Center Fuselage Parts

In and around holiday events this past weekend I was able to put in a few hours on center fuselage parts. Not much to show, other than a bunch of floor ribs that have been cleaned and primed.

Speaking of priming – I found that I spend a lot of time on this step, so I’ve been looking for ways to speed this up. I am still deburring and lightly sanding parts as before, but I’ve switched up the cleaning routine. Rather than using a combo of simple green, water, acetone, and isopropyl alcohol, I’ve started simplifying to a one-step product that’s recommended by the manufacturer of the primer I’m using (SEM self-etching primer). The cleaner is called SEM Solve, which comes in a spray can and wipes off with a clean towel. So far the results are great – the primer is adhering well and the finish looks good. SEM doesn’t give guidance on how much of the cleaner you will need, but I’m finding that I need one can of SEM Solve per 4-5 cans of the self-etching primer at 3 coats of primer.

I switched to the gray primer color for the fuselage, for no other reason other than aesthetics — there are likely to be primed parts that are visible even after putting in the interior, and I think it would be nicer to see a neutral gray color instead of green.

Preparing the rear floor panel
Various ribs to attach to the floor panel
Rear spar carry-through assembly, to which the ribs above will attach to
Attaching an autopilot servo bracket to the main spar carry-through assembly. Access was really tight — I had barely enough room to get this relatively slim rivet gun into place.
Completed autopilot servo bracket

I have to put in an order to Aircraft Spruce soon, among the items I need to buy are:

  • Garmin GMU 11 Magnetometer plus connector kit
  • Garmin GSA 28 servo (x2) plus connector kit
  • Shielded twisted pair wire for the CAN connection to servos and magnetometer, as well as some normal straight wire for power & returns
  • Soundproof insulation for the interior skins (I want something more substantial than what is provided in the kit)

Anyone have guidance on how much length of wire I need to order, especially the shielded wire for the servos & magnetometer? There may be more wire I need at this point, like antenna wire for comms, ELT, etc., but I need to figure that out.

Right Wing Skins and Starting Fuselage Assembly

I consulted TAF about my damaged rear wing spar, and they advised against repairing it so they will send me a new one. That limits how much I can do on right wing assembly for now, but we had some nice weather this weekend so I decided to prime the right wing skins along the rivet lines so that they’re ready to attach. I already have most other components for the right wing primed and ready for assembly.

I occasionally like to make sure the primer is adhering well, so I perform tape pull tests after the primer has been given a day to dry. I wasn’t too happy with primer pulling up on a recent part I was working on, so I made a slight process change – instead of using Scotch Brite to scuff the surface, I’m now using 400 grit sandpaper. I think the plastic protective sheeting that’s applied to the aluminum leaves behind an adhesive residue that the Scotch Brite doesn’t quite release. Wet-sanding with the 400-grit paper and water seems to work pretty well, so that’s what I’m doing going forward.

Sanding and cleaning the skin. I’ve had some mixed results using Scotch Brite pads, so now I use 400 grit sandpaper only and have had much better results with primer adhesion.
Same skin after cleaning off the sanding residue. First I wipe off the wet sanding residue with a clean cloth, then wipe with a clean cloth with a small amount of acetone, finally wipe with a clean cloth with a small amount of isopropyl alcohol.
All primed and ready – I usually get the desired finish with 3 coats of the primer

I decided to start assembling fuselage components, starting with the ribs of the rear fuselage. Assembly of these components was straight-forward.

Rib 8
Completed rib 8 and rib 9; they come together later on in the assembly.

Left Wing Spar Assembly started

Got started on the aux wing spar late last week and into the weekend, it’s coming along pretty well.

I ran out of the primer that I was using (SEM), so I had to use some backup primer (Rustoleum) for the wing skin support bracket – it’s not as pretty, but it gets the job done. A fresh case of SEM showed up Friday, so I’m ready for more parts.

I used little sticker dots to mark off holes that don’t get rivets yet – ribs get attached to these locations in the next step. Looks like some may be tight fits to get the rivet tool into, should be interesting.

Tonight I put together these tooling jigs that go on either end of the wing structure – they call them “wing twists” in the build manual. I’m thankful I don’t have to prep and prime these!

Painting by the Garden

I have some artistic friends who would tell me that my version of “painting by the garden at night” is a little too literal

… nonetheless, my left auxiliary wing spar is now primed 😬