After more than a year of looking at the fuel tanks, it was finally time to test them before riveting them in place. Yes, I can always unrivet them if there is a leak, but why not check it first?

Fellow builder Yeol discovered a great technique for testing. No balloons, no barometers, no checking whether or not the air temperature changed impacting the other readings. Really simple and easy, which is perfect for me! We used blanking off fittings to seal the fuel inlet and outlet. We put a solid rivet in the end of some tubing and attached that to the vent. Then we put about 2 gallons of fuel into the tank and put the cap on. We put duct tape over the fuel cap to prevent pressure from leaking out there, but it turns out we didn't need to do that, at least not with this caps.

We then rolled the tanks (still cleco'd into the wings) into the sun and shook them a little bit. The idea is to heat it up and shake it up to increase the evaporation of the fuel and build pressure. After we let it warm for a few minutes, we sniffed all over the tank and didn't smell any fuel (liquid or vapor) coming out. Then it was the moment of truth - we ripped the duct tape off of the fuel cap! It was...uneventful. No noise, no smell, no nothing. Just a good seal. Then we opened the fuel tank and heard what sounded like a Coke can being opened, but without the "Ahhhhhhh" that goes with it because it smelled like fuel rather than an icy cold drink. In any case, I am now convinced that the fuel tank is leak tight.

We did the same thing to the other tank with the same results.

Now I can rivet it in place, put in some control rods, rivet on the winglets, and call it done!