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Struggling with tank skin RV9

David Lowe

Active Member
I followed Vans instruction and clecoed the top skin from front to back to the ribs.

But clecoing the bottom part of the skin to the rib from front to back is proving almost impossible. I made the cradle to hold the tank, an on checking it is perfectly shaped to the rib plus 1/16th to allow for the skin. But no matter how hard I try I cannot get the bottom within less than 1/4 inch of the matching holes.

I watched a little YouTube an could not find anyone having the same problem, it is almost like the skin is a little under bent.

I have reread the instructions 10 times an I do not understand what I am doing wrong.

Any ideas or suggestion would be greatly appreciate.

Thanks
David
 
I followed Vans instruction and clecoed the top skin from front to back to the ribs.

But clecoing the bottom part of the skin to the rib from front to back is proving almost impossible. I made the cradle to hold the tank, an on checking it is perfectly shaped to the rib plus 1/16th to allow for the skin. But no matter how hard I try I cannot get the bottom within less than 1/4 inch of the matching holes.

I watched a little YouTube an could not find anyone having the same problem, it is almost like the skin is a little under bent.

I have reread the instructions 10 times an I do not understand what I am doing wrong.

Any ideas or suggestion would be greatly appreciate.

Thanks
David

I think you're in good company. Just because people don't talk too much about their struggles doesn't mean they don't happen. This is a common struggle. You're magic sequence might not be exactly how the instructions read. Try clecoing it together in a different order. Try applying force at a different location. I.E., maybe a lot of force at the leading edge and clecoing top and bottom toward the rear...

You'll get there.
 
Check the ribs. The tips might need adjustment. Use a strap. If nothing works get a beer and stop for the night. Tomorrow it will fit :)
 
You can smooth down the very tips of the ribs where all of the little flanges are bent. This will let the rib sit a bit more forward on the inside of the tank skin. I used the large scotchbrite wheel to make the tip of the rib smoother and more rounded. Once you can cleco it all together, and match drill the holes, it will be easier on subsequent fittings. It got even easier after dimpling the holes.
 
Ribs

You can smooth down the very tips of the ribs where all of the little flanges are bent. This will let the rib sit a bit more forward on the inside of the tank skin. I used the large scotchbrite wheel to make the tip of the rib smoother and more rounded. Once you can cleco it all together, and match drill the holes, it will be easier on subsequent fittings. It got even easier after dimpling the holes.

+1 Most common problem.
You can also use a pin punch or awl to coax the two holes together.
 
This is pretty effective -- just bend the leading edge a bit more. I put a 1 1/2" pipe in the leading edge and clamped it there so I wouldn't over-bend it. This helped a lot. I used a stout beam to distribute the load so that I wouldn't ripple the surface with a series of local bends. It took a lot of force.

I also made a set of Howe Fittings to put direct pressure where I needed it. Here are some that helped me with my outboard leading edge skin on my RV-3B. The photo was taken before I settled on the final contour, which more bending helped me achieve. You'd need to make yours to put pressure in the area that you need.

WZX1XZA.jpg


Be careful not to crush the leading edge of the ribs. Its not hard to do.

Dave
 
Same Issues

I did have the same problems when I put my tanks together recently, it was extraordinarily difficult to get the holes aligned. For the end ribs I used a clamp to pull the skin up a bit, which was enough to get the holes aligned, but the inner ribs were a pain. I did modify the shape of the cradle and that helped quite a bit by holding the skin in the right shape near the ribs. Also as other mentioned, I smoothed out the nose of the ribs to get a better fit.

I tried draw cleco's, small punches, and even sitting on the skin (gently of course, with blocks under the ribs) to get the holes aligned. Once everything is match drilled and dimpled it seems to go together a lot more easily.
 
I had the same problem with mine. I found that I hadn't fluted the ribs enough. I had to make them "a little smaller".
 
Just me

I heard all these peoples advice, but it still didnt work. In the end i build a guide and reshaped the ribs every so slightly. It didnt take much.

These will be gooped with proseal so I wasnt too worried about making the ribs really tight against the skin.. But i did all the ribs the same, even the tip ribs
 
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Awl-ful chore

Me too. Clecoes are not strong enough and break or damage the holes. Bought two awls and dulled their points. It made life easier and ended up being one of those "Why didn't I think of that before?" moments.
 
Rib tips

Most of the guys already touched on this in one way or another, but I remember having to tighten the radius of the tips of the ribs often and may have even filed an edge or two where it scratched the inside of the skin.

They will fit, just keep working em! Good luck!
 
Eventually it does come together

I had all the same issues as described getting the ribs into the tank skins. I did not resort to using straps like some have shown but found that taking some time to shape, smooth and bend the nose of the rib does help.
I found that Clecos have a habit of damaging the pre-punched holes in the skins if you try to use the cleco to lever the skin into position. A 3/32 pin punch seems to do a much better job of levering the skin in the farthest hole from the nose of the ribs then a cleco can easily be put in the hole next to it.
I found that a couple of clecos at the nose on the top skin side followed by a cleco on the bottom side farthest away from the nose using the pin punch technique resulted in all other clecos going in quite easily.
 
Awl an a little patience.

Thanks for all the suggestions, I went to the carpentry store this morning and purchased a nicely tapered awl.

With a little care it made a big difference, I just aimed to get one cleco in on each side and then used the awl to gently improve the alignment. I will never walk past any RV an fail to appreciate the effort that went into getting the tanks together... an I am not even up to the proseal excitement yet !

David
 
just me

I found that without reshaping the ribs, the tank skin and outer leading skin would not be smooth across the rib surface. I would advise you sandpaper the ribs as explained in section 5 to get all the sharp bumps out, and cleco it up. Then see if you like the smoothness of the skin. I read once that 90% of the performance comes from the first 10% of the chord. i decided it would be best to smooth out the leading edge and make as perfect as possible. But that is just me. With the radius of the leading edge, i was told the ribs provide little support at the extreme front; i did not see a need for such a tight fit.
 
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