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-   -   Struggling with tank skin RV9 (https://vansairforce.net/community/showthread.php?t=179030)

dcl 01-26-2020 11:59 AM

Struggling with tank skin RV9
 
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

scard 01-26-2020 12:17 PM

Quote:

Originally Posted by dcl (Post 1403217)
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.

Vlad 01-26-2020 03:15 PM

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 :)

bruceh 01-26-2020 04:07 PM

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.

wirejock 01-26-2020 04:12 PM

Ribs
 
Quote:

Originally Posted by bruceh (Post 1403279)
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.

David Paule 01-26-2020 04:57 PM

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.



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

Dave

GeoffP 01-26-2020 06:01 PM

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.

RV10Man 01-26-2020 06:23 PM

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".

PilotjohnS 01-26-2020 06:27 PM

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

eric.the.blonde 01-26-2020 07:40 PM

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.


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