Fuselage

Console wiring, wing wiring penetrations

Posted on October 18, 2020 by pclifton

Back at it with the console today. With all the wires pinned, next up was positioning the heat shrink labels and getting them shrunk. That was a bit fun trying to hold the wires where I could heat one at a time without accidentally shrinking one that wasn’t ready. Also, this printable heat shrink stuff is awesome, I’m loving this as a way to label things.

Anyway, with that done, it was time to start inserting the low-current pins into their connector housing. Continuing with a recurring theme, there wasn’t anything especially challenging here, just tedious. With both connectors in place, it’s gradually looking more organized:

Next up, time to break out the lacing and get everything bundled. Now it unequivocally looks organized and not rat’s-nest-ey at all:

And from the opposite angle (looking from “below” rather than from the side):

Later, when this is ready to be installed for real, I intend to bundle both connector housings together with silicon tape, just for a bit more organization. Right now I’m not doing that for a couple reasons. For one, I want to be able to easily see all my heat shrink labels when it comes time to pin up the mating connectors in the fuselage harness. For another, all these switches will need to come back out of this console at some point, so I can get it painted and labeled.

Last step for this bit-o-fun was to cleco the console back in place in the fuselage. All the bundles are tucked up nicely and don’t show at all:

So…what to do next? I’ve been kind of avoiding some of the more prickly fuselage wiring prep work. I still need to do the conduit runs below the seat floor, but before I can do those I need to drill a hole in a bulkhead, but more importantly, work out the positioning of the terminal strips and other stuff just behind the spar carry through. That, in turn, is somewhat affected by exactly where the wing conduits will enter the fuselage. So I decided it was time to bite the bullet and make those holes in the fuselage.

A while back I attempted to make a jig out of scrap wood for this purpose, and after a decent amount of work, I decided I really didn’t feel like it was a great option when compared to just doing some careful measurement. The fun part of figuring out these measurements is deciding on the right reference points to use on the fuselage. What I decided to go with were the center section for fore-aft location, and the lower skin that will mate with the wing ribs for vertical location. To determine these measurements, I used a square to measure the distance from the bottom of the inboard most wing rib to the edge of the conduit, and at the same time, I marked the location on that rib flange where I took the measurement. I then measured from the aft face of the spar along the rib flange to that mark. The outside diameter of the conduit is about 7/8”, so by adding 7/16” to my vertical measurement, I had what I needed to mark the center of the hole  on the fuse.

So I started with the left side; measuring back from the center section (where it would mate with that aft face of the spar) along the lower skin, marking the fore-aft point, using my square to extend that line inboard to the side skin, then using the square to draw a vertical line from there and mark it at the appropriate distance. I did a double sanity check on the fore-aft distance, verified that it looked right, and got to drilling – first a #30 pilot hole, then going to town with a big step-drill bit. I went with 1-1/8” holes, mainly because there was a very prominent step on the bit there, but also because there’s no need to make these super precise. I may end up putting large snap bushings or grommets into these anyway.

Then it was time to do the right side. Rather than just reuse my measurements, I did the whole procedure again with the right wing, which entailed temporarily installing the conduit there (it had already been in the left wing) Upon marking the pilot hole location on the right side, I noticed that…this mark seems lower than the other one. Oh boy, time to find out which one is wrong. Sad news: these measurements were right. I made the first hole on the left side too high. Good times. Well, first thing is to go ahead with the right side hole, but be REALLY sure to get it right. Then there was the question of what to do on the right side.

There were two issues to really consider here. The first and most obvious was to consider the consequences of enlarging that hole as needed. Simply going further with the step drill would result in a seriously gaping hole, bad for both not having a super drafty cabin, and also for questions of structure. Besides, by the time I made the hole large enough, the top edge would likely be unacceptably close to the seat angles and rivet line above. No, I needed to essentially mark the correct center and redial the hole entirely. That presented a different problem: I doubted if the step drill would necessarily center itself well if it was overlapping into an existing hole.

So what I decided to do was to add a doubler; this would both help with any potential structural weakening (which I didn’t think was a huge deal, but still better safe than sorry), while at the same time allowing me to basically have virgin sheet stock when drilling the new penetration hole. OK then, time to get to work.

First up, here’s the offending hole. In retrospect, this is obviously wrong; the conduit sits in the bottom of the lightening holes in the ribs, and thus should be closer to the bottom of the fuse:

The doubler was made from .040” sheet, the same thickness as the mid side skin here. It was basically sized to provide good clearance both from the rivet rows above and below, and around the original and newly-planned hole locations. Rivet spacing is maybe a bit overboard, but it’ll definitely be strong. Here it is after drilling to the fuselage, and laying out and drilling the new center hole for the penetration:

And here’s the skin after drilling the new penetration hole to final size and removing the doubler. Huh, that’s less of a sort of figure-eight hole than I expected:

A measurement check revealed that…the new hole is still too high. I screwed it up again.

I’ll be honest, some part of me considered not mentioning this misstep. It was definitely a confidence crusher, and my first gut reaction was to quit for the day in disgust. But I pretty quickly realized that as bad as fouling a thing up twice in a row sounded, the solution wasn’t that bad at all. There’s plenty of margin at the bottom of the doubler layout…I just needed to make yet another doubler, and start from scratch again marking the penetration center.

Back to not mentioning this…it would have been pretty easy to just gloss over this, but that’s just not a good way to do things, regardless of how embarrassing the mistake might have been.

Anyway, I went and made another doubler, used the first doubler to drill the rivet holes on the bench, and got it clecoed in place. Then I laid out the hole center again. This time I went back and forth between the wing and the fuselage roughly 473 times, making really really really really really sure I wasn’t going to have to write about screwing up three times in a row. Back through the drilling process again, and now I just have an even more elongated hole in the skin:

In retrospect, the doubler is almost surely structural overkill. The left side of the fuselage has a second hole far larger than this, a bit further back – this is where the fresh air intake for the rear seat will come in from a NACA duct under the wing. But as mentioned before, the doubler was useful for effectively moving the hole, and for sealing things up a bit better. I may consider adding some fabric boots where the conduit enters for good measure, but that’s a decision for another time.

I also stopped short of actually riveting the doubler in place. On the off chance that I need to enlarge the hole even more when it comes time to fit the wings, I think it’ll be easier to deal with with the doubler still removable. I should probably cleco it back in place so it doesn’t grow legs and walk away, though.

Not shown in photos here was when I started trying to lay our the terminal strips in the floor area. These will provide the interface between fuselage and wing wiring, and they’re looking to be a bit problematic actually. Since they’re long and skinny, and since I’d like them to be accessible without removing the riveted-in rear seat floors (as opposed to the removable forward seat floor), and since I’ve already got the comm antennas in that area…this might be interesting.

One possibility is mounting the strips to the side skins under the floors, assuming they won’t interfere with the rear seat footwells. Even if they don’t that location would make removing the terminals on the bottom side kind of fun. Though now that I think about it, if those are the fuselage-side terminals, then they shouldn’t need removing except in an extreme case (well, even having to remove the wings ever is already an extreme case, this would be even mores).

The other option would be to give up on my desire to have these be easily accessible – maybe they just have to go further back, under the riveted floors. Decisions, decisions…

Oh, I also have to find a home, probably down in this same area, for the Flyleds strobe controller. Looks like I’m in for a few more head-scratching and chin-rubbing work sessions.

Posted in Electrical, Fuselage | Hours Logged: 4.5

Chin-scratching, fixing the aileron trim

Posted on October 20, 2020 by pclifton

Yeah, it was mostly a deep-thinking kind of night. As per usual, there’s been a lot of that lately, and for the past night or so, it’s all revolved around packaging stuff under the forward seat floor. I kind of already made one major decision earlier today, which was to ditch the idea of using the terminal strips for the wing interconnects. While they definitely make for some very organized connections, the downside is that they take up a lot of space, and that’s kind of at a premium in this area.

Instead, I’m just going to use inline interconnects in most places. For the landing, taxi, and pitot heat connections, I’ll go with handshake/knife connectors, which I can encase in heat shrink to make a semi-permanent connection. The autopilot network cable for the right wing can just use a DB9 connector, which is pretty simple, and the nav/strobe connections will just “detach” by extracting their pins from the DB15 connector on the Flyleds control board.

This decision means that I now only really have to deal with finding a spot for that control board. As part of worrying about this packaging, I decided it’d be prudent to temporarily reinstall the control column, just to help me visualize potential conflicts here – though my intent is not to mount anything in the center bay under the seats, since that’s where the column lives. I will need to run a wiring bundle through here though, but that can be snug against the floor and thus well out of the way.

I also decided to temporarily install the aileron trim servo and push tube as well, since that’s another potential obstacle. In order to see the worst-case scenario, I also ran the servo out to full extension, which in turn means the push tube sticks out as far on the right side as it ever will (and likely further than any real-world scenario). But when I got that in place, I noticed something was off. Let’s take a look at the photo:

(side note: this photo also shows how much space those terminal strips take up down there)

As a reminder, this trim system works via spring bias. A spring attaches to each of the eyelets on the trim tube, and each spring runs to a hook on one side of the column. Movement of the trim servo, then, tends to pull the column to one side or the other. The problem here is that the eyelets appear to be roughly equidistant from the control column – basically a nearly neutral position – but that shouldn’t be the case, since the servo is fully extended. 

Well, it turns out that I messed up when I fabricated that push tube. The drawings specify the location of the first eyelet hole relative to the forked end of the tube that mates with the servo, and the location of the second hole relative to the first. But I measured from the end of the tube for that second hole, and so it was about 1.5” too close to the servo.

The fix was simple – drill another hole. This does leave the tube with an extra unused hole, but I don’t see it as an issue here. If this was a highly stressed component – particularly if it was subject to significant bending loads – then I’d worry bout that hole weakening the thing, but here the tube will only be subject to very light tension/compression. No worries, and this is a lot easier than fabricating another tube – getting that fork right is rather painstaking.

Things look much better now. The second eyelet (on the bottom of the photo) is now out of view past the seat rib, and clearly much further from the column. In this position, the trim system would be exerting a pretty strong pull on the column, which is what we want with the servo at full extension:

In the other-news department, today I placed yet another decent size order with SteinAir. This time I’m getting the coax I need for all the antenna runs, plus some additional D-sub connectors, and some more solder sleeves, and the handshake terminals for the wing interconnects, and I forget what else. I also ordered some large gauge welding cable, which is what I’ll use for the really large wire runs for the starter and alternator circuits. I went with welding cable over Tefzel because it’s a lot more flexible and less prone to failure at the terminals. Quite a few RVs are running around with welding cable in this application, so it’s not a crazy choice on my part.

Next up, more packaging stuff. I’ve settled on a location for the Flyleds controller, and also decided to add holes for the lateral wiring runs under the control column, so I reckon I can go ahead and get those drilled. I probably ought to bite the bullet and get that bulkhead conduit hole drilled for the wiring run to the tail as well…kind of been putting that off.

Posted in Fuselage | Hours Logged: 1

Underseat wiring prep

Posted on October 24, 2020 by pclifton

After a pretty lazy start to the day, I got right back to work scratching my chin while looking at how to arrange all this stuff under the seats. The good news was that it was simplified quite a bit by my decision to ditch the terminal strips. Now I just had to figure out where and how to mount the Flyleds control board. The board comes with four snap-in plastic standoffs that are kind of absurd in length:

I wasn’t quite sure I wanted to use those, so I tinkered around quite a bit here. I thought semi-seriously about working out something involving machine screws and spacers, but that would have required yet another hardware order, and so eventually practicality won the day. If I invent new methods for every little thing, not only will this project take forever to finish, but I’ll go broke from paying shipping charges.

Also, one nice thing about the plastic standoffs is that the hole locations in the mounting surface don’t have to be super precise – and in fact, I intentionally made them not quite match up with the holes in the board. Since these standoffs are so long, they allow the board to move around a little more than I like. I did an experiment with some scrap, where I set the mount holes slightly further apart than the board, with the result being that the standoffs are splayed a bit and provide just bit of extra stiffness.

This also gave me something to use as a drill template for the seat rib in the airplane. I ended up locating the board on the right-side rib, facing outboard. The long standoffs mean that the location of the footwell is a bit of a concern, but by putting the board as far aft as possible, there’s no interference (I checked by putting the forward floor assembly in place with the board in there)

The vertical orientation minimizes the space taken up on the floor/bottom skin here:

Next up, I decided it was time to address the conduit runs back to the tail section. The first order of business was to take care of the missing 3/4” hole in the bulkhead below the rear seat. I’ve probably written about this before, but for some reason there are a pair of 3/4” holes in the rear spar carry-through, but only one corresponding hole in the bulkhead aft of the spar. And getting to this location to drill a hole is challenging.

I ended up buying a hex-shank step drill bit off Amazon; this was still too large to go in the adapter for my angle drill, but that problem was easily solved by way of some home machining…by which I mean chucking the bit backwards in a drill and turning the shank against the bench grinder:

But hey, now it works in the angle drill:

After getting that hole deburred as best I could given the tight quarters, I measured and cut my two conduit lengths, and then set about the joyous task of pulling the stuff through the bulkhead holes. This isn’t too bad of a thing when you have good access, like I did for the wings a while back, but here it was a lot more awkward. Since the conduit runs close by the seat ribs, getting a solid grip on it to give the firm pull needed to get it moving was tough. Nothing to be done but just keep plugging away, though.

With that worst part done, I got to work securing the conduit ends in place. Since there aren’t any bulkheads at either end of the conduit, I needed a different way to secure the stuff. A while back I ordered some little stick-on bases that a zip tie can pass through, and this was my first time actually using them. They came with some 3M foam adhesive, but I elected to scrape it off and use some 3m VHB stuff instead, which ought to provide plenty of long-lasting adhesion.

A close look at one secured conduit end:

I also went ahead and ran pull strings through each conduit before fully securing them into place. When it was all said and done, I had a nice conduit run on each side of the aircraft:

A close look at the forward ends; on the left side, the conduit ends just ahead of the roll trim servo mount, and on the right it’s pretty similar but positioned a little further outboard:

And at the aft end, the conduits somewhat follow the baggage ribs, and end just ahead of the rear avionics shelf:

With the conduit in place, it became somewhat easier to begin visualizing the harness layout, and so I started sketching out a diagram of the harness on the large whiteboard I had nearby:

None of this is to scale at all; the intent is rather to identify “nodes” in the harness, where branching occurs. I’ll be able to use ribbons or something like that to later figure out the length of each run between nodes, which can be used to figure out the actual length of individual wire runs. It also currently glosses over what’s surely the most complex part of the whole thing, as indicated by the “panel fun” bit. I’ll need to finally settle on component positioning behind the panel before I can get that part sketched out.

I’ve seen where some people attempt to construct the entire harness outside the airplane, get it laced up all nice, and then install it. That sounds interesting, but I’m not sure it’s going to be feasible. What I’m roughly expecting right now is to get the main “trunk” of the harness – the section between the panel and the rear shelf – assembled and laced, but I expect to terminate and lace up everything else inside the plane. Fortunately most of that work will be not hard to get to (the panel area), but I’m sure it will yield some nice rats-nest photos down the line.

For now, though…I really need to pause this wiring work and get the bottom fuselage riveting done. The more stuff I put in here the less fun it’ll be to shoot those rivets, and I’ve been putting them off way too long.

Posted in Electrical, Fuselage | Hours Logged: 4.5

Shop org, battery mount

Posted on October 25, 2020 by pclifton

Well, not the most productive day in terms of shop time, but progress is still progress. The first thing I attacked today was some reorganization. With the recent electrical stuff I got, plus some other hardware, I was kind of outgrowing the parts bins I had, and I picked up another one when I was at Harbor Freight last weekend. What started as “find homes for this stuff” eventually turned into a pretty involved shuffling of parts.

Among other things, there was a lot of ground to be made by consolidating hardware – because of the way Van’s ships hardware bags, it’s very possible to have the same item split up in multiple places, That was doubly true since I had some hardware I’d bought independently. In the end, I emptied out probably ten or so assorted hardware bags, either by combining items or just being able to dump the contents of s bag into a dedicated bin.

With that done, I was once again left to figure out something to work on, and I settled on fabricating a mount for the two Skyview backup batteries. I’ve had this idea for a while, as a way to simplify packaging behind the panel, and I even had a rough cardboard template that I made up a while back. I’d been unsure whether I wanted to do this or not, but there’s been a little too much imagination involved in considering the layout behind the panel, and I felt I needed something physical, even if it ended up not getting used.

The fabrication was pretty straightforward, again using some scrap .025” sheet that was lying around. Even though I had that cardboard template, I laid out the piece here from scratch, using an actual battery (unlike the template, which I made based on dimensions from the Skyview install guide).

After the first rough cut, I had the general shape – a central rectangular part that the batteries would rest against, two triangular ears to provide support, and tabs to hold the screw holes that will secure the thing:

A bit later, after cutting out the area between the ears, finishing all the edges, and laying out and drilling the mount holes:

Then it was time to break out the dead blow hammer and commence physical violence, using the workbench as usual as a bending form:

Some final tweaking with the hand seamers, and it was done. I’d intended to go ahead and screw the batteries in place, but…I need some longer 8-32 screws than what I have right now. So I had to make do with clecos instead:

The mounting of the batteries to the piece will use the aforementioned machine screws, along with nylock nuts. That’ll be a little tedious to install and remove, but the idea is that if I ever need to service these, the batteries and mount will come out as a unit. I also like how this setup puts both wiring harnesses right on top where they’re 1) easy to access and 2) don’t take up any of the shelf footprint.

I do think I’m going to add another screw hole in each mounting tab though, now that I look at this. Otherwise I’m imagining the center web of the mount gradually abrading the shelf since it’ll probably be able to vibrate a bit. I may even go wild and cut a lightening hole in the center web to save a teensy bit of weight…

With that done, it was time for yet another Tetris session with the avionics shelf. This time I ended up breaking out some clamps to accurately envision parts that will go in the baggage bulkhead. That matters since that’s where about half the stuff may end up going. And after a bunch more shuffling, I think I may finally have a workable arrangement here:

 Most of my previous plans had the EMS module (second from the right on the vertical bulkhead) on the shelf, to the far left. That module presents fun packaging challenges, since it has a DB9 Skyview network connector on one side, and two more D-sub connectors (37- and 25- pin) on the other. Having it on the edge of the shelf seemed like something that might bite me later; in that same area I’ll have scat tube coming up for the fresh air vent along with the brake line from the gear tower. It seems prudent not to pack this area too tightly with giant harness plugs as well.

This layout leaves lots of rook for those big connectors, and I think overall makes better use of the baggage bulkhead space than previous ideas. There are still a couple things to consider before I finalize this. First, I really need to get my CPI2 ignition ordered so I have the real unit to play with. I’m not too concerned about the actual control module (the cardboard piece far right), but the backup battery mount may not fit where I think it will (but boy I sure hope it does). Second, I also need to consider the various D-sub connectors on the stuff in the panel, especially the displays. Which makes me think that maybe I really need to get the panel cut.

Posted in Avionics, Fuselage | Hours Logged: 3.5

Panel cut layout

Posted on October 26, 2020 by pclifton

So as I mentioned last night, I think it’s high time to go ahead and get this panel cut so I can convince myself for once and for all that my avionics shelf layout is solid. Plus I’ll need this done before I can start finalizing the harness behind the panel as well.

A perennial question has been whether to cut this by hand or have it CNC’d, and I’ve decided to go with the former. My motivation here is that I feel like I’ll spend as much time making a precise CAD drawing (mostly figuring out how to do so) as I will just doing everything by hand. Also pertinent here is that I haven’t finalized the exact location of some things, which I think is easier done drawing on actual parts.

So with that in mind I printed out assorted layout sheets and went to work with a ruler and a Sharpie. The first order of business was to figure out the vertical location of the whole group of stuff; basically, I want to place everything as high on the panel as possible. The limiting factor there ends up being interference between the brace behind the panel and the upper outboard corners of the intercom and knob panel. Those flank the GPS-175, which is centered on the panel, so it was pretty easy to draw out the horizontal edges of the bezel outlines and then figure out the highest point the bezels could be.

Once those three items were laid out, the rest of the design flowed from there, and I got the bezel outlines traced out for the two displays and the radio and AP panel. I took some time at this point to hold various components up to their outlines just to sanity-check that I hadn’t done anything grossly wrong.

Next up was working out the actual panel cutouts. The displays are pretty easy; they just have slightly smaller rectangular cutouts. The same is true of the intercom and GPS-175 cutouts. The other three Dynon units are a little more fun, as they require sort of cross-shaped cutouts – I guess they needed extra space in the modules to fit more stuff? Whatever the reason, those were a little more tedious to get done, but not horrible.

So now I’ve got all my cut lines all laid out. I haven’t bothered to mark any of the attach screw locations; my intent is to use the actual components in place to mark and drill those. That way I can clamp everything in place where I want it and ensure it all lines up properly; there will be enough room to work with the cutouts to adjust positioning as needed.

Yay, lines:

The remaining question is how I want to actually cut this. Typically I’ve done stuff like this with a Dremel cutoff wheel, but it’s not especially precise and will probably not like the thick material here. I’ve seen where people mention using a jigsaw with a metal cutting blade, which I have, but I’ve never been a huge fan of jigsaws for making precise cuts. The other option, which I looked into last night for a bit, is to buy something like a Dremel SawMax, a compact high-speed circular saw. They’re supposed to work well for making straight cuts, though I think it might be a bit much for the smaller cutouts. I’m somewhat tempted to get a cheap vibratory saw and see how it does against aluminum.

So…we’ll see…

Posted in Avionics, Fuselage | Hours Logged: 2

Panel cutting, part I

Posted on November 1, 2020 by pclifton

Yup…today it was time to start making a whole bunch of cuts. Last time I was trying to decide what tool to use, and after some research, I ended up picking up an oscillating Dremel multi-tool. I was far from certain it would work well for this purpose, but based on some feedback from friends, I decided it would be worth having one around in general even if it didn’t work for this. Which is a good thing, because after some testing, I decided it wasn’t the right tool for cutting the panel. It’ll go through thinner sheet quite well, and is very controllable, but for thicker material it’s slow going…and I figure the slower the going, the more time I have to mess up a cut.

So in the end I went with the good old jigsaw. The main downside to this was that it meant having to make a lot of big pilot holes in which to start the saw – unlike the plunge cuts I’d hoped to make with the oscillating tool. So the first order of business for the day was to lay out and drill a bunch of holes – first, #30 holes at all the inside corners I’d be cutting, then 1/2” entry holes for the jigsaw blade. Essentially, I spent about the first hour of the day just drilling.

Then, with all the various holes done, it was time to go to work with the jigsaw. Not much to go on about here, just lots and lots of careful cutting, plus frequent pauses to sweep/vacuum up the copious aluminum dust I was making. Here’s a look at the state of things after making the first couple rough cuts:

Eventually, I had all the rough cuts done. I intentionally cut a bit away from the final cut lines, wanting to carefully sneak up on final dimensions instead of risking overdoing anything. Another fun part of this was dealing with clearance issues that affected the jigsaw. For the lower right cutout below, the stiffening lip at the bottom edge of the panel made it impossible to effectively cut the two outside vertical lines – hence why that cutout is a bit rougher looking than the rest. I got creative to remove as much material as possible with the jigsaw, but there was just going to be more to take off later for that one:

Next came the tedious part of the process: getting those cutouts up to size. I started with the large display cutouts, which are pretty straightforward but also pose a bigger challenge in getting the long edges straight. The first display cutout took me probably an hour or more – I was really being conservative in sneaking up on final size. The second went a lot faster, since I had a better idea of how the cut lines I’d drawn related to final size. Basically, it was a case of removing the lines entirely (vs removing material right up to them) for a good fit.

The tedium paid off with some motivating test-fit action:

Then it was on to the real fun: working with the sort of cross-shaped cutouts for the AP/knob/radio heads. Working up to the fit here was a whole lot more fun, since it wasn’t just a matter of “the cutout’s too narrow here” – there was also the question of whether it was the inner or outer edge that was too small. And here I repeated the previous performance with the display; I probably spent an hour and a half getting the first piece (the AP panel) to fit, and afterwards decided it was time to break for dinner. After that, the other two I got done in less than half an hour each.

And at this point the test-fit action was even more fun to look at:

The good news is that this is probably the worst of this work. The intercom and GPS-175 cutouts are fairly normal squares, none of the crazy stuff, and should go faster. The one thing I need to figure out is how I’m going to attach the GPS-175 rack to the panel – probably something to ask around on VAF about.

Once I get the other cutouts done, I’ll do a final test fit of all the components at once, and then I’ll actually drill the screw holes and get the nutplates installed; by doing this last, I can ensure that everything line up really nicely while I’m doing the holes, though to be honest everything is looking great so far just fitting snugly in the assorted cutouts. Then I can actually hang this thing in the fuselage and evaluate my behind-the-panel layout.

(I’d also like to climb in the thing and play with the avionics while making airplane noises, but that would require taking the fuselage off the rotisserie…not really worth it. Later…)

Posted in Avionics, Fuselage | Hours Logged: 6

Various stuff

Posted on November 5, 2020 by pclifton

So this is sort of a catch-all post, and also includes some work from a few nights ago that I never got around to writing up. The first thing one might notice is that this post is not the “panel cutting part II” that one might have expected, and that’s where the story begins.

Before I even went out to try and work Monday evening, there were some questions about whether my panel cuts were going to work. One thing I didn’t think through before I started cutting was how I’d attach the GPS-175 rack to the panel. For all the other components, the attachment is really simple; the GPS rack is a different matter. Basically, it’s a sort of sleve that the GPS unit slides into, and how it gets attached to the panel is up to the installer. The most common way would be a short piece of angle on each side of the rack, one side screwed to the rack, the other riveted to the panel. But since I put the knob panel and intercom right up against the GPS, there was no room for that. But I had a couple idea I was going to tinker around with.

That all became a moot point as I was preparing to finish the last two cutouts, because I noticed that I bungled the intercom cutout. Basically, when measuring in from the device outline to lay out the cut lines, I switched the measurements, and as a result cut a hole that was too narrow and too tall. And because of the way this worked out, I’d cut out the material needed for the attach screws. No coming back from that one, unfortunately. But it didn’t bother me too much, since I was already considering that the GPS rack might be a deal-breaker.

I still got some stuff done that night though, just went looking for menial stuff, which resulted in me digging out the antenna doublers I made a while back and getting their rivet holes dimpled – that’s in preparation for the fuselage riveting session that I really hope I can get done soon.

That brings us to tonight. I’ve got a new panel blank on order from Van’s, which should be here early next week. In the meantime, I needed to find stuff to work on – in fact, I need to generally get in the habit of finding stuff to do even if my “main” desired task is held up by something. I’m never going to finish this if I can’t find ways to be productive outside a narrow area of focus.

So I started by going ahead and jabbing up the GPS rack attach stuff. Nothing too exciting here – I cut a couple short pieces of angle, shortened one leg from 3/4” to 1/2” to minimize the amount of dead space I’d have to put between the GPS and its neighbors, marked and drilled it for the screw holes in the rack, and installed nutplates in the angles. Got those installed in the rack for a test-fit, and they look good:

Note that they’re still oversize; I’ll need to remove them and trim to final size before I fit them to the panel for real.Also worth noting here is that the real fun is positioning these angled properly relative to the forward end of the rack. The rack needs to be carefully located relative to the panel surface for the GPS unit to sit flush like it should. I ended up here with the angles a bit further back than I want, but that’s the error I’d prefer; I can add shims in between the rack and panel if needed, and I expect I’ll end up doing just that.

OK, now what to work on? Well, there was a new service letter released for most of the recent tailwheel RVs a couple months ago. Not a mandatory service bulletin, but something recommended to be done if desired. Basically, there have been instances of deformation of the last tail bay, believed to be due to stresses from the tailwheel, specifically if the tailwheel hits a significant bump while turning – thus putting a strong side load on this area. The fix is to add a diagonal stiffener on each side of the skin in this area to provide some reinforcement.

I decided this was worth doing preemptively, and so when I ordered some parts from Van’s a while back, I included the two stiffener pieces, and I decided tonight was a good time to take on this project. Overall, it’s pretty straightforward.

First up, the two end rivet holes for each stiffener are located. The service letter provides instructions for these; basically, you draw an arc a fixed distance from a few reference rivets, and use the intersections of those arcs for the rivet holes (note the marks upper left and lower right):

These holes are used to initially locate the stiffener on the outside of the skin, where it’s used as a drill guide for the other three rivet holes. After some demurring, it’s time to cleco the stiffeners in place inside the skin and check for interference. It may not be super obvious from this photo, but the aft end of this stiffener overlaps the aft bulkhead flange, so it’ll need to be trimmed:

After trimming both stiffeners (they both had the same interference with that bulkhead), doing some trial-end-error to get everything right, I got them all polished up on the bench grinder and dimpled. Then it was time to dimple the holes in the skin. The upper/forward three were easy enough to do with a 3” yoke, but the other two on each side required breaking out the pop rivet die set – which is really hardly up to the task of dimpling this thick skin. I ended up dressing those dimples with a countersink bit to get the rivets to sit properly flush – the dies themselves didn’t quite cut it. Now the stiffeners are clecoed in place and ready for riveting:

Since it was nearly 10:00 now, and since some of these rivets will have to be done with the gun, and since I want to be nice to my neighbors, that’s where I called it a night. I figure I should be able to finish this up tomorrow.

Posted in Avionics, Fuselage | Hours Logged: 3

Service letter done, more planning

Posted on November 10, 2020 by pclifton

Another fairly unexciting day, following an unproductive weekend. I shot the rivets for the tailbone stiffeners for the service letter fix, then decided to look at doing some actual mounting of stuff to the fuse block shelf. So I pulled that shelf out, took it to the bench, and started laying things out again, but this time with the actual wire on hand to at least consider routing for the big power feed.

Before long, I’d decided that I no longer liked my original plan of using cheap plastic clips to secure the wire bundles here, and that I wanted to use legitimate adel clamps instead. Only problem with this is that I don’t have the right size ones on hand. Also, it’d be nice to at least get the interconnects between the fuse blocks and other stuff done, but I don’t have the right terminals on hand for that.

So long story short, looks like it’s time for yet another Spruce order.

But hey, I still did stuff, and tomorrow I should get in my new panel blank, and I can get going on attempt #2 at getting that cut.

Posted in Electrical, Fuselage | Hours Logged: 1

Instrument panel do-over: layout

Posted on November 10, 2020 by pclifton

New panel blank came in today, so I decided to get right to work on it this evening. First step, like before, was to do the layout of the actual devices and the required cut lines. Adding a slight twist was the need to modify the layout a bit; as mentioned before, I need to provide some empty space to the sides of the GPS-175, instead of putting the two Dynon units right up beside it. I decided to complement that bit of empty space by also separating those two units from the screens below; this will probably be more clear as we get to the work here.

First step is to mark the no-go areas of the blank. The removable panel attaches to two side “wings” with screws; those wings are in turn secured to the fuselage. The wings sort of arch together in the top center area, and the end result is an overlap where I can’t really safely cut any holes. So I just checked the wings into place and traced the edge with a sharpie:

 

Next up is working out the locations of the top three units; I want them as high as they can go without interfering with the wings, and their position essentially drives everything below. So I start out by marking the lateral extent of these. First up is a centerline, then I line out the outside edges of the GPS-175, followed by the empty space required for the rack mount, and finally the knob panel and intercom units. Before going any further, I laid the actual units in place to sanity-check my marks:

And then the intersection of the outermost marks and the “no-go” zone becomes the upper alignment line for these three things. With that as a baseline, I can then draw in the lower edges of the GPS and Dynon units. Additionally, the bottom edge of the GPS becomes the reference line for the top of the displays and other stuff below.

Here the spacing under the two Dynon units becomes more obvious; they’e spaced out about 1/2” from the edges of the GPS, and then by aligning them with the top of the GPS, I get about 1/4” margin between them and the screens below:

Next up is marking the edges of the two screens, plus the radio and AP panel alongside. I also paused to clean up some of the superfluous Sharpie marks to remove any confusions. This is required a folded paper towel soaked in acetone and a very steady hand:

This finishes up outlining the actual bezels of the units; that i the physical space they’ll take up on the front of the panel. Next up is the real fun, drawing the actual cutouts, using the outlines as a reference. It’s just more of the same as before, lots of careful marking and measuring with a ruler and Sharpie. Once that was all done, I did another cleanup session of superfluous marks. And now it’s all ready to go (side note: it sure is fun trying to take decent photos of a reflective surface):

Next up, I get to repeat the fun exercise of doing rough cutouts, followed by lots and lots of filing and such.

Posted in Avionics, Fuselage | Hours Logged: 2

Panel do-over: rough cutting

Posted on November 13, 2020 by pclifton

Not a ton to write here; last time I got all the cut lines laid out, tonight it was time for another marathon session with the jigsaw. This time I was a little more intentional about where I made my pilot holes to start the jigsaw cuts, but the AP panel cutout (down by the lip at the bottom) still couldn’t be cut out as fully as the rest. Oh well, just gotta make do.

After doing the rough jigsaw cuts, I went to work with the Dremel and a cutting bit to remove some extra material around the corners and so forth; this i just to reduce how much I have to remove with files down the line. I’m pretty much at the point now where I shouldn’t need to remove more than 1/16” of material in most places.

So that’s enough for one weeknight; I should be able to find the time to get one filing done this weekend, and hopefully I can finish out all the holes. With any luck, I’ll have a done-ish panel ready to hang in the plane temporarily by the end of the weekend.

Posted in Avionics, Fuselage | Hours Logged: 2