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

Vertical stabilizer completed, again

In my first tech counselor visit, quite a while ago, they identified that the rear spar caps in the vertical stabilizer were not properly deburred (not surprising, it was the first part I ever made):

Vertical stabilizer's poor deburring from 2014

After much hesitation, I decided to redo that rear spar and its attached parts, so I had a lot of rivets to remove:

Vertical stabilizer skin rivets to remove

For the 1/8" rivets that attached it to the ribs, I had to remove them through the shop head, but that turned out to work well with exactly the same technique - drill to some depth, break the head off, and then the actual rivet hole is evident to finish drilling:

Vertical stabilizer attachment to middle inspar rib being removed

After just a few minutes (easier than I expected), I had the whole thing off:

Old rear spar removed from the vertical stabilizer
I got the new parts from Van's, and got to work like it was 2014 again:

New rear spar being drilled

Since I already have the completed tailcone, I skipped ahead and final-drilled the VS rear spar into the tailcone now, so I could countersink the bottom holes and prime the whole thing:

Rear spar attached to the tailcone

Rear spar match-drilled and bolted onto the tailcone
Like before, I added a nutplate for the grounding strap, slightly closer to the brackets this time:

Grounding strap nutplate

After primer, I riveted everything back together:

Rear spar riveted together

Vertical stabilizer completely riveted again

The holes that attach to the middle inspar rib got cherry rivets (CR3213-4-2) instead:

Cherry rivets attaching the middle inspar rib to the rear spar
Overall, the results were a lot better than before (who knew, 5 years of building experience makes a difference :) ):

New (left) and old (right) rear spars

Time lapse:

Total vertical stabilizer rivets: 350 (I didn't count repeat rivets again, so no diff from last time)
Total vertical stabilizer time: 76.1h

Experimenting with paint for the interior

Even if I go with one of the many interior cover options, there are several parts that are still exposed in the fuselage's interior, which will need to be painted. I wanted a matte gray tone, and wanted something that I'm likely to be able to buy more of later (e.g. for touch-ups or future mods), so I picked up a few spray cans at Home Depot to test them out (and it's surprisingly hard to find spray paint without primer). I applied them on the bottom part of the baggage floor so it's not visible later:

Various paint types tested on the bottom of the baggage floor. Left to right: Rust-oleum chalked country gray, Rust-oleum chalked aged gray, Rust-oleum pro dark machine gray, Behr Chalk classic noir

I liked the 3rd color (dark machine gray) best, but it's unfortunately quite glossy (notice the reflection of the can on the paint), so I'll likely go with the first one (country gray) instead. The other two were matte but too dark or too light.

Large batch of fuselage primer

We primed quite a few parts from various fuselage sections (and even some from the empennage attachment, and for rebuilding part of the vertical stabilizer):

Various fuselage parts after scrubbing with Prekote

Primed fuselage parts on the floor (ran out of space elsewhere)

Primed fuselage parts on the workbench

Primed fuselage parts on top of the fuselage

This unblocks a ton of work, so expect many more posts in the near future.

Time lapse:

Total time: 6.5h (but I'll count it towards each section instead)

Empennage attachment progress

I'm going back to finish section 11 in order to be done with all the tailcone drilling before attaching it to the fuselage, since it'd be quite a bit harder to do afterwards.

I installed the rod end bearings into the elevators:

Rod end bearing attached to elevator

I then attached the elevators to the horizontal stabilizer to match-drill the bearing into the elevator horns:

Elevator attached to horizontal stabilizer

Both required some adjustment (loosening up a half turn of the rod end bearings) for the bent-edge blind rivets not to catch on the rear spar rivets, but it was fine after that.

I attached both at the same time to drill the pushrod attachment bolt hole at the bottom:

Elevator horns attached to horizontal stabilizer bearing

Both elevators attached to horizontal stabilizer

Drilling the pushrod attachment hole on the elevator horns

I then removed the elevators and match-drilled the horizontal stabilizer to the tailcone:

Horizontal stabilizer aft holes attached to tailcone

Horizontal stabilizer forward holes attached to tailcone

Horizontal stabilizer attached to tailcone

Since I'm also working to rebuilding part of the vertical stabilizer, I also match-drilled the rear spar into the tailcone:

Vertical stabilizer rear spar attached to tailcone

I removed and put away the HS and VS, and will prime the shims on the next primer batch. After that, the next time I come back to this session will likely be for the final attachment.

Time lapse:

Total empennage attach rivets: 40
Total empennage attach time: 20.8h

Wing attachment started

There's a bit of fabrication in section 44 before actually attaching the wings, so even though I'm not in the hangar yet, I got started with that.

I final-drilled the wing root fairing stiffeners:

Wing root fairings with stiffeners attached
and also fluted the fairing supports into the right curve, then final-drilled them:

Wing root fairing supports

I had hoped to use the TCW tech fittings for the fuel line exit hole, but detected that it'll cause interference with the lower wing fairing root support, so another solution will be needed (which may mean trimming both the fitting and the root support a bit):

Interference between TcW tech machined fitting and lower wing fairing root support

I also trimmed the flap pushrods to the desired length, but that takes some tuning after the wings are on, so I can't finish it yet.

With this, the rest of the section has to wait until I'm ready to attach the wings, much later.

Time lapse:

Total wing attachment time: 4.5h

Control systems progress

After primer, I riveted and installed the idler arm:

Riveted idler arm

Installed idler arm

and reamed and installed the brass bushings:

Control stick bases with reamed brass pushings

I also drilled the pushrod ends (not yet primed):

Pushrod with hole template attached

Main elevator pushrods drilled for the rod ends

Main elevator pushrods with rod ends and bearings
I attempted to drill the pushrod end for safety wire, and failed miserably - the 1/16" drill bit is just too thin, and it broke in the drill press, destroying the material around the hole and leaving drill bit bits buried into the part :/

Failed attempt at drilling safety wire hole

I ordered a new one, re-drilled the tube into it, and drilled the safety wire hole again - by hand, this time, so I could feel the pressure on the bit, and it turned out to be surprisingly well-aligned:

Safety wire hole through rod end

Next steps are priming the longer pushrods and installing the whole thing. As of this writing I don't have the tailcone attached (and don't have the horizontal stabs or elevators attached to that), so I can't adjust their length just yet.

Time lapse:

Total control system rivets: 9
Total control system time: 10.2h

Baggage area mods

In order to reduce interference with the ventilation holes at the top tailcone bulkhead, I used different patterns for the inboard nutplates - one is slated so I only have to trim a small part of the vent flange, and the other is a single-lug nutplate facing away from the vent:

Alternative nutplate holes to accommodate vent holes
I cut out the baggage floor inspection panels near the step sites. I had originally hoped to use the Airward baggage inspection panel, but that just doesn't fit (you'd think they tested it?), and they didn't bother replying to my email, so those went to the bin and I used the parts from the stall warning inspection panel instead:

Positioning the baggage floor inspection panel doubler to not interfere with the stiffener

Cutting out the baggage floor for the inspection panel

Baggage floor inspection panel

Baggage floor inspection panel with doubler in place

Baggage floor inspection opening

I also made an opening for conduits - the space between the right baggage cover and the skin was just not enough unless I wanted to remove part of the rib flanges underneath, so I did that through the rear seat floors:

Marking for the rear seat floor conduit hole

Rear seat floor conduit hole

Rear seat floors with conduit holes

Conduits through the rear seat floor

I drilled the corresponding holes through the rib, and used some right-angle Panduit mounts (RAMH-S6-D) for routing it aft, attached with LP4-4s:

Conduit holders through the rear bulkhead

Conduit holders in place

Conduit holders in place

Riveted conduit holders

Riveted right-angle conduit holders

TAS antenna conduit path through the bulkhead

Conduit holders riveted on

For running the static pressure tube, there was, fortunately, enough space on the baggage floor, so drilled a 3/8" hole for a snap bushing, and used another Panduit mount for routing the tube:

Hole for the static line to go through the baggage floor

Right-angle mount to route the static line

Bushing for the static line to go through the tailcone bulkhead

Static line fitting through the tailcone bulkhead

I also did all the required deburring, so I can now prime and start riveting the floors.

Time lapse:

Total baggage area rivets: 24
Total baggage area time: 22.8h