Baggage area O2 tank attachment points and dimpling

As I was getting ready to prime a batch of fuselage parts, I devised the attachment for the O2 tank. I decided that the best way to secure it would be horizontally - there's really not much structure on the tailcone bulkhead or the side skin to attach vertically, and I didn't want to install it in the tailcone because battery fire + O2 tank = death. This does mean losing some baggage space (about 7-8"), but I also added nutplates before the tank area so that I can make a steel cover to isolate and protect the tank, letting us still put baggage on top of it, and preventing the baggage from hitting the tank (or most importantly, the tank head/fittings which are more sensitive).

I used 6 7/8" acrylic disks to get the tank tie-down structure the right size, and measure/mark the bolt holes on the floor. Finding the right position for the bolt holes that wouldn't interfere with the underlying ribs took some trial and error, but I managed it:

O2 tank attachment parts in place for reference

To reinforce the attachment of those bolts, I made some doublers from .064" aluminum, and drilled them for the AN4 bolts and nutplates:

O2 tank attachment doublers under baggage floor

To further make sure that reinforcement would hold, I cut the corners of those and bent them to form flanges, making them stronger in two more axes. The size and folding of the brackets was carefully calculated to avoid the underlying ribs and stiffeners, which is also why one of them faces the other way (notice the line of holes for the rib) and to avoid the overlying side cover, one of them also has more machine-countersunk holes for flush rivets than the others:

O2 tank attachment doubler with the nutplate for drilling and corner removed

O2 tank attachment doublers with flanges bent

Final form of the O2 tank attachment doublers, clecoed to the floor

After priming, then, I dimpled all the parts for this section:

Dimpled baggage area parts

Next comes painting the visible parts, riveting the doublers, and installing the Clickbond attachments for conduit, while I wait for the 5" GripLockTies to come out/arrive so I can secure the conduits before riveting the floors down to the fuselage. (I tried getting a few 8" ties, but they're too wide/tall for the Panduit attachments)

Time lapse:

Total baggage area rivets: 36
Total baggage area time: 33.2h