HS balancing: perfection vs. weak counterweight

[Paul Eastham]

Hey all,
I've been drilling my counterweights like mad recently, trying to get a perfect balance. I think I'm just shy of balanced, but now I'm wondering if my counterweight is dangerously weakened by all the drilling:



(Those are 3/16 holes, some all the way through, some mostly, with liberal countersinks)

Also, any thoughts on how balanced the HS needs to be? It feels pretty close, but if I deflect it each direction it seems like it's still following through a little bit more in the counterweight-too-heavy direction.

I would have liked to just cut off part of the counterweight, but sadly this is difficult because my fiberglass tips are already riveted on.

Tip to those who haven't yet attached your counterweights: make them a little smaller than the plans say, or at least don't rivet on your HS tips until you've got the balance pretty close...

[mlw450802]

Originally Posted by Paul Eastham

... but now I'm wondering if my counterweight is dangerously weakened by all the drilling: ...

no, it isn't.

[wv4i]

I would email this picture to Van's tech people and ask what they think.

[Ironflight]

Paul,

I know you probably know this, but don't forget to allow for future paint weight - in other words, you aren't looking for perfect balance in an unpainted condition. I left my elevators overbalanced by several ounces - I didn't want to have to go back and add weight back in after painting. Worked out fine.

Paul

[Mel]

Like Paul said. Leave the elevators over nose heavy before paint. As a matter of fact, even after paint, a slight over balance is better than under balance.

[cobra]

If you are worried about the structural integrity, why not fill the holes with epoxy and/or cover them with some fiberglass?

[Kevin Horton]

Leave the elevators over nose heavy before paint. As a matter of fact, even after paint, a slight over balance is better than under balance.

But, be aware that having the elevators over balanced will reduce the stick force per g - i.e. if you are trimmed at one g, it will reduce the amount of aft stick force required to pull a certain amount of g.

The reason that an over balance reduces the stick force per g is that when you are pulling g, the counterweight will be pulled down, which moves the trailing edge of the elevator up, which is in the direction to give you more g. This means you don't have to pull as hard as you otherwise would.

If you are at aft CG, this could increase the odds that you do an unintended over stress, or get in a pilot-induced oscillation in pitch.

So don't get too carried away with the over balance, and there should be no reason to leave the elevators over balanced once they are painted.

[Steve]

The balance will change after installing the elevator tips. Could be significant depending on fasteners and resin, etc. Save some lead for later.
Steve