Tank Caps and Install

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Last Update:

May 12, 2011

 

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To calculate the length of the fixed top tank straps, I did like most folks and shimmed and wedged the tanks into their final position. To figure the length of the top straps and the distance between the holes at either end I used a flexible seamstress tape. First cleco the tape into the main spar mounting bolt hole with the tape running over the top of the tank.

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Here is the view looking up at the aft side of the bottom capstrip of the main spar. The cleco goes through a hole that was conveniently already in the tape.

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Now pull the tape taught to the strap bolt hole in the false spar. Note the overall length and the distance between the two bolt holes to fabricate the top straps.

I used similar measurements to figure the adjustable bottom straps also.

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Again, I’m doing things a little different from most other builders. I’m cutting the hole in the skins first and then mounting the filler caps to the tanks to match. I’m able to do this because I haven’t closed up the top of the tanks yet.

I figured where the hole in the skin for the filler cap should be. Be sure and miss the strap nearest the filler cap and leave enough room around the hole if you want to install a hole reinforcement ring.

I used the router again to cut the hole in the skin.

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The tank top was temporarily pop riveted to the tank and the tank reinstalled into the bay. I then could mark the center of the filler neck hole directly onto the tank top through the hole in the skin.

The white dot inside the blue dot is the center of the hole to be routed into the tank top.

Here is the tank reinstalled after the tank top has been routed for the filler neck hole. They lined up very nicely.

Since the tops have not been riveted to the tanks yet I was able to clean all of the router chips out of the tank before final assembly.

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The top of the tank was then prepped to receive nutplates with which to screw the filler neck to the tank.

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Since these caps were designed to be flush caps I needed to raise them up about 1/4” to make them fit flush with the skins. I made phenolic rings to fit between the filler neck ring and the tank top. The phenolic material allowed me to grind/sand a good fit to the curved top of the tank.

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The filler neck mounted to the tank. I installed a .032 ring under the filler neck flange to fill the gap between the filler neck and the wing skin. The phenolic spacers support that ring and raise the neck flange to the proper height to be flush with the skin. Screws into nutplates secure the filler neck to the tank and ProSeal closes all the joints.

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Here is the filler neck mounted to the tank. I glued a butyl N rubber ring on top of the outer flange to cushion it from the skin.

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A stiffener ring was added to the skin to support the filler neck hole.

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The filler neck fit when the tanks is strapped into the bay. I’ll seal the remaining gap with some variety of flexible, fuel-proof sealant

The aft fuel line comes straight out and just clips the #2 center rib aft lightening hole flange. I went ahead and relieved the radius on the flange and added a doubler to the rib to add back the strength in that area. Rubber grommets will be used to support the fuel line’s passage through both ribs. I drilled the hole in the “meaty” part of the root rib and will bend the fuel line to fit.

The fore fuel line makes a more direct approach to the meaty part of the #2 center rib but I felt better by adding a stiffener here too.

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