Stabilator balancing....

[YME]

I am working at home in the garage and getting ready to disassemble the Empennage section for storage so I can make room for the wings kit. Is it necessary at his point to balance the Stabilator (with fairings) for neutrality or can I wait until after the flight testing phase and then, after painting, balance it. Not sure if this would affect flight testing.

I did some calculations and it seems if I remove 260 grams (9-1/8 oz) from the counterweights it would be neutrally balanced. Any insight is apprecitated.

-Martha

 

[N8DAV8R]

I am working at home in the garage and getting ready to disassemble the Empennage section for storage so I can make room for the wings kit. Is it necessary at his point to balance the Stabilator (with fairings) for neutrality or can I wait until after the flight testing phase and then, after painting, balance it. Not sure if this would affect flight testing.

I did some calculations and it seems if I remove 260 grams (9-1/8 oz) from the counterweights it would be neutrally balanced. Any insight is apprecitated.

-Martha

The KAI describes balancing the stab as optional. If you are going to balance, it would make more sense to wait until after paint, else you are likely to end up re-doing things and adding more paint. I know of at least one builder that had to do this, and it's not a trivial thing to do on a painted airplane.

I checked mine just after paint and it was balanced nearly perfectly. I decided to leave good enough alone.

 

[Riessen]

I recommend foregoing “performing a preliminary trim” of the weights (as instructed) until after paint, or at least preparing for flight before paint. When trimmed as instructed by a fellow builder, weight was added back to balance - after paint. I think it’ll be worth the wait, because adding lead back is seriously kludgy.

 

[YME]

The KAI describes balancing the stab as optional. If you are going to balance, it would make more sense to wait until after paint, else you are likely to end up re-doing things and adding more paint. I know of at least one builder that had to do this, and it's not a trivial thing to do on a painted airplane.

I checked mine just after paint and it was balanced nearly perfectly. I decided to leave good enough alone.

Nate,
Thank you for the response. So it sounds like you did not remove any weight during assembly and it was ok after painting. Good to know.

 

[YME]

I recommend foregoing “performing a preliminary trim” of the weights (as instructed) until after paint, or at least preparing for flight before paint. When trimmed as instructed by a fellow builder, weight was added back to balance - after paint. I think it’ll be worth the wait, because adding lead back is seriously kludgy.

Thanks for the input. The consensus so far is leave alone, go through testing phase, then paint and check for balance.

 

[N8DAV8R]

Nate,
Thank you for the response. So it sounds like you did not remove any weight during assembly and it was ok after painting. Good to know.

That's correct. Admittedly, I did the final balance test slightly different that the KAI would suggest. I was at the paint shop and I ran bolts into the attach points, then used safety wire and a helper to suspend the HS assembly. It was in balance. This differs from the KAI in that in was not in place with the AST linkage resting on the top. IMO, this difference would be negligible, especially given the context of the whole assembly and the balance being optional to start with.

The reason I did it this was is that doing it in place becomes a fairly difficult process and/or adds risk of damaging the paint. If you need to add or remove lead (sorry I said paint above, funny mistake) you'll need to either climb in and work inside the tail or you need to remove the assembly. Removing the assembly introduces a real risk of scratching the tail cone at the forward-inner corners of the HS. If you do this after paint, I recommend you protect it by taping on a layer of paper covered with a layer of metal tape.

 

[YME]

That's correct. Admittedly, I did the final balance test slightly different that the KAI would suggest. I was at the paint shop and I ran bolts into the attach points, then used safety wire and a helper to suspend the HS assembly. It was in balance. This differs from the KAI in that in was not in place with the AST linkage resting on the top. IMO, this difference would be negligible, especially given the context of the whole assembly and the balance being optional to start with.

The reason I did it this was is that doing it in place becomes a fairly difficult process and/or adds risk of damaging the paint. If you need to add or remove lead (sorry I said paint above, funny mistake) you'll need to either climb in and work inside the tail or you need to remove the assembly. Removing the assembly introduces a real risk of scratching the tail cone at the forward-inner corners of the HS. If you do this after paint, I recommend you protect it by taping on a layer of paper covered with a layer of metal tape.

View attachment 83800

Thanks for the info. I will definitely make note of the paper and metal tape if I need to remove the stabilator.

If you remember how did the plane fly, during the testing phase without removing any lead weight and then after the painting?

 

[CTCole]

This is a question I would call in to Van's, rather than trust this forum. What you want to know about is the possibility of flutter near Vne, and that's something few people on this forum are likely to have experience with. IMHO (= built, balanced & painted before testing per acceptance protocol, no flutter) I would not fly without knowing the stabilator was balanced to specs.

 

[seagull]

I balanced mine using the “pivot” bolts hanging from a beam outside the aircraft. To compensate for not having the AST linkage attached I set the trim at center and put a gram scale under the pivot ball that attaches to the elevator. I created a weight of the same amount and taped it to the elevator even with the control horn. Also I taped the surface level. It is much easier to balance outside of the aircraft.

 

[rvbuilder2002]

This is a question I would call in to Van's, rather than trust this forum. What you want to know about is the possibility of flutter near Vne, and that's something few people on this forum are likely to have experience with. IMHO (= built, balanced & painted before testing per acceptance protocol, no flutter) I would not fly without knowing the stabilator was balanced to specs.

The legacy RV-12’s are actually slightly over balanced and there was no requirement to adjust to neutral balance.
Flutter risk is mainly a product of being under balanced.

The main purpose of doing an adjustment to achieve neutral balance is for the weight reduction it provides at far aft location. That is why it is specified as being optional.

 

[N8DAV8R]

This is a question I would call in to Van's, rather than trust this forum. What you want to know about is the possibility of flutter near Vne, and that's something few people on this forum are likely to have experience with. IMHO (= built, balanced & painted before testing per acceptance protocol, no flutter) I would not fly without knowing the stabilator was balanced to specs.

We aren't speculating or lacking experience. I generally agree that when something is unclear it's a good idea to ask the question, but this is published information. Do you also calls Van's to verify stall speeds and takeoff distances? Muddying the water doesn't help anyone.

11is/U-11

 

[rvbuilder2002]

The legacy RV-12’s are actually slightly over balanced and there was no requirement to adjust to neutral balance.
Flutter risk is mainly a product of being under balanced.

The main purpose of doing an adjustment to achieve neutral balance is for the weight reduction it provides at far aft location. That is why it is specified as being optional.

Adding an additional note For those that are balancing without the AST push pull rod assembly…
When doing so, you are actually purposely under balancing the assembly because its added weight is not being considered, which is not a good thing.
There is no downside to being over balanced other than having excess weight in the aft tail of the airplane, but being even a little bit under balanced is causing you to operate in a realm that has not been tested by Vans.

 

[dbhill916]

Adding an additional note For those that are balancing without the AST push pull rod assembly…
When doing so, you are actually purposely under balancing the assembly because its added weight is not being considered, which is not a good thing.
There is no downside to being over balanced other than having excess weight in the aft tail of the airplane, but being even a little bit under balanced is causing you to operate in a realm that has not been tested by Vans.

To be sure that I am understanding this correctly, here's my rephrasing of what you said.

Overbalanced is the state when the stick will move forward on its own. This acceptable.
Neutral balance is the state when the stick will stay where it is placed. This is optimal.
Underbalanced is the state when the stick will move aft on its own. This is dangerous.

Can you point me to some literature where I can read & try to understand what is going on with respect to flutter risk and the balance of the h-stab?

Thanks always for your contributions,
-dbh

 

[Mel]

To be sure that I am understanding this correctly, here's my rephrasing of what you said.
Overbalanced is the state when the stick will move forward on its own. This acceptable.
Neutral balance is the state when the stick will stay where it is placed. This is optimal.
Underbalanced is the state when the stick will move aft on its own. This is dangerous.
Can you point me to some literature where I can read & try to understand what is going on with respect to flutter risk and the balance of the h-stab?
Thanks always for your contributions,
-dbh

Maybe I'm missreading what you are saying, but it sounds like you have it backwards. If the elevator is not balanced at all, the stick would move forward because the elevator would fall down. This would be under balanced and not good. Over balanced, the elevator would move up pushing the stick back.

 

[seagull]

My elevator is perfectly balanced off the plane with the weight of the servo pushrod added. Once on the plane the control stick goes forward. The control stick weight causes it to tilt forward.

 

[dbhill916]

Maybe I'm missreading what you are saying, but it sounds like you have it backwards. If the elevator is not balanced at all, the stick would move forward because the elevator would fall down. This would be under balanced and not good. Over balanced, the elevator would move up pushing the stick back.

No, you didn't mis-read. That's exactly what clarification I was seeking -- the definitions of "over" and "under" balanced because the reference wasn't clear to me. (I was able to figure out "neutral" on my own ).

I'm now interpreting these thusly: "Over balanced" means too much lead weight on the counterbalance arm, causing the stick to move aft. "Underbalanced" means not enough lead weight is installed and the stick will move forward.

Assuming that's the correct understanding, how does being underbalanced increase flutter risk?

-dbh

 

[rvbuilder2002]

No, you didn't mis-read. That's exactly what clarification I was seeking -- the definitions of "over" and "under" balanced because the reference wasn't clear to me. (I was able to figure out "neutral" on my own ).

I'm now interpreting these thusly: "Over balanced" means too much lead weight on the counterbalance arm, causing the stick to move aft. "Underbalanced" means not enough lead weight is installed and the stick will move forward.

Assuming that's the correct understanding, how does being underbalanced increase flutter risk?

-dbh

Consider the state of the surface if you removed the counter balance weight entirely.
That would be the most severe case of being under balanced.
So if you are close to balanced, but still under balanced, you have moved in the direction of potential control surface flutter.
No one can say how much closer because an RV – 12 has not been flight tested to the point of flutter so it is an unknown.
That is why best practice is used to do what is possible to stay as far away from that unknown point as is practical.

 

[dandmdan]

My elevator is perfectly balanced off the plane with the weight of the servo pushrod added. Once on the plane the control stick goes forward. The control stick weight causes it to

My elevator is perfectly balanced off the plane with the weight of the servo pushrod added. Once on the plane the control stick goes forward. The control stick weight causes it to tilt forward.

I have found the same issue and I balanced my elevator as per Van's instructions on the aircraft. Not sure if I should add some weight back, however I have put a number of hours on the plane since balancing and have not noted any problems.

 

[whity1231$]

I have found the same issue and I balanced my elevator as per Van's instructions on the aircraft. Not sure if I should add some weight back, however I have put a number of hours on the plane since balancing and have not noted any problems.

As I remember, the stick cables were not supposed to be attached when balancing. Even with no weights removed, the weight of the cables and sticks made the stick go forward.

 

[seagull]

As I remember, the stick cables were not supposed to be attached when balancing. Even with no weights removed, the weight of the cables and sticks made the stick go forward.

Exactly!

 

[dandmdan]

As I remember, the stick cables were not supposed to be attached when balancing. Even with no weights removed, the weight of the cables and sticks made the stick go forward.

Mine was actually neutral before adding the SB brace and balancing. But as stated I have noticed no issues in flight with the change.