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03-31-2020, 10:13 PM
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Join Date: Mar 2018
Location: Henderson, Nv
Posts: 28
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Thanks for the info. Will wait till paint to see where it?s at.
__________________
Todd
RV14a
Henderson , NV
Wings done
Fuselage in progress
N617CT Reserved
Dues paid 2018 X2; 2019
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04-01-2020, 06:29 AM
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Join Date: Mar 2017
Location: Birmingham, Alabama
Posts: 1,644
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Quote:
Originally Posted by mturnerb
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.
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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 
__________________
RV-14A #140376
N196 (Flying)
2019 Bronze Lindy
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04-01-2020, 07:02 AM
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Join Date: Jul 2015
Location: Aiken, SC
Posts: 620
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Quote:
Originally Posted by bkervaski
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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Ditto. Followed the plans and it flies beautifully. 😎
__________________
MED
140236
N435MD
Miss March 2020
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04-01-2020, 08:19 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Caution, Will Robinson. Elevator balance has practically nothing to do with how well it flies.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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04-01-2020, 08:35 AM
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Join Date: Mar 2017
Location: Birmingham, Alabama
Posts: 1,644
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Quote:
Originally Posted by DanH
Caution, Will Robinson. Elevator balance has practically nothing to do with how well it flies.
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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)
__________________
RV-14A #140376
N196 (Flying)
2019 Bronze Lindy
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04-01-2020, 09:17 AM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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Quote:
Originally Posted by bkervaski
so what is the importance of balancing the elevator? (assuming there is no gross out of balance situation)
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As far as I know flutter is the primary concern.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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04-01-2020, 09:33 AM
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Join Date: Oct 2007
Location: Sacramento, CA
Posts: 3,351
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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.
__________________
Mehrdad
N825SM RV7A - IO360M1B - SOLD
N825MS RV14A - IO390 - Flying
Dues paid
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04-01-2020, 09:40 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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Quote:
Originally Posted by bkervaski
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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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.
__________________
Dan Horton
RV-8 SS
Barrett IO-390
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04-01-2020, 09:41 AM
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Join Date: Mar 2017
Location: Birmingham, Alabama
Posts: 1,644
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Quote:
Originally Posted by Bavafa
It is really not that difficult to balance them and considering this is a safety related issue, why skip it.
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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.
__________________
RV-14A #140376
N196 (Flying)
2019 Bronze Lindy
Last edited by bkervaski : 04-01-2020 at 09:45 AM.
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04-01-2020, 09:55 AM
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Join Date: Mar 2017
Location: Birmingham, Alabama
Posts: 1,644
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Quote:
Originally Posted by DanH
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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Ahh. Makes sense. Thanks for the explanation!
__________________
RV-14A #140376
N196 (Flying)
2019 Bronze Lindy
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