Joshua's RV-9A Project

Finished up the wing skin riveting tonight (excepting the nutplates for the inspection covers).  I’m clearly not as good of a left-handed riveter, as I managed to put an ugly ding in the right wing bottom skin by slipping off the bar.  Sigh.  Smoothed it out a bit and will either leave it alone or use some filler before paint to level it.

Cleaned the shop up and made room for the wing attach, hopefully coming up this weekend.  The rudder & elevators were removed and stored, then the fuselage was turned into the center of the shop and leveled in both axes.  Measurements were taken, and it appears that there is enough room to fit the wings without having to clear the piles of stuff from the side walls.  The canopy was also removed, as it would hit the garage door opener if opened fully, and having it off will give better access for leaning over to reach the spar bolts.

Next step: read up on what needs to be done prior to the wing attach (so far: trim rear spar stub, trim fuel/vent lines, and some sort of marking for the root fairing holes…what else?)

Continued riveting the right wing bottom skins…got through about 2/3 of the outboard skin before calling it a night to avoid annoying the neighbors.

Finished the left wing bottom outboard skin, and riveted on the right bottom inboard skin.  Clecoed the right outboard in place for the next session.

Started work on riveting the wing bottom skins.  Finished the inboard left, and half of the outboard left, so the left wing is 2/3rds complete.

Shop time has slowed considerably as the beginning-of-the-year crunch hit hard at work; a number of different need-it-now projects for different constituents, and I come home feeling wiped and not really motivated to do anything but nap after dinner.  Hopefully with a concerted effort to head out for at least a bit on most nights, forward motion can be maintained.

Ran another cable in the right wing conduit for the OAT probes, that had been left out in the previous bundle.  This terminates at the middle inspection panel, as I thought that would be better than placing it at the outer panel with the bellcrank and autopilot servo…keeps the wire away from the controls that way.

Put the nutplates and cable wear blocks on the baggage wall halves and set them aside.

Clecoed the inner bottom wing skins to the rear spar.  I need to look up and see what pattern others have found works for riveting the bottom skins.

Worked against the weather today to get the wing skins primed.  While the spray gear was set up, the baggage wall pieces were primed and painted, as well.  Thinning the Rustoleum paint has been hit-and-miss, and today’s batch was a miss…I think it was thinned out too far, and the panels ended up with very heavy coats to get the coverage needed without pinholes…they have a different look than the rest of the interior; for now, we’ll let it go, since there are other inconsistencies, and these panels can easily be pulled out, stripped, and repainted later if it becomes bothersome.

Also finished wiring the internal parts of the wings, trimming the wires to length and crimping on the connectors for the landing lights and the D-sub for the autopilot servo, and terminating the leads to the pitot heat control board.  I later realized that I have not yet run cable for the OAT sensors which will be installed in the right wing to feed the EFIS boxes.  I also epoxied some zip-tie bases to the underside of the seatback bulkhead for holding the headset jack wires, and installed the baggage light strip under there as well, using it’s built-in adhesive strip.

Neighbor Jeff stopped by to check on the progress; it’s been awhile since he’s seen the project.  People who see it now say it looks like an airplane.

A collection of things happening in the shop today.  First thing up, finish the canopy sealing.  The excess Sikaflex was rubbed off the exterior of the top skin and the inside of the rear window and canopy (from gluing the spacer gaps), followed by removal of the rear window spacers and insertion of sealant into those gaps.  Smoothed those over with tongue depressors and all looks good.  Some canopy work remains, of course, but the plexi is in place (which was the big summer goal).

Before the gear can be put on the fuselage, the wings need to be fit, which was skipped earlier in order to get the canopy done in the warmth of summer.  In order to do that , the wings will need to be finished (bottom skins riveted on, which means that they must be wired and plumbed).  Out came bottom wing skins, which needed edge deburring and a few dimples made.  After those were done, the skins were etched for priming along with the rear baggage wall; unfortunately it was too windy to prime until after dark, so that’ll have to wait for another day.

Cleaned up the inside of the wings, which had naturally collected a layer of shop dust and spiderwebs, and set about running the various wires and tubes for the in-wing systems (pitot heat, lights, strobes, AOA, and autopilot).  Everything except the pitot tube was run inside the corrugated conduit which was installed during the wing build.  A hole was drilled in the conduit near the aileron bellcranks, to permit wires to emerge for autopilot and pitot heat; once these wires are in position, some RTV can be used there to prevent any chafing on the conduit edge.  The control module for the heated pitot was installed on the rib near the bellcrank inspection hole, which should allow access to hook up the pitot wires later on.  The pitot tube was secured underneath the aileron bellcrank with an adel clamp to prevent interference or chafing.  All the wiring and tube will terminate at the wing root in connectors, to allow the wings and fuselage to be fully wired in the shop, and easily joined at the airport later on.

Installed the rear window today; not a big deal, after the learning that happened on the forward canopy.  Masked the lines, scuffed, cleaned, primed.  The back of the plexi was primed where it contacts the inside of the top skin, and a thin bead of Sikaflex was laid onto the plexi between the screw holes and the mask line (which marked the skin edge).  The window was lifted and slid into place, and when the screws were installed, there was squeeze-out of sealant around the line, which was the goal; this should keep water from entering via that route. The squeeze-out was tooled down and the tape line pulled, which gave a clean edge; the excess on the outside of the skin will rub off easily tomorrow.

With the rear edge screws in, spacers were inserted between the roll bar and the plexi, and sealant was placed between the spacers.  The spacers were inserted from the front edge, rather than from behind the roll bar, both for ease of removal, and because it allowed for filling in the entire joint on the aft side of the roll bar and tooling it smooth.  This time, the tape was pulled in the tack-free time window (less than 50% humidity today, which helped), and everything turned out alright. While the sealant was out, the spacer gaps on the front canopy were filled in and tooled.

Pillows are a necessity when working inside the fuselage, especially when trying to reach odd angles, or curled up in the baggage compartment.  And laying a 2×4 across the fuselage, spanning the longerons, provides a solid place to sit when working on the canopy or roll bar, and can be stood on as well, which puts the rear bow of the canopy at a good working height when it’s fully open.

After the gluing was done, I spent awhile cleaning up the shop, which had become a disaster area during the canopy work.  What a difference a broom and vacuum make.  Tomorrow I should be able to pull the spacers and fill the gaps on the front, and the canopy will be done, save for the skirts (and sanding the front fairing, but that’ll be later on after it’s had more time to cure hard).

Popped out the the shop after dinner to investigate the progress of the canopy.  The Sika datasheet indicated that cure time for a 4mm bead at 50% RH would be around 24 hours, so I poked at it a bit and determined it looked safe to open the canopy.  No problems there; it has set up quite nicely and appears to have a very firm grip on the plexi.

Unable to resist, I decided to futz with the thing, removing the spacers and cleaning up the Sika joints.  True to what has been said by others, the Sika rubs right off plexi or bare aluminum where there is no primer applied.  The interior paint is a different story, and the Sika appears to have a good grip on that too; this applies to the rear bow where I had to re-smooth the fillet after the skin pulled off.  I’ll rub on it some more after the spacer gaps are filled in and the masking tape removed, but the worst case would be to sand down the smeared areas, mask the canopy, and re-spray the rear bow.

The front cleaned up better than I had hoped; the really awful parts were mostly on the bare plexi, so they peeled and rubbed off.  The remainder actually looks pretty decent — a little bumpy in spots, and not perfect, but I’m much happier with it than I was last night.

As it sits now, the canopy is prepped for filling in the spacer gaps, so I will try to set the rear window and fill these gaps in one session, then fill the spacer gaps in the rear window in one final shot.  I think I should be able to get all that with the remaining tube of sealant.

Today was the day, decided to jump in completely and glue the forward canopy.  A trip to the store was required first, to pick up some 400-grit sandpaper to do the final polishing of the edges, along with more masking tape and electrical tape to set the edges of the primer and sealant.  I also found some long, skinny plastic nozzles that looked like they would work for laying the bead in the tight angles at the front of the canopy.  (Hint: they’re not with the caulk supplies, they were in with the concrete-anchor type stuff, apparently these “mixing nozzles” are made for epoxying anchor bolts into slabs…they come with a spiral mixing thing in them, but it pushes out readily with a nail.)

Before gluing the canopy, I decided to fit the canopy latch lugs to the frame, so that was done, and they were temporarily bolted in place.  I set them so that the latches apply just a slight down-force on the canopy, which will hopefully compress the weatherstrip nicely and seal the gap between the frame and the canopy deck.

On to the gluing…First things first, sand the edges to their final smoothness.  I was going to trim the aft edge of the canopy back, but since all the fitting was done the way it is now, and I’m happy with the fit, I decided to leave the edge where it is, and sand it back once both front and rear plexi are glued in place.  Once the edges were smoothed (which goes faster than I expected, perhaps because I already finished them with 220-grit), I set the canopy in place and laid out the sealant lines with electrical tape: inside sides and back, as well as the outside front on both plexi and aluminum.  Then the canopy was removed for taping the inside front line on the plexi and aluminum.  Both surfaces were roughed up with scotchbrite and cleaned with acetone (on the aluminum; a dry paper towel sufficed for the plexi).  Sika cleaner was applied according to the directions, and allowed to dry.

Once the Sika primer goes down, you have a 2-hour window to set the glue, so a lunch break was taken before starting that part of the job.  The primer is definitely very black, and is supposed to be laid on in a single coat, without any second coating; I had read from others to be wary of brush marks, so I loaded the brush and laid on a good solid coat on both surfaces.  It took a few strokes to get the feel for it, which is why I started with the inside front area…that part doesn’t show through the plexi like some of the other portions.  The primer is left to dry for 20 minutes, and when it dries, it has an almost rubbery appearance and texture.

With the primer set, the canopy was lifted into place and adjusted to match the alignment marks made in 4 places during the earlier fitting (since the rear window was removed to allow entrance and exit to the cabin, the canopy can’t be aligned to that anymore…)  Once things were aligned, 1/8″ spacers cut from vinyl tubing were inserted around the perimeter, and the side skirts clecoed in place to hold the canopy in alignment.  The rear bow was clamped to the roll bar using the 7/8″ spacer blocks made during the fabrication process.  The Sikaflex sealant comes in cartridges for a caulking gun, and the sealant was pumped into the space between plexi and canopy frame from inside; the spacers are left in place for now; later they will be removed and the gaps filled with more sealant.  I had modified a stack of tongue depressors to have the radius I wanted on the sealant, so I used those to tool the joints, and had it looking quite nice.

Next, I climbed out of the fuselage to lay the bead on the front outside of the canopy, which is essentially a ton of sealant squirted out and then shaped into an overly-thick fairing.  Later, once it cures for a couple weeks, this will be sanded down to the needed shape and profile for the front canopy fairing, but for now, I squeegeed it into an approximate shape.

This is where the Sikaflex learning curve comes in.  With all the sealant in place, I cleaned up the tools and my hands, and climbed back into the cabin (that’s an interesting task, through the rear window opening…) to pull the edge tapes.  Doing so, I found to my chagrin that the sealant had already skinned, and the skin was being pulled and stretched along with the tape, the other edge of the skin remaining attached to the canopy frame.  So much for my nicely-tooled joints…I smoothed the skin back down as best I could, though the front inside of the canopy I fear will be rather ugly, since it’s difficult to get good access in that area to re-tool the joint.  Later, reading the documentation again, I discovered what went wrong…the 1-hour tack-free time (which I was barely within) is given at 73 degrees and 50% humidity.  The sealant cures via moisture, and today was upwards of 80% humidity (not to mention over 80 degrees).  Hence, the tack-free time was shortened.  Alas, the only casualty was to the aesthetics of the beads, and my pride.  The next plane (ha!) will be perfect, right?