Here is the way I deal with fuel tanks on my MiniMax and HiMax.
I never quite understood why Wayne started placing the tanks in to the wings when there is plenty of room in the fuselage for 10 gallon tank (or even more) and it's much easier to install.
Three important criteria can be met,
1 - being able to tell how much fuel you have - you can see the bottom half of the tank
2 - being able to use all the fuel (well almost) ,the sump bump takes care of that
3 - being able to remove the tank to flush/clean in the case of suspected or real fuel contamination.
The first pic shows the 7 gallon minimax tank finished and to be installed.
The second pic shows where it goes, when and after the fit is checked and exact placement found the curved top ply will be glued on.
The third pic shows the tank installed in the himax, it's held by door springs as the original plans show, only I use 2 springs on each side.
The fourth pic shows the two tanks I made for the himax the finished one on the right is really huge and was newer installed, the one on the left is in the foam stage and ready to be fiberglassed. That's the one I'm using now, it can take 10 gallons.
Making the fuel tank is relatively quick and easy, you use foam (insulating) to make the shape you want , no great surface finish is required here, you apply 2 inch packaging tape all over it , that acts as a sealer and release, wax the thing for even easier release, then put three plays of fiberglass using 7500 style cloth over the whole thing all in one work session, the sump bump is made separately, after the tank is laminated and cured you cut out the part where the sump goes and remove the foam through that hole, then laminate the sump in place,
If you want to know the details of it, just let me know.
Note, to resist the alcohol additives now used in many parts of the country vinyl ester resin needs to be used
When I posted the pix of my 10 gallon fuselage tank and listed the advantages of doing it that way, some implied that the change to two wing tanks was made because the 10 gallon fuselage tank would put the CG out of the limit. My numbers of the cg shift of 2.8 inches at that time were only calculated. I got the scales back now and did the actual measurement. The CG shifted (To My Best measurement) 2.9 inches between no fuel weight 508 lb and full fuel 565 lb, that is well within 3.2 inches allowed by the factory
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