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Prop Balancing Question

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Old 08-24-2010, 10:53 AM
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R-Duhb
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Default Prop Balancing Question



I have a wooden 11x7 Master Airscrew prop that isheavy on one side. I'll sand down the heavy end to get it to balance, but I'm curious if there is a rule of thumb method for sanding a prop.

Thanks!!

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Old 08-24-2010, 10:58 AM
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Dr1Driver
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Default RE: Prop Balancing Question

Don't sand it. My preferred method of balancing a wooden prop is to spray light coats of clear poly-u on the front of the light blade. Unless it's drastically OOB, one or two coats will do it. Sanding the prop may cut through the thin coat of varnish, leaving the prop exposed to the elements, dirt, and fuel.
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Old 08-24-2010, 11:02 AM
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Default RE: Prop Balancing Question

If it's a Master Airscrew, you will need to remove the mold flashing from around the edges. This is where the two halves of the mold came together and there will be a very sharp edge that you will want to remove by scraping a knife or razor along the edge (Note, use a scraping motion, not a cutting motion)

Once you have done that, you can re-balance it and just scrape a little more off the trailing edge of the heavy side - although to tell the truth, many pilots (including myself) don't even bother balancing props that small
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Old 08-24-2010, 11:14 AM
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Default RE: Prop Balancing Question

Minn

Think he said it was wood. I would go ahead and sand. Should not take much. Sand the front side evenly and lightly until it balances. Try not to change the shape of the prop.

Vince
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Old 08-24-2010, 11:31 AM
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big max 1935
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Default RE: Prop Balancing Question

I check all my props with a balancer & mark the heavy end with a marker & when it is installed on a engine I put the marked blade 180 degrees from the piston at top dead center. On my twins I do a little better with them . Max H. AMA 14958
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Old 08-24-2010, 11:42 AM
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MinnFlyer
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Default RE: Prop Balancing Question

Oops. I missed that



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Old 08-24-2010, 12:20 PM
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Default RE: Prop Balancing Question


ORIGINAL: big max 1935

I check all my props with a balancer & mark the heavy end with a marker & when it is installed on a engine I put the marked blade 180 degrees from the piston at top dead center. On my twins I do a little better with them . Max H. AMA 14958
An out of balance prop is an out of balance prop, no matter how you slice it. Causes vibration, which is your enemy. Air frame and radio and engine will suffer if the prop is not balanced. So many good balancers out there, there is no excuse for not properly balancing your prop.


Vince
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Old 08-24-2010, 01:39 PM
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Jetdesign
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Default RE: Prop Balancing Question

I use clear nail polish on the back of the light blade.
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Old 08-24-2010, 07:35 PM
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Default RE: Prop Balancing Question

I agree with the painters. I use masking tape and a paper towel to cover all but about an inch of the light end of the prop. I spray it lightly with white(or some other bright color). Let it dry, check the balance. I may have to do this two or three time to get it balanced. Usually, if I must end up with one end a tiny bit heavier than the other, I let the painted end be ever so slightly heavier. Then as the prop is used, grass, sand, etc. wears away the paint making the prop even more balanced.
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Old 08-24-2010, 10:14 PM
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Default RE: Prop Balancing Question

I just picked up some nail polish (Yellow) for my next set of props....have been using Red nail polish, but it is hard to see unless you have some red/white/red or better yet white/red/white tips.

Keep adding nail polish to the light blade until it is 'almost' perfect. Let dry and see what you get - dries quickly!
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Old 08-25-2010, 06:43 AM
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Default RE: Prop Balancing Question

Did anyone say"Hub Balance" Best way to go.

Bob
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Old 08-25-2010, 07:33 AM
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Default RE: Prop Balancing Question


ORIGINAL: R-Duhb



I have a wooden 11x7 Master Airscrew prop that is heavy on one side. I'll sand down the heavy end to get it to balance, but I'm curious if there is a rule of thumb method for sanding a prop.

Thanks!!


When sanding, it is preferable to sand only the blade face and the entire face not just on the tip. The face is the side that faces toward the rear of the airplane in normal layout. This minimises changes in the airfoil and thinning the blade when sanding on the more curved blade back.

John
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Old 08-25-2010, 03:22 PM
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Default RE: Prop Balancing Question


ORIGINAL: JohnBuckner


ORIGINAL: R-Duhb



I have a wooden 11x7 Master Airscrew prop that is heavy on one side. I'll sand down the heavy end to get it to balance, but I'm curious if there is a rule of thumb method for sanding a prop.

Thanks!!


When sanding, it is preferable to sand only the blade face and the entire face not just on the tip. The face is the side that faces toward the rear of the airplane in normal layout. This minimises changes in the airfoil and thinning the blade when sanding on the more curved blade back.

John
Ah, the unending debate. If you sand the the face facing to the rear of the plane you can change the pitch of the prop. If you sand the face facing forward you may change the airfoil but this will have less effect on prop performance than changing the pitch. Therefore you should sand the forward facing face of the prop.

Bruce
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Old 08-25-2010, 04:45 PM
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Default RE: Prop Balancing Question

No problem and to each his own I generally find it less intrusive on blade thickness and airfoil to always sand the face when doing a simple balance which does not move a lot of material. Its a simple skill to do so without changing pitch and that to me is more important than thinning and changing the airfoil.

There are of course the times when I am deliberately repitching the prop which does get more aggressive on both sides.

John
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Old 08-26-2010, 12:23 PM
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Default RE: Prop Balancing Question

Something that is not being addressed is the hub. You can balance the blades, then have the prop hub heavy. I've noticed ALL my top flight wooden prop have been both tip heavy AND hub heavy (off center hole). To fix this you have to add/remove weight from the hub. Some will say to never remove material from the hub for safety reasons, & I agree. I remove small amounts from the heavy side of the hub near the root of the blade, then recheck the blades till it will stay at any angle on the balancer. The hub balance seems to be much closer and APC props compared to the wooden props.

I always balanced my props, but have heard many people say they never balance there's. I took a chance and put an APC 12x8 unbalanced on my Hobbistar 60. About 10-12 flights later, I noticed a low pitched rattle in flight, so I landed to check over the plane and found the firewall was coming loose. I fixed the firewall then balanced the prop! I guess we all have to learn somethings the hard way.
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Old 08-26-2010, 12:35 PM
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Default RE: Prop Balancing Question

+1 for balancing hubs. I do it to all my props. Small props, the nail polish can be enough. Larger props, a piece of fuzzy velcro and some wicked CA on the light side.

Balance the hub after you balance the blades. On the balancer, turn the prop so the blades are at 45 degree angles; the heavy side of the hub will fall. Add weight to the light side.
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Old 08-26-2010, 01:00 PM
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Default RE: Prop Balancing Question

I'm a clear paint guy. I like easy. Other then speed planes I have never balanced the hub. It's that lazy thing I have going. Like Mike, I don't do a lot to small props, I do balance them but usually when I have nothing else to do and I'm out in my shop for a smoke.
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Old 08-26-2010, 01:40 PM
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Default RE: Prop Balancing Question

balancing small props is a waste of time. I dont bother. My airframes dont fail and futaba 2.4 receivers dont have ceramic bits inside that can be killed through viration.These props are so light removing a gram or two does not alter the radius od gyration.I would not bother, fit it and fly.This is the point where the pro balancing brigade jumps to proclaim heresy...
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Old 08-26-2010, 10:26 PM
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Default RE: Prop Balancing Question

ORIGINAL: TimBle

balancing small props is a waste of time. I dont bother. My airframes dont fail and futaba 2.4 receivers dont have ceramic bits inside that can be killed through viration.These props are so light removing a gram or two does not alter the radius od gyration.I would not bother, fit it and fly.This is the point where the pro balancing brigade jumps to proclaim heresy...
Ding, ding, ding, ding, we have a winner, just throw those balancer's away guys, there just not needed. LOL


Of course we need to balance those props.

Bob
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Old 08-27-2010, 09:20 AM
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Default RE: Prop Balancing Question

Reaching back a loooong ways: vibration will eventually kill anything. It just depends on how long you want things to last.

Les
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Old 08-27-2010, 02:37 PM
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ORIGINAL: gaRCfield

I use clear nail polish on the back of the light blade.

I'm telling your wife!

(Wood) I sand the back of the prop on the heavy side until it balances. (Fiberglass or APC), I scrape the front edge like MinnFlyer mentioned. Not balancing a prop, that's sacrilege! [sm=cry_smile.gif]


Pete


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Old 08-27-2010, 02:41 PM
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Default RE: Prop Balancing Question

go on do the math
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