Corona Sub-Rotor Balancing - RC Groups
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Mar 04, 2004, 07:29 PM
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Corona Sub-Rotor Balancing

I just added all new rotor parts as well as a Crazy Crutch, Carbon Feather Plate, Belt Drive Tail Rotor, Oversized Titanium Shaft and a few other things.

Anway, I would like some suggestions on balancing my new sub-rotor blades since it does not appear I can do it the same way the manual stated using the Crazy Crutch.

I have also read something about a Dubro Prop Balancer but I do not have one and need to balance everything.

Someone also mentioned to me not to worry about it as long as I get my main blades balanced.

Any thoughts, suggestions or help is greatly appreciated. Thanks.
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Mar 04, 2004, 09:40 PM
the other, other dave
easy and effective method would be to dynamic balance it...
Mar 04, 2004, 09:44 PM
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How do I do that?
Mar 04, 2004, 11:01 PM
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gregw's Avatar
Dynamic balancing means that you just hover, looking at the bottom of the vertical tail fin to see how much vibration there is... Land, put a small amount of tape on one blade, go back to a hover and see if vibrations have increased or decreased.. If it has increased, then move the tape over to the other blade. Repeat until vibration has been eliminated/minimised.

I have to say that on a Corona, it is almost impossible to eliminated 100% of all vibrations, but it has little or no impact as long as your blades are tracked properly..
Mar 06, 2004, 08:19 PM
Registered User

I balanced mine using the Dubro High Point Balancer that you mentioned. I simply mounted the Rotorhead assembly onto a spare mainshaft and popped it on the high point balancer. The first step is to balance the flybar paddles (with the main blades removed). Just add balancing tape to the light paddle. Next you install the main blades and balance them, applying balancing tape to the light blade as you did with the flybar paddles.

One thing I would like to mention is this....even after I did this procedure and had the head balanced out on the HP balancer, I still had some vibration. It wasn't anything too major, but I think it did cause occasional feedback problems with the Gyro.

I ended up removing the main rotor head from the heli and running the heli up with only the Tail Rotor Assembly. It was smooth as can be, so I knew that the vibration was coming from the main rotor head. I put the main rotor head back on with the main blades/grips removed and ran it up. The vibration was back. I played around with adding/removing weight to the flybar paddles, but it did not help. Then I reinstalled the main rotorblade mounting bolts and experimented with adding small washers to each bolt for fine tuned balancing. On the main arms that the Rotor Blades mount on, you will notice that the one arm has a small window cut-out, and a linkage rod that runs through it. This was the heavy side. When I added a washer to the opposite side, I was able to completely eliminate the vibration.

The strange thing is that this imbalance did not show up on the High Point balancer. It was not until I ran it up in the heli that the centrifugal force caused the imbalance to show up. Hope this helps
Mar 06, 2004, 11:12 PM
Registered User
Thanks.... I have always wondered about the Feather Plate having a hole in it and how that would affect the balancing. I would figure that the side with the whole would be lighter though. Can you show any pictures of where and what you mounted to even this out? Thanks again.
Mar 07, 2004, 12:30 AM
ab amicis auxilio parvulo
Aerospacer's Avatar
Head Balance

Finally someone has confirmed what I found when I was balancing my rotor head, the feather plate axis was out of balance. I discovered this using the standard balancing procedure in the LMH assembly manual. I reasoned that even though the feather plate had a hole in the heavy side, there is a link and two arms on that side that must more than offset the mass lost from that hole.

I threaded a short #8 screw in the end of the feather plate where it is drilled out to allow the installation of the subrotor pivot shaft. The round head of this screw just clears the blade grip. If I had to correct the imbalance with tape on a main rotor blade it would have offset the moment balance of the two blades so much that it never would have run smooth.
Mar 07, 2004, 08:53 AM
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Here's a pic of the washer that I mounted on the feathering plate. The side of the feathering plate with the window cut-out and the linkage arm is in fact the heavy side. Because the linkage arm is so close to the center, it may not show up on the high point balancers. You don't really notice it until you run it up, then the centrifugal force takes over and the linkage arm throws it off balance.

Once I added the weight to the opposite side of the feathering plate, the rotor head was perfectly smooth

Mar 07, 2004, 09:04 AM
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Nitro--- How many washers did you use?
Mar 07, 2004, 09:55 AM
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I used the #4 oversized washers that came in the kit. You should have some left over from when you built the heli.

When I ran the rotor head up with the main blades removed, it took three of these washers to get the head completely smoothed out.

Since I already had three pieces of balancing tape on the main blade that mounted on that side of the feathering plate, I was able to remove two of the washers after I put the main blades back on. I really don't think that you could safely fit more than two washers on after you install the main blades. With two washers installed, the threads of the the main rotor blade mounting bolt pass completely through the bottom half of the blade grip. When you go to three, you will see that the threads aren't quite passing through and I would not recommend this due to safety risks of throwing a main blade during flight. If you should need more than two washers, you'll have to make up the extra weight needed by applying balancing tape to the main blade on that side.
Last edited by NitroCrushr; Mar 07, 2004 at 09:58 AM.
Mar 07, 2004, 08:15 PM
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gregw's Avatar
I've never had to do this and I'm just wondering what is the difference between adding more tape to the blade rather than using the washer? It should have the same impact since it basically adds weight to that side of the main rotor blade.

On my Corona, I normally do a static balance on my main rotor blades by making sure the CG is the same, and both blades are the same weight, down to 0.1 grams accuracy.. Then I would do dynamic balancing for the paddles to minimise any vibrations..

I've found that the tail rotor is a main cause of vibrations and should be static and dynamic balanced without the main rotor head prior to balancing the main blades.
Mar 07, 2004, 08:33 PM
Registered User
I think the only issue might be the amount of tape needed to balance it out. I had three pieces of tape on my light rotor blade and it was still out of balance when I ran it up. I don't know what the limit is for tape on the main rotor blades, but I didn't feel too comfortable adding any more. Adding the washers was a simple solution for balancing without adding any more tape.

I would also think that adding the tape to the rotorblade to make up for an imbalanced feathering plate could throw off the spanwise balance between the two sides? Although the total weight would be the same from side to side, the weight distribution would be different for each side. I think I read something about this in Ray's Authoritative Heli manual.
Mar 07, 2004, 08:59 PM
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gregw's Avatar
Originally posted by NitroCrushr
I would also think that adding the tape to the rotorblade to make up for an imbalanced feathering plate could throw off the spanwise balance between the two sides? Although the total weight would be the same from side to side, the weight distribution would be different for each side. I think I read something about this in Ray's Authoritative Heli manual.
Interesting point.. However, I think that since the main rotor blades significantly outweigh the feathering weight, it would probably be better to add weight to the CG of the MR blade rather than to add the washer on the feathering blade.. Any idea what's the weight of the washer? You will probably need less weight on the CG of the main blade since it is much further out..
Mar 08, 2004, 06:09 PM
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I'm not sure of the weight of the #4 washers.

I see your point about trying to add the weight to the center of gravity of the main blade. This is the way that I balanced the blades on my raptor. I used my Koll Rotor Pro to match the CG, chordwise balance, and overall weight for each blade, then fine tuned the rotor head on the highpoint balancer by adding a slight amount of tape to the cg of the blade on the light side of the rotor.

The problem that I ran into on the Corona is that I already had 3 pieces of tape on the blade of the light side, and the rotor head was still out of balance I'm not sure what the limit is for adding tape to a blade, but I would think that excess tape would start to affect the lift/stability of that blade?? I would guess that it would have taken several more pieces of tape on that blade until the rotor head came into balance.

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