Alright, so it hasn’t been a great week for shop time…but that doesn’t mean nothing’s been getting done. I’ve been spending a lot of “inside time” working through all the assorted stuff that needs to be ordered. I placed a fair-sized order with Digi-Key, which contains what should be the entire array of switches for the plane, along with some other miscellaneous stuff. From elsewhere, I order a few PWM dimmers – one of these will be used to control the panel lighting, the other two will be temperature controllers for the heated seats, in lieu of the two-position switches that will come with the heat pads.

While I’m here, a quick word about those heated seats. When I mentioned these to Josie, specifically asking a usability question for the rear-seat passenger, she laughed at the idea. Who would need heated seats in this area? Well, for one thing, RV-8s are notorious for not getting much hot air to the rear seat, since there’s just an inlet on the firewall. But also, after getting some advice from folks, I’m actually going to bypass the heat muff on the exhaust for that heater inlet – that is, instead of it being a way to get hot air into the cabin, it’ll just be another fresh air vent, but fed off pressurized air from the cowling. This should be very nice for those hot summers. Hopefully the seat heaters plus dressing warmly will work for these Houston winters, but if not I can also consider connecting the heat muff for part of the year as well.

Anyway, I was talking about ordering stuff. I heard back from SteinAir on Thursday – my avionics are in! So I paid off the invoice balance (ouch), and hopefully those should be on my doorstep this week. Finally, I spent a bunch of time on McMaster-Carr and elsewhere learning way too much about quarter-turn fasteners. I’ll use these to hold my fuse block shelf in place, but allow for a quick release for servicing. I ended up ordering these fasteners from McMaster-Carr, and while I was working that order, I got to thinking about the rear stick, which will eventually bring us to tonight’s bit of work.

The rear stick is a two-piece affair from the factory, with the stick itself sliding into the base that’s attached to the control column. Back when I was working on this I drilled the 3/16” hole through both items, and added an AN3 bolt to hold it on place. I wanted a way to make the stick a little more easily detachable, so while I was shopping I started looking at quick-release pins and other options. Simple having a pin in place of the bolt seemed like a decent idea, but the one thing that got me a bit is that it’ll be sharing that space with the wires coming from the stick grip. It’s probably me being overly concerned, but I figure blindly sticking a pin through a tube containing a wire bundle might one day result in damage.

Thing was, there’s an alternative that lots of builders have done. Instead of a pin or bolt, they use these little spring clips from McMaster-Carr. They’re intended to go in telescoping poles, and provide a little spring-loaded button in two opposing holes. With one of these in the stick, it just pops in and out. The only real hangup is that the smallest size hole they make them for is 1/4”. But I decided to go with them, and tonight I drilled those passthrough holes out to 1/4” and installed the clip, so now I’ve got a slick detachable stick.

Detached:

Attached:

Of course, there’s still a remaining issue for making the stick detachable, and that’s figuring out how to make the wiring for the grip detachable. That problems existed independently of this whole button thing, though. One of the cool ideas I’ve seen for this is to simply take two mating connectors and epoxy one side inside the stick, and the other inside the socket, such that they mate together when the stick is installed. This seems nice and elegant, and it’s probably what I’ll go for, but it does seem potentially fun getting those plugs epoxied in the precise correct location. The other alternative is to have a hole in the stick above the joint, with the wires coming out of that, and mating with a connector outside the stick. Which would be ugly but also functional and simple.

Decisions, decisions…

Boy, it’s hot outside. Kind of hard to maintain motivation to get stuff done, but about the best I can do is just ensure that something is happening, even if it’s not much of something.

I started out the morning taking care of my final antenna location. Research indicated that going just aft of the bellcrank bulkhead was a fine place, so that’s what I chose for my transponder antenna. Just tabbed up another doubler and got it drilled in the proper location and orientation. So that concludes my antenna prep work for now, though I guess I could go ahead and dimple the doublers and the skin for eventual riveting.

OK, so what next? Well, I guess I can revisit the static system. I’ve done a decent amount of thinking on this the past few days; basically, what I need back here is to connect the two ports with tubing, and provide a T-junction for the line that will lead to the actual avionics. There are prepunched holes on the adjacent bulkhead for just this purpose, but…how to secure the tubing?

The official plans method is to just use zip ties, but that seemed inelegant to me. Adel clamps seemed a better option, but that would also require opening those holes up and installing nutplates. Which wouldn’t be the end of the world, but…well, something about that bothered me too. Eventually I hit one of my “stop overthinking this and just do something” points, and decided to just go with the zip tie method.

So here it is. On the left side of the fuselage (right in the photo), the T-junction is placed very close to the static port, the idea being that this will keep it more or less secured. I also cut a short piece of tubing to insert into the open end of the junction and capped it; this is to prevent the possibility of our ever-industrious mud dauber population from plugging it up.

OK…now what next? The thoughts occurred to me to maybe get my conduit runs done back here. What that meant for today was another period of staring at things and scratching my head. One topic was how to handle the conduit run into the tail. I spent some time looking at what other people have done, and it seems common to run a conduit down at the bottom of the tail, roughly on-center. But there aren’t any holes in the bulkheads for that, and it seems weird to make a whole new set of holes when there are preexisting ones, albeit not quite laid out where I want them.

Eventually, I decided that I’m not going to do conduit back here after all. My rationale with conduit is to provide routing through areas that are inaccessible, such as under the seat and baggage floors. And while the tail will be difficult to access, it won’t require removing permanent fasteners. And I’d still have to crawl into the tailcone even to access the forward end of my planned conuduit run. Finally, that planned run would result in a curved path, which would remove some of the convenience of trying to easily run new wires.

So yeah, I’m just going to install snap bushings in some of the existing holes, add a couple adel clamps where needed to support long runs, and if I ever need to add wires back here, I’ll just be crawling an extra foot or two into the tailcone to get it done.

There’s also the question of doing the runs under the seat floors. Here, I have some prepunched holes, though oddly not a matched set. The rear spar carry through has a 3/4” hole on either side, but the next bulkhead back only has one on the left side. So I’m going to want to add a hole there too, but that’ll be challenging. Put simply, there’s no way to get in here with my unibit – no room for a regular drill, and no way to chuck the unibit in my angle drill. I think what I’ll end up doing is buying a knockout punch set to get this done. Another thing that has to wait for stuff.

The other question is how to terminate those conduit runs. They need to go further both forward and aft of those two bulkheads if the ends of the conduit will be accessible. Neither termination spot is at a bulkhead, though, so I think I’ll end up making some small termination pieces that will rivet to adjoining structure. This might be one of the things I work on fairly soon.

Eventually, I got tired of all this head-scratching and needed to do something tangible again. So I took a look at the aft end of the fuselage, where there are four unfilled rivet holes on each sides. These are where the stock external rudder stops would have been attached, but since I went with the internal stop, I now needed to get these holes filled. The two aft pairs aren’t much trouble – they’re on the portion of the skin aft of the last bulkhead, and so can be easily dimpled for a flush rivet. The forward pairs, though, are in assembly with the forward flange on that aft bulkhead. I could maybe dimple those with my pop-rivet dies, but I find them barely adequate for a single sheet of material; two sheets of relatively heavy gauge seems maybe a bridge too far.

I the end, I elected to lightly countersink all the holes and install NAS1097 rivets. Since these have an undersize head compared to a regular flush rivet, I can countersink the skin without enlarging the hole. So now those are done.

Oh, I also spent some time thinking about wiring for the landing/taxi lights. A challenge to be dealt with here is that the terminals for the landing projectors are on the front side of the unit, but the terminals for the taxi light are on then back. I’d like to run these as a four-conductor bundle out to a Molex plug at the wingtip, but haven’t been sure how to do this while still making the light unit removable. I need some way to route the wires from the front two terminals to the back of the unit that doesn’t prevent removal. After a bunch of poking around, I have a plan now, involving snap bushings and some slight modification of the mounts. It’s probably better shown than explained, so that’s all I’ll provide for now. Also, it’ll be a while probably before I get that done – I need some smaller snap bushings than I have, and I’m not going to pay $8 worth of Aircraft Spruce shipping fees to get a pair of ten-cent bushings on-hand. They’ll get to wait until my next parts order.

Well…time to bite the bullet and drill some holes in my nice fuselage. I knew it was going to happen, but it still felt kind of wrong…

First up were the two comm antennas, and I started by preparing the doublers. I ordered four pieces of .040” sheet to use for these a while ago, and since then I’ve been thinking about how to form them. There seem to be lots of approaches to these doublers, ranging from people who just add a flat piece of sheet inside and call it done all the way to people who make joggles in the doubler so it can be riveted in assembly with nearby structure. Technically, the latter is best practice, but really kind of overkill for our (relatively) slow aircraft.

Anyway, my initial plan had been to make my doublers with flanges on all four sides, to maximize stiffness. But there’s one issue with that, and that’s dealing with skin curvature. Immediately behind the main spar where the comm antennas were going, the skin is flat laterally, but longitudinally it has a slight curve to it. Having a flange in line with that curve would make it tougher to get the doubler to conform properly. And realistically, both these locations are close to solid structure, so I eventually decided forward and aft flanges only would be fine. (this, by the way, is how Van’s supplies prefab doublers for RV-14 kits)

I also had to settled on the precise location for the comm antenna. Things were a bit tight here; first, there’s the location of the aileron pushrods just behind the spar, and then just behind those are the passenger footwells, which project down below the floor. So I needed to make sure I located the antenna center behind the pushrod region, but ahead of the low point of the footwells. I ended up making a cardboard template, which I used to trace the footwell profile on the outboard seat rib, and that let me lay out the fore-aft location.

Finally, there was the issue of drilling the three antenna mount holes correctly. The layout is pretty simple – three holes in a line, the center one 9/16” to accommodate the antenna connector, and the other two 3/16” to accommodate the mount studs. Spacing between the holes is 7/8”. I was a little concerned about marking and drilling all these holes freehand, so I decided to make a drill template instead.

The template just has three #40 holes, which I use to make pilot holes in the actual thing to be drilled, and then I can open those up to the proper size:

Next, I wanted to try the template our on a piece of scrap, to make sure it was correct before I put holes in something I couldn’t easily replace. Works like a charm:

Then there was just a lot of drilling, positioning, clecoing, unclecoing, etc. In addition to the three antenna mount holes each doubler has a row of rivet hole around the perimeter, with which it will be permanently attached to the skin. But eventually I got it all done, and had my comm antenna locations done:

After that, I moved on to relating this process for the ADS-B antenna, just ahead of the rear spar carry through. I still have the transponder antenna, furthest aft, to deal with…for that, I want to do a bit of research first. My original plan was to put it basically adjacent to where the elevator bellcrank lives, but now I’m thinking that puts it below the avionics shelf, which may make routing the coax cable a little interesting. So I’m thinking of putting it just behind the bellcrank instead, but the potential issue there is that the skin isn’t nearly as well-supported there.

Additionally, the curvature issue I discussed before is reverse here – it’s straight longitudinally, but curved laterally. So optimally, I’d put the flanges on the sides – and that might actually be best here, since that’s the dimension in which the skin can flex the most. I still kind of think I’d want a lateral flange at the aft end, though, since it’s far away from a bulkhead and the skin’s pretty floppy.

So once again, it’s time to go look at what other people have done. Hopefully tomorrow I can get this last doubler done, and then…well, I guess I’ll set them aside, since I’ll need a helper to get them riveted. Probably wait until the same time I finally finish the forward bottom skin riveting for that.

Eh, not much tonight. I just decided to get that last bulkhead riveted in place. Which only constitutes 24 rivets, but they’re kind of interesting to access with a squeezer (or anything else), so yeah, it really took an hour to get them done.

That’s all.