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Balancing control surfaces

J

Jeff Wilde

Member
Greetings, I am currently painting my Rv12. My neighbor is the FAA inspector who will sign off my airplane. He has been stopping by from time to time checking on my progress. Since the check off will be soon he ran off a list of things that I needed off the top of his head. He asked if I needed to balance the flaberons and stabilator after painting. He stated that it was common practice in G.A. aircraft after painting. I told him I had not heard of anyone balancing the flaperons and stab after paint but since he is the guy I have to make happy I told him I would find out. I have searched the forum and cannot find anything on the subject. I suspect that I do not but can one of you A&P types advise on this issue. I am not looking for speculation, just the facts. Thanks, Jeff Wilde in Geneva Florida
 
Facts only...

The only things you technically have to do are all of the inspection / check items in the PAP (production acceptance procedure).
That doesn't mean an inspector wont choose to require something else, but in the context of control surface balancing, there is no published procedure, because as long as typical painting practices are followed it wasn't deemed necessary.
 
balance

Personally I would balance all control surfaces. Flutter is a bitch.
 
If an RV-12 is built to be certificated as an E-LSA. The builder can only do what he is told to do in the construction manual. There are specifically designed (weight value) counter balance weights that are specified to be installed on the stabilator and flaperons during construction.
There is no other documented procedure for doing any other balance adjustments on the RV-12.
 
Thanks, that's what I was hoping (expecting) to hear. I will advise him that there is nothing published outlining a proceedure to balance them. Mine is an ELSA built to factory specifications. I'll go easy on the paint though.
 
Flutter is also speed related. We do not have a 250+ kt airplane! Well, maybe once...
 
balancing

Balancing control surfaces after painting is a standard practice. It's not a big job. Yes even on slow airplanes. Cessna requires it on a 182.
Anyway if the inspector wants it done he wants it done. It is his arse he's signing away.
 
balancing

But the if the manual does not specify a balance, there is no reference material to use.
 
Hi Bill, Could you please post the procedure for balancing the control surfaces on the RV-12 after painting? Since the factory doesn't have one maybe you could help us out here. Thanks, Larry
 
If you mean "me" when you say Bill, I have no clue. The flaperons have a counterweight inside that that is not adjustable once installed. The stabilator's counterweight would be adjustable if you crawled back there and cut off some of the lead or added some - but who knows how you would determine if you needed more or less or how much! I think the person with the inspector's concern should talk to Van's about it. All we can do is speculate.
 
rvbuilder2002 said:
If an RV-12 is built to be certificated as an E-LSA. The builder can only do what he is told to do in the construction manual. There are specifically designed (weight value) counter balance weights that are specified to be installed on the stabilator and flaperons during construction.
There is no other documented procedure for doing any other balance adjustments on the RV-12.
Click to expand...

Is there a documented paint procedure?

If not, what stops a builder from putting on 10 heavy coats of Imron and screwing up the expected balance?
 
az_gila said:
Is there a documented paint procedure?
Click to expand...

No

az_gila said:
If not, what stops a builder from putting on 10 heavy coats of Imron and screwing up the expected balance?
Click to expand...

As in anything with airplane building (or life in general) nothing stops them any more than with any of the other RV models (and if I recall correctly, none of the other construction manuals specify doing any additional balancing).

If a person takes on something as technical as building an airplane, it is expected that they will do so with a certain level of common sense reasoning. I know that doesn't always happen... The RV-12 stabilator counterweight is sized by quite a large margin over what is actually required, so as long as someone doesn't make the rivets disappear with coats of paint, they should be alright (but then everyone else that sees the airplane will know that no common sense reasoning was used when doing the painting).
 
"The RV-12 stabilator counterweight is sized by quite a large margin over what is actually required".....What does that mean? Does it mean that mo is betta?
 
gossend said:
"The RV-12 stabilator counterweight is sized by quite a large margin over what is actually required".....What does that mean? Does it mean that mo is betta?
Click to expand...

In simple terms, it is not neutrally balanced (would be obvious to any 12 builder when they first install the stabilator).
The weight value selected makes re-balance after painting not necessary as long as builders don't get extremely carried away with their paint application (as in Gil's example).
 
Over balance range ?

Does this mean paint inside and out and how about two 1.25 lbs fairing tips?
Scott I would like to see the math and the highest total of over balance number that van's anticipated.

rvbuilder2002 said:
In simple terms, it is not neutrally balanced (would be obvious to any 12 builder when they first install the stabilator).
The weight value selected makes re-balance after painting not necessary as long as builders don't get extremely carried away with their paint application (as in Gil's example).
Click to expand...
 
Last edited:
I knew that this might be analysed with an electron microscope. That is why I asked "I am not looking for speculation, just the facts." in my request. I am satisfied with there being no documented proceedure or request to balance after paint. This is the info I will give to my inspector. Thanks again for your assistance. Jeff
 
rvbuilder2002 said:
In simple terms, it is not neutrally balanced (would be obvious to any 12 builder when they first install the stabilator).
The weight value selected makes re-balance after painting not necessary as long as builders don't get extremely carried away with their paint application (as in Gil's example).
Click to expand...
OK, I get it. So Van's is slightly overbalancing in anticipation of a reasonable, not excessive paint job. My question would be if you took the time and effort to check on it, would you rather be slightly over or slightly under. Or is that curve symmetrical, with the ideal being exact neutral balance?
 
Stabilator Balance questions

Good question
I like to add this.
Is the center of balance on the stabilator rotation point or its center of lift?


gossend said:
OK, I get it. So Van's is slightly overbalancing in anticipation of a reasonable, not excessive paint job. My question would be if you took the time and effort to check on it, would you rather be slightly over or slightly under. Or is that curve symmetrical, with the ideal being exact neutral balance?
Click to expand...
 
Please Help

Scott is there not a value for the anticipated paint and primer or the lack of both and some way to check the balance if you are outside of the paint estimate.

rvbuilder2002 said:
The RV-12 stabilator counterweight is sized by quite a large margin over what is actually required,).
Click to expand...
 
Very interesting

It's an interesting question, to be sure...

My vague and incomplete understanding of flutter and balancing the elevator on my rv6 is that the elevator and horizontal stabilizer should be balanced so they move together with turbulence. The elevator gets balanced in neutral position with the stabilizer. But, this is very different from an rv12 and i'm not convinced the same rules apply. This comparison is as useless as the previous comparisons with cessnas with elevators and stabilizers.

What does Piper require on Cherokee's or Comanche's that get repainted? That would be a more useful data point.

Still not sure what you would balance to as it's already a single structure. Does it even need a counter balance other than to relieve stick force weight before the trim tab has any effect? Wouldn't this just be so your arm doesn't get tired holding full aft stick during taxi? Does a counter balance have any other purpose on a stabilitator?

I know local rv12 builders that i'm pretty sure did not balance the stabilitator after painting with a base coat / clear coat system.
 
classic approach to balancing controls

Interesting article by Tony Bingelis on the matter...

http://members.eaa.org/home/homebui... Mass Balance Control Surfaces.html#TopOfPage

Following just a small section of the article:

"...The old trial and error method is effective and hard to fault. That is, you simply add pieces of lead (old wheel balance weights are handy for this purpose) to the location where the weight is to be affixed, until the desired level of balance, or overbalance, is reached. You can do this by temporarily taping the lead pieces to the control surface or you can suspend a tin can (or any kind of small container) from the point where the lead weight is to be ultimately secured. Ducting tape, wire or a similar means should hold things in place during the process.

Keep putting pieces of lead in the can until the control surface reaches the proper level attitude. Remove the can and weigh the whole thing on a scale. Now you know exactly how much weight it takes to balance the control surface.

If you have no weighing scale you can still balance the surfaces although you may never know how much dead weight you'll be hauling around.

Dump the lead pieces into a ladle or other container and melt them down for casting. Add a little extra lead to allow for the weight of the can, trimming and sloppy pouring. Skim the surface impurities from the molten lead with a "metal stick". The molten lead is now ready to be poured into whatever form you made. Be careful with that hot stuff, amigo!..."
 
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