Hi, I am new to planes - have flown heli's for about a year.

My question is about prop balancing. I have finished building my SIG LT-40 and am balancing my props on a high point. I have found that three out of four of my props seem to balance horizontally, but need alot of material removed from one side of the hub to balance vertically. I have noticed this with both the Zinger 11x6 wood props and the Master Airscrew G/F 3 series 11x6 props.

Is this normal or am I messing this up somehow?

Thanks,
Rob

Im still new, but from what I've read, prop balance isnt really an issue unless its WAY WAY off...

But it seems to be one of those topics of debate...so depending on who u ask, you will get a different answer..

rjm1982 hasn't been reading my posts. To me, prop balance is ALWAYS very important. I wouldn't worry too much about side-to-side balancing, the mass is too close to the centerline to matter much. However, end-to-end balancing is very important. Do not remove material or length from a prop to balance it. Rather, spray some clear poly-U on the front of the blade on the light side. If the prop swings hard on the balancer, consider taking it back and exchanging it. Composite props are usually very well in balance, while wood props can be wildly out sometimes.

Dr.1

I have been using APC props for a while now and found that, for the most part, these props come pretty much in balance, although I check each and every one. Shaving a tad bit off of one side or the other using a real fine grit sand paper seemed to make them just about perfect. I have heard that Master Airscrew and Zinger are not that close when shipped. Just my viewpoint, I don't own either one because I get very good performance out of the APC props. Bolly is another good prop, by the way, and also come pretty close.

Our field is grass and rather bumpy so we go through a lot of props in the course of a season, so buying a good 14-6 for around eleven bucks is a pretty good deal, and to get them pretty much in balance is another big plus.

BUT, balance IS important, that's why I check them (even the APC's which I am so faithfully using) before putting them on the aircraft. Even a little out of balance can cause vibrations that can eventually do damage. The worst damage that can be done is to the crystal of the receiver which will cause a devastating crash if it breaks in flight. One way to help... HELP... eliminate that or reduce the possibility is to balance the prop. Sure, there are other causes of vibration, however, the prop balance is probably the single most important one to consider and the easiest to correct.

DS

And apparently DR1Driver hasn't been reading mine

I have been flying since the late 50's and I have never seen a Store-Bought prop that NEEDED balancing.

If you fly Extreme Speed Planes, balancing is important, but you can throw any un-damaged prop on your LT-40 and you'll be fine.

Double post --- see below

Rob, you are trying to commit suicide. Trash each & every prop that you have removed hub material from --- right now before you use them again. You have unknowingly committed a major no-no & seriously compromised the structural integrity of the propellers. They will eventually throw a blade, and could quite easily kill you or someone else nearby.

Don't worry overly much about horizontal prop balance, the moment is very small, whereas span-wise balance is relatively important, depending on prop diameter & engine RPM. Big props must be balanced, & small props that spin at very high revs need balancing, but props in the 9 - 11 in diameter sizes that are turning in the 11K - 14k RPM range are not terribly bothered by minor imbalances and can often be used right out of the box.

I would NEVER remove a lot of material from any part of a prop. And I would NEVER remove ANY material from a hub. One thing about DRdrivers post--spraying something onto the prop will cause a build-up of material on the surface of the prop (this is what the intended purpose is). Build-up on the surface of the prop will change the airfoil of the prop--thereby reducing it's efficiency. Creating more drag on one end of the prop and not the other will cause the same effect on an engine as an out of balance prop would--wear and tear on the bearings and or bushings. I like to follow Minn flyers advice--just put the prop on there and fly. The only thing I do occasionally is to lightly sand the sharp edge off of the TE of the prop--especially on MAS, they seem to be the worst about leaving sharp bits of plastic on the TE.

I have only seen 1 prop at our field that was out of balancce so that it showed. When the guy tried to rebalance by shaving some off the back of it, he wrecked the prop and it had to be thrown away. I did find that when the grass gets taller and the prop hits some of it, it tends to collect on one side of the prop only and this throws the balance off noticably. Scrape it off with my finger (turning it green) nd I'm set to go. The fact that the grass can affect the balance after a few flights, I am not worried about a factory prop unless it is really bad. I only use APC props and some MAS. [8D]

Ditto on britbrat and others. On heli baldes, both span-wise and chord-wise balance is critical for good tracking blades. On props, you only need to be concerned with span-wise. An even that is not as critical as heli blades. Close is good enough. Single piston engines are already pretty much out of balance and shake the snot out of everything without a soft mount, so a little more buzz from the prop doesn't really matter, as long as it is just a little more. This does not mean you shouldn't check your props, but I have rarely found any store bought prop that wasn't close enough out of the package.

In case you missed it in previous posts, throw away any prop you removed material from the hub or root area. This is like balancing heli blades by removing area in the blade grip... bad idea. Chalk it up to a learning experience and move on.

When balancing props we don't have the luxury of changing the lead weights in the blade like you can on wood heli blades. You really don't want to sand a prop as that changes the airfoil shape. If you change the airfoil a lot, each blade will apply different loading, which works on the bearing. This is kinda like blades out of track on a heli, only with a prop there is no easy fix. Quite honestly, if the prop only needs a light sanding to be "balanced", it was close enough to begin with in my opinion. If it needs heavy sanding, you are removing to much material indiscriminately IMO. I guess what I am saying, that IMO you should never sand props. The best way to balance props is to evenly add material in thin coats, such as a clear coat spray. But even there, if you have to add a lot of material there is something wrong with the prop in the first place, so use it to stir paint and get another prop.

Cheers.

Well thanks to everyone for showing me the light! I read on some web page somewhere about balancing vertical and shaving the hub. I thought it sounded not right when I read it. I only did it to one wood prop and one G/F prop and had not run them yet. I broke the motor in with a different wood prop that only needed a little spray clear coat on one of the blades to balance perfectly. I was balancing the rest for when I break the first prop on my first flight - you all know I will!

I am still using the two modified props though......one is a key chain for the flying field gate and the other is garbage can ballast.

Still trying to figure out how to mount the heli training gear to the plane......helped me alot in learning to fly the Raptor!!!

Thanks everyone!
Rob

"Still trying to figure out how to mount the heli training gear to the plane......helped me alot in learning to fly the Raptor!!! "

LOL...

Maybe hooking the Heli training cord to an intructor's box would help. OH !!! you said Heli training GEAR, my mistake but maybe a good idea, think about it and ENJOY !!!!! RED

I watched a video somewhere about balancing the hub of wood blades by glueing a piece of velro to the light side and then applying layers of CA until it was balanced. Is that the correct way?

YES! Training CORD is a good idea - I actually joined the local club and AMA yesterday and have a club instructor lined up.

Thanks again everyone.

Jonesy, I suppose that would work, but I don't know anyone that bothers with balance along the chord axis. The mass along the chord axis is limited to a location very near the center of the prop, so it would take a large out of balance situation to casue any noticible issue. It's kind of like the CG on a plane, you can add a lot of mass to the plane without effecting the balance of the plane if the added mass is near the CG. The only time I can invision chord axis balance being critical is on very high rpm (pylon racing?) or very large (fullscale?) props, but I have no experiecne on props in those applications. Cheers.