Prepping for fuse riveting

Well folks, it’s almost time to go back and do this fuselage riveting that I’ve been putting off for so long. Today I wanted to go review the construction manual and get familiar with what needs to be done, with the idea being that when Josie is able to help me tomorrow, we can focus on shooting rivets instead of me having to spend a bunch of time staring at plans and stuff while scratching my chin.

This actually took a decent bit of time, just by virtue of me triple-checking everything. In particular, I couldn’t figure out for the life of me why we hadn’t already riveted the row along the forward side of the center section. I even went back and read through all my old build log posts about the fuselage riveting, and that led me to the amusingly obvious answer – whereas the rivets on the aft side of the center section only go through the belly skins, the forward row also rivets in assembly with the forward bottom skin – which is exactly one of the components we’ll be riveting tomorrow.

Anyway, basically what we’ve got for tomorrow is to shoot a few rivets on the side skins, that row along the center section, and then the forward landing gear crossmember. Then we get to install the forward left and right side skins, shoot a few rivets in each one of those, and add the cooling ramp. There are also a bunch of fish screws at the base of the gear towers that I’ll probably recruit her help with.

The other thing I’d like to get done tomorrow will be riveting all the antenna doublers. I still needed to get the rivet holes in the lower skin dimples for this, and doing this meant getting out the old pop rivet dimpler. It’s not my favorite tool at all, but it gets the job done when nothing else will. I ended up recruiting Josie to help with this too, since it’s a lot easier with someone on both sides of the skin.

So I think we should be set for an afternoon of riveting tomorrow. Hopefully we can get it all done tomorrow, but if not I think we can maybe bleed into some weekday evening sessions as well. And then I guess I won’t have any excuses left for not getting busy on the main wiring harnesses…

Posted in Fuselage | Hours Logged: 3.5

More fuse shelf stuff

Yep, more work on the fuse shelf. Today I drilled the mount holes and installed the nutplates for the e-bus diode. I considered also going ahead with the holes and nutplates for the assorted adel clamps that will secure the wires here, but I think I want to wait until I have the wire bundles mostly in place before I do that, just to be sure I’m locating everything well. No real reason to commit just now other than the general desire to make holes in things.

Instead I decided to go ahead and make the short jumper wires to connect the diode to the two fuse blocks. Hey look, things are, like, connected!

After that, I set about working on the quarter-turn fasteners used to secure this shelf. As originally installed, these are just a bit too long for the application – they’ll grab the receptacles OK, but I didn’t like how easy they were to disengage – seemed like they might be prone to coming loose with vibration. My original fix for this was to just slip some small o-rings onto the fasteners, and that did indeed snug them up nicely – but the o-rings also got squished out and fell off the fasteners in short order. Obviously not a satisfactory solution.

So when I placed my last order with McMaster, I got some new retaining rings for the fasteners (these are one-time use items, no good way to remove them without ruining them). For spacers, I just used some thin AN4 washers. Actually, I originally tried regular AN4 washers but they were too thick. Fortunately I was smart enough to only do this to one fastener before testing. This still took a few iterations of test-fitting the shelf in the fuselage, though.

Then I decided it was high time to get the fuselage prepped for finishing the bottom skin riveting that’s been put off forever. So I set about removing all the stuff I’ve been working on these past weeks – the upper shelf with its stuff, the panel and supporting structure, and all the baggage bulkheads/floors/panels and attached components. Oh, and the control column came back out too. Don’t want that flopping around when I roll the fuselage upside down again, after all.

Finally, I revisited the aft mount points for my two under-floor conduit runs. Some time ago, I secured these runs using zip-tie mounts attached to the lower skin with 3M VHB tape. Most of these stayed put, but I guess I had a little too much tension on the aft mounts – probably I was trying to stretch the conduit a bit to try to straighten it and make running stuff easier. In any case, both the zip-tie mounts unstuck from the tape squares. So I removed the old tape (which definitely had plenty of adhesion to the aluminum), cleaned the area, and re-stuck two mounts. This time, though, I didn’t immediately secure the conduit to the mounts – I’ll let those set up for a day or two first, and this time I don’t think I’ll try so hard to pull the conduit tight.

And that was a good half-day’s work. I need to go dig out the manual pages for the riveting so I can refamiliarize myself with what needs to be done. I also need to get some dimpling done on the antenna mount locations, where the doublers will attach. That’s going to be a fun job – I think the only real way I can do those is with the little pop-rivet dimple dies, and those aren’t the most fun thing in the world to use. Got to be done, though…

Posted in Electrical, Fuselage | Hours Logged: 3.5

Fuse block mounting

Quick little jaunt in the shop this evening – it cools off pretty quick after dark, and I guess after seven years Houston has fully transformed me into a warm-blooded creature. Anyway, I just finalized the fuse block locations, drilled the mount holes, and got the nutplates installed. Probably could have gotten the e-bus diode done too, but the soup I chucked in the Instant Pot for dinner was done at that point, so I retreated into the heat.

Posted in Electrical, Fuselage | Hours Logged: 1

Fuse shelf planning and such

Alright, time to figure out some stuff with this fuse shelf. Shouldn’t be that hard, right? After all, I’ve already spent untold hours scratching my head and conceptualizing the layout and all sorts of stuff. Surely all I have left to do is finalize it all…surely…

First up was answering the question of whether using screws from above to nutplates was an OK choice. I mentioned last time I was wondering if this might be problematic with my knees being in the same area. So I brought over the low sawhorse, dropped the fuselage off the rotisseries setup, and temporarily installed the seat floor and front seat. Sitting inside, it was quickly evident that I had nothing to worry about with the nutplates. Even if I stretch my legs out as far as they can go, where my feet touch the firewall, my knees were just barely even with the back end of the shelf, and way below it. If I pull my feet back so my knees stick up further, my knees are completely behind the aft cabin brace, and thus totally clear of the shelf. I don’t think it’s physically possible for my knees to touch the bottom of this shelf.

OK, good deal. Next up was the question of attach screws for the fuse blocks. The original screws I bought for this have heads that don’t fit into the recesses in the blocks. The screws I bought to remedy this have the wrong thread. I could go searching for the perfect screw for this job…or I could just modify the ones I have. As you might guess, I went with the latter; the screw heads were only about 0.03” too large, so it was pretty easy to just grind them down a bit so they fit in the recess.

Alright, just solving problems left and right, time to nail down the component positions and get some holes drilled! Well…not exactly. It’s incredibly hard to visualize the routing of all the wire bundles here, and I felt like I really needed to work that out before committing to anything. At one point I decided to get some Romex I had lying around, pull the individual conductors, and use that for trialing the runs. But that didn’t seem to help that much, and in fact just made me more unsure about the whole setup. The problem was always the same no matter what I tried: there was a lot of stuff going a lot of directions and not a lot of space to make it all work.

This led to me doing a few research sessions, and after lots of poking around and thinking I decided to do some rearchitecting. Basically, the decision was to relocate some components off this shelf – specifically, the battery bus fuse block and the endurance bus alt feed relay are going to move forward of the firewall. This is actually good from a safety standpoint, since it means there won’t be an always-hot wire entering the cockpit, which would have been the case with the battery bus inside. That wire would, of course, have been fused, but it does still pose the possibility of a spark in the cockpit in case of an accident.

Anyway, removing those components vastly simplifies the fuse shelf. Instead of two power feeds that have to go several directions and join at the e-bus, now there are just two fuse blocks, two power feeds, (one for each block), and the e-bus diode tying the two together. This allows for super simple routing, and also leaves lots of room for the other bundles to be routed cleanly.

I did still go with my Romex routing idea, just to better visually represent things:

Here we can see the main bus block on the left, the e-bus block on the right, and the diode tying them together. Entering at top left are the two power feeds; these will be a fat 6-ga wire for the main bus, and a smaller 10-ga wire for the alternate fed to the e-bus. Individual circuits from the two blocks will route around the perimeter, along the lower (ie aft) side, and back up on the right before exiting at upper right.

One seemingly odd thing here is that the components aren’t centered on the shelf. This is actually intentional, and is done to support the need for the shelf to pivot. The wire bundles entering/exiting the shelf will be close to the pivot point, but they’ll still need to twist a bit to allow for movement; with that in mind, I need to make sure I provide a long enough “unsecured” run on each to allow for the twist. This is why, at both corners, there’s a plain plastic loop at the edge, and an adel clamp further inboard. Both bundles will also have an adel clamp just outboard, mounted to the baggage bulkhead, so each bundle will be snugly clamped in two spots about 4” apart, with just the loose loop in the middle to keep the bundle clear of the shelf edge.

So that’s pretty much the final layout; by the time I got to this point it was a bit late, and I want to sleep on this before I commit to actually making any holes, even though I’m feeling solid about this, far more than I was with previous iterations.


Posted in Electrical, Fuselage | Hours Logged: 3.5

Baggage bulkhead component mounts

Well I sort of took a lazy approach to today, but did still get out and get some stuff done. With the upper shelf done, that left me with two things to attack: either the baggage bulkhead or the fuse shelf. I ended up going with the former, mainly because it was a lot more straightforward.

I already had all the component locations here laid out and marked a while back, so there wasn’t a lot of decision-making involved. Really the only thing missing here is the CO detector, which should be here this coming week. That’ll only need a couple screws, so no worries there.

I also decided to take a different approach to mounting these components. Instead of going with the nutplates like I did for the upper shelf, here I went with a sort of home-brew stud mount approach. My motivation here was twofold: first, to avoid having a lot of nutplates and screws sticking into the forward baggage compartment, and second, to hopefully make working with these components easier in the future, since I could slide them into their stud mounts and add nuts.

The idea here is to just drill the mount holes, and install screws from the compartment side, with thin jam nuts and star washers to lock everything together. Then the component just slides over the ends of the screws and nuts hold them in place. The end results leaves the baggage compartment side looking nice and clean:

Everything worked out pretty well, but I did have to make one change: I was only able to get 2” long machine screws for the EMS/ARINC stack mount, and those weren’t quite long enough to accommodate things as they were. But I had some margin between the two components, so I just shortened my four spacers a bit to tighten everything up, and now things site nicely:

I guess now I’ve got to figure out what to do with the fuse shelf. I ran into an issue with my mount hardware previously – the long #10 screws I got for the fuse blocks have heads too large to fit into the recesses in the blocks. So with my last hardware order, I added some smaller-head screws…except when they came in, I discovered I’d inadvertently ordered #10-24 coarse thread screws, instead of the -32 I needed. So…can’t use those with the nutplates I have.

I’ve kind of thought about doing my stud mount thing here as well, since anything sticking off the bottom of the fuse shelf will be where my knees go. I’m not quite sure how big of a deal this is, so before I decide to go fancy here, I think I’m going to put the fuselage back on the sawhorse so I can climb inside an evaluate how close my knees might get to the shelf. If it’s not super close then I’ll probably just keep it simple and go with nutplates.

Posted in Avionics, Electrical, Fuselage | Hours Logged: 2

Upper shelf complete

Well, in terms of structure, this thing is done. Tonight was just attach points laid out and wrapped up.

The shelf attaches to the two forward braces, both of which have a Z-shape profile. At the forward end, the horizontal part of the shelf lays on top of the middle of the brace, while at the aft end, the vertical part of the shelf sits just behind the brace flange. The forward spot was pretty easy; I laid out the holes, drilled them, and installed the nutplates. The attach hardware here will be AN3 bolts; way stronger than needed, but these mount holes will double as attach points for the adel clamps that will hold the wiring harness trunk.

The aft end was a bit more interesting. Since the shelf and the brace mate in a vertical plane, that means there’s no natural support for the weight of the shelf unless the screws or installed. My intent is for this shelf and all it components to be removed as a unit for service, which would probably make this a cumbersome choice. So I decided to add some support tabs on the shelf, to allow it to rest naturally in place even with no screws installed. Some scrap Z-bracket material from the fuel tanks worked great for this; I just made two small angle tabs and attached one at each end:

Then it was just the same routine of laying out the screw holes, drilling, and getting the nutplates installed. Here I’m just using #8 screws, which is probably about all I could manage anyway, as there’s a lot less material on the flange as opposed to the center of the brace.

So here it is, the shelf installed in the fuselage:

And a different angle, showing the forward attach hardware. I added the adel clamps just to give an idea of what the wiring routing would look like:

I’m kind of wondering if I should use screws here instead of the bolts. My thought with the bolts was that using a screwdriver deep behind the panel and up against the baggage bulkhead would be unpleasant. But getting these bolts started through the adel clamps isn’t exactly fun either. For now I guess I’ll stick with this, and see how much I hate my life when the time comes to install this shelf for real…

Posted in Avionics, Electrical, Fuselage | Hours Logged: 2.5

Upper shelf buildout

Well, at some point, it comes time to stop looking at devices mocked up on a shelf and actually start making some holes. I decided to make today that day for the upper shelf. This was mostly uneventful, just lining stuff up, drilling mount holes, and getting nutplates laid out. The one dumb mistake I made came while I was doing the mount holes for the Skyview backup battery mount – I’d unwisely left multiple drill bits lying around, and instead of grabbing the #21 for a #8 screw, I used the #12 for a #10 screw…so yeah, that’s now mounted extremely securely with four #10s.

With all the nutplates installed, it was time to add stiffeners. I’d been holding off on these until all the mount stuff was done, since they necessarily had to work around those nutplates. I decided to add two longitudinal stiffeners, roughly evenly spaced, plus another lateral stiffener right beside the CPI2 backup battery (the heaviest thing on this shelf by a good margin).

The stiffeners I made from some .032” sheet I bought a while back, using the cheap Harbor Freight bending brake I also bought a while back. This was a much nicer way to make this bent stuff than the hammer forming I’d been doing before. Then it was just time for more drilling, dimpling, and finally riveting. The finished product can be seen here:

Then I figured I ought to do a test mount of everything, you know, just to make sure it all fit up OK. Seems pretty decent:

Now I’ve just got to get this thing where it can be mounted in the fuselage. Just got to lay out a few more screw holes and get the matching holes and nutplates installed on the forward braces.

Posted in Avionics, Electrical, Fuselage | Hours Logged: 5.5

Hardware order

Yes, really, that’s what I spent three hours doing today: looking at all the components I have to mount and conjuring up a list of needed hardware. It’s mildly amusing that this is at least the second time I’ve carefully considered components and ordered stuff…maybe this time will do the trick? In fairness, I didn’t find some new stuff I needed for mounting the CPI2 ECU, and I also changed my approach to mounting some other stuff.

Anyway, in the interest of thoroughness, I made a list of every component I needed to mount, then made a list of every piece of hardware needed for each component, checked against what I had on hand, a noted items as either on-hand or needed. Then I got myself another good-size Spruce order going.

Along the way, I was gradually pulling apart the temporarily laid-out shelves and stuff, marking component locations as I went. My intent here is to remove all the stuff up in the forward fuse, and get things cleared out to get the remaining two-person riveting done, hopefully on one of the two upcoming long weekends. Separate from that work, I’ll be able to start doing mount holes for various components on the shelves and baggage bulkhead.  That should get me set up to actually start building those harnesses like I’ve been talking about for a while now.

Posted in Avionics, Fuselage | Hours Logged: 3

Panel harness layout, again

It’s kind of challenging sometimes to keep a positive attitude right now. Even though I’m rationally aware that the stuff I’m doing is progress, emotionally it doesn’t seem super productive spending time standing around staring at things, grunting sporadically, and maybe sketching on a whiteboard from time to time. And that’s pretty much how I spent today, just really try to think about how to best route all the wiring runs behind the panel. Along the way, I changed my mind about some stuff…again. Sometimes I’m never quite sure if I’m being indecisive here and going in circles questioning myself, or actually refining things over time. I’m pretty sure it’s the latter, but the human brain sure is a pesky thing sometimes.

Anyway, the one big decision I made was about how to route the wiring runs going forward of the firewall. I’ve always been planning to bring the main power supply cables in through the left side of the aircraft, through a prepunched hole, but then there’s all the sensor connections and so forth. My working plan had been to route this bundle just inside the deep part of the forward baggage compartment – this would keep the wires from being exposed to potential damage in there.

But the more I considered the logistics of this, the less sense it made. Most notably, trying to work out the harness junction over by the right gear tower would be challenging, but also, I’d have to figure out how to get that bundle to turn a really tight corner to head for the firewall, which would mean also getting liberal with adel clamps or something to secure the bundle. The real kicker, though, was this – keeping the wires out of the baggage area to avoid damage seems good, but instead putting it right beside where my feet will go every single time I fly maybe isn’t such an improvement.

Now, there is a stiffener riveted to the side skin about halfway up from the floor, but it doesn’t stick out too far. Still seemed like this was a potential spot to route the bundle, and keep it protected and somewhat out of sight. Question was…how big would this bundle be? Kind of an important consideration. So I gathered up some of the preexisting harness pieces that would make up this bundle – the eight thermocouple wire pairs and the CPI2 bundles for the coil packs and crank trigger sensors. The only thing missing was for the other engine sensors…OK, time to go refer to my schematics. Turns out this is simpler than it seems, and all those sensors only require eight more wires. This was starting to seem manageable.

Finally, I checked the harness pieces I had against a snap bushing, and found one that they went through with plenty of room for a few more wires. Overall it looks like the bundle will be 1/2” to 3/4” in diameter. Very manageable for this spot. Really, the only thing to work out is how to secure the bundle. There are a couple of options here, but so far I’m leaning towards adding another piece of angle to create a protected space for the bundle…or I might just put some of my ample conduit supply here, just not sure the best way to secure it.

That can wait, because even if I don’t know the exact solution I’ll go with, I’m sure it’s a solvable problem, and all this head-scratching was just in service of figuring out where the harness would split back by the gear tower. Between this decision and a few other similar (but less complex) machinations, I finally got to a point where I felt comfortable expanding on my harness diagram, to cover the entire area behind the panel:

This lays out the general architecture back there: the harness will split somewhere near the right side of the upper shelf, with one bundle serving the components on the shelf, baggage bulkhead, and panel wings (the righthand branch), and another serving the removable center panel. That latter will need some kind of allowance for a service loop, so I can pull the center panel out and disconnect everything for, well, service. Of course, even as I write this, I realize that I forgot a few components here, but nothing that majorly changes things.

The one conclusion I’m coming to here is that it’s probably high time I stopped trying to envision the entire harness in my head, and started actually stringing wires and solving problems in the real world. Which means that I absolutely need to get off my butt and finish the fuselage riveting that I’ve been putting off for so long. Once that’s done, what I think I’ll do for the harness is build up the portions between the tail of the aircraft and the top of the right gear tower, and pull that through the fuselage. For the rest, including all the behind-the-panel and firewall-forward portions, I think I’ll be better off building the harnesses in place, rather than trying to carefully measure each one of those branches above and prepare harnesses on a table.

In the meantime, I can still go ahead and get components mounted to the shelves and baggage bulkhead, in addition to doing the cutting on the wings. But I still feel like I’ve got to stop putting off the riveting work. That’s sort of the elephant in the room that’s roadblocking real progress.

Posted in Avionics, Electrical, Fuselage | Hours Logged: 3

Panel harness layout work

So tonight was about starting to figure out what the harness behind the panel ought to look like. It started with sitting inside and looking over my schematics, with the main goal being to decide whether to not I wanted to add in disconnects for certain modules (like the center panel or the upper shelf). After doing a bit of thinking and tallying up pins that would be needed, I decided that adding those disconnects wasn’t worth the effort. I think the main benefit of doing a single disconnect would be simplifying the service loop needed to allow removing the panel, but at the cost of more planning, more parts to order, and more wire terminations that could be a source of issues down the road.

With that decision made, it was time to start making a go at the layout. I decide to try and do some sort of iterative whiteboard work, sketching out the layout and visualizing the interconnects between devices. The idea is just to layout the paths that wire bundles will have to take, not to detail every single wire. The end result I’m going for is a diagram like the one I drew a while back for the harness to the tail of the aircraft – basically just laying out the wire runs and nodes, which I can then turn into measurements that become the baseline for harness building.

This, in turn, made me rethink some of my wire routing decisions. Initially I’d expect to have significant wire bundles exiting the upper shelf on both the left and right – on the right side would be power/ground connections, plus the beginnings of the run to the aft fuselage, and on the left would be the firewall forward runs, for the engine management system. The main hangup with the latter is that I intend to run the CPI2 FWF harnesses just inside the forward baggage well, to keep the wiring runs manageable. I think it makes more sense to run all the FWF EMS runs through that point, rather than splitting them up. That will leave me with just two firewall penetrations for wiring – the CPI/EMS one we’re talking about here, and one on the far left where the main power feed from the battery will enter.

I think this will be good for packaging behind the panel as well. On the left side I’ll have some SCAT tubing to feed the fresh air vent, which would potentially make routing a decent size wire bundle more interesting. By taking the bulk of the wiring off the left side, this makes things a little simpler. There will still be some wiring over here, but it’ll be limited to a pair of coax runs (for the radio and GPS antennas) and a few wires for fuel pump power and the left tank level sender.

Anyway, the end result of this was some fairly indistinct whiteboard material. Probably this entire diagram will go away and I’ll start over again, because while it decently depicts the interconnects between boxes, I don’t think it’s going to work for depicting the actual harness layout. I expect to end up with sort of two horizontal “trunks” – one that represents connections being router from the far right across assorted boxes, and another that links all the main panel stuff (and this can include the aforementioned service loop).

So at a glance it kind of seems like wasted work, but I think it did wonders for helping me get a better rental image of how things will go together here. I’ve just gotta do a lot more drawing…

Posted in Avionics, Electrical, Fuselage | Hours Logged: 1.5