Fuel Tank, Part 2

Part of the process involved in building the tank was to consider some alternatives that other builders have previously encountered.

First item of consideration was the sight gauge.  After reading numerous stories of leaks around the sight gauge as well as it practical uselessness for the intended purpose, I somewhat reluctantly decided to forgo the installation.  The next issue was to decide whether or not to install the Moeller mechanical fuel gauge as an adjunct to the sight gauge.  Again, after reading what turned out to be all of the glowing remarks about its usefulness, it became a no-brainer to jump on the bandwagon.

Below is a shot showing the Moeller unit with its nutplated mounting hole at the prescribed dimension of the fuel tank lid by a successful user.  The unit appears to function quite nicely and should be readable both from the pilot's seat as well as when refueling from outside the aircraft.

 A third and final consideration to be made involved the purported problem with the fuel tank reuturn line fitting coming loose and causing a leak.  Several builders have constructed hold down clamps (for lack of a better term) that get riveted to the bottom of the tank and attempt to keep the fitting from rotating when torqued upon with a wrench for final fuel line attachment.  I could never fabricate one to the tolerances required to keep the fitting absolutely fixed and free from rotation under a torque load.  After some thought, another builder, Donald suggested the use of a weldable, threaded bung...in fact two of them, back to back, each one holding the AN fuel fitting.  That's what I decided to do.  It was a bit of work, but the fittings will be riveted onto the bottom of the tank, in a similar fashion to the fuel pick up line.  There will be one on the outside and another on the inside of the tank as shown below.

 The final steps prior to assembling were all about surface preparation which mainly consisted of aggressive scruffing up of the mating or faying surfaces of the tank components.  Note the scuff marks on the interior of the bottom skin as shown above.

Without much further to do, it was...Proseal time!

Unfortunately, the process as yet undetermined by a leak  test, was not as I had envisioned.  It was fraught with breakages of my 3 riveters and the need to constantly clean up the internals of each tool after only a few driven rivets.  I ended up breaking my awesome Avery Tools Tight Space Pop Riveter (but there's a happy ending to that story featuring Bob Avery who will be mailing me a replacment part at no charge) tool in the heat of the battle.  I am still dumbstruck to think that I could have been using too much Proseal that it caused these numerous problems.

Undoubtedly, there were other issues such as the MS-42 rivet stems being too large to fit in any of the standard nose pieces as well as the necessity to drill out my other awesome Avery Tools angled rivet holder thingy so they would fit in it as well.  To top things off, I must have had a bad batch of the AD-41H tank rivets as I had several pull the stem out without breaking!!!!!

Here is the documented mess, in no particular order.

Noteworthy is the fact that I am without my fourth pair of gloves as I finally gave up in frustration with the lack of dexterity since I was disassembling/reassembling/repairing riveters throughout the process.  In the shot below, I am attempting to do some cleaning up of excess Proseal.

This was some of the final riveting of the front panel...followed by an attempt to clean up.

Same as above.

A decent view of the two fuel fittings - the inlet and return.

More cleaning.

A view of the forward underbelly of the beast.

Picture showing the blobs in the inboard forward corner of the tank.  I was very careful to keep the 4 baffle passageways (not really visible here) clear to maintain the prescribed fuel flow at low tank levels.

Close up of the fittings and more of the "blobs".

Shot of the external fittings.

The fuel sender mounting plate gets 5 nutplates.

The finished product now awaits its turn for final mounting during the second major ProSeal effort to come later.

In the mean time, the fuel tank's filler neck must be fitted to the fuselage skin adjacent to the bulkhead wall.  Once it is cleco'd into place the neck is match drilled to the pre-drilled holes in the fuselage skin.

The neck is removed and minor bends added to the mounting flange such that it makes a nice uniform junction with the skin.  After several iterations, the junction between the filler neck flange and the fuselage skin is perfect.

 Following are some pictures of the tank temporarily mounted into the fuselage to accomplish the fuel filler neck fitting.

Prior to the final ProSealing was the installation of the fuel return line.  Shown below is the AN fitting with the 1/4 inch line after it was torqued down to the welded fuel bung for the return.

A more complete picture of the return line shows the terminus taking a final upward bend into the future location of the filler neck, as specified in the plans.

The next picture is of the top skin of the tank with the mounting ring ProSealed and riveted into place.  Note also that one of the return line clips is in place as evidenced by the cleco.