Fuse Bottom Skins - Firewall

Finished riveting the fuse bottom skins tonight! There really weren't very many rivets left to do from yesterday, just a few dozen that couldn't be reached straight-on from the backside with the back-rivet set. Sarah and I bucked them in fairly short order, which put an end to Section 26... woo! Time for a photo op:

Selfie by the completed fuselage aft bottom section!

View of the completed fuse aft bottom section without us in the way

Pretty cool part of the plane! For now, this piece gets set aside and we will begin work on the forward fuselage sections (firewall, front seats etc) then eventually they all get joined together. We slid the assembly out of the way and decided it was early enough to get started on the next section, the firewall! Cleaned off the work tables, flipped the page in the plans and went parts-pickin' for the 20 or so pieces that make up the firewall assembly.

All the firewall parts prior to initial assembly

First order of business was to prepare the F-1001K Recess, which is that box-looking thing with the three holes in it in the photo above. This is our first time working with stainless steel, which the firewall and recess are made out of (the rest of the parts shown are either powdercoated steel or aluminum). Stainless steel is hard on drill bits, and has very sharp edges so we'll have to be careful with it and take our time.

Working with the recess box clamped together, we final-drilled all the corner connection holes and dimpled everything so that the flush side of the rivets will be facing forward. The plans mention that dimpling one of the #30 holes will be difficult because it's near an edge, and recommended using a female dimple die and a #4 flush rivet. I ended up having to cut the rivet down quite a ways to do this, and used a bucking bar on the flush side and rivet gun attached to the female die on the other side:

Our specialty dimpling setup consisting of a female dimple die, a chopped-down #4 flush rivet (basically like an AN426AD4-1), and a bucking bar. The offending hole (already dimpled) is at the upper right of the photo above.

Looks like we'll need to use this setup on four more holes on the firewall itself, but that's for later (I peeked ahead in the plans). Anyway with the recess deburred and dimpled, a quick dozen rivets later it was assembled into the box it needs to be to proceed with assembling the rest of the firewall for final-drilling. Clecoing all the parts together was actually a bit more frustrating than I had imagined-- many of the aluminum pieces either fit into each other or overlap in some way with very close tolerances. Plus, many of the holes (especially with the powdercoated parts) weren't quite big enough for a cleco to pass through easily and/or didn't line up perfectly with the underlying structure. In time, I was able to get it all together though, it just took a bit more coercion than I had expected.

The F-1001 Firewall clecoed together, ready for final drilling

Side view of the firewall

Pretty cool piece! Definitely some very strong components in here, at the four corners for the motor mounts and then in the lower middle to support the nose gear. With everything together it made for a fairly quick final-drilling session, after which the clecoes behaved much more nicely holding everything together. Next step is to pull it all back apart for more deburring, dimpling, countersinking, scuffing and priming (aluminum parts only of course)... and then rivet it all together!

We'll save that for another day.