Fitting fuel tanks

[Benbell4140]

In regards to fitting the fuel tanks on a series 7 did you guys trim the flanges of the tank to square up with the wing ribs? Also the manual says to bond the edges to the #1 and #3 rib with hysol but I’ll have a very large gap here on both sides of the tank. And my ribs do measure 35-1/2” center to center as required for flaperon hinges. Not sure how to proceed.

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[Jerrytex]

I ran into the same thing. One tank popped right and fit good. The other I had to trim and adjust more. I did what I read on here and ended up sliding the tanks out as far as I could to get clearance for the fuel strainer fitting. This required sanding the edge of the tank flange and sliding the tank out, until the "gap" was even, or as close as I could get it, between the tanks and #3 Rib. I used hysol where I could and fiberglass where the gap was larger. I drilled holes for rib stitch on the #3 rib. Smoothed it all out with the blue poly fill.

Don't forget to varnish the inside of ribs #1, and #3 before setting the tanks.

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[Benbell4140]

Thanks for the help Jerry. It appears that I have a much larger gap but I’m sure I can fill it with glass. Just need to check with the factory for resin type to make sure it’s compatible. Thanks again.


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[efwd]

I applied masking tape from the underside of the tank flange and capstrip to bridge that gap. Hysol (allow to set up some) placed in that gap. If it isn't set up some, it will run. When dried, it will likely be recessed a bit so that you will need to fill in the small valley. I used Smurf poop. Palm sanded when it dried it was ready for cover.

[jiott]

Ditto what efwd said; worked well.

[alexM]

I sanded my outboard edge so that it was perfectly parallel to the #3 rib, and slid the tanks outboard as much as possible before bonding them in place. I'm ignoring in inboard gap and just plan on covering it (it's pretty large in my case). I'm surprised that Hysol (with no fiber reinforcement like flox) would withstand the test of time, but if it works then that's awesome.

If you do sand the edges after you've done your leak test then you need to do it again.

[Benbell4140]

Thanks everyone. This is all useful information.


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[Delta Whisky]

One more way to think about it - the inboard gap (to the #3 rib) is handy when rib stitching. The fabric covers it nicely.