SB00036 Possible aggravating factor?

[wawrzynskivp]

Just had a pre-buy inspection on my build and the inspector struggled with the asymmetric weighting on my elevators. Electric trim installed on the left made the counterbalance on the left greater than needed on the right. But the thing that stuck out was that the inspector was adamant that the proper way to balance is AFTER the elevators are tied together. Of course I did check balance after they were tied, but only after balancing individually first.

So is it common for folks to carry individually imbalanced and thus oppositely balanced elevators provided that their total balance is neutral? If so then there will be residual torque carried from one elevator to the next at each upset. One elevator will be more responsible for the correcting or neutral inertia and that load will probably concentrate at the outer hinge.

So just for consideration here is a quickie survey that may or may not convey any useful conclusion.

(if this has been run to ground and I just didn't catch it then post that here and I'll delete)

 

[Bavafa]

After finishing my first RV in 2007-2008, VANS told me that elevators need to be balanced and it is best if they are balanced individually, which of course tying them together should remain balanced.
Fast forward to 2018, it seems VANS recommendation was that there is no need to balance them unless there is sufficient imbalance as a result of painting or other factors.
I have always balanced my elevators, first individually and then after tying them together to make sure they are still balanced.

 

[bjdecker]

Margin + Build Technique

Personally, I don't think it matters if you balanced the elevators together or separately (or not at all). All of the RV's that I've seen so far look like bad builder technique contributed to, and may have been the root cause of, the cracks.

Of the ones I've observed with cracks, all of them had one or more of the following:

1. Holes not deburred.
2. Shop head on the thinner material.
3. Rivets Bucked instead of squeezed.

IMHO the .032" 2024-T3 material (E-603PP) is probably a wee-bit thin for the hole spacing used at the outboard bracket location. The later models (-9,-10,-14) used thicker material for the H-stab aft spar.

 

[Bavafa]

I am not going to dismiss the idea of the imbalance will attribute to cracks but it is the first time I am hearing this.

My understanding for the need to balancing of the elevators has to do with flutter and not preventing cracks.

 

[Stevea]

First, balance them individually. After assembly, check the balance again. Problem solved.

Just to poke the inspector a bit (and maybe find out why he thinks that), you can always ask where the manufacturing/maintenance/process specification for that balance method is located. And as a follow up, what is the physics behind it.