Again, I'm borrowing very heavily from Mark Langford's fuel system, which you can find at his website.
After my wing spars were attached, I was able to begin by cutting slabs of foam for the top and bottom of the wing. I cut templates for the inside of the wing out of 1x4s, glued the 1x4s to the foam, and sanded the foam to the contours. (Note: After doing this for the transfer tank, I decided to do something a bit difference for the other side. See Fuel Tanks (Part 3) for what I think is a better setup.)
I made a bit of an error during my next step. Vinylester is touted as fuel resistant, and therefore, the best fuel tank resin. Unfortunately, not all vinylesters are created equal, and most manufacturers aren't willing to specify if a given vinylester is "fuel safe." As far as I can tell, it's due to the ethanol that winds up in gasoline today. I purchased vinylester from FGCI, went through the process of laying up my fiberglass, and as it was curing I bothered reading the pamphlet that came with it. "Not recommended for fuel." Guess I'll be adding another layer once I get more vinylester, which I ordered from Aircraft Spruce (sold specifically for fuel tanks).
1. Draw lines ⅜" down from the top of the inside of the spars, and ⅜" up from the bottom
2. Flox and attach front and rear tank walls to front and rear spars, using previously drawn lines
3. Apply duct tape to the tank bottom (to keep from attaching the bottom permanently at this time), then use tape and supports to hold the bottom in place
4. Use flox and fiberglass tape to build a ledge for the tank bottom to attach to
5. Attach tank sides and baffles using flox, taking care not to attach them to the tank bottom
6. Mark location for tank sump
7. Remove tank bottom, secure tank top in place (with duct tape where tank seams will be)
8. Build ledges for tank top as in step 4
9. Remove tank top, apply flox to tank bottom, and secure tank bottom in place permanently
10. Install all lines and fuel level sender
11. Fill with water for a leak test
Assuming the leak test doesn't reveal any catastrophic leaks, I'll fix anything that needs fixing and then install the tank top the same way I installed the tank bottom. The final leak test will be a mild pressure test; at this point if it fails, I'll have to cut open the tank from the top and try to find the failure.
For my fuel and vent lines, I cut ⅜" aluminum plates and drilled and tapped them for AN fittings. Next I cut away the foam where I wanted the lines to pass into the tank and floxed the plates in place.
Continued in Fuel Tanks (Part 2)