SB00067 Mass Balance Weight Removal

[rcarsey]

Originally Posted by Jcurry

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

[Tony_T]

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.

[Piper J3]

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.

[Jcurry]

Originally Posted by Tony_T

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_T]

Originally Posted by Jcurry

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.

[Jcurry]

Originally Posted by Tony_T

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.