Section 18 - Fuel Tank (final prep; first Proseal session)

A few last-minute prep chores were completed prior to the dreaded first Proseal session.  These tasks consisted of countersinking the fuel cap flange, fabricating the attach bracket assembly, scuffing the hell out of all mating surfaces with scotchbrite pads (that took hours), and cleaning with Acetone and a final wipe or two with MEK. I then Prosealed using the fay-seal-and-forget method, as recommended by Rick on VAF:  fully cleco the mating surfaces that have Proseal slathered on them, try to work a fillet seal around the edges, and let it cure overnight or over a couple/few days. At that point, I'll wet-install the rivets (swirl Proseal in the dimple, stick rivet in hole, and bang n' buck).  Even using a Semco sealant gun with pre-filled cartridges from Aircraft Spruce, the process was messy.  But mess favors the prepared mind ... and workspace.  Have a plan, lots of wipes, double glove, and don't turn up the pressure too high on the sealant gun (40psi on mine works well ... 90psi is like a noodle-maker), and it is manageable. Thanks, Ken B., for recommending the Semco gun and pre-filled cartridges - I can't imagine doing it any other way!

Countersunk the fuel cap flange:

Deburred, final drilled, and attached shims, nutplates and bearing to attach bracket:

Other side:

THE START OF THE DREADED PROSEAL!  Outside of the fuel cap flange ... doesn't look too bad:

Inside flange Proseal job is a work of (abstract) art:

Had a little trouble with the drain flange; when it was all gooped up with Proseal, I couldn't line up the holes.  The slight mess will be cleaned with MEK when cured for a day or so:

The outer ribs have tooling holes that each need to be filled with a -6 rivet.  3x rivet gun, holding a specially designed set that has a 3/16" hole that itself accepts a -6 universal die, did the trick - I only had to mash the rivet just enough to fill the hole.  That and a whole lot of proseal as I wet-riveted the -6 rivets, and then encapsulating them on each side, hopefully will do the trick.

The inboard, aft-most rib needed a few fuel flanges and a hex anti-rotation plate.  Try as I might, it was extremely hard to keep the proseal out of the hex part.  I mostly cleaned it using the thin part of a mini-popsicle/craft stick, but this is another area that will require careful cleaning using MEK, once the proseal has hardened.

Inboard, tip rib, with the tooling holes riveted and prosealed:

Ah, the stiffeners ... 11 in all; surprisingly this wasn't as messy as I had imagined.  Proseal squeezed through all the holes, and dripped off the tips of the clecos like icicles. After trying various methods to fillet-seal the edges, I haven't quite settled on a system.  I don't think these really need to be fillet-sealed, since there is so much proseal under the stiffener ... but I pushed some around each edge, just to be certain.

Outside, fully clecoed:

Another view: