Thu Mar 15 2007

Working on tank skin gap problem

Now that I'm back in the flow of things, I'm ready to tackle this tank gap problem. Here is the gap between the tank skin and the top main skin on the left wing. I'm gonna send this picture to Van's and see what their support people have to say about it.

Bruce thought the likely culprit is that the ribs weren't seated all the way forward in the skin. Looking at the inboard-most rib, I can see some gap between the little finger flanges around the nose of the rib and the skin. His theory sounds plausible.

So I un-clecoed the whole skin and just left it clecoed to the baffle.

No gap! Good news!

I figured I'd use the rivet gun to form the finger flanges around the nose of the ribs so they match the curvature of the skin a little more. I fabricated this little forming block from a piece of oak and rounded the edge over with a 1/8 inch radius bit in my router.

Using the rivet gun and the forming block, I kinda curved the finger flanges a little. It's not very noticeable.

While working on this rib, I noticed that the flanges weren't exactly 90 degrees to the web anymore. They must have moved when I was fluting them. I didnt' get any shots of this, but after tweaking this inboard most rib, I did a test fit into the skin. Frankly, I didn't think it fit any better than it did before. The holes lined up quite well before I reworked it and they still lined up after. So I thought I'd try a different tact.

I left all the ribs out and just clecoed together the skin, baffle, and Z brackets. When I set the assembly on the spar, the gap was gone!

...but dangit I dont' think it's fixed. I can see that the skin is bowed outward more on both the top and bottom of the wing. I bet what this is doing is just flexing the baffle upward.

Sure enough, I laid a scrap piece of aluminum over the baffle and it was visibly bowed.

Same thing near the bottom of the wing.

This bowing of the baffle is what's eliminating the gap...not taking the ribs out. Argghhh! I'm gonna call it a night and think about this more tomorrow.