The left side longeron still needed to be drilled to the skins, so that was step one today. I started at the tail and worked my way forward until I got to the downward bend of the longeron (well, upward with the fuselage upside down).
Forward of the bend in the longeron, it also twists so that the skin starts to curve near the top of the fuselage and will create a nice transition to the top skins. It's a pretty significant twist, so I clamped the skin to the longeron, also making sure that the edges lined up. Then it was the same story with drilling and clecoing. I did this to both sides.
The instructions mention that the longerons need to have 3/4" clearance to the front of the skins so that the firewall will be able to nest there. I trimmed them to a little beyond 3/4" (the instructions say going short is fine - I've read about too many builders having to take everything apart to re-trim them, so figured I'd give myself some wiggle room). I wasn't sure if I should square off the longeron or trim it to match the angle of the skin. I matched the angle of the skin - I'll find out if that was a good or bad idea at some point I'm sure. I clamped a thick plate of metal behind the longeron to protect the skin and used my cutoff wheel.
Now things are getting serious! The firewall is ready to go on. The instructions are pretty weak on this topic, so I spent quite a bit of time looking over the plans and digging up information I could find online. The firewall has steel brackets at all corners - I nested the upper brackets (bottom side right now) in the longerons and temporarily clamped the fuselage in place while I started to work through measurements and alignment.
The bottom skin has to go on to lock the fuselage distance from the 904 bulkhead into place. I drew a line down the center of the firewall aluminum angle. I'll line the holes of the bottom skin up with this.
The bottom skin is thick! I suppose that's comforting since I'll be stepping on it. I lined up the aft end and clecoed the two rows of holes through to the 904 bulkhead (that's the big gold bulkhead that the wing spars mate with). After I took the picture I actually went ahead and put clecoes along the sides as well to do my best to keep it all fairly square. The front edge has two rows of holes - one for the aluminum angle on the firewall and one for the stainless flange itself.
I lined the holes up with the center line of the aluminum angle and drilled one hole on each side. For now that's all I need to keep the firewall in place. The nerve wracking step of drilling the longerons to the steel brackets is next. No screwing up there! The weight of the firewall makes the longerons sag a bit, so in order to keep it all aligned I put rivets into the skin/longeron holes (bottom of the picture below). You can't use clecos at this stage because the steel firewall bracket is pressed up against the inside of the longeron. The rivets can at least keep the skin and longeron in place while I drill the bracket.
