I have been flying for about 3 years now and am into a bit of 3D.

Recently I saw quite a few posts regarding prop balancing. Now, I have always used Master Air Screw on all my airplanes simply because they are less likely to break as compared to the more expensive APC. Also I always use K series props as their paddle design gives a bit more bite (I believe) over Scimitar series. But I have never balanced these props. For all my props, as soon as I get them, I deburr the sides with fine sand paper. This I do to remove the possibility of cutting my fingers should I finger start the engine. Just a little bit of sanding makes both leading and trailing edge smooth without rough edges. But I never check for balancing. I never had any issues with props. However on my Reactor and many other ARFs I see a lot of vibrations at idle. These cause all the tail feathers to vibrate hard but only at idle. One or two clicks of throtthe removed the vibrations. I always use good spinners (Dubro or GP with aluminium backplate) and they never seem to be unbalanced.

So my question is, how critical is balancing for these props?

Ameyam

It's as critical as you want to get with it.

Some people wouldn't dream of starting an engine before they balance the prop. Personally, I never balance any prop under 16" - The only exception being: If I am having some sort of problem, I will check the prop's balance, but even that is very rare.

i balance every prop. I'm surprised to see how out of balance these things are. I just have the $3 great planes balancer that has a needle and two conical devices that screw together to hold the prop. You balance it by holding either end of the needle and see which way the prop drops. I've yet to see a prop that was balanced from the manufacturer.

I never balanced any prop, neither I have any prop balancer nor do I know how to balance a prop honestly speaking


Mody

The low idle vibration is most likely caused by the engine. Low RPM's cause the engine to shake more, high RPM's don't give the engine enough time to move between cycles.

ADD a couple of speaker magnets and a scrap wood frame... worked for me for years.

I seldom balance on most of the typical smaller sport props.

On occassion if I have one with a known heavy blade I sometimes will mount it with the heavy blade opposing the piston at TDC.

I do normally balance the propellors on my competion airplanes and a I do balance propellors that I have shortened or altered the shape in planform.

When I do balance I use a use a selection of Magnetic or wheel type balancers. I would only use the fingertip type in a bind.

John

Just though someone would get a kick of my balancer I still have from the late fifties and early sixties. Even commercial fingertips were almost non existant so a couple of single edge razor blades, a chunk of balsa, an eighth inch steel rod and a bit of masking tape to fill out for differant propshaft sizes and you were good to go.

John

Ok John, yours has me beat. I used the finger tip balancer, and 2 disk drive magnets for nearly a jeweled movement. Do you get a little "edgy" around the razor blades?

It does make a difference in the wear on your airframe to balance the props. Also about sanding: If you are removing the sharp trailing edges that cuts the efficiency of the props. And there's not much you can do to make the ends safe. Any prop strike bad enough to cut you with a sharp prop will still cut you with a blunted one. Sanding the leading edge smooth is helpful, but leave the trailing edges and ends sharp.

i always make sure to balance my props...especially on my gassers

of all the props ive balanced ive only had one that was near perfect and left it alone...its was an apc 12.25 x3.75

I definitely think it's a good idea to balance all of your props regardless of size. Just think of an average car that weighs 3000 lbs at average highway speeds your wheels are turning about 1000rpm, if your wheels are out of balance 1-2 oz it can make the whole vehicle shimmy/vibrate/shake whatever you wanna call it. IMO there is no reason not to balance a prop

Jester,

I dont actually make anything "blunt". When the GRP comes out of the die, there is a burr (similar to when you cut a metal sheet). I just remove that. So that if you run your finger lightly over the trailing edge, you dont come back with a cut. It is still very sharp. I get lines on my left palm from the prop (even old used ones) when I try to install or remove them. If you press hard on the prop, you will still end up with a mark. I am sure that the burr doesnt add to aerodynamics of the prop, more likely it adds drag through the production of turbulent vortices at the trailing edge.

Anyway, I am opening an new can of works: which prop balancer is the better- fingertip type or some other?

Ameyam

I balance all my props no matter the size or type. The manufacture may say that their props are balanced but from my experience THAT'S NOT ALWAYS THE CASE.

For all of you who don't balance props, I ask only one favor? Get another prop that's the same size to the one that is already on your plane, ( it can be a spare) or another brand new one to what you are using now and balance it to your best ability.

Now just for kicks, go to your favorite airfield and bring along that balanced prop, and fly the plane first with your unbalanced prop like you normally would.

Once you've landed your plane, swap out the prop that wasn't balanced and replace it with the one that is, and tell me if you notice any difference?

I did that little test, now I balance all my props. And when flying season is over, I rebalance my props again due to bug splats, grass and dirt. It can knock the balance off after a while. So, evey 6 months of flying, " or " If I notice unwanted sound vibration, I recheck the balance just to be safe. That's just me.

Nice Prop Balancer Bingo Field!

Pete

With all the time we spend on all of the other details on setting up a plane it just seems amiss to not balance the prop.

It's relatively quick and easy and it gives you a chance to putter around with the toys. If you do them all at the same time then it's a simple operation.
I balance new props before I hang them on my "reserve stock" wall and then I know that they are ready to go when I grab them.

As MinnFlyer said, It may not be as critical on smaller (composit/plastic) props, but on larger ones it really begins to show if a prop is out of balance. I like wood props and they can be WAY out of balance due to differences in wood density over the length of the prop. I've had 9" and 10" wood props so bad that they made the plane sound as if it had a doorbuzzer on it at mid RPMs on the bench. You could literally see the wave form/rippling on the wing covering from the vibration...that certainly had to be stressfull on the glue joints.

It's missing the small details sometimes that causes a failure that wrecks a plane. Getting into a habit of paying attention to detail, such as balancing, may be tedious, but it can save a lot of grief later. Good habits never hurt. Some folks can carry that to an extreme, but I don't think that balancing props is obsesive.

I always check the balance of my props...you might be surprised at how far OUT of balance some of them are!
I've seen holes drilled off center as well...so IMO it really pays to check them.

Your servos, receiver, airframe...etc. etc. will last longer if subjected to lower levels of vibration, (not to mention fuel foaming ) so why not try to eliminate as much of it as possable?

I balance my props always. Used to ignore it but once I started balancing them and thinking about the revs they spin at I realized it was a no brainer for me.

One flyer at our field who is quite into electrics said it's more important with them. I have several electrics and just balance the prop as a standard course of action.

I always balance mine - usually with a trick I was shown back in my free-flight days. Hold the prop horizontal in one hand and in the other take a "T"pin and hold it up at a 45º angle and set the prop on the pin so the tip of the pin is halfway through the thickness of the prop in the shaft hole. Let go of the prop and the heavy side will drop. Scrape the backside of the prop with a knifeblade on the heavy side. Repeat until it stays level. I have done 20" props with this method and it works as well as with 6" ones.

I'm with oberst, I balance my props before use. I use a reamer first to make them fit the shaft, then put them on the adjustable DuBro Prop Balancer. I balance the spinners, too. I use 11" & 12" props. I've seen props vibrate too much and cause poor flight performance and keep my OS .46 & .55AX from idling well. I've also seen my spinner nose turn in a wobble pattern with the same result, esp. the plastic backed ones. I have also had APC props come in 11x8 & 11x6 that put on the balancer one blade drops all the way to the bottom (180 degs) position. My TF wood props will always need balancing. It does affect the flight performance of the plane and engine. So.. don't be lazy & do the balance. Bigger props in the 14" and above can actually cause prop damage. I don't about engine damage. A couple of guys at my field have said that their 4S have suffered damage because of out-of-balance props.

Me I just let the dog chew on them till I feel they are balanced! Want to balance them right? then get a dog!

I balance each and every prop I buy no mater what make or size.

So if I nick my APC on the runway is it ok to just clean up the tips, balance it and go fly?

Depending where the nicks are you can, just make sure you don't have any cracks. To be safe, I'd just replace the prop.


Pete

For my first year, APC props didn't even look right to me unless the tips were knocked off.