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Leading Edge, Fuel Tank Alignment

mackd

mackd

Active Member
There have been several posts about the leading edge and fuel tank skins not aligning properly during final assembly, after they've both been riveted, but I'm having issues with earlier alignment. I just recently worked through the Checkoway z-bracket drilling method and got to the point where I set my fuel tank in place on the spar. The two aren't even close to lining up, as you can see in this picture.

rv07.jpg


This is the worst alignment problem, but the gap between the fuel tank skin and main skins is bigger than I would like. By pulling down on the top of the fuel tank I can eliminate that gap, but the nose area gap is too big to eliminate this way.

I'm trying to decide how to tighten this up.

I've thought that maybe I should disassemble the fuel tank and reassemble it more carefully, somehow, but I don't see how that would make a difference. The fuel tank skin to rib holes line up just fine now that the thing is fully clecoed together.

Anyone else have this issue during early assembly and how did you remedy it? It's not something I want to ignore.

Thanks!

David
 
David,

Do you have the splice strip in there?

If you do, is it hitting the flanges on the outboard tank rib and creating this?

Are your tank brackets bolted down tight?

I would not drill the splice strip till you get this resolved. There should be no reason not to be able to get 100% alignment in this area.

Also make sure your spar is perfectly flat and not bowed or sagging.
 
First, follow Brian's checklist above. Then...

How do your tank skin to spar flange holes line up in that picture? If it is hard to get clecoes in, then pulling down on the tank is necessary. Given what I see in your picture, I can't imagine that those tank skin-spar flange holes line up very well right now.

I used a couple of wide tie down straps and slowly (and lightly) ratcheted the tank down until its skin holes matched up with the the spar. It took very little. This solved much of the problem but I still had a little bit of mismatch b/w the leading edge skin and tank leading edge. I was then able to work much of it out by the order in which I set the screws into the splice strip. Still again, though, there was a slight mismatch. I left it at that pending some other solution.

There have recently been a lot of posts suggesting to use shims under the leading edge skin to get it to match up with the tank skin. This seems to work. What I found, however, is that over the past year or so the skin on my tank has relaxed such that the gap is now almost non-existant. In this case, I'm relieved that I didn't try to shim it becuase it would have left me with a different problem--the leading edge skin being too far forward relative to the tank skin. So my general suggestion is get as much of it worked out as you can now, then just give it some time. If it's still a problem later, fix it then. Until you get your bottom wing skins riveted on--MUCH later in the processs--it's not a big deal to keep working on the alignment of the tanks.

As Brian mentioned above, though, try to get it "close" before you drill the splice strip.

One other thing I'd recommend... use your edge forming tool (especially if you have the Cleaveland vis-grip kind) on butt joints as well as lap joints. I lightly edge formed all sides of my tank skins and that helped eliminate some of the problem too. This also works well on the leading edges of the main skins and aft edge of the outboard leading edge skins where they butt together.

Hope this helps. Good luck.
 
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David

I had a similar problem. It taught me that if it doesn't fit there is something wrong.....so....I LEARNED.......don,t drill, edge form, rivet,......until the real problem is found.

My guess is either spar miss alignment (not Level) or Z's not flush to the spar.

Please don't force alignment as it will, usually creat more greif!!!!!

Frank @ SGU RV7A "NDY"
 
Thanks for all of the helpful suggestions!

Brantel said:
Do you have the splice strip in there?

If you do, is it hitting the flanges on the outboard tank rib and creating this?
Click to expand...

The splice strip is in there and drilled to the leading edge, but I have held off drilling it to the tank until I resolve this.

I'll check the other issues mentioned above when I get home tonight.

Thanks!

David
 
One other thing, cleco your skins on as well to see how well the fit between the tank skin and the top and bottom skins looks. I bet there is a large gap.

Hopefully it is just sitting up on the splice strip.
 
David,

You've already gotten some great advice. I had the same issue, and like Steve I used some ratcheting straps to snug down the tank prior to drilling the splice plate. This helped and I was able to get the leading edge and tank to match perfectly. See here.

Unfortunately, even though I had it all aligned perfectly prior to riveting, I ended up with some slight pillowing between the first two screws on the top of the wing after riveting. This "pillowing" was easily solved by inserting some shims between the rib and splice plate, but I wouldn't worry about that now. My point is only to say don't be surprised if things shift a tiny bit during the riveting process.

Good luck!
 
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Caution: Cleco Interference With Spar Caps RV-9

First off, thank you, thank you, thank you, to all of the people on this forum who advised: "If you have to force something, you have probably done something wrong."

I had a small gap between fuel tank skin and the wing skin on the initial fitting (RV-9). I read about using ratchet straps to close the gap. This is also discussed in a back issue of the RVator.

Before I tightened (forced) the ratchet straps, and remembering some sage advice, I gave everything one last look. I discovered the 10 inboard fuel tank baffle clecos rested on the spar cap (again, RV-9). The fuel tank was resting on the clecos instead of the 'Z' brackets. This is what was preventing the fuel tank skin from butting up to the wing skin on the initial fitting. I removed the 10 inboard fuel tank baffle clecos, and very little pressure was required to close the small gap between the fuel tank skin and the wing skin. Everything fit perfectly.

Thanks, guys, you saved me a bunch of heartache and headache. If I would have gorilla cranked the ratchet straps, I'm sure the clecos would have dug into the spar caps or elongated the holes in the fuel tank skin. Instead, I have a perfectly fitting fuel tank with no collateral damage.
 
On my RV 10 I just finished the fuel tanks. I did my first test fit and the outboard tank side which covers the splice strip is not lining up. The holes along the splice strip for the screws do not lineup perfectly and there is a slight difference in the position on the aft sections of skin. It seems the tank is about 1/64” more forward than the outboard skin. I tried pushing it and nothing seems to make skins even and skin screw holes line up.

I saw some pro seal that I got too far in on the tanks and that was causing an issue. I removed the extra proseal and same issue persisting. I even tried sanding down the primer… Nothing is working. It is still having a 1/64 inch gap.

GOING CRAZY
 
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