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SB00067 Mass Balance Weight Removal

Jcurry

Well Known Member
Hey Guys,
I have a legacy -12. Evidently my stab was never balanced. While complying with SB67, I discovered my stab is nose heavy. Just trying to get an average amount of weight that was removed on the legacy -12 in order to obtain neutral balance if your stab was not previously balanced. Thanks.
 
I did not measure how much weight was removed.. but I waited until the stabilator was painted before balancing. A few photos are attached here.
 

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Thanks

Thanks Walt and Rob.
Rob, what did you use to trim your weights?
 
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Since legacy RV-12s have flown just fine for hundreds of hours with a too heavy counterweight,
it is better to err on the side of too heavy, especially if the stabilator will be painted in the future.
RV-12iS plans page 11iS/U-11 says to err on the side of too much counterbalance
 
Im planning on just climbing into the tailcone with my drill and remove material until the counterbalance stays in a neutral position when moved. Seems like the fastest method to get to the same result.
 
Thanks Walt and Rob.
Rob, what did you use to trim your weights?

I (actually the shop it was in) used grinding/sanding disc on a rotary tool. I didn't mind if they got lead shavings and dust all over their hangar :). We thought about whether the trim servo should somehow be connected while we were balancing.. and decided against it. We trimmed until the stab (including the AST which we taped into a neutral position) was balanced. (we hung the stab from the ceiling with wire by its pivot bolts)

Once we mounted the stab in the plane and hooked everything up though, it seems we removed too much weight. So I guess my advice to others is to either trim it in place, or somehow account for the trim servo weight.
 
I (actually the shop it was in) used grinding/sanding disc on a rotary tool. I didn't mind if they got lead shavings and dust all over their hangar :). We thought about whether the trim servo should somehow be connected while we were balancing.. and decided against it. We trimmed until the stab (including the AST which we taped into a neutral position) was balanced. (we hung the stab from the ceiling with wire by its pivot bolts)

Once we mounted the stab in the plane and hooked everything up though, it seems we removed too much weight. So I guess my advice to others is to either trim it in place, or somehow account for the trim servo weight.

Going by the KAI, I placed weight on the stab until I reached neutral. This turned out to be 18 0z total. The KAI says to divide this by 2. This gave me 9 Oz to remove. I decided to only remove 8 0z to account for blade width material loss and to ere on the side of being a little nose heavy. Happened to work out
to be perfectly balanced.
Thanks for all the info everyone
 
Going by the KAI, I placed weight on the stab until I reached neutral. This turned out to be 18 0z total. The KAI says to divide this by 2. This gave me 9 Oz to remove. I decided to only remove 8 0z to account for blade width material loss and to ere on the side of being a little nose heavy. Happened to work out
to be perfectly balanced.
Thanks for all the info everyone

Ugh.. this updated KAI would have been nice to know about two days ago. Prior to 2020, I think the instructions were pretty terse about how to balance it. . so we tried doing what we thought was logical..

KAI says "Tape the AST assembly into the "trail" position at one of the outboard corners and rest the pushrod on top of the pushrod attach bolt" .. Grrrr.. ok that explains how we trimmed off a bit too much. Luckily there is an extra hole through the weights where I can re-add. Looks like I get to do the Tailcone Crawl again :)
 
I am in the middle of adding the reinforcing straps to my stab weight so have been reviewing this thread in detail. The straps only weigh 2 1/8 oz. and my stab was in perfect balance when I disconnected the cables in order to start the SB mod. It won't take much weight removal to rebalance, probably less than 2 oz. My aircraft is S/N 202, an early build completed in 2010. I have a heavy paint job, internal priming and no fiberglass stab tips.
The thread here is confusing. Some are reporting removing quite a lot of weight. No one is reporting in detail the parameters of their airplane. Here are my thoughts:
The iS stab is quite different from the early stab and much lighter. KAI 11iS/U-02 in step 8 has the builder do a preliminary weight removal of of 3/4" from the end of two of the four weights. That is a lot of lead!
Paint would make the stab balance, at least on my early build, without tips installed. The original 12 had no fiberglass tips available from Vans. There were some after-market tips made and some early builders used those.

So unless all of the parameters are known, reports of weight removal for this SB are useless.
Is it a iS or legacy 12?
Built per the KAI regarding weight removal?
Painted or unpainted?
Internal primed?
Fiberglass tips, factory or after market or none?
Conclusion:
There are probably no specific weight removal guidelines to rely on here, there can be many differences in the airplanes.
 
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Hi Tony....

We just did a friend's legacy 12 that was built by Synergy as E-LSA. Primed and with heavy paint. We balanced by suspending the stabilator with strong mason string and achieved a near perfect balance. Watch that the string is not touching upper travel stop. Process was slow going with about a dozen swipes / reassemble on the outside lead pieces. We removed ~ 1/2" on both pieces.
 
So unless all of the parameters are known, reports of weight removal for this SB are useless.
Is it a iS or legacy 12?
Built per the KAI regarding weight removal?
Painted or unpainted?
Internal primed?
Fiberglass tips, factory or after market or none?
Conclusion:
There are probably no specific weight removal guidelines to rely on here, there can be many differences in the airplanes.

Tony,
I am the OP. You are correct and your points are well taken. However, for me, the information in this thread was value added as I had no clue on how much weight might be required to be removed. I was looking for ballpark, not exact numbers. Between this thread and 2 others, I was able to determine that I would most likely need to remove between 6-10 Oz. So, as I began the balancing process it was no surprise when I discovered that I would need to remove 8oz........
 
Tony,
I am the OP. You are correct and your points are well taken. However, for me, the information in this thread was value added as I had no clue on how much weight might be required to be removed. I was looking for ballpark, not exact numbers. Between this thread and 2 others, I was able to determine that I would most likely need to remove between 6-10 Oz. So, as I began the balancing process it was no surprise when I discovered that I would need to remove 8oz........

That seems like a lot, considering the two straps only weigh 2 1/8 oz. Did you check the balance after removing the cables but before doing the first removal of your stab?? It was probably a bit nose heavy.
We just completed balancing mine today and ended up cutting off about 3/16" from each of the two outside weights. The cut off pieces weighed a total of 2 oz. but some metal is lost in the cutting with a hacksaw.
 
That seems like a lot, considering the two straps only weigh 2 1/8 oz. Did you check the balance after removing the cables but before doing the first removal of your stab?? It was probably a bit nose heavy.
We just completed balancing mine today and ended up cutting off about 3/16" from each of the two outside weights. The cut off pieces weighed a total of 2 oz. but some metal is lost in the cutting with a hacksaw.

Hi Tony
It was totally nose heavy and bottomed out. I did not build my plane. It was painfully obvious after disconnecting the cables that it was not balanced. The weights also did not show any material previously removed. I read where a couple of people with legacy 12's had to remove around 8-9oz.
 
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