arobatx

Hello All,

I know this topic could be handled in other areas of the forum, but I spend most of my time chatting with you guys here...and know I'll get some good ideas.

For the most part I've had great success first balancing the tips, using some clear lacquer, then moving on to the hub, using the velcro and ca method. However, once in a while I get that prop with the seriously out of balance hub, as if the shaft hole was drilled out of center. There's only room for so much velcro and CA, and though my caliper says this hole is centered, or damn close to it....I obviously need some tips on how you guys are handling these unfriendly hubs.

Chad

driesbabe

Hi Chad,
I drill holes in the hub to lighten the heavy side accross from the velcro and CA. I only drill them about 6mm deep until I get it right.
never had anything fail.

tail strike

My Feedback: (1)

I am sure you will get many good ideas from the x-perts but here is what I do.
I use lead split shot like what fishermen use on their fishing line.
I first tape it to the light side to roughly determine how much weight I need to balance the hub
I cut it in half through the split that is already there if necessary
Then I drill a slight indent with my drill press in the light side of the hub just enough for the weight to sit half way into
Put some epoxy in the indent place the led shot in the epoxy and put a little over the top of the shot.
After it sets up then you can fine tune your balance by filling a little off of the led if necessary.
Hope that helps.

Larry S

majortom-RCU

My Feedback: (40)

Like Larry, I use a tiny bit of lead. Split shot, or nip off bits from a Great Planes 1/4 oz piece of ballast. I also tape it with a bit of doubled over masking tape or whatever, so I can stick little bits together until I get the prop to balance. When it balances, I put the bits of lead in a pile on top of my shop vise, the little square block that vises have, and pound the bits of lead into a strip of foil. The strip will conform to the shape of the hub, and then a bit of epoxy under and over to capture it. Doesn't take long, works pretty well. Never had a piece fly off.

outssider

My Feedback: (23)

i drill a small hole/holes in the light side and fill them with lead filings. pack some in a little at a time until it balances perfectly then seal the hole with a drop of thin ca.

mrbigg

My Feedback: (21)

I had a Bolly carbon that I got used and the hub was way out of wack. The velcro trick didn't work. I put some 1/8" balsa on the light side with epoxy. Then I added a strip of solder using epoxy and it balanced. Looked weird, but it worked!

MR G

Sorry for the ignorant question...But how can you tell that the hub is out of balance?

MR G

tail strike

My Feedback: (1)

After you balance the prop horizontally then place the prop blades vertically, the prop will begin to turn till the heavy side of the hub is down.
The side that is up is light

Larry S

arobatx

When tips and hub are both balanced, the prop blades can be placed in any position 'around the clock' on the balancer, and it will stabilize there. With just tips balanced, the prop will not sit idle in any position on the balancer, aside from horizontal.

Oh, and thanks to all that are responding with their preferred methods of handling this. I'll let you know what I dream up when I get home, and post my results.

Chad

JoeAirPort

My Feedback: (41)

Like he said....first balance the tips with the prop horizontal. After that's done put the prop perfectly vertical and see which way it rotates. Add weight to the side of the hub that points up after it rotates 90 degrees. I always use masking tape or tape and a little washer to experiment how far it's off. If it's too far off I won't use the prop (if the tips are off too). That happened only once though.

arobatx

Well, here's the ugly duckling! I relieved some material on the heavy side with 5 shallow holes in the drill press. On the barn door sized piece of velcro side, I relieved a small recess in the center of the velcro, and added a small screw to finally get it to balance. Man this one was WAY off. Next time I will use much heavier ballast with a prop that is way off like this, like the lead mentioned above. Who knows, maybe i won't see another one as bad as this one

rcdude7

My Feedback: (264)

I have had to glue small washers to the hubs of some of my props. It works fine, I have not yet had one come loose.

I would avoid removing material from the prop hub if at all possible. This is a highly stressed area and removing material can only bring the hub closer to failure than it already is. Just my 2 cents..............


Mike

karolh

I know that it's just about an absolute must to fully balanced large dia props, but is it really absolutely necessary to hub balance smaller size props like say 15 or 16" dia.

Karol

Truckracer

My Feedback: (19)

Karol,

Some time back, I asked myself this same question .... but also about our larger props. Decided to do an experiment to see how much vibration an out of balance 2" disk of wood could produce with different amounts of weight attached to one side .... just like a prop hub. Got out my trusty hole saw and cut a 2" disk out of a 1" piece of pine. Drilled a 1/8" hole in the center for my balancer shaft and balanced it. From there, I inserted a 1/8" piece of music wire and chucked the whole thing in my Dremel for a bit of a spin test. Painted the disk black with white on two extreme sides so I could tach it. My Dremel won't go below about 4500 RPM but it likes to turn up. I decided that about 10,000 RPM was about the safe limit of my piece of wood but it ran silky smooth at all speeds. From there I attached the typical CA soaked piece of Velcro to one side of my disk .... the soaked Velcro weighed exactly 1gr. and was 2" long and 3/4" wide. On the balancer the Velcro side crashes to the bottom quite quickly! Back to the purely unscientific Dremel test to see how bad the thing vibrates ...... Hmmmmmm.... not too bad really! Even at 10K RPM the vibration was so low that you would not notice it compared to the impulse and recip. vibration that any of our engines have. OK .... back to the wood disk .... screwed a small #4 sheet metal screw into the center of the velcro ... screw weight .6gr. Back to the Dremel ..... yup, it was shaking some now but still way less than I expected.

I'm not sure I really proved anything with my little experiment but I did learn that hub imbalance produces way less vibration than I expected. Will I continue to balance my prop hubs? ... probably. But, I don't think I'm really accomplishing much in the process. Lengthwise balance is far more critical and I know from experience that small changes there can be felt in the airframe.

JoeAirPort

My Feedback: (41)

It's very true that weight at the hub has much less effect than weight at the tips so that all makes sense. If you have a 24 inch prop with a 2 inch dia hub then the tip weight causes 12 times the vibration as the hub weight. I still prefer a perfect balance on tips and hubs though.

karolh

Thanks guys.

Karol

buck1856

My Feedback: (49)

I was at TBM looking at props to purchase and i read as iwas looking at the dubro prop balancer[i have the MAS that looks and works just like it though].Any way,it said to just balance the tips.Then it said to check the hub and when you find the heavy side of the hub,bring your piston up to TDC.Then you put the heavy side of the hub down.It said that most manufacturers cheat on the crankshaft journals to lose weight and when you mount your prop in this manner it helps to balance the engine better.I have not tried this yet,i will next time i mount a prop.Just thought i would add this and see if any of the more experienced gas pilots have heard or done this.

Truckracer

My Feedback: (19)

Putting the heavy side down can sure help on smaller glo engines and especially on high RPM racing engines. Not sure what effect it would have on our gassers. I'm guessing it could have some effect on vibration but it would be just luck to get the prop aligned for easy hand starting though.

buck1856

My Feedback: (49)

Ya,i didnt think about that.I usually put my sensor just to the right of TDC on my conversion engines so it wouldnt be a problem.I also just purchased a RCGF 26cc and when looking at the front my sensor is located just to the left of BDC,so it wouldnt hurt anything on this motor either.The tip is at roughly 2 oclock for starting.It would not be that hard to relocate the sensor if you where mechanicly minded but then you might,and probably would lose the warranty.Oh well,it was just a good thought and would probably work in some circumstances.I knew a more experienced gas engine pilot would know something i didnt think of.I can still try it on mine as soon as i break it in a little more.

PAPE

There is a really nice intructional video here on RCU about how to properly balance a prop, by Dubro I think. one thing I wanted to share here was about the time I balanced my prop with duct tape.

Whell I had everithing balance prop spinner, and when I when to balance the prop I though of the great idea of using strips of duct tape, well little by little I balance my prop hub with strips and strips of duct tape. I though duct tape has to stay on, well I was wrong, the chunk of tape fell of the prop inside the spinner and at full RPMS my spinner exploded in mid air, it had unbalanced the spiner to the point it just blew apart. so make sure what ever u use it stick on, imagine what could hapen if it happened on the ground.

jack1933

My Feedback: (2)

Hello I have put longer bolts on the counter weight side (3) on a 5.8 Sachs and that helped with this bad shaker.

arobatx

I've learned to appreciate the minimized beating of the airframe with a well balanced prop, since i occasionally overpower an aiframe by an obscene amount just for kicks. But the thing I notice and appreciate the most about balanced props, is the affect it has on the battery load. You can actually see the difference you've made by balancing your prop, with the use of a simple amp meter. This isn't unlike the use of hyde soft mounts...

JoeAirPort

My Feedback: (41)

Yep I agree. My take is always that the engine vibrates the air frame enough. I'm gonna do whatever it takes to not add more. Prop balancing is the easiest way to do that. And those poor aileron servos.....they take a beating.

karolh

With all my props the largest of which is 16" I always blade balance them, but to date I have never bothered with hub balancing. Now that I know how it's done I think I'm will do one and see how much of a difference it makes.

Karol