - so any weight nearer the end of the prop has a significantly more pronounced effect on the prop balance), causing MA props to be more vulnerable to imbalance in the manufacture process.

MA props are more rugged though. A nose-over on a windy day on grass will nick an APC prop enough to be discarded, but an MA prop will just get dirty ....

gus

My experience tracks with Gus'. I do use MAS props in 9" and 7" on my combat planes, and, to be honest, I dont usually balance them, they don't last long anyway. But when I have put the 9" ones on my balancer, they vary quite a lot.

Well I'll be darned!

Wanna know something even funnier? I've seen as much as a 500rpm difference between "identical" props from MAS on the same engine, one run right after the other.

Also, if you use MAS props, you should always shave off the flashing along the LE and TE of the prop blades. It actually can result in a few hundred extra RPM, and it can reduct the depth of any cuts on your fingers. (never cut myself with a prop, so I don't have direct experience with that last one).

Anyway, the point is that props can vary a bit no matter what they are made from. And the variance can be noticeable or measureable, but usually isn't worth the effort.

Now I'm one of those oddballs that prefers MAS props to APC. But I will second the fact that you MUST scrape off the flashing from a MAS prop. Early in my return to flying (Back in the 80's) I installed a new MAS prop, and after tightening, I flipped it a few times (as anyone is likely to do). Next thing I knew, there was blood everywhere! The Trailing Edge of that prop was like a razor blade!

But back to balancing...

lrumd, you do not HAVE to balance a prop. They may not be perfect from the factory, but they really don't need to be. I own a prop balancer only because I received one as a gift 10 years ago. I that 10 years I have balanced maybe 3 props.

The above quote applies to APC also. I dull the TE on all my
APC props. Balancing will make a difference. It depends
on weather you want the best all a round performance
from your prop. YES a out of balance prop will make
your plane shake. Some has stated other wise but I
TOTALLY disagree with those statements.