I have an aluminum tank that was welded and leaked. A tiny pinhole. Built by someone else.
At the time I did not have experience with or equipment for aluminum welding, so I drained it, filled it with water, drained it again and went about aluminum brazing to fix the pinhole. Similar to your question. It did not work. The braze did not flow like solder does with flux on copper. The braze does not wet out like the solder on copper. I have not found a flux that might get the aluminum brazing rod to fully wet out. If there were such a flux then it might work. There are gas tank liner kits you can buy to plastic coat the interior of metal fuel tanks to stop leaks. The tank should be Ridgid and damn near water tight before application Many aircraft use a rubber or plastic liner called a bladder which is removable for service and replacement. A polysulfide sealant is used for fuel contact sealant in the Lake amphibian. If you want a fast build tank you could just build it up out of sheet aluminum and rivets or fiberglass panels and have a bladder made for it. There are more than a few custom fuel bladder shops out there. My Lake has a 40 gallon bladder. Attachments to the bladder for the filler neck, drain, sediment sump and fuel gauge sender have to be well designed for no leaks. I don't know if jb weld is made for constant fuel contact as are polysulfide sealants or whatever they use in the tank reseal kits at the auto supply store. Having had several types over the years I would go welded and pressure tested or bladder types. So many planes in excess of 40 years or more in service makes the bladder attractive as you can replace it every few decades and without having to deconstruct the aircraft from around the tanks to service the bladder. Or maybe you are a good enough engineer to make the tanks easy to remove when it finally corrodes through. Cheers! Could you make an aluminum gas tank by brazing the seams and using JB weld > to seal the seams > Sent from my iPhone >
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