Anyway, tonight wasn't a night of crazy progress or ground-breaking discoveries, but early on I did catch a mistake I had made while riveting together the firewall. This leads me to my second "GOTCHA" installment: The mystery of the "empty" lower 16 holes on the firewall!
Rivet Diagram on pg. 27-5, holes in question circled in red
The rivet callout diagram on Page 27-5 is misleading, in my opinion (I even pondered what they were for in my entry from 6/11). It shows AN426AD4-4 rivets should be installed into these 16 holes, and they are not included in the markings that say "do not rivet when creating subassembly..." Furthermore, elsewhere in the plans it calls out to dimple all holes, and install 4-4 flush rivets into any unused holes. My conclusion? These holes won't be used and they should be dimpled and filled with 4-4 rivets.
So what are these holes for? It didn't become clear until page 28-7 step 1, where they have you final-drill #30 the holes between the firewall and the Fwd Fuse Floor Ribs. Hey, guess what? They are referring to those 16 holes for the first time ever in the plans... and they really shouldn't be dimpled at this point, or at the very least they shouldn't have rivets installed into them! Aarrgh. Carefully drilled out 16 perfectly-installed 4-4 flush rivets. Not the greatest "first" task after getting back to the project after a week off from building, but hey what can you do. It actually went pretty easy, no holes damaged and we were back to good in short order.
My suggestion if I were to do this again? (1) Do not drill, deburr, dimple, or rivet these 16 holes while constructing the firewall assembly in section 27, leave them completely alone. (2) Final-drill per instructions on 28-7 step 1. (3) Deburr and dimple these holes in the firewall after everything comes back apart on page 28-10.
Side view of the lower firewall after drilling out the rivets in question and drilling/dimpling the mating flanges on the floor stiffeners.
Anyway, other than this ordeal, all we really got done was some more final-drilling of the bottom skin and installation of the Fwd Cabin Floor Panels, which was kind of cool ("This is where our feet will go!"). Here's a pic of the current state of affairs:
R forward floor panel, looking towards firewall
R forward floor panel, looking towards rear
That's pretty much it for tonight! As soon as these floor panels get final-drilled and a bit more prepwork and deburring, looks like we'll be mating the forward and mid fuselage sections for the first time ever... excited for that to come!