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Nov 30, 2001, 01:34 PM
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blade balancing


just wanted to see how everyone balances their blades>
I am flying a ep concept ( currently with the stock foam blades)

1. is it really neccessary to check the CG of each blade before balanceing and makeing the CG of the 2 blades the same.
generaly I just balance the blades by adding weight to the ends of the lighter blade, but have heard it may be better to add weight in the center (CG) of the lighter one??

2. I plan on using the wooden or even the carbonsome day, if so will my balancing practices need to change for these vrs the foams

3. what would making the CG of each blade do for you??

thanks
Jon
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Nov 30, 2001, 02:52 PM
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You should match the CG's first then add weight on the CG of the light blade - not the end. With foam blades I would think the CG might be spot on to begin with, check it bybalancing the blade on a1/4" drill bit or similar and find the point where it tips, mark then do the other blade and compare.
Nov 30, 2001, 02:57 PM
cnk
cnk
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You should really balance each blade so that the CG's of both are within 1/16" of each other. I don't know how to really explain what would happen if you didn't because I don't know how to put it into words. Let's try this. . .imagine the blades in their circular motion and where each of the CG's are. If you could track each of the CG's then you would see one CG making a bigger circle than the other one. If you understand centrifical forces, then the one making the bigger circle is going to be putting greater pull forces on the other blade, which can influence how your heli flies. If the CG's were the same, then you would have the centrifical forces of one blade counteracting those of the other blade. I would imagine that this would also put less stress on the components of the heli. You add weight to the CG since that is the only place that wouldn't upset the equal balance of the blades.

To be honest with you. . .I am new to heli's and am still awaiting my first heli, but I do understand the physics behind how the heli should fly. So if I'm wrong. . someone please correct me.

As for using different blades, I would say that it doesn't matter what material the blades are made out of because the physics are the same. You'd still need to balance them dynamically and statically. Dynamic balance refers to matching each blades CG and static balance refers to balancing the blades against each other.

Hope that helps.

Calvin
Nov 30, 2001, 03:01 PM
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Thread OP
Chris,
I have a balancer, but never had directions for it. i was just wondering what difference it would make if the cg was the same on each blade or not? I guess 15 years ago when I flew40 sized gas fixed pitch we just balanced by adding weight to the ends of the blades. I had just read a article on balancing and it says to first get the cg the same by adding weight to the end of one blade, then balance them by adding weight to the middle of the light blade.
Nov 30, 2001, 03:43 PM
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Like Calvin - I just know it is the right thing to do, I can't give you all the technical reasons why. If I had to guess I would think the two blades would lead/lag differently if the spanwise CG's are not the same. That would mean one blade is making slightly more lift than the other and the extra lift is whirling around at you headspeed.


If the CG's are fairly close and the blade balance is fairly close to begin with then adding weight to one tip may work out OK. The proof is in how smooth is the heli? I have had blades that were so far out of whack CG wise that no amount of balancing would get them to run smoothly until the CG was fixed first.
Nov 03, 2006, 08:03 PM
Registered User

Answer to blade CG


Here is the deal.
Not only is it the right thing to do, but a couple of minutes per blade for static and dynamic balancing will save you $'s down the road.

To answer the dynamic balance question (CG's in the same place): if they are not in the same place on the blade, it is NOT that they will pull out from the hub at different strengths (that is static balancing) but that the the center of lift of the blade (CG) will be at a different distance ("arm")from the hub. The effect would be the same as one blade lifting more than the other as it tracks around. (Think of each blade creating .5 lbs of lift. If one blade created that lift right next to the hub and the other blade created that lift out at the tip, the blade with the CG at the tip will have an "easier" time lifting and will overpower the other side.) You will not see this imbalance until you start to create lift with the blades. Just idling on the ground you will not see it. Once you lift off there will be lots of shaking!!!!

Cheers,
Rich
Nov 03, 2006, 08:46 PM
That'll hold until ...
swatson144's Avatar
Wow you managed to dredge up an almost 5 yr old post with only 4 previous replies. That must be a record of sorts.



Steve
Nov 03, 2006, 11:43 PM
Registered User
Laws of physics never change.

I have been scouring the groups for info because I am actually bittin' by the heli bug. I have flown ther real deal and now must learn this way. I have a Real Flight G2 that is helping out alot.

I just learned today what unbalanced blades looks like when they are on a machine. I thought the Walkera 36 came RTF!!! Not. The blades are way off. I thought the ship was going to disintegrate in front of my eyes.

This is coming after a rebuild. I had four very successful flights on the Walkera right out of the box. I friend gave it to me. All went well. Then I started researching it and folks are bashing the electrics. Seems okay to me so far.

Rich
Nov 15, 2006, 11:45 AM
dynamic balance has nothing to do with lift. The purpose of dynamicly balance the blades is to minimize vibration. If the CGs are located at a different distance from the main shaft, then the CG in each blade creat a differential centifigal forces. These differnetial centrifigal forces creat vibrations.
Nov 15, 2006, 11:52 AM
one more thing, centifigal force is a function of angular velocity, so when throtle is applied, headspeed increases, as headspeed increases the effect of "dynamic unbalance" also increase.


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