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Elevator Balance?

mturnerb

Well Known Member
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 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 balanced mine individually which is per advise/instruction that I had got from VANs and also based on pervious experience on my 7A which was also based on advise from vans.

This is exciting time so my congrats .
 
The 14 plans don’t call for it, so I have not, yet. You might/would need to balance again after paint.
 
Van's - tell me what I need to do.

I balanced mine individually which is per advice/instruction that I had got from VANs . . .
If Van's has advice for balancing control surfaces why don't they make that available for 14 builders; maybe they do but it is tucked away so you have to ask or search for it.

Curious minds sure would like to know more about this.
 
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If they want them balanced individually, it definitely does not mention it in the plans (9-26). The weights are all the same. The individual elevators are not the same weight since one has the trim servo and tab and the other does not. Balancing them to the same neutral point individually makes sense on one hand but the elevators are bolted together and work as a system so balancing them together is the way they function. Neutral balancing one at a time would seem to benefit only if the halves would separate at the pushrod and if that happened, you have many other issues than to worry about balance of each half. FWIW I balanced mine together and have never had any issues.
 
On important issues such as this which could potentially be the source/cause of a flutter, why not go to the mothership for advise. The phone call is free and the advise, one would think, more scientific.

Anyhow, that is my 2 cents,
Balancing the elevator might have done something for me, might have not. But for sure it gives me a bit more of peace of mind.
 
Yep - call Van?s.

On the RV-8A I went to great pains to balance the elevators, taking weight off before paint then adding it back on after paint (big mistake). On the RV-10 I was surprised the elevator weights were way short of achieving balance, even before paint. Van?s told me that is by design. Counterbalanced for flutter protection does not necessarily translate to perfectly balanced.

For the new RV-8 I just bolted the weights on per plan and built on.

Carl
 
I had contacted Vans this week and they were here nor there on balancing the elevator short of maybe balancing them individually slightly forward but keeping in mind they are bolted together.

While working on my elevator fairings this week and the horizontal laying flat on a table, I noticed the right elevator was 6 oz heavier forward than the left when using a digital scale. Left side with tab was almost neutral give or take an ounce. I had to put about 5 oz on the trailing edge to to get them even. Any one else experience this or build on? Taking out the trim actuator made little difference. Maybe I shaved one lead weight down more than the other. Perhaps nut plates on these fairings are smart for the future..... Thoughts.
 
I had contacted Vans this week and they were here nor there on balancing the elevator short of maybe balancing them individually slightly forward but keeping in mind they are bolted together.

While working on my elevator fairings this week and the horizontal laying flat on a table, I noticed the right elevator was 6 oz heavier forward than the left when using a digital scale. Left side with tab was almost neutral give or take an ounce. I had to put about 5 oz on the trailing edge to to get them even. Any one else experience this or build on? Taking out the trim actuator made little difference. Maybe I shaved one lead weight down more than the other. Perhaps nut plates on these fairings are smart for the future..... Thoughts.

Todd,
Your left elevator will require more weight than the right due to the trim tab. Prior to paint, mine were fairly balanced for the left and light on the trailing edge of right side. After the paint, I added 5.5 oz of weight to my left elevator and none to the right which were checked each of them balanced individually and then bolted together.

Hope this helps.
 
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 :)
 
Caution, Will Robinson. Elevator balance has practically nothing to do with how well it flies.
 
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)
 
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.
 
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.
 
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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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!
 
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.

Vans has apparently satisfied themselves that an elevator built to plan and not loaded with additional mass aft of the hinge line (for example, body filler, excessive paint, or an extra servo) falls within the acceptable range. Nothing wrong with that.
 
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.

This is one of the best/easiest explanation of the process that I have heard, many thanks for putting it in such way that even I can understand it.

Here is a video but there are others on youtube

https://www.youtube.com/watch?v=egDWh7jnNic
 
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At rest in the hanger my elevator seems to set more or less neutral, without a tendency to either up or down elevator. Does that mean it is more or less balanced without any extra effort on my part? All I did was make sure the weights I added were as close to the same as I could make them, according to the plans. :confused:
 
At rest in the hanger my elevator seems to set more or less neutral, without a tendency to either up or down elevator. Does that mean it is more or less balanced without any extra effort on my part? All I did was make sure the weights I added were as close to the same as I could make them, according to the plans. :confused:

If it is disconnected from the control push/pull tube, then yes.
My process was to put each elevator at any given position, full up, full down and natural and to observe if it will hold that position.
 
Risks, without test data to support a decision with respect to the RV-14

Balance the elevators individually- none
Balance the elevators together- possible torsional response and flutter, loss of aircraft
Use the standard weights i.e., not checking balance- possible flutter and loss of aircraft.

You decide your acceptable risk consequences.
 
So how did the RV3 survive over 48 years without any balanced elevators.....

The early RV models have a lower VNE. And it's possible to reach critical speed without the oscillation being divergent to failure, given fortuitous design. For a probably example, read Smokey's RV-4 story:

https://www.vansaircraft.com/wp-content/uploads/2019/01/hp_limts.pdf

I was able to repeatedly demonstrate a wing torsion/aileron mode in a Kolb, prior to the addition of aileron counterweights, a service bulletin item many owners considered optional. I suppose it was, given that the wings did not break off, and I had a ballistic chute.
 
So how did the RV3 survive over 48 years without any balanced elevators.....

Simple. Not all designs have a structural resonance at the aerodynamic excitation frequency. If the aircraft was flight tested to validate that assumption, then no problem. If not you become the test pilot. Today we do Ground Vibration testing which establishes the structural resonances as a risk reduction for flight test.
 
I removed my lead weights and re-weighed and found they were at least 6 oz difference. As others have mentioned the left side with the trim tab is definitely heavier. I trimmed the heavy one down to almost match the other side.....weight slightly forward of the hinge. Hopefully after paint it will be close.
 
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