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Dang-it: Options?

WingsOnWheels

WingsOnWheels

Well Known Member
I re-mounted my mostly complete fuel tank to the main spar today and the tank skin is setting about .023 proud of the LE skin (actually is .030 pround, but becasue of the difference in skin thickness it should be .007 high normally). The tank is completely drilled and ready for final deburr, dimple, and riveting. All the nutplates are installed and the LE is riveted to the spar.

I'm not sure how this happened, the skin was tight when I drilled it. Maybe the LE was not setting all the way down on the spar - it was only clecoed in place at the time, now it is riveted...

Any ideas or am I looking at a whole new tank?

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I've seen lots of flying RVs with worse gaps than that. You could shim the outboard leading edge skin and take care of most of that gap, unless you are going for a Gold Lindy winner.

Ah, the joys of pre-pre-punched construction! Good to see the low S/N 6s still being built.
 
Rick,

I read through the post you referenced. The only problem is that mine is not pillowing between the screws along the top or bottom surface (those areas are fine) The nose of the tank is just sitting a bit high. My LE is already 100% riveted in place, so I'm not sure if I could squeeze an shims in there. Maybe I am just misunderstanding your solution (which worked great in that situation).
 
No Gold Lindy Winner here, but I'd like to get as close as possible for my own sake. If I can't find a solution that doesn't require replacement I'll have to think serious about how to move forward. If I do decide to re-do the tank, it would be much easier before all the skins are riveted on and I still have access to the back of the nutplates to back-mark the skin.

I figure someone has to finish these old kits. I am at least the 4th owner of this one and the third builder. Not a whole lot was done by the first two owners, the third didn't take it out of the crates..


sprucemoose said:
I've seen lots of flying RVs with worse gaps than that. You could shim the outboard leading edge skin and take care of most of that gap, unless you are going for a Gold Lindy winner.

Ah, the joys of pre-pre-punched construction! Good to see the low S/N 6s still being built.
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WingsOnWheels said:
Rick,

I read through the post you referenced. The only problem is that mine is not pillowing between the screws along the top or bottom surface (those areas are fine) The nose of the tank is just sitting a bit high. My LE is already 100% riveted in place, so I'm not sure if I could squeeze an shims in there. Maybe I am just misunderstanding your solution (which worked great in that situation).
Click to expand...
Colin,

Both wings on my RV8 had a similar mismatch condition at the nose of the LE and as yours...after the LE was 100% riveted in place. The solution was as I previously described: to remove a series of rivets on the leading edge assembly (both top and bottom surface), shim as required, reinstall. Don't be stingy about drilling out rivets. With adequate shimming, you should be able to remove most of the mismatch. Worked for me.

2ebu6vc.jpg
 
So does the shim go between the rib an the splice plate or between the splice plate and the skin? I'm assuming the former.

Thanks,
 
WingsOnWheels said:
So does the shim go between the rib an the splice plate or between the splice plate and the skin?.....
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Colin,

I hate to sound cryptic about this but....it depends upon the situation. To pull out a LE mismatch, you have to....in effect...stretch the leading edge assemby skin to meet the LE of the fuel tank. I suggest you install the repair shim(s) between the rib and the splice plate because in your case, if you installed the shim between the splice plate and skin......you will likely create a mismatch along the gap where none occured before. Clear as mud?
 
Rick,

I'll give that a try and see what happens. Worst case, I'm back where I started. That LE skin is pretty tight already so we'll see if I can even get a shim in there.
 
Rick,

You mentioned that you think the root cause is too liberal screw spacing (too few screws). What spacing (how many screws) would you recommend to mitigate this problem at the outset? I'm at the point of starting to build a tank and have an undrilled skin to start with and can make the spacing what ever I need it to be. IIRC the spacing called for in the plans is 2.5".
 
longranger said:
Rick,

You mentioned that you think the root cause is too liberal screw spacing (too few screws). What spacing (how many screws) would you recommend to mitigate this problem at the outset? I'm at the point of starting to build a tank and have an undrilled skin to start with and can make the spacing what ever I need it to be. IIRC the spacing called for in the plans is 2.5".
Click to expand...
Miles,

If you review the photo I posted above, you can see that the screw spacing is about 2.5." This spacing contrasts significantly with the solid rivet spacing directly across from the screws which as the photo also shows is about 3 rivets spanning the same distance. Since all the holes already come matched drilled, the builder has no control over the spacing the designer settled upon. I believe that ordinarily, especially on a flat surface, the screw hole spacing is not an issue. However, the spacing does becomes an issue when the screws are expected to hold the (tank) skin down as it curves more and more towards the leading edge. As my photo shows, some pillowing occured. This seems to be a very common occurance, some builders experiencing pillowing far worse than mine. If I were laying out those screw holes on a blank skin, to avoid potential pillowing I would space the screws nearest the leading edge at some value less than the plans callout of 2.5."
 
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