Idiot builder can't flatten his ribs.

[LukeS]

So I'm setting out the components for my other wing to assemble and I see one of the .025 center ribs needs to have the lightening holes flanged. All of the others were done when I bought the project. I think to myself, I'm not going to set up dies just for one rib. I'll just Bobstick it. Well the Bobstick worked just fine for the flange, but distorted the crap out of the rest of the rib. It looks like a twisted potato chip. I've tried the Beartracks idea about pushing on the flange with a stick, and tried stretching with a Bobstick the 3 and 9 o'clock sides of the lightening hole flange with little success. I can't believe I can't get this thing to sit flat. Any input would be greatly appreciated. I've also watched Desert Bearhawk's video on flattening ribs with pliers. I haven't made a soft jaw set of pliers yet because I didn't see the difference between his use of the pliers and just using a stick. Obviously I'm missing something.

[bestbearhawk1231]

Have you tried clecoing the stiffening angles to the rib yet? I had a few that I couldn't get the twist out of but once I clecoed the stiffening angles to it most of the twist came out and the remaining twist will be easy to take out once the rib is clecoed to the attach angle on the spar. Have you tried twisting it the other way to see if you can take any out? Not sure what else to tell ya, sorry.

[LukeS]

Thanks Joe for the reply. I haven't tried the stiffeners yet. I would really like to see it flatter first. I'm going to work on it some more tomorrow and we'll see what happens.

[mswain]

Have you tried fluting the rib? I used this method: http://youtu.be/pIvFpVV6kIQ

As Joe mentioned, the stiffeners should take out any remaining curvature.

[LukeS]

The ribs are already fluted, and are pretty straight from nose to tail aspect. They are cupped across the height of the rib. Imagine the rib lying on the table, flanges sticking up, and the only part touching the table is the middle section of the rib between the top and bottom surface. The twist is pretty minor, but the cupping isn't. There is enough tension required to push the rib flat that I'm concerned it could damage the stiffeners. I have the next three days off work to mess with it and build my c-frame dimple/rivet tool.

[mswain]

Got it. There is a nice write-up on straightening the direction you mentioned on this page: At the bottom: http://www.woodtic.com/wingconstruct...centerribs.htm

[Chris In Milwaukee]

I'm not entirely satisfied with how not-quite-flat my ribs are, either, but I'm hoping that riveting the stiffeners on them will help out a lot. Hope hope hope. I'll know soon...

[Chewie]

So with the flanges UP, the rib rocks top to bottom when you lay it on a flat surface?

I ask because I just ran into this yesterday. I think what happened is you bob-sticked it too far at the 3:00 and 9:00 positions of the holes. Need to push those areas back down a little. If you can determine the axis of the bow, that's where your bob-sticking should be maximized. Imagine your rib is on the table in front of you, running left to right, with the flanges up. Now you're real mad, so you slide the piece toward you and bend it in half the long way over the corner of your workbench. What will those hole flanges do? Right where you bend it, those hole flanges will flatten. So that's the extreme case of what you will need to do.

Double check your top and bottom flanges are 90 degrees by pressing it flat on the table and sliding a square up to it.

Also double check your flutes. I thought I was done, but I decided to flip the rib over. I squatted down and looked through the holes with some light shining from behind. This will tell you with brutal honestly if it's overfluted in some areas and not enough in others.

Capture.JPG

I also found that the squaring, fluting and bob-sticking all have to be done in iterations, because one tweak affects the other two.


Re: pliers, I didn't grind these, just slipped on some covers. You can get them from Sears: http://www.sears.com/craftsman-plier...p-00945446000P They work great! In this picture, I'm lifting up on the plier to flatten the nose rib, but same concept for the center ribs.

Hope this helps!


IMG_20141102_184134293.jpg

[LukeS]

I think you're right Mark. I backed off the lightening hole flanges a little and that took out a lot of the distortion. I'm not quite satisfied yet, but heading in the right direction.