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Marv,
We are currently building two Lancair IV-P's and have recently completed leak checking the wing tanks. Found no leaks in the tanks, but it was several days/tries before we determined this, as there are a surprising number of planned/intentional holes in the tanks that were not easy to secure to the level needed. (fuel filler, vent, feed, return, two water drains and fuel gauge probe--I think that's all the planned holes)

We plugged all holes but the wingtip vent, then inflated a heavy-duty balloon (the party balloons used for helium worked well for us) and secured it to the vent pipe with a piece of rubber band. It took several tries to secure all the planned holes--and we were initially very concerned. Two initial failures illustrate the problem: initially used grease to seal the fuel filler caps--not even close to good enough. Then used two pieces of overlapping release tape to cover the caps completely--better, but still got a small leak along the overlap joint. Think that was about the last problem; once we'd sealed that, the balloon test held for at least three days. Moral of the story for us was to be sure we'd securely plugged all the planned holes before presuming we had a more serious problem. By the way, we decided to do the test before installing the ailerons, flaps and other hardware, thinking any leak would be much easier to repair/get to. Having "perfected" the leak check method, intend to do it again after plumbing installation to be sure we have the rest of the system as tight. Hope this helps.

Bob Pastusek
N437RP

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