Need help with Wing Twist.

[Bullseye]

Well, I keep chugging along on this right wing skeleton.

Except by ?chugging along,? I really mean ?don?t seem to be making any progress.?

Yesterday, I spent some time leveling the inboard and outboard main spar webs to 0.0?. After that, I dropped some plumb bob?s from the spar and carefully measured from the plumb bob string to the top of the rear spar. The outboard side showed 2 1/4″, and the inboard side showed 2 3/4″. A half inch of twist doesn?t sound like a lot, but of course I wanted this to be perfect.

I chose to split the difference. I pulled the outboard edge of the rear spar down (aircraft axes) and clamped, then pushed the inboard side up and clamped.

Here?s my problem. It seemed like I really had to push the rear spar ends to get it exactly where I wanted it, and there was plenty of (what I?ll call) springback force.

Of course, after clamping the rear spar in place, I remeasured the spar, and it was now no longer square. (Moving the rear spar moves the ribs, which twists the main spar.)

I releveled the main spar and really tightened up the clamps all around. I?m now level with the main spar and within 1/32″ on the rear spar.

I?m sure I can get it even closer, but I?m worried about how much force I?m holding with the clamps. I know the skins are supposed to keep the wing straight once riveted, but this seems like a lot of force to hold.

Thoughts?

[bkthomps]

did you put skins on yet? you're on the prepunched kit like i am, the twist thing is a null issue- once you cleco both sets of skins on, it will be dead on, other than the slant of your stands/garage floor

[Bullseye]

Good point. I've only clecoed on the top skins.

I'll cleco on the bottom skins tonight and see what happens.

[bkthomps]

The other tip I have is that the spar will still want to flex down in the center without the leading edge/tanks on.......so the bottom/top skins might not be enough, just keep that in mind if you find yourself back here with the same issue

I followed jamie painter's blog and decided not to spend countless hours with the lasers/bobs/etc that I had and I just built the wings doing only the basic level checks and a string down the spar length to get rid of the droop, after finishing them, they are dead level in every dimension, if that helps w/ encouragement

[Bullseye]

That does help and is encouraging. You just saved my mood for the rest of the day.

I'll push on...

(And yes, I've got a rear spar support on a threaded rod to keep the spars from drooping.)

[bkthomps]

Originally Posted by N999ZA

(And yes, I've got a rear spar support on a threaded rod to keep the spars from drooping.)

if anyone else is reading this in the future, it took me a few to realize that pushing up the center support to take the droop out was causing my stand-ends to go up as well, I had only configured them to handle a direct load from the top, I didn't consider they'd be subject to a load from the bottom so I was throwing the whole thing outta whack as i would jack up the center support

good luck and keep us posted!