To get the longeron lines to align with the holes, I had to deburr/trim the top edge a bit, since it fits underneath the mid-cabin deck:
Mid-fuselage skin top edge, flush against the mid-cabin deck
With this, I match-drilled the skins to the longerons:
Match-drilled right forward fuselage longeron
Match-drilled left forward fuselage longeron
I then clecoed the forward side parts in place, including the forward side skins, and final-drilled/match-drilled all the holes:
Forward fuselage side parts in place (except for the skin)
Forward side skin, match-drilled to the understructure
All forward fuselage side parts in place
Upper channel match-drilled into steel firewall support bracket
While drilling the firewall bulkhead, I had a small alignment problem - the longeron was slightly too long and pushing the flange forward, making the holes not align - so I had to do those later, after trimming the longeron:
Misaligned holes on the firewall bulkhead flange
Longeron pushing the firewall bulkhead forward
Trimming the longeron forward tip
We also drilled the longerons to the gussets, which was slightly challenging since the pilot holes are in a tiny corner and "upside-down" - at least 3 hands required:
Match-drilling the longeron gusset holes
Longeron gusset match-drilled into longeron
Longeron gusset holes (very tough location to match-drill from below)
Another challenging (actually impossible without modifications) hole is the forward-most hole in the forward fuselage channels:
The right-most hole is impossible to drill or later rivet (upper fuselage channel)
Same impossible hole on the lower fuselage channel
For this one, apparently I will need to trim some of the firewall side angles for access - I wish I had realized this while still building the firewall.
I drilled all the other holes, which includes all the channel to firewall bracket holes:
Firewall bracket match-drilled from upper fuselage channel
as well as the floor to lower fuselage channel:
Floor panel match-drilled to lower fuselage channel
With almost all the drilling done, it's now time for a lot of deburring and countersinking, then primer and dimpling.
Time lapse:
Total fuselage side skin rivets: 0 Total fuselage side skin time: 60.4h