Electrical

OK, so technically this is the summation of a few really short work sessions, none of which (until today) seemed worth writing about, but I guess in the end it comes to the same general conclusion, which is that I haven’t done much in the past week or so. I really need to make my transition to my summer schedule, by which I mean getting up early on the weekends and getting as much done as I can before it gets stupid hot out in the hangar.

In any case, I just put up with the heat around midday to get some measurable progress done on this switch console. I’d been putting this job off, figuring it’d be not much fun to do – after all, the harness end for the console is tucked over by the right gear tower, and will only have a short stub coming out of the tower. Good makings of some tight-quarters work.

Eventually I bit the bullet, put all the supplies and tools I needed in the fuselage, laid a few 2x4s on the seat ribs, and climbed in to get to work. And like most tasks on this build that I’ve somewhat dreaded, it ended up not being too bad at all, though it was still tedious.

I did discover one issue, though…after clipping each harness wire to final length and sliding on the heat-shrink label…I had an extra label. Apparently I never did lay in a ground wire for the Flyleds wig-wag switch I put over here. This is mildly annoying, but in the scope of issues I might have run across while working on this harness, this is way on the minor end. It’s also easy to fix – rather than running an additional wire from the ground bus over to the switch console, I’m just going to tie the wig-wag ground into another switch inside the console. Since none of these are signal/audio type grounds, there should be no danger at all in combining them. This is all handy since it’s just work I have to do on the console itself, which means I can do it on the bench vs in the airplane.

Anyway, with that obstacle addressed (in theory at least; I haven’t done the fix yet), I got to work terminating all the wires with sockets, and then started loading up the connectors. The large micro-fit connector which constitutes the majority of the circuits was straightforward. The other connecter is a mega-fit, required for the higher current circuits, and here’s where things got interesting. Try as I might, I could not get these sockets to go into the connector.

Eventually I retreated inside for some research and discovered something really important…it turns out Molex makes two different series of mega-fit connectors, and the housings and contacts for each series are only compatible with that series. Well, I bought one variety of housings and pins, but got the wrong type of sockets.

Given the tight confines inside the fuselage, I think the best way to handle this is to leave the sockets I installed today alone, and swap out everything else for the TPA mega-fit hardware…again, much better to rework the stuff in the console, on the bench, vs in the airplane. But it also means I’m done with this housing for a while, depending on whether I decide to go ahead and place a Digi-Key order now (probably) or put the parts on my list for a future order.

Update: After some research, turns out this distinction only applies to the connector (female) side, so in fact all I need to order are new connector housings for the sockets I’ve already installed. This both simplifies things, and makes the resultant order more annoying since I’ll probably pay twice as much for shipping as I do for the actual parts.

But hey, at least I’ve got one nice-looking connector to show off:

Well, it was only half an hour, but half an hour is something, and I need to get back in the habit of doing something. I still don’t have the parts to finish up the switch console – Digi-Key still doesn’t have the right plug in stock. Guess I might break down and order them from Mouser or somewhere else at some point.

Anyway, I figured to quit putting off the fuse shelf. Tonight I disconnected the avionics shelf stuff and got the shelf out of the way so I could look at the fuse shelf. And I’m happy to see that my concerns about the fuse wire lengths appear to have been unfounded – looks like I should be able to route the wire bundles like I want and still reach everything. So I shouldn’t need to add a disconnect or extend anything here.

Now I just need to actually do some of this work, starting with securing the bundle to the baggage bulkhead and shelf, which will control the portion of the bundle that’ll allow the shelf to actually pivot down as needed.

Well, for some reason I went out and tried to work tonight and it clicked and I actually got some stuff done. This isn’t the only time I’ve touched airplane stuff since I last posted, but between then and now it seems like I’d touch something every now and again for a few minutes but just never seem to actually get going. Motivation is a weird thing…

Anyway, this is what I’ve been trying to tinker with for a week or so now; getting the hardware mounted to secure the wire bundle. The idea here was to have two adel clamps, one mounted to the shelf, and the other to the baggage bulkhead, which will secure the bundle in both spots and provide an area where it can flex when the shelf needs to be pivoted down. So all I needed to do was lay out and drill a couple mount holes.

But hey, that’s done now. I’ve got the clamps temporarily mounted just to check routing, but this seems good to me. I think next I’ll need to get this portion of the bundle laced, then I can start working on the rest of the routing around the shelf, which will involve even more lacing, plus just in general working out the splitting of the bundles.

(Note: the screws I’m using with the adel clamps right now are absurdly long. I need to get some that are less ridiculous, but these work for mocking things up.)

Did some more work on making the fuse shelf nice tonight. Basically I’m working through lacing up the wire bundles and getting them routed. The first part of this was pretty easy, just lacing up the main trunk as it enters the shelf through the adel clamps I put in place last time. From there I needed to think about splitting the bundle as needed, so I ended up sitting in the fuselage for a bit splitting off the four branches (one for each side of the two fuse blocks) and arranging the entire bundle so that each branch could split off fairly cleanly.

From there, I got as far as pulling out the first branch for the essential bus, then lacing up the rest of the trunk as it passes down and along the other side of the essential bus, with the individual leads branching out of the trunk. Terminating these will come later; I figure I’ll deal with that after I get the routing taken care of.

Starting to look more organized, but still plenty to do:

Before I continue lacing over towards the main bus, I need to decide how to handle the dual power leads for the seat heat circuits. In most other spots, I did window splicing down in the harness for split leads like this, but here I brought both power leads all the way to the fuse blocks. Notably, I also did this with the com radio circuit; there’s a lead for the remote radio as well as the actual panel. In that case, it’s easy to handle since they’re small gauge wires; I’ll just combine both wires into the terminal. But that’s probably not doable for the 14AWG seat heat wires, so I think I’m going to need to work a window splice into the harness here. That should be a fun one to work out with the heavy wire…I’ll probably want to do a test run on the workbench before I try it on the real harness…

Well, between the late summer heat and multiple things to do around the house today, I didn’t get a ton of time, but it’s still more than I’ve done in a day for a while, which felt pretty nice. I think it helped a bit to be able to tune in the OSH arrival audio on LiveATC while I was working…a bit of a reminder of what I could be doing with this plane in a year’s time if I can keep my work ethic up.

Anyway, first step was continuing with lacing and branching out the fuse block bundle. Last time I’d gotten as far as the end of the essential bus, this time I got the rest of the run all the way around the main bus, with all the individual circuit branches separated as needed. I did run into a couple iffy wire lengths, which resulted in me shuffling some circuit assignments around, but nothing really troublesome at all. I just made sure I was updating my schematics as I made those decisions.

It’s not the great to look t, but here’s the bundle all routed around the main bus. With the branches sticking out every which way it’s still pretty chaotic:

Next was the real fun: starting to terminate the branches. I only got as far as on side of the essential bus, which consisted of four whole circuits, but the results are pretty satisfying:

Since the individual wire runs are pretty short, I had to keep the heat shrink labels minimal, which is why they’re only labeled with the block position. The main purpose of the labels here is so that if I ever have to disconnect anything here, I can reliably reconnect the runs to the proper fuses. Actual identification of the circuits will come from a little table I plan on printing out and attaching to the open area of the fuse shelf – it’ll be pretty similar to how cars generally have a diagram and key to identify which fuse is which.

I’m looking forward to getting the rest of these terminations done – just seeing that one side of the block, I think this is going to look really slick when it’s complete. Of course, probably no one but me will ever see it again once the airplane is done, but at least I’ll get to enjoy the satisfaction of good workmanship.

In other news, I got my Mouser order in, which includes the Molex housings I need to complete the switch console plugs. Probably something to look at once I finish with the shelf. After that, I need to worry about getting the ground bus installed and all the terminations done…once that’s complete, I think it’ll be about time to try powering some fo this stuff up, which will be a nerve-wracking exercise…

Again, not a ton of time out in the shop today, but I didn’t need much to finish terminating all these branches and make things all nice and shiny. Just lots of trimming, stripping, crimping, and heat shrinking. But this mostly finished up the shelf, with the exception of adding the actual power feeds from the engine compartment. I guess I could go ahead and pull those feeds and just leave them unterminated on the forward firewall side, though I’d also need to order the right terminal lug for heavy-gauge main feed wire; I don’t have that on hand right now. But all that will be relatively simple compared to this somewhat tedious work.

Anyway, enough talking, it’s time for photos. As probably mentioned before, the branch circuits all exit the shelf on the right side, and from there split off into a few smaller bundles going to different fuse block spots. I like how neat this all ended up, though a really picky part of me wants to shorten up that M5 wire (rightmost branch on the top-right bundle). Pretty sure I can live with that, though…

Note: all the securing of the bundles here is temporary. That’s likely obvious where the bundles are secured with twist-ties, but that also applies to the zip ties; I used those where I needed the bundles held a little more securely while working in here. When this is final-assembled, the bundles will be wrapped in silicon tape anywhere a zip-tie is used for security, to prevent the zip-tie cutting through insulation.

So yeah…I can’t exactly point to a lot of shop hours this weekend, but I like what I have to show for what time I had.

Since I finally got in the parts I needed from Mouser, I figured tonight I’d revisit the switch console where I got hung up a while back. I got the sockets all installed in the plug housing, and did a test fit with the console. So now it’s all hooked up:

While working on that, I noticed how some of the lacing on the harness trunk along the baggage bulkhead had moved around. I think when I originally did the lacing on the harness, I didn’t really snug the stuff down very well, or else the bundles tightened up while being moved and installed. In any case, I decided to redo some of that lacing where it was clearly too loose. For all I know the new lacing might move around eventually too, but at least it looks better for now.

What to do next? I feel like I’m in a weird state where I have plenty of small things to do but somehow it’s hard to decide which to work on at any given point. Well, tonight that thing was the OAT (outside air temperature) sensors. The Dynon OAT sensors connect to the ADAHRS units; this is why I have two to install (one per ADAHRS).

I’ve been sort of thinking for a while about exactly where to locate these. Some folks really like to put them out on the wings, but I didn’t want to deal with the wiring to make that happen. Second-best choice seems to be back at the tail. In this area, there seem to be two locations that people use; the first is on one side of the fuselage, under the horizontal stab, the other is on the aft most bulkhead, so the sensors are inside the empennage fairing.

I kind of liked the first idea from the perspective of keeping the exterior of the aircraft clean (plus not drilling more holes in my skins), but there are a couple potential issues with that spot. The first is that as the name of the sensor indicates, it really is supposed to go outside the aircraft; the idea is to read the ambient air temperature. Arguably, the area inside the empennage fairing isn’t really getting warmed by anything, so the difference might be trivial in most aircraft, but I expect to have the tail painted a dark color, which means there’ll be a good chance of significant solar heating of this area.

So it seemed that outside was the place to go. Next question, where back here? My strong desire for symmetry made me want to put one sensor on either side of the fuselage, but I didn’t like the consideration of dealing with the wiring for this – specifically routing one pair of wires from one side to another, in a way that it wouldn’t have a chance of interfering with the elevator push tube, which will pass through here. So instead I just put both sensors over on the right side.

That just left making the holes; laying them out far enough down to be away from the longerons, and properly spaced apart. Next was feeding the wires for each sensor through the hole, then feeding the nylon washer and nut from the backside and getting the sensors snugged in place:

Then I fed the wires forward, where they’ll run alongside the elevator trim and tail light wires. A look at the backside of the sensors through the aft deck:

Then I got to re-lace the wire run I put together a while back, adding the OAT wires to the bundle:

Next up I’ll need to get these terminated at the ADAHRs units. Which is another decision point; both sensors came with a lot of wire, pre-terminated with micro Molex pins. So I have a choice of either retaining the full provided wire length, which means coiling up and properly securing several feet of extra wire, or trimming and re-terminating the wires…assuming I even have the micro Molex pins on hand. I think I do, but I’m far from sure, and I didn’t check before coming in for the night. I’m leaning towards the latter just because my desire for neatness will be offended by coil of wire just sort of hanging around.

Another thing I did tonight was to finally commit to removing my fuselage rotisserie fixture. After thinking it over a lot, I don’t think I’ll need to roll the fuselage over again, and I want to have access to the firewall so I can start working on stuff there. First and foremost will be getting the ground bus installed and doing all my ground wire terminations, but there’s also adding the wiring passthrough hole on the right side. Once that’s done, I can pull through the harness bundle, then feed the ignition coil connectors back through into the cabin, and finish lacing up the harness section that’s waiting on that bit.

All that is to say, here’s the first look I’ve had at the bare firewall in quite some time:

Alright, time to start thinking big-picture. Electrical stuff is fun and all, but I need to start thinking about working on the canopy at some point. This matters because the brittleness of Plexiglass is directly related to temperature – the warmer, the better. Basically, I don’t want to find myself starting on canopy stuff when it’s getting colder outside (of course, “cold” in Houston is very relative).

So what I’ve been thinking is that I want to get most of the electrical stuff behind the panel done, and then pretty much pause that work and move on to the canopy. Practically, my general plan is to get the ground terminations done at the firewall, do a final inspection, and do the ceremonial first power-on of the panel. Once that’s done, then I’m going to break out the Plexi.

Tonight I was looking at the grounding. First up was getting the ground bus block installed on the firewall. This block provides a bunch of 1/4” tabs on the interior side for my individual grounds, and a big fat lug on the firewall side for grounding to the battery. Practically, mounting it is easy, but I’ve spent a lot of time worrying about inadvertently putting it somewhere that will cause problems down the road when I get to working on FWF stuff. But after a lot of studying the FWF drawings, I decided on a spot and did the deed tonight.

Interestingly, as provided the block only provides one usable mount hole, where the big ground lug goes through. I didn’t feel this was enough for secure mounting, so in addition to the main lug hole, I added a smaller hole at the other end, where a #6 screw and nut keep the thing from rotating. So now I have the bus block mounted in place:

Next up was looking at the routing of the big bundle of ground wires. I laced this bundle up on the bench a while back, but like a lot of the lacing work from then, things seem loose – the individual laces like to move around. So as I’ve done other places, I pulled the bundle out of the gear tower and re-laced the whole thing. With that done, I should be able to get it in its final routing next time out, and start doing some terminations. None of this will be too complicated, but there are a lot of wires, so I’m just going to be doing a bunch of trimming, labeling, and crimping. Plus there’ll be a bit of work figuring out how to secure the bundle, but I have a pretty good idea how I’m going to approach that.