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  #11  
Old 03-31-2020, 10:13 PM
squarebush squarebush is offline
 
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Thanks for the info. Will wait till paint to see where it?s at.
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  #12  
Old 04-01-2020, 06:29 AM
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Quote:
Originally Posted by mturnerb View Post
I can't find any guidance in the plans about elevator balance. I've seen conflicting information in the forums (surprise surprise).

Just wondering how other -14A builders have approached this. I've installed the counterbalance weights per plans but don't know if I need to otherwise balance the elevators and/or whether to do each individually or as a unit. I'll be flying soon, but paint will wait until after initial flight test phase.
I just made sure the counter balance weights were the same, flies straight as an arrow, the trim tab didn't seem to matter much, maybe I got lucky
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  #13  
Old 04-01-2020, 07:02 AM
MED MED is offline
 
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Quote:
Originally Posted by bkervaski View Post
I just made sure the counter balance weights were the same, flies straight as an arrow, the trim tab didn't seem to matter much, maybe I got lucky
Ditto. Followed the plans and it flies beautifully. 😎
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  #14  
Old 04-01-2020, 08:19 AM
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Caution, Will Robinson. Elevator balance has practically nothing to do with how well it flies.
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  #15  
Old 04-01-2020, 08:35 AM
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Originally Posted by DanH View Post
Caution, Will Robinson. Elevator balance has practically nothing to do with how well it flies.
Hmm .. thinking it through .. the pressure is not always equal (turns, etc) so what is the importance of balancing the elevator? (assuming there is no gross out of balance situation)
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  #16  
Old 04-01-2020, 09:17 AM
Bavafa Bavafa is offline
 
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Quote:
Originally Posted by bkervaski View Post
so what is the importance of balancing the elevator? (assuming there is no gross out of balance situation)
As far as I know flutter is the primary concern.
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  #17  
Old 04-01-2020, 09:33 AM
Bavafa Bavafa is offline
 
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OK,I go out on the limb and ask this;

If the balance wasn't important, why bolt that big hunk of metal to the control surfaces to begin with, wouldn't that be the best and easiest way for weight reduction.
If it is important, then why not make it as good as one can. I built a plane and taking a bit more time to make the best plane I can, would be worth the time and effort.
It is really not that difficult to balance them and considering this is a safety related issue, why skip it.
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  #18  
Old 04-01-2020, 09:40 AM
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Quote:
Originally Posted by bkervaski View Post
Hmm .. thinking it through .. the pressure is not always equal (turns, etc) so what is the importance of balancing the elevator? (assuming there is no gross out of balance situation)
The primary purpose is to decouple the elevator from motion (torsion or bending or both) of the horizontal stabilizer. Consider this basic example.

Case A has the CG of the elevator well aft of the hinge line. Case B has the elevator's CG located on the hinge line.

Cause a sharp vertical displacement of the horizontal stabilizer.

With A, the hinge line will displace with the HS, but because the elevator CG is aft of the hinge line, inertia will cause the elevator to lag behind the motion. The deflected elevator applies a force to the hinge line, driving it in the same direction as the original motion.

With B, the hinge line and CG will be displaced equally. There is no relative motion of the HS and elevator, thus no new force applied to the hinge line.

Now consider the same A and B, but this time instead of a single vertical displacement, make the HS displacement repeating, driven up and down and up and down by aerodynamic forces.

With A, the elevator will always lag behind the HS motion. The amplitude of the relative motions may stabilize, or it may be divergent, gaining amplitude with every cycle until some component fails due to structural overload.

With B, the elevator remains in sync with the HS stabilizer displacement.

The complete picture is much more complex, and best understood with math beyond my capabilities. We have some very bright people here who can offer a more in depth explanation.
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  #19  
Old 04-01-2020, 09:41 AM
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Quote:
Originally Posted by Bavafa View Post
It is really not that difficult to balance them and considering this is a safety related issue, why skip it.
I wasn't suggesting to skip it, but rather, how would one know?

The topic does seem to be lightly controversial in that Vans doesn't think it's that important.

The RV-14 manual doesn't have any steps (that I can find) for balancing beyond making sure the counter weights are matched.

So for a first time builder, which most are, they may never know to balance them.

Edit: Maybe during phase 1 flutter would be an indicator? Seems flutter may not introduce itself until perhaps an over speed condition.
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Last edited by bkervaski : 04-01-2020 at 09:45 AM.
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  #20  
Old 04-01-2020, 09:55 AM
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bkervaski bkervaski is online now
 
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Quote:
Originally Posted by DanH View Post
The primary purpose is to decouple the elevator from motion (torsion or bending or both) of the horizontal stabilizer. Consider this basic example.

Case A has the CG of the elevator well aft of the hinge line. Case B has the elevator's CG located on the hinge line.

Cause a sharp vertical displacement of the horizontal stabilizer.

With A, the hinge line will displace with the HS, but because the elevator CG is aft of the hinge line, inertia will cause the elevator to lag behind the motion. The deflected elevator applies a force to the hinge line, driving it in the same direction as the original motion.

With B, the hinge line and CG will be displaced equally. There is no relative motion of the HS and elevator, thus no new force applied to the hinge line.

Now consider the same A and B, but this time instead of a single vertical displacement, make the HS displacement repeating, driven up and down and up and down by aerodynamic forces.

With A, the elevator will always lag behind the HS motion. The amplitude of the relative motions may stabilize, or it may be divergent, gaining amplitude with every cycle until some component fails due to structural overload.

With B, the elevator remains in sync with the HS stabilizer displacement.

The complete picture is much more complex, and best understood with math beyond my capabilities. We have some very bright people here who can offer a more in depth explanation.
Ahh. Makes sense. Thanks for the explanation!
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