Airworthy fuel tanks, finally! §21 complete for L and R

(Mea culpa:  I wrote this 4 days ago and never hit the "Publish" button.  Doh!)

The fuel tanks are officially "done."   While I never was able to get them air tight, as some VAF members have been able to do, I have been successful in demonstrating that they would hold water and as of yesterday, that they could hold 100LL.

(recap) As you may recall, I spent nearly a month trying to get the fuel tank sensors installed correctly and without leaks.  The first few attempts were definitely learning experiences for me because it was obvious that I had done a poor job.  Each one got better (e.g., the residual leaks were smaller & slower).  I finally got the obvious leaks sealed and then proceeded to pressure testing.  There were some dumb leaks that were easily corrected, but then I really got serious about trying to make them airtight.   

I gave up on Van's idea of using a kid's balloon because there were some very thoughtful and data supported comments from VAF that it's an exceedingly poor gauge and should best be thought of as a pressure 'fuse' that will blow if you end up putting too much pressure into the tank.  Instead, I bought some clear plastic tubing, added colored water and used that as a simple manometer.   15 inH2O = ~0.5 PSI and is roughly double the pressure of a full tank of fuel, so I figured that would be a good value to use.  Unfortunately, despite everything I could think of, I could never get the tanks to hold pressure for more than 30 min.

I suspect it's the fuel caps that are leaking.  I couldn't prove it, but I just don't like their design.   I even tried sealing them with condoms, but could never find a leak nor maintain pressure.

Lada & I filled them with with water and left them to soak for a long weekend.  No leaks!    100LL is half the viscosity of water, so there might be a hole too small for water to leak through, but might pass avgas.  I drained all of the water and borrowed 29 gal* of 100LL from the Cirrus and tried it again in the Left tank.   Success!  I managed to salvage about 28 gal and put it in the Right tank.  Another success!  Neither tank had any visible moisture after 24 hr of containing 100 LL.

This officially completes section 21, as it was published on the day I received the wing kit.  More about that later!

*I have 3 jugs of 8 gal each that I use to buy premium auto gas and pump into the RV-12.  I also have a 5 gal container.  Together, they are 29 gal. The fuel tanks are 30 gals, so "close enough."  If there's a leak at the very top, it will not be operationally important because fuel won't leak up against gravity.  In addition, aircraft tanks are rarely stored in a completely full state.