wing skin...

[Jean Poirier]

Is there a &/"%"?HBSEF$%%&/" way to put the wing skin under the gas tank
skin/leading edge skin without make me crasy? Most people who come in the
shop think I am patient to deburre and rivet .... They should have hear me
this afternoon...

I am game over, I go back home

Jean
Rebel 747R





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[bransom]

Jean,
Yes, this is can be a difficult problem. I assume that you have plenty of room
for the skin to fit under the LE skin, but it is the fuel tank skin area that is
having trouble and preventing everything else from working. The answer is
two-fold.
1.) Remove excess proseal that has squeezed to the outside of the tank area
(underneath the tank skin). I used a scrap piece of aluminum to cut and
scrape the soft proseal and my fingers to rub it away, and feel that it is
clear. I also ran that piece of scrap aluminum between the ribs and tank
skin, and between the stringers and tank skin to clear out any excess
proseal. Take care not to push too far in and ruin the proseal that is needed
between tank skin and rib or stringer! I had also used Mike Betti's suggestion
to use dummy waxed strips of aluminum as spacers when I riveted the tank
skin down -- at least on my second wing. :) This helped, but the job is still
doable if you hadn't done this.

2. This is related to the first part... MAM calls for at least 1/4" edge distance
for the rivet holes on the main skin where it underlaps the tank skin. Make
sure whatever you have meets that spec and is not way over (e.g. 3/8"),
bumping into the tank bulkheads. The hardest part is squeezing the main skin
under the tank skin at ribs 1,2, and maybe 3 or 4. On mine, a tank skin to rib
rivet happens to be 1/16" aft of the rest in that row, so I also rounded a
1/16" divit into the main skin edge to allow the skin to get close enf to that
rivet. (hard to visualize but even at this divit, I still have at least 1/4"
distance to the next hole because the hole spacing is set by the ribs instead
of the row behind the bulkheads)

Both of these helped enf to finally get the skin in. Difficult, but do-able
instead of frustrating and impossible before the above. I can't remember off
the top of my head, but I had also made my tank skins and overlap rivet
holes go a tiny bit further aft (1/16"?) to allow for more room between the
overlap hole distances where it picks up the main skin, i.e., I should have
been able to keep > 5/16" edge distance for my main skin edges if I wanted,
but on fitting the skin in there, I shaved off to barely over 1/4".

Hope this helps. Let me know if unclear, which wouldn't surprise me!
-Ben/ 496R





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