Harness detail planning

Posted on April 19, 2021 by pclifton

This was a longer day than the hour count suggests; while I didn’t put it down as shop time, I spent several hours this morning running several parts orders. Some connectors and wiring supplies, both the charge ports I’m going to use, plus some other goodies like wiring tools and a 30A 12V power supply. Right now I only have a 10A supply, and I’m looking towards the time when I’ll want to power up a fair amount of the avionics at once, and 30 amps should do the trick nicely.

As far as shop stuff, I started out by ripping out all the fun stuff I installed yesterday. Seats are back in their box, floors and flap stuff are back on the shelves, and so on. Then I wanted to get the CO monitor box mounted on the baggage bulkhead. The spot I was intended worked out nicely, so I just had to drill a couple holes. Even better, I had enough spare hardware from previous work so I could mount this immediately without having to wait for anything:

And then it was time to get down and dirty with harness planning. The overall intent was to take the line drawing I did a while back and 1) refine all the despited branches and groupings and 2) give each branch an actual length so it could be turned into a harness. The general idea for doing this was to run ribbon through the aircraft and use that to simulate wiring runs. I started by just running a single long ribbon along the longest continuous harness path – that is, starting back at the tail, going under the baggage compartment and seat floors, up the right gear tower, across behind the panel, back down the left gear tower, and to the firewall.

The original plan was to then add individual ribbon runs for various branches, but I decided that was overkill. Using that long run as a baseline, I marked up all the major junction points, and then made individual measurements along branches and to components and wrote those down. By using a tailor’s measuring tape, I could pretty well simulate curved paths branches might take. And at the end of the day, none of these branches need to be millimeter-precise or anything. While I’ll probably assemble the bulk of the harness on the table, I don’t intend to do any actual terminations to complex lacing until the whole setup is installed in the plane. So when measuring branches, I was just conservative with my lengths, with the expectation that I’ll trim to final length in place in the airplane.

The decision to terminate everything in place comes down to a couple points: first, I don’t really trust that I’ll get every measurement exactly right, no matter how careful I am, especially compared to seeing things in place. Second, since significant portions of this harness will have to be carefully threaded through the fuselage, I think it’s to my advantage to not lace a bunch of stuff up and compromise the flexibility of the thing. It remains to be seen exactly what the results of this decision look like…

Anyway, after a whole lot of marking up my line drawing, it was time to pull the long ribbon out and take my last batch of measurements, between the various junction points I’d marked previously. Kind of impressive to see all ~20’ of ribbon stretched out in a straight line, though I imagine it’ll be even more impressive when there’s a wire bundle this long:

And for the final exhibit, here’s the heavily marked-up harness line drawing, which was the main product of today’s work:

Next up, I get to put together a similar layout on my big work table, which is where I’ll be starting to actually put things together. This is when the fun will really begin. I also need to take a final pass through my schematics, I have a couple punch-list items to address there before I actually start routing wires. I think I also need to make some final decisions on what my grounding scheme for everything will look like. I know I’ve planned to do local grounds out in the wings for the landing and taxi lights, but I think most everything else I’m going to end up taking to a single ground bus on the firewall. I should probably get rigorous with the schematic and give each ground-bus item a discrete tab label so I’m sure I’ve got enough terminals up there.

Posted in Avionics, Electrical, Fuselage | Hours Logged: 5

Assorted detail wiring prep stuff

Posted on April 18, 2021 by pclifton

Now that was a good solid day’s work, which is exactly what I wanted. Since I haven’t taken much in the way of vacation time over the past year or so, I’ve got a ton of time saved up, and with no plans to go anywhere any time soon, I decided to just take myself a two-week staycation. My intent is to go bananas on airplane work, and today was the kickoff day.

The general idea is to get going on these wiring harnesses. I’ve got most of the big ideas in place from previous planning, but there were still some details to work out, and that was my focus today. Overall, the day’s work was kind of all over the place, but that’s honestly my comfort zone when it comes to abstract work like this, sort of taking it all in and working on things as they come to me. Anyway, the main stuff remaining to finalize were locations and/or wiring runs to: both seat heaters, both control sticks, charge ports front and rear, rear headset jacks, and the ELT antenna.

The ELT was the first thing I looked at, figuring it’d be fairly straightforward. My plan has been to mount the antenna on the right rear armrest, with the antenna curving around the bulkhead above the seat. Locating this antenna on an RV-8 is a little interesting; there’s not much in the way of exterior skin space that’s usable. On top of the tail would be a traditional location but the sliding canopy means almost all that area has to be clean. The old 121.5MHz antennas would go well underneath the empennage fairing, but the newer 406MHz antennas are too long.

Anyway, remember how I thought that’d be simple? Well, the antenna seems like it needs to be mounted at an angle to make that work, and I never could settle on how I wanted to do that, and eventually I sort of quietly moved on to something else, namely the seat heaters. Figuring out where to route the harnesses seemed like it really required that I have the heaters installed so I could see where the plugs would sit…so I pulled out the seats and heater pads and got to work.

These pads are kind of cool; they’re trimmable (in one dimension, at least) to fit inside the seat cushions. The pads for the setbacks didn’t need any trimming, but the bottom cushions definitely needed some work; I trimmed those both for length, as well as cutting a slot in each to allow the harness crotch strap to pass through. Here’s one of those pads, marked for cutting, but with me taking a photo and trying to put off the point where I started chopping off parts of these non-cheap (but not stupid expensive, though) pads:

Of course, I wanted to test out the pads as well, so for both the front and rear seats, I laid the cushions out on the workbench, attached the pads to the provided wiring harness, hooked them to my power supply, and cranked the heat. Yup, they get nice and warm. Hey look, another photo!

In practice, I’m not going to actually use the harnesses shown above. As provided, the heater system provides a switch with off/low/high positions, and makes use of a bulky relay to do some of the switching. I’m going to be ditching that entire setup and just controlling the heat level using a couple of PWM dimmers. Before I could do that, though, I needed to figure out how the wiring would work, which meant reverse-engineering the heater harnesses. Turns out, at the end of the day, it’s pretty simple: with the switch on low, the two heater pads are connected in series, and with it on high, they’re in parallel. Thus on high they draw about four times the current and get warmer. For my setup, I’ll just be wiring them up in parallel, since I want the highest PWM setting to correspond to maximum heat.

So there…seat cushions with harness pigtails. Next up was a whole lot of installing the seats, moving the pigtails around, scratching my chin, removing a cushion or two, thinking some more, reinstalling, etc. Most of the thinking here revolves not so much around being able to connect stuff, but wanting to keep the harnesses as hidden as possible, while still allowing for serviceability; the seats are going to come out on a semi regular basis, as are some of the covers in the vicinity that are involved. So kind of a lot of thinking forty steps ahead.

That was the main thrust of the day, but just to list some other stuff I was considering:

  • How to handle stick wiring. Will the grip pigtails come out the side of the stick? Where? How will I allow the rear stick to detach?
  • Where do I want the rear headset jacks to go? My initial idea was unworkable. I think I’ll end up putting them on the right armrests, but not 100% sure. I’m going to go looking for ideas tonight.
  • Oh hey, I didn’t even account for wiring the flap motor in my harness diagram. Oh wait, how will my up limit switch work? Do I need/want a different control system?
So while actual work in the shop is done for the night, I’ve got a whole list of research topics, which will probably culminate in some part/component orders. Which sounds like it could be a hangup for wiring progress, but I don’t think it is. All of today’s work was just leading up to pulling ribbon through the fuselage so I can work out all the assorted branch lengths for the harness. With the exception of the charge ports and headset jacks, I’m pretty much at a point to keep going with that.
 
So, let’s see what tomorrow holds…
Posted in Electrical, Fuselage | Hours Logged: 7.5

Finish kit inventory and cleanup

Posted on April 14, 2021 by pclifton

Just more menial stuff tonight. I got the hardware bags inventoried – a task that I thought was going faster than expected right until I got to the bags with mixed rivets in them. Nothing like spending 30 minutes of your life examining every member of a pile of rivets to determine if it’s 1/4” or 9/32” long. I may be a bit cross-eyed for a few days…

Once I was sure I had everything from the inventory sheet, I cleaned up the giant pile of packing paper. I probably could have crammed it all into the bed of my truck as it sat, but I’d have felt like a jerk pulling up to the recycling center and having everyone trying to cram these giant balls of paper into the baler. So I at least got the stuff bundled up so it can be handled pretty easily. Should be able to haul it off mayor be Friday.

Now I guess I should get back to wiring type stuff.

Posted in Uncategorized | Hours Logged: 2

Finish kit is here!

Posted on April 13, 2021 by pclifton

Yup, it’s the big day. The finish kit showed up this afternoon, and with some help from my neighbor and fellow RV-8 builder, the crate was in the hangar and cracked open in no time. This evening I couldn’t resist diving into the inventory, which really didn’t take all that long – there aren’t a ton of parts here. I stopped short of inventorying all the little bags of stuff, though, which I’ve learned is usually the more time-consuming part.

In the meantime, I have the requisite giant pile of packing paper, which made for a good backdrop when I posed for the traditional wheel-pant-as-headgear photo:

Posted in Uncategorized | Hours Logged: 1

More random assembly stuff

Posted on April 11, 2021 by pclifton

Busy day with assorted stuff, but I got a little bit of time in. I hadn’t yet reinstalled the components mounted on the baggage bulkhead, so I got that stuff in place. This also involved reworking my stacked mount for the EMS and ARINC interface, since previously I decided to reverse the orientation of those. There was also the question of where to mount the Aithre CO detector; I figured out the general area but didn’t work on getting the holes drilled yet. I also reinstalled the hard brake lines from the gear towers to just above the rudder pedals, along with the ducting from the cabin air inlet to the vent in the panel.

One thing I looked at a bit was where to mount the converters needed for my capacitive fuel level sensors. I’m pretty sure I want to mount these on the side skins near the fuel tanks, but I’m not exactly sure where. I think, for the purposes of wiring, I’ll probably just run the wires for these to the general area, and leave enough extra material to finish the connections out once I have the tank mount stuff in place.

Other remaining housekeeping stuff to do is to figure out how to do the plug for the removable rear stick, as well as finalizing routing for the wires to the seat heaters, particularly the rear seat. Oh, and I need to figure out what power plugs I’m going to use and get those ordered, so I can get them mounted. Gotta figure out where the wire drops for those will be…

Posted in Fuselage, Panel | Hours Logged: 1

ELT switch, panel assembly

Posted on April 11, 2021 by pclifton

OK…time to get back towards wiring harness stuff. But first there was that pesky ELT switch that I totally forgot to mount before. Fortunately, I figured out yesterday that I had room for it on the right sub panel, so tonight I got that hole laid out, cut, and the mount holes drilled. That done, it was time to start putting stuff back together again. So as of now, I’ve got both the shelves back in place, and all the stuff installed in the panel again. Which, of course, means I can finally get a look at what my real-live panel will look like. Well, mostly, it’s still not painted or labeled…but anyway:

So yeah, a good couple hours’ work on a weekend. Next fun, I get to pull some string or ribbon or something all over the place to figure out the branch lengths for my harness diagram…and then things will really start to get fun.

Posted in Fuselage, Panel | Hours Logged: 2

Deburring stuff

Posted on April 9, 2021 by pclifton

No photos tonight, nothing especially cool to speak of. Most of the time was spent finishing the edges of the forward upper skin – filing off the little nubs from where I removed the unused sections, smoothing everything out, cleaning up the edges. I also deburred a few other remaining things that I hadn’t picked up yet, namely the baggage hinge support and spacer.

The other thing I wanted to get a bit ahead of was figuring out where to mount the ELT remote switch. I started trying to sort of visually estimate the fit of the switch on one of the panel wings, but it was far from obvious whether or not it would fit. So I ended up using some scrap to make a little rectangular plate the size of the switch mount face, just so I could get a better idea of the fitment. That allowed me to see that yes, it’d fit over on the right panel wing just fine. Now I just have to actually make that hole…

Posted in Fuselage, Panel | Hours Logged: 1

Forward skin disassembly

Posted on April 7, 2021 by pclifton

Well, my plan to leave the skin on long enough to do a trial fit with the canopy turned out to be a bust. Mainly this was my fault too, which is kind of the best part. Originally my estimated delivery date was this past Tuesday, and as off Monday my crate was in Dallas, so things were looking up. Well, I missed the call from ABF Monday afternoon, and then when I called them back it was just past 5:00…too late. No worries, I can wait a few more days. Except when I called back the next morning, I discovered that they only make a delivery run out here once a week…on Tuesdays…and I was calling on a Tuesday. So yeah, my delivery date will be six days from now. I didn’t want to let things sit that long, so I decided just to get going with things tonight.

First up was getting these skin support ribs fitted. I went looking for info on fitting these and found basically nothing. When I’m stressing about something and this happens, it’s usually a pretty good indicator that I’m overthinking things. What was getting me in this case was that while the manual says to just put the ribs in place and match drill through the skins, there’s plenty of room for these to move around – that is, there isn’t any obvious “this is the right spot” position to work with. I decided to draw a desired rivet line on the rib flanges, line that up with the skin rivet holes, and match drill that way. A little reworking of the ribs got them to fit snug against both the skin and the base of the roll bar:

With that done, I started taking things back apart. That aft upper skin I put on just for canopy fitting? Back to storage. I also went ahead and did all the demurring of the holes I’d match drilled, on all the different parts – skin, bulkheads, flanges, spacers, etc. Plenty of that to go around.

The last real thing I want to get done here is to get the edges of the forward upper skin cleaned up. There are still some little nubs from removing the cutout stuff, which nee to be removed before I move on to the usual skin edge work. What’s going to be fun is storing this thing, because the forward right side has just this long skinny strip sticking out that seems like it’d be really easy to bend up and damage.

Also, I realized something last night about the panel, which I thought I was done cutting – I forgot about the remote switch for the ELT. I think I’ll put the over on the right sub panel, but that’s another small hole I need to lay out and cut before I can get to wiring. Should be pretty straightforward though.

Posted in Fuselage | Hours Logged: 2

Match drilling

Posted on April 3, 2021 by pclifton

Yeah, that’s pretty much it. I did all the match drilling on the forward upper skin this morning, which is basically all the work to be done here. The only other thing remaining to fitting two ribs that go between the roll bar and the aft edges of the forward upper skin. I poked at those a little this morning before moving on to household stuff, and I think I want to go read some other people’s description of these because I’m kinda not super happy with the instructions. These ribs aren’t predrilled at all, so you have to manually align them with both the roll bar and the skin, which seems to leave a whole lot of room for variance…hopefully some other builders can shed some light on this.

So yeah, that’s about it for now. I did go ahead and cleco the aft upper skin in place today too, just as part of getting ready for the trial canopy fit I want to do once the finish kit comes in. We’ll see how that goes in a few days…

Posted in Fuselage | Hours Logged: 1

Panel assembly, forward skin fitting

Posted on April 2, 2021 by pclifton

Tonight I got straight to work with the riveting on the panel parts. First up were the nutplates, by which the center panel section will attach to the subpanel “wings.” Then I got to rivet the attach strip onto the subpanels; in this case, only some of the rivets are set, specifically omitting some near where the subpanels connect on the aircraft centerline. If all of these rivets were set, the entire assembly would be made rigid, and it’d be impossible to get it in and out of the aircraft…and I’m not ready for permanent mounting yet. If nothing else, these things need to be painted…

Next up was installing some stuff preparatory to fitting the forward upper skin. In addition to mounting the panel assembly in the aircraft, I also brought the roll bar back over and temporarily bolted it into place. 

With all that in place, it was time to break out the skin itself for fitting. The manual specifically calls for removing the vinyl covering on the inside, presumably because this is a tight fit and that extra material wouldn’t be very helpful. I just want ahead and removed all the vinyl, in keeping with my general practice of just ripping the stuff of and not keeping it on like some people do. Then this skin needed some trimming – I’d removed one of the portions a while back, for reasons I don’t even recall – this was the cutout section where the skin wraps around the roll bar. Tonight I also needed to remove the section where the baggage area door will be.

With that done, and with the baggage door support strips prepped and clecoed onto the skin, it was time to attach the thing to the structure. This was a bit tedious due to the thickness of the skin and the curvature involved, but nothing too awful. Just got to be liberal with the clecos to make sure everything sits good and flush.

That got me to a good stopping point for the night, so it was just time to take some photos. It’s kind of impressive to see in person just how sizable the forward baggage compartment opening is:

It actually extends beyond the aircraft centerline:

And just for more illustrative purposes, I temporarily installed the baggage compartment floors and such to show the space available up here, with one of my milk jug cleco holders for scale. Not bad at all:

I guess next up I get to do a bunch of match drilling, though there are also a few more small parts to be installed first.. Reading ahead in the manual, I’d be removing this skin not too long after doing that work, but in this case I think I’m going to leave it a bit longer. The reason for this is that my finish kit will be here in a few days, and I’d like to at least briefly lay the canopy on top of the fuselage so I can get an idea of what area of this skin will be inside the canopy. That’s of interest to me since I intend to install both a GPS antenna and a couple of cooling/defrost fans on the glareshield, and I want to make sure I have a good idea of the space available.

Besides, it’ll just look cool, and that’s important too.

Posted in Fuselage, Panel | Hours Logged: 2.5