I’m only calling this one shop hour, even though I’ve spent a whole lot longer over the past two days with this stuff. This is just me drawing a (somewhat arbitrary) line between being out in the shop doing stuff vs. sitting inside with a laptop researching until my brain turns to jelly. If I logged all the latter time I’d probably be close to 2000 by now…
Anyway, the shop time mostly revolved around continuing to play around with component locations. I’ve ended up adjusting things a bit more, though I don’t have any photos of tweaked layouts this time around. The first big change was to the lower shelf. Even though moving the CPI2 ECU off of it made it less crowded, I still wasn’t really happy, and I eventually decided to relocate the voltage regulators to the baggage bulkhead, which turns the lower shelf into basically just a fuse block shelf.
The nice thing about this is that I can move the block around a bit and make the layout a lot more logical – which I count as a win, as the essential-bus architecture can be a bit weird at first. The new layout will better visually show what’s going on. Another benefit is that I don’t have to make this shelf as wide as possible any more. Instead, I can make it just as narrow as the upper shelf, and not worry about it interfering with the gear towers, and also bring wire bundles up around the ends instead of having to go through the shelf with a snap bushing.
Now, the downside to this change was that I needed to move the Skyview backup batteries off the baggage bulkhead. Packaging these was proving to be a pain, since they were kind of wide and flat…but then I came up with the idea of stacking them and putting them right beside the CPI2 backup battery. They’d be no taller than that battery, and have half the footprint. I figured I could just cut some aluminum tube spacers to go between the top and bottom batteries, but the thought of finding the necessary hardware (ie some long screws) was interesting.
But then I came up with an even better idea – mounting the two batteries vertically. I can pretty easily fabricate a small vertical “wall” of sorts, and then just have one battery on each side of it, and instead of needing long spacers and longer screws, I can just use short screws and nuts. It doesn’t really save a lot in terms of footprint, but it’ll be a lot more elegant.
It’s actually kind of bothersome to me that I can only work this stuff in hypotheticals, using little cardboard mockups and imagination. I’d really like to have this stuff on hand so I can do some real packaging work! But it shouldn’t be that much longer – at this point I’m planning on making big purchases probably around the end of August. I don’t know what kind of lead time I can expect on avionics orders, but hopefully I’ll have a lot of this stuff on hand by mid-September.
In the meantime, I can be focusing back on airframe stuff…like the wings. This whole systems planning odyssey came from me wanting to get materials to wire up the wings, and not wanting to make a bunch of piecemeal wire orders, and thus feeling like I needed to at least rough out systems stuff so I could get an idea of wire materials needed. I think at this point I’ve kind of surpassed that…but it’s so much fun…
This leads to the major effort of the weekend, which was just doing the grinding required to gin up a bill of materials of sorts. I did some rough measuring in the airframe of expected wiring distance between various locations – avionics shelf to panel, shelf to switch console, console to underseat (where wing wiring terminations will happen), back to the rear shelf and to the tail, etc. This was information I could use to rough out wiring distances between various components.
A lot of the wire runs are pretty simple. Network and serial data wires can all be plain old 22AWG white wire. Power wires are a slightly different matter – here you can picture me spending a few hours refreshing my knowledge on wire sizing, and working out the proper gauges for power supplies. And there’s also multi-conductor shielded wires for certain applications. All of this information then got applied to the distance chart I’d made earlier, and the end result being a big list of wire types/gauges and required lengths.
The end result comes out to a total of a little over 1300 feet of wire, of various sizes, types, and colors. I’ll end up ordering more than that – I figure that on average, adding about a 15-20% buffer is a good idea. I’d definitely rather have too much than too little, especially when it comes to the super-common 22AWG white stuff.
I also spent a bunch of time researching tools, and ended up ordering a few more crimping tools, some tools for inserting/removing pins in D-sub and Molex connectors. Still left to do is to work out a starting order for connectors. The easy part will be D-sub connectors, backshells, and pins – this list is pretty well dictated by my equipment, and not long. The one thing to consider is that I want to have service connections on the upper forward shelf, which will probably be D-sub, and I’ll need to plan those out. I also expect to use some Molex connectors in a few select places as well. I don’t expect to get that list 100% right off the bat, but I at least anticipate using them at the wing tips for connecting the pitot heat/lights/etc. Got to think that one through a bit.
One final end result that I’m strongly considering is to redo my electrical schematics kind of from scratch – an idea I do not take lightly, as I’ve invested a ton of time in them already. But the current ones are divided into various sheets mainly from a functional standpoint – one sheet for power distribution, one for all the simple switched stuff, etc. I think what will serve me better as I move towards building up harnesses will be sheets divided by physical location – so the forward upper shelf can be one (or more) sheets, and can depict the service connectors I want to add. These sheets should be a lot simpler to translate into harnesses, and also more useful for troubleshooting down the road. I probably won’t start this immediately, though, since the layouts will depend on final packaging, which I don’t expect to nail down until I have all the avionics on hand.
Anyway, that’s the weekend in a nutshell. Not a lot to show in terms of hands-on stuff, but I feel like I’ve gotten a lot done, and I’m definitely getting excited about systems stuff, despite the challenged involved.