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  #1  
Old 03-12-2021, 07:32 PM
downundarv8builder downundarv8builder is offline
 
Join Date: Mar 2017
Location: Melbourne, Australia
Posts: 8
Default RV8 elevator balancing

I'm trying to balance my elevators and the left one is heavy (elevator trim servo) and would need some weight placed internally at the tip to allow it to trail (85 gm or 3 oz) and the right one is light. When coupled together it's pretty close and only a small amount of weight would need to come off the right. Does anybody have any thoughts? I would think that there would be some coupling or interaction at the centre point when under load, maybe coming up as a twisting force at the pushrod but I don't know whether it would be significant or not. I understand that the weight is different when painted and also the 85g weight when attached is suitably secured. Is it best to balance the elevators individually or treat them as a single unit? Thanks in advance.
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  #2  
Old 03-12-2021, 08:07 PM
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 5,891
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Quote:
Originally Posted by downundarv8builder View Post
I'm trying to balance my elevators and the left one is heavy (elevator trim servo) and would need some weight placed internally at the tip to allow it to trail (85 gm or 3 oz) and the right one is light. When coupled together it's pretty close and only a small amount of weight would need to come off the right. Does anybody have any thoughts? I would think that there would be some coupling or interaction at the centre point when under load, maybe coming up as a twisting force at the pushrod but I don't know whether it would be significant or not. I understand that the weight is different when painted and also the 85g weight when attached is suitably secured. Is it best to balance the elevators individually or treat them as a single unit? Thanks in advance.
I am not an expert on the theory but you want to balance each one separately. And, BTW - the blue wrap is about the same area density of paint, so if you balance with that on, then you should be good. If not . . . I did many calculations and determined how many in-grams (yeah - mixed units) of counter weight was necessary for paint balance and made an extra (removed at paint) weight mounted to the inboard side of each elevator.
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RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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  #3  
Old 03-12-2021, 08:20 PM
Bavafa Bavafa is offline
 
Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,540
Default

As Bill mentioned, best practice and advice that I got from VANs was to balance each side individually. Now, you have not mentioned if the plane has been painted and if not, are you planning on painting or not. Paint will add enough weight that will change things a fair amount. As a reference, my first plane (RV7) was very light aft for the right side and the just right for the Left side before paint. After the paint, my Right side became just right and the Left was heavy aft so I had to add weight to the Left.
My RV 14 which I planned for it from the beginning was the same way and after the paint, I end up adding 5.5oz to the left and zero to the right side.

Good luck
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  #4  
Old 03-13-2021, 05:30 AM
Scott Hersha Scott Hersha is offline
 
Join Date: Jan 2005
Location: Cincinnati, OH
Posts: 1,808
Default

Balancing the elevators separately, to lighten the right one, just remove lead from the counterweight with a drill bit. The more lead you can remove the better, so on that one, drill out lead starting at the aft end. Go easy, you can always remove more after paint if needed. If you need more weight on the left elevator, adding it as far forward inside the counterbalance arm will minimize the amount needed for the desired balance. I used to make golf clubs. Golf club supply houses have all sorts of different types of lead weights to adjust swing-weight when building your clubs. One of the types I’ve used when balancing elevators is lead tape. You could also use wheel balance weights available at any auto store, like autozone. These things stick on, can be cut to size, and epoxied in place after you fine tune the weight.
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RV6/2001 built/sold 2005
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  #5  
Old 03-13-2021, 07:39 AM
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Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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I offer that going to extreme lengths to get a perfect balance is not the objective.

I did this on my first RV-8A - cutting open the end of my carefluly finished elevator tips to add weight after paint, then fixing the hole. On my RV-10 I noted that using the supplied weights the elevators were far from balanced - as in there was not enough lead, and this was before paint.

I called Van’s to let them know the weights were too small. I must have caught them on a bad day as I was promptly “schooled” on the weights being for flutter, not balance.

On the new RV-8 I just installed the weights on per the instructions. All is well before and after paint.

So I suggest a call to Van’s before you get carried away and ask them.

Carl
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  #6  
Old 03-13-2021, 08:07 AM
Bavafa Bavafa is offline
 
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Location: Sacramento, CA
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Quote:
Originally Posted by Carl Froehlich View Post
the weights being for flutter, not balance.
Carl
Carl,
As I understand it, this is precisely the reason for balancing, to reduce the possibility of flutter. There are a number of youtube videos on flutter.
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  #7  
Old 03-13-2021, 08:36 AM
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wirejock wirejock is offline
 
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Location: Estes Park, CO
Posts: 4,379
Default Nutplates

Probably too late but a nutplates installed in the forward tooling hole makes a convenient place to add weight.
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  #8  
Old 03-13-2021, 08:47 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
 
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Location: Dogwood Airpark (VA42)
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Quote:
Originally Posted by Bavafa View Post
Carl,
As I understand it, this is precisely the reason for balancing, to reduce the possibility of flutter. There are a number of youtube videos on flutter.
Adequate weight for flutter may or may not be adequate for balance.

Carl
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  #9  
Old 03-13-2021, 01:58 PM
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rjcthree rjcthree is offline
 
Join Date: Jan 2007
Location: Bay Village, OH
Posts: 956
Default Rivnuts

Not wanting to cut into my FG, I put two rivnuts in and safety wired the the bolts holding the supplemental weight to balance. I misread the plans and cut too much off the trim motor side (made it the same as the non-trim side) so I had to add some weight. It fits inside the profile of the elevator tip rib. I also used fender washers (the an number escapes me) and haven’t had any lead creep leading to looseness. I did balance after paint.
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Last edited by rjcthree : 03-14-2021 at 10:41 AM.
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  #10  
Old 03-13-2021, 09:50 PM
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fl-mike fl-mike is offline
 
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An970 washers and a nutplate in the rib tooling hole.
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