Switch console wiring, rear shelf work

Posted on October 10, 2020 by pclifton

Well, it was another day of road blocks of a sort, but I did my best to get stuff done in spite of it all. I’d intended to try and get most of the switch console wiring done, though I knew going on that I had at least one roadblock. One thing I replaced in this second console attempt were the circuit breakers; when I was ordering my regulators rom B&C I saw they had mini Klixon breakers, much more compact than the ones I got from Digit-Key previously. Since I was worried about the clearance between the breakers and the side of the console, going with those was a no-brainer. The problem is, these breakers need a #6 ring terminal, unlike the #8 for the original breakers. Guess what ring terminals I don’t have on hand? Yup.

But I figured I’d at least get started on the wiring stuff anyway; I’d probably not get to the point of loading up the connectors or bundling the harness, but I could at least get some terminations done. So I drug all the assorted wires needed out on the workbench, and here I was confronted with another problem: I’ve been intending to terminate the console harness with a pair of Molex Mini Fit plugs; this was the best way to get a fairly compact connector overall, since Molex doesn’t do more than two-row connectors in this form factor.

The problem is, I saw that the current rating of those connectors was fine for everything I have, but didn’t consider the wire gauge the pins could accept. And it turns out the biggest they’ll take is 18AWG, whereas I need both 14 and 12 for the seat heater and pitot heat, respectively. I did find that there’s a Mega Fit series that will work with this wire size, so I’m going to rework my connections here into a 6-pin Mega Fit connector for the high-current stuff and a 20-pin Mini for the rest. More stuff to order…

Oh, and that still wasn’t the end of it. I also didn’t have the right blade terminals for the 12AWG wire needed for the pitot heat circuit, so I couldn’t terminate those to the switch either.

I still decided to go ahead and cut the wires that I could and crimp on the terminals needed to connect them to the switches, but that was as far as I went. I’ll have to wait until I have the rest of the stuff I need before I can turn this rat’s nest into something that looks actually organized:

So – what to work on next? Part of me wanted to sit down and start getting more parts orders together, but I can do that any time, and maybe wait until tomorrow in case I find more stuff I need. I still don’t want to finalize anything on the forward shelf until I get the CPI2 ignition stuff on hand, but I’m quite confident I can get everything I need up there – and that means I can start finalizing the rear shelf.

What actually started me on this path was trying to think of other wiring things I could do fairly independently, and the one thing that came to mind was the Skyview network connections in the tailcone – specifically the runs from the network hub back to the ADAHRS units. I won’t want to bundle those until I have the trim and strobe runs going back as well, but I can still get through all the pinning. But first I needed to have the hub location nailed down.

Before that, though, I needed to actually make the shelf attachable. So I carefully positioned it, got the four screw holes drilled, and installed the nutplates in the longerons. Then I pulled out the pertinent components and worked on a decent layout for them – which I’d already roughed out, so this was just finalizing things. Nothing much changed here, except that I think I had the hub and ADS-B receivers switched previously. This new layout makes it easier to get tot he receiver’s harness connection, and positions the hub close to where the pitch servo will live. By doing that, I’ll be able to just terminate the wires on the servo with a D-sub, and plug them directly into the hub – no intermediate cable needed.

So that was pretty much today’s work – I didn’t quite get to laying out mount holes in the shelf before I had to go to an afternoon appointment. Tomorrow I should be able to get this stuff mounted and at least start on those network cable runs. And I guess place some parts orders…

Posted in Electrical, Fuselage | Hours Logged: 4

Switch console fab

Posted on October 9, 2020 by pclifton

So a couple weekends ago I made my first failed attempt at getting the mount holes done in the switch console. That, of course, ended in me ordering a replacement part. Well, the replacement (plus some raw stock for making a better switch retainer plate) came in last weekend. This week I’ve again been sort of dodging the mosquito population, though it’s finally died off enough that I did some evening work tonight, and I decided to pick back up on the new console.

Now, the issues last time mostly revolved around the holes in the console not lining up with the holes in the retainer plate. At the time I’d decided that when I redid this, I’d rivet the plate to the console to make sure everything lined up. In the intervening time, though, I decided that that wasn’t necessary, and would add decent complexity getting those rivet holes lined up. The real issue wasn’t so much a wandering step drill as it was my dumb decision to make those holes while holding work pieces by hand on the drill press.

So I decided to have a go at it doing it the same way as last time – drilling the pilot holes in assembly between the two pieces, but enlarging the holes to final size separately. This time, though, I’d make sure the work pieces were clamped securely while drilling. To facilitate this, I built up a sort of jig with a couple 2x4s. This made a piece tall enough for the console to sit on, and I next used the console to drill holes in the block matching the screw holes, which would allow the console to be clecoed in place while working.

Then I made up another retainer plate strip, laid out the pilot holes on the console, drilled those pilot holes, and transferred those holes to the retainer plate. Here’s the console with pilot holes clecoed to the block:

Next up was laying out and drilling the small retainer holes in the backing plate. Since I wanted to use that same jig block for drilling the retainer as well, I drilled the retainer plate with it clecoed to the block using the pilot holes. This allowed me to cleco both pieces to the block while drilling.

Then it was over to the drill press to start opening up the mount holes. This worked a lot better than last time, and reclamping the work for each hole was nowhere near the annoyance I might have thought it was. Here I am partway through opening up holes on the retainer plate:

Finally, after making a whole lot of metal shavings and sawdust, it was all done and it was time to see if they matched up. If they didn’t, it wouldn’t be the end of the world actually – since I didn’t mess up any of the console holes (unlike last time), worst case I could make another retainer and trace the holes from the console onto it, It’d be really painstaking to open those holes up by hand, but it’d work.

But it wasn’t necessary – everything lined up perfectly this time, and I was able to get all the switched, circuit breakers, and the PWM dimmer installed:

And of course, with that done, I just had to cleco the console into the plane. You know, just to check fitment. Very important. Plus I could lean over the cockpit and flip switches like I was doing my preflight check. Also very important.

So that was a good night’s work, and it’ll set me up nicely to start putting together the wiring harness for the console tomorrow.

In other news, manic ordering of parts has continued. I got my finish kit ordered this week, mailed off order forms for the engine and my seats, and in really big news, found out from Whirl Wind yesterday that my prop is going to ship next Tuesday! That’s barely a week-and-half turnaround on something I expected to possibly take months (based on other stories I’ve heard about Whirl Wind). To say that I’m please would be an understatement, though this also means I’ve got to find somewhere to store that thing for several months.

Next up on the ordering front is the CPI2 ignition; I shot an email off to Ross at SDS today, but didn’t hear back; I’ll probably give him a call on Monday to get that rolling. Oh, and I also got both my voltage regulators from B&C this week – another component I’ve got on hand to work out the behind-the-panel stuff.

Now I’ve just got to work on getting all these parts to fly in close formation…

Posted in Electrical, Fuselage | Hours Logged: 3

Ignition switch harnesses

Posted on October 4, 2020 by pclifton

Started the day off today with some much-needed cleaning, though it had an ulterior motive as well – to clear up some good working space on my big table. I wasn’t sure whether I wanted to start mounting things the fuse block shelf, or something else, but eventually I settled on at least starting with some more harness work…which ended up being basically the one thing I worked on today.

For the backstory – these switches will be for the CPI2 electronic ignition. Since this will be my sole form of ignition, I’m ordering a dual-ECU system for redundancy. Accordingly, I need a separate power switch for each ECU. To make things more fun, each switch needs to be double-pole – the CPI2 had separate power feeds for the ECU itself and for each ECU’s associated coil pack.

That’s not the end of the fun, though. As outlined above, each switch will control the power feeds to one of the ECUs. But since the CPI2 has its own dedicated backup battery, all that will happen if the power is turned off while the engine is running is that the CPI2 will automatically switch to backup power. This is actually a good thing for preflight purposes – by turning the power off, I can test that the backup battery switchover works as expected. That’s pretty important, since losing power to the ignition means the engine goes quiet.

Anyway, the other takeaway here relates to the traditional preflight mag check, during which each magneto is switched off in succession to check that the engine will run on just one. I want similar functionality here, but as outlined above, turning the power off won’t cut it. The CPI2 does provide a function from the controller to do this, but it’d be nicer to have external switches. These could also come in handy if I ever need to cut the engine right now, ie when pulling the mixture is too slow. The CPI2 provides kill inputs for this purpose.

The question becomes how to do this. This convenience didn’t seem worth adding two more kill switches, but integrating it into the existing two switches would work well. The end result is that I bought three-pole, double-throw switches – up is power on, center is power off, and down (a momentary position) sends the kill signal for one coil pack. So the runup procedure will be to kill power to verify backup battery functionality, then pushing each switch down in succession to test individual coil packs.

Here’s the catch with this plan – while single/double pole/throw switched can be found just about anywhere, these beasts aren’t so common. That’s a concern if one of these ever craps out, since it’s a safety-of-flight item. Being stuck somewhere while waiting on a Digit-Key order doesn’t sound like much fun. So when I ordered these a while back, I went ahead and ordered three so I could carry a spare.

One final bit of fun – this particular configuration was only available with solder lugs. I would have preferred fast-on tabs (which all the other switches have), but, well, too bad. So to facilitate a possible in-the-field swap, I decided to install a stub harness on each switch to allow for easy swapping.

That’s a really long way of providing background for what I did today, which was to cut the various wire colors and gauges, solder them to the appropriate switch lugs, heat shrink over those joints, print heat shrink labels for the wires, crimp on Molex pins, and insert the pins into their connectors. Well, only 2/3 of the way for that last one…because I forgot I ordered a spare switch on that Digit-Key order, and only ordered two six-pin connector sets. Oh well, when I get the connector all I’ll have to do is insert the pins.

So yeah, this is what I got out of those three hours of work:

Posted in Electrical | Hours Logged: 3

Landing light wiring; lower shelf detail

Posted on October 4, 2020 by pclifton
I swear, I’ve been trying to work this week, but now that we’re a week+ out from all the heavy rain, the mosquito population boom is in full swing, which makes being out in the hangar any time in the afternoon an unpleasant thing. Saturday meant I could finally get out there in the morning when things were a little quieter.
 
I will say though, it hasn’t been a dull week. I took the time to start pulling the trigger on a lot of big purchases, specifically stuff whose lead time I was worried about. I now have my order in for a Whirl Wind 300-72 prop, and I just need to send in my order forms to Titan for my engine and Van’s for my finish kit. I also hit up the three popular interior vendors, and will probably be mailing off that order form early next week as well. Finally, I’m waiting on some information from Titan so I can send my order to SDS fo the CPI2 ignition system – which I want on hand so I can finalize the avionics shelf stuff behind the panel. Oh, and I also ordered and received my ELT this week, and hopefully should get my voltage regulators from B&C in the semi-near future.

This should take care of all the long lead-time stuff, the things that have the potential to stop me from making steady progress into next year. I think the only thing I still need to find out about is my exhaust from Vetterman. I saw some comments on VAF this past week that imply they may be pretty busy right now too. I note that Aircraft Spruce sells some Vetterman products, but I don’t think they have the specific exhaust I want – as far as I can tell, they stock the two-pipe crossover systems, but I want the four-pipe, which should make the cowling a little less busy. Guess I’d better reach out about that next week too…

 
Anyway…let’s talk about this weekend. The Spruce order I received this week included the small snap bushings that I needed to work out the wiring issues with the landing lights. I mentioned this a while back, but to review, the Flyleds light units have two sets of terminals: the taxi-light terminals are on the back side of the light unit, but the landing-light terminals are on the front. I was stuck a while back on figuring out how to route both those pairs of wires to a single plug, while still allowing the light unit to be removed from the mount. Basically, I needed a set of wires to pass through the light unit.
 
What I worked out was to add a tiny hole in the edge of the light unit, outside the actual printed board area, with a snap bushing, and then to modify the mount to accommodate this. Getting this done started with a whole lot of careful measuring, thinking, marking, reconsidering, and so forth. I didn’t have a lot of margin outside the circuit board area to get this done, so getting this right was pretty important.
 
But eventually I was satisfied and drilled my nice little 1/4” hole, which can be seen below. Note the circular line just inside the hole and outside the terminal; this is the edge of the “safe zone,” ie the area I really needed to make sure I didn’t breach: 

Next up, I needed to adapt the mount to accommodate this hole and the snap bushing. I started by screwing each light in place, and using the hole to trace a starting point for the mount modification:

That was followed by a fair amount of trial-and-error, trying to remove just enough material to clear the snap bushing. It took a bit, but eventually it all worked out:

Next up, I went to work adding the wiring pigtails, which will stretch to the outboard rib and mate up with a connector from the main wiring. Here we can see the power and ground wires for the landing lights, going into the snap bushing:

Then, from the back, we have the wires from the taxi light. These wires pass through a sort of tight space between the two pieces here, which got me worried about chafing, so I added some snakeskin wrap and secured it with heat shrink. The unwrapped wires are the ones from the landing light:

Each stub harness was then finished with a four-pin molex connector. This was really my first chance to use my printable heat shrink, which I’ll be making extensive use throughout the aircraft. I also got to work on my cable lacing chops a bit – the job I did on the pitot heat harness a while back was kind of so-so, but I found a nice technique video on Youtube that helped me do these a lot more efficiently and cleanly:

 And then it was time to put these back in their box…again. I moved on to one detail I glossed over for the lower shelf (where the fuse blocks will live) – I needed to secure the two hinge pins. Nothing really fancy here; I cut two hinge eyelets, added a strip of sheet to tie them together, then located and added a nutplate in the bulkhead for the retainer to tie into. Now my shelf hinge pins are properly secured:

It was about this time that the invading mosquito force started ramping up, so I made that quitting time. I’m kind of thinking I might go ahead and mount the fuse blocks and other stuff to this shelf, maybe even start tying together the components that don’t require external wiring. Except I think I need some of the heavier-gauge wire to do that. Guess I might be making another order for stuff this week. I’m starting to think that shipping charges might make up 5% or so of the total build cost…

Posted in Electrical | Hours Logged: 4.5

ADAHRS mount, part 4. Plus some console work.

Posted on September 26, 2020 by pclifton

Good productive Saturday. I got started bright and early, marking the spacer pieces and their matching spots on the angles, getting the rivet holes countersunk, and then getting everything primed. I left the parts out in the sun to dry while going out for some errands – hauling off a load of recycling, and stopping by the hardware store in town to look for mount hardware for the ADAHRS. As I may have mentioned previously, these need to be attached with non-ferrous screws. My intent was to snag brass machine screws, which will definitely be non-ferrous, but the only things they had at the store in Brookshire were slotted head screws…and I really don’t ever want to wriggle back into the fuselage to remove an ADAHRS and then have to fight with one of those.

That left a couple options. They had some stainless Phillips head machine screws, which might be non-ferrous. Otherwise, I’d have to try the Ace hardware in Katy (probably on another trip) or just order some screws online. And I really wanted some hardware today, since I’d need it if I was going to finish the mount. Back to those stainless screws – all I needed to do was hold one near a magnet to see if it was attracted, but where to find a magnet? Fortunately one of the guys there figured that out for me – they had a big magnet used for picking up nails. And sure enough, no attraction for the stainless screws. Sold!

Back home, I got the spacers riveted to the angles, final-drilled and tapped the screw holes, and finally used my nice new screws to attach the units to the angles. This effectively meant I had a single mount unit, which I then took over to the fuselage to lay out the rivet holes with the longerons. Got those drilled and deburred, and that pretty much wrapped up the work I needed to do on the mount. I’m not going to rivet these in place just yet; I see no need to limit access back here right now.

I did decide to go ahead and install the fittings for the pitot/static/AOA lines, and get some layout done there. I went ahead and cut the three lines that tie the primary and secondary ADAHRS together, and also cut a new line to handle the routing from the static ports to the ADAHRS. That left the remaining pitot and AOA ports open, so to stave off any potential mud dauber mischief, I took another short piece of the static tubing (of which I have an insane surplus) and connected those two ports together.

Behold the ADAHRS setup!

A slightly different angle, showing the static routing a little better. I think when I finalize this, I’ll add an adhesive zip-tie mount inside the skin, and use that to secure the line to the skin, rather than just having it hang out in midair.

With that bit done, I decided to move on to working on the right-side switch console. This started with just some generic experimentation – I had a general idea of how to do the panel cutouts for the switches, but some tinkering on scrap was definitely in order. Which was a good thing…for some reason, I had it in my mind that the panel itself should be drilled both for the switch center bushing and the anti-rotation washer tab. The latter is just a small second hole offset from the main one. I’m not sure why I thought that the switch itself would cover up that second hole, but that was definitely not a correct idea.

Some research inside told me that there were a couple different approaches to this issue. Some folks just did away with he anti-rotation washer entirely, depending on the star lock washer included with the switch and the nut torque to secure the switch. This seemed potentially reasonable, but also highly annoying to deal with during installation – I’m imagining trying to hold the switch straight while tightening the attach nut.

Another alternative was to have the anti-rotation tab hole drilled from the back of the panel, and not all the way through. This allows the tab to rest in the hole, with nothing visible not he outside. I liked this idea, but in my case the console material was nowhere near thick enough to handle this. So I decided to fabricate a backing plate for the switches, a piece of 1/8” thick aluminum stock that I’d drill for the center and anti-rotation holes. The actual console would only be drilled for the center holes. At first I figured I’d rivet the backing plate to the console, but then realized there was no reason to do this – the switches, once installed, would hold it in place.

So that took care of that plan – next up was to transfer the switch layout I’ve iterated on a million times to an actual part. I had to take into account part clearances here – for example, putting the forward most switch too close to the end of the console would cause it to interfere with the gear tower (which the console attaches to). So basically the first switch location was determined to address this issue, and everything else was positioned relative to it.

Another consideration is the the console is wider at the forward end than the aft. Since I’m using most of the length of the console, I have to be concerned about clearances at the aft end. I also have to worry about the angle on the side skin that the console mounts to. All this meant that I had to experiment a bit to figure out the lateral position of the switch lines. I ended up drawing two positioning lines, one 7/8” from the inboard edge and one 1” in. Then I laid out the fore-aft switch locations, and did some eyeballing to decide which position to choose.

The 1” line seemed too close for comfort to the angle, so I went with the 7/8” position. It’s also worth noting that while I’m calling the a switch console, there are also a couple circuit breakers and a PWM dimmer here. This is one reason why the marks shown on the following photo aren’t spaced equally. (the other is that there’s some separation between groups)

So after checking, double-checking, triple-checking, starting to drill and then going back to re-verify something, and so forth…I finally started center punching hole locations and got ready to drill.

The approach I took was to first drill #40 pilot holes in the console. I also laid out and drilled the first hole location in the backing plate; this let me cleco the two pieces together to get started match drilling. With the backing plate lined up properly, I drilled all the center holes out to #30, then to #12. I took this stepwise approach to drilling, as it let me correct hole locations along the way to try to get the best alignment. In the end, the alignment came out looking pretty good.

The next step was to drill the #30 alignment holes in the backing plate –  no big deal – and then open the center holes up to 15/32” with a uni-bit. Well, not all the holes…the circuit breaker and PWM dimmer holes needed to be 3/8” instead. So I had to be careful to mark those holes and not get on a roll and drill them all to the larger size.

Since the pieces weren’t riveted together, I drill each piece individually. The backing plate went well, though I sure did make a bunch of aluminum chips. The thin console material would be a whole lot easier…and that attitude ended up biting me. Remember the part about being careful to mark the holes that needed to be 3/8” and not 15/32”? Yup, I drilled the PWM dimmer hole to the larger size. From a quick look at the dimmer, though, it seemed the nut would cover the larger hole…worth a try, so I kept on going.

With all that drilling done, it was time for some victorious temporary assembly work…but unfortunately, things got problematic from there. The first issue I ran into was the layout of the circuit breakers, which I didn’t really consider beforehand. With the way the circuit breakers are oriented in the panel, and the way their terminals are laid out, those terminals come really close to the side of the console. Since the airframe will be a ground, any contact here would be a Bad Thing. I suppose I might be able to heat-shrink over the terminals once everything was attached, but I wasn’t sure how I felt about that:

It turns out to be a moot point anyway. Once I tried putting the backing plate and the console together, I found that in the process of drilling the large center holes in the plate, a few of them had wandered a bit, probably due to me being a bit careless holding the piece in the drill press. The result was that the holes in the two pieces didn’t really quite line up. It’s possible that some careful filing might alleviate the situation, but taken alongside the other issues (the misdrilled dimmer hole and the breaker clearance issue), I’ve decided to junk these pieces and start over again. This effort gets chalked up as a learning experience.

This isn’t all bad. One side effect is that I can get more suitable material for the backing plate. The 1/8” stock I used is almost twice the thickness needed to accommodate the anti-rotation tab. Since I’m ordering from Van’s anyway, I can get some material that’s closer to the minimum required thickness – a little more weight saved.

This also gives me the opportunity to rework the console layout. The breaker clearance issue could be mitigated by shifting the switch line over a bit, but that gets me back into space issues at the aft end, so instead I’m going to rotate the breakers 90°. The effect of this, though, is that they can’t be in line with the other switches as before – they’ll need to be side by side. It’ll take some tinkering to see how that shakes out.

The real lesson out of all this, though, is that drilling the two pieces separately was a poor choice. For the next iteration, I’ll definitely be riveting the plate to the console, and that will happen before I start taking the switch mount holes up to final size.

So all in all, the day ended up a bit of a low note, but I’m not too bothered by it. Some things you just don’t figure out until you commit to trying, and this was one of those cases. Besides, I was about ready to order some stuff from Van’s anyway, now I’ll just add a few more parts. At least they’re pretty inexpensive.

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

ADAHRS mount, part 3

Posted on September 25, 2020 by pclifton

The first and most interesting question of the evening involved laying out the mount holes to match the ADAHRS units. Normally, I’d use the actual unit as a drill guide for something like this, but that wasn’t going to work for this – because the holes through the mounts need to be undersized, since they’ll get tapped for the 10-32 attach screw. Laying tham out manually seemed fraught with peril, especially since the hole spacings are 4.2” – not exactly a nice even division.

Eventually, though, I realized I could use the unit itself for this. I’d already drawn a line along the length of both angle pieces, marking where I wanted the mount holes to lie; I just needed a way to draw an intersecting line to mark the hole centers. So I clamped an ADAHRS in place on the angle, butted against the mark at the lateral center (ie where it would butt against the other unit), and then traced the inside of the mount holes. The outboard intersections between those circles and the previous mark would be my hole centers, and I could know they were the right distance apart since I used the unit as a guide.

So with those marks, I got the four holes drilled in one angle, then clamped both angles together and drilled through both of them to make the matching holes in the other angle. For the moment, I only drilled them to #30 – the final hole size before tapping will be #21, but I want to drill that final hole in assembly with the bar stock pads I’ll be adding to provide adequate thickness for the tapped threads.

As for those pads – last night I’d figured on just cutting 3/4” strips, making them the length of both ADAHRS units together, and riveting them to the angles. I decided instead to just use short pieces as needed; here again I can save a bit of weight and material. So there end up being three mount pads per angle piece: the two outboard ones cover the single outboard holes, while the center ones cover both inboard holes for the units. Each pad will be attached with a pair of flush rivets.

Anyway, there was just a decent bit of measuring and cutting and deburring and laying out holes and so forth. Also a brief break after my bandsaw blade decided to break – good thing I have a spare, or I would have been rather annoyed. I got to the point of having all the rivet holes drill between the pieces, and called it a night:

So tomorrow I’ll just need to mark the pieces so I can keep track of which goes where, get the rivet holes deburred and countersunk, then shoot primer on all this stuff before getting the riveting done. I’m going to wait until everything’s riveted together before I final-drill and tap the actual screw holes – I really want to make sure those are lined up properly.

I guess I need to think of my next mini-project – which I think will be putting together the switch console. That should provide a good solid couple days’ work…

Posted in Avionics, Fuselage | Hours Logged: 1.5

ADAHRS mount, part 2

Posted on September 24, 2020 by pclifton

Not a ton to report tonight. I laid out and cut the second angle piece that will constitute the ADAHRS mount platform. Next up will be deciding how to add the thick plate material that I’ll be tapping for the attach screws. Originally I was going to bridge the angles together with that stuff, but I don’t really feel like there’s a need to do that, and it’ll just add weight. So now I’m leaning towards just cutting two bar-shaped pieces the same width as the angles and riveting those in place.

It was fun to do a little mockup at the end of the night though:

Posted in Avionics, Fuselage | Hours Logged: 1

ADAHRS mount, part 1

Posted on September 24, 2020 by pclifton

Sort of a two-parter here. Tuesday night, I did a pretty extensive inventory of all the avionics, in an attempt to document all the assorted fasteners I’d need to get things mounted. Once I had that done, I assembled a decent-sized Spruce order, and added the ELT because 1) I figure I’ll want to mount it semi-soon and 2) it allowed me to get free shipping. Now all that stuff’s on the way.

Tonight, I got started on the mount setup for the ADAHRS units. Originally I’d planned to build a sheet shelf like I have elsewhere, and put it right behind the baggage bulkhead, but I’ve rethought some of that. For one thing, I decided to move the mount back to just ahead of the next bulkhead. The reasoning here is to get some separation between the units and the baggage area. A concern here is ferrous material that might affect the magnetometer (aka electronic compass), especially ferrous material that moves around or isn’t always there – for example…baggage! This location will make maintenance less fun, like if I ever need to service or replace one of these, but that’s better than having them be unreliable.

I’m also fabricating the mount out of a combination of angle and thick stock. This is to 1) provide really good rigidity and 2) provide a mounting surface thick enough to tap for screws. In keeping with the ferrous-material concerns above, these units must be mounted with non-ferrous hardware, such as brass screws. I really don’t want to do screws and nuts here – I’m imagining trying to work a screwdriver and wrench back here to service one of these – and while stainless nutplates do exists, they’re harder to find and still not necessarily non-ferrous. So I’m just going to tap the mount and have the screws thread directly into it.

Anyway, all I did tonight was set the location of the rear angle piece and get it cut and trimmed to fit. Next comes the more fun part of laying out the second angle at the precise distance forward, and figuring out the fit of the plates that will tie them together. Tomorrow…

Posted in Avionics, Fuselage | Hours Logged: 1.5

Wrapping up the lower shelf

Posted on September 20, 2020 by pclifton

Hooray for shelves! OK, I didn’t finish them yesterday like I thought, but that’s cause I ended up not doing airplane things yesterday. So I maintain that this counts, you just have to interpret “tomorrow” as “the next workday.”

The first part of the day was just figuring out how to get these quarter-turn fasteners installed. I attempted to find some documentation for these Friday night, and about all I ran across were some engineering drawings. So I did some mocking up and tinkering today just to wrap my head around how these should work. The overall idea is obvious: two rivet holes to attach the base to its mounting surface, and one larger one in the center to accommodate the actual fastener.

What’s interesting is that the specs on McMaster-Carr seem to indicate that the center hole should be a different size for the two panels – but that makes no sense, as the fastener has to go through both panels. So I just started experimenting with scrap. A 1/4” hole was a good size to accommodate the fastener shaft with a bit of wiggle room.

Next up was how to actually locate that center hole. I couldn’t just use a base as a drill guide, since the center hole isn’t really round. Instead, I worked out the rivet hole spacing, and just made myself a drill guide using a piece of scrap angle. With this, I could drill three #40 holes in a piece, then enlarge the center hole to 1/4”. I did a test run drilling a set of holes in another piece of scrap angle, and it worked perfectly.

Next I drilled a 1/4” hole in a strip of sheet, and used the fastener to attach them. This worked, but didn’t hold the pieces tightly together. This wasn’t automatically an issue, though; in practice, there’s a little retainer that goes on the fastener, which is what keeps it captive in the panel. I measured one of those and found that it was .040” thick. Just right for me to use a piece of scrap hinge as a pseudo-retainer to test the final fit. (I couldn’t just use the retainer; they’re a one-time use thing, and I had no spares)

So finally, after probably an hour and a half, I was satisfied that I could actually mount these things. Next I had to actually fit them. The challenge here was accurately drilling the center hole in assembly between the shelf and mount brackets, in position in the airplane, clamped together tightly. What I ended up doing was first laying out those holes in the shelf. To do this, I installed the shelf in the plane (for, I dunno, the fourth or fifth time) and marked the outlines of the four brackets. Then the shelf came out again and I marked the counterpoints for each bracket, then drilled a #40 hole at each spot. Then the shelf went back in again, got clamped in place, and I drilled the center holes through the brackets. Finally, it all came back out again, I used my drill guide on the brackets, enlarged holes as necessary, countersunk for flush rivets, and then it was time for primer.

By this time it had been raining steadily for a while, so I ended up shooting primer on the brackets inside the hanger. It’d been windy all day, so ventilation wasn’t really an issue:

While the primer was drying, I went to work finalizing the shelf itself. I still hadn’t final-trimmed it to length, so there was that, and I also wanted to add a small flange to the aft side. The sheet has a bit of a curve to it, which has been annoying while fitting it. In practice, the hinge would keep one side straight, and the quarter-turns ought to take care of the other, but I really wanted to have it be naturally straight. So I laid out a 1/2” flange, did the cuts necessary to set that up, cleaned up the edges, and got the flange bent.

By the time that was done, the primer was dry, and I got the bases riveted to the brackets and clecoed those back into the fuselage. That made it time for a real live test fit, albeit without the fasteners actually captive in the shelf. And…it fit! Whew. So I installed the retainers (necessitating removing and then reinstalling the shelf again), and gave it another test fit.

The only thing I didn’t like was that the fasteners didn’t quite seem super snug – it took hardly any force whatsoever to turn them. It seemed to me that, in this state, they could very possibly vibrate loose in flight, which would not be a good thing with the shelf being right above the stick. I already had a loose plan for this from my earlier experimentation – I went into one of my O-ring kits, got four little 3/8” ID rings, and put one on each fastener above the retainer. With those in place, the fasteners fit nice and tight. At this point, i was satisfied enough with everything to take the final step of riveting the brackets to the brace.

So finally: pictures! Here’s the finished shelf stowed, with the brackets still clecoed. The wings on the fasteners are just visible, as is the flange in the aft end of the shelf:

And the shelf lowered, showing a little more detail on the brackets and bases:

Next, it was time for some live mockups. After having worked on placing the electrical distribution stuff on cardboard cutouts for a while, I could finally look at it in place:

This was a worthwhile exercise. The E-bus alternate feed relay (top right) has vertically-oriented terminals. It’s not obvious from the photo, but the forward upper brace is in somewhat close proximity. I think that large wires going into and out of the relay would be problematic with this layout. Fortunately, this seems easily solvable just by reorienting the battery bus a bit.

A part of the layout tinkering, I laid out some cable guides in their rough locations, and then decided to go to town annotating a photo of the setup to demonstrate the planned wire routing. All wires enter/exit the shelf near the hinge line, necessary to allow the thing to pivot properly. Power feeds enter on the left, while all the individual circuit lines exit on the right.

The red line represents switched power from the master contactor. Normally, this line will be supplying almost everything on the airplane, with the exception of a couple things on the battery bus. The switched power feed first goes to the main bus fuse block on the left, and then continues to the E-bus fuse block, going through a Schottky diode. More on that in a second as well.

The blue line represents an always-hot line, directly from the battery – where it will be protected by an ANL fuse. The line feeds to the battery bus, then continues to the E-bus alternate feed relay. This relay is controlled by a switch in the cockpit, and it allows for feeding the E-bus directly from the battery bus. In the case of a master contactor failure, or any sort of electrical fault with the main bus feed, this will allow keeping minimum equipment online using just the ship’s battery. This situation is also the reason for the large diode between the main and E-bus; without this, closing the alternate feed would also energize the main bus, which is not desirable for a few different reason.

Finally, the green lines represent all the individual wires from circuits, making a nice little bundle. That bundle will also include a switched ground wire that will control the E-bus alternate feed relay.

(now the only question is: will it look anywhere this neat when I’m done with it?)

(also that turned into a lot more of a lecture than I intended)

Av shelf

So now…what next? I think I need to start working up a fastener inventory for actually mounting all this stuff. Between that and the need to get the ELT ordered, I ought to have justification for a Spruce order. I wonder if I should also go ahead and order the large-gauge wire needed for the bus feeds here. With those in hand, I think I can finalize the component locations here and get stuff mounted.

In the meantime, I guess now that I have avionics on hand, I can fabricate the ADAHRS mount in the aft fuse; that’s pretty independent of other stuff, and I could also finalize the static system routing – by which I mean cutting one more piece of tubing probably a couple feet long…

I think I’m going to stop typing now.

Posted in Electrical, Fuselage | Hours Logged: 3.5

Almost done with that pesky lower shelf

Posted on September 18, 2020 by pclifton

So yeah, made good progress on the shelf tonight. First order of business was working on the other half of the piano hinge, which attaches to the lower baggage bulkhead. I already had my layout lines there from a previous session, so this went pretty quickly. About the only real challenge was that since the hinge half is pretty much in the middle of the bulkhead, there was no good way to clamp it in place for the first few holes. I just resorted to holding it by hand while drilling the first three holes, then with it checked it was in a good spot to drill the rest of the holes. Then I just did all the demurring and prep and riveted it on. Nothing to it.

Next up was dealing with the attach point for the aft end of the shelf. I’ve planned all along to handle this by attaching aluminum angle to the aft upper brace, and the projecting lip of the angle is where the quarter-turn fasteners will live. I did change that plan up a bit, though – originally I was going to have the free side of the angle pointing forward, but I decided to reverse it instead. The reason for this was to provide more room on the shelf – with the angle forward, I’d have about 3/4” of the shelf where I couldn’t really run anything. Turning it the other way gets me that space back.

I’d also originally planned to use a single piece of aluminum, but I decided to do the extra work necessary to just have four small pieces in my fastener locations. Might as well save a little weight here and there.

Laying out the angle was a bit more fun than the hinge half, especially since I was working inside the fuselage and not on the workbench. Plus, messing up the brace would be annoying, so better to be careful here. Here’s a look at the brace with the four angle pieces clecoed in place:

Next up, it was time to reinstall all the baggage compartment pieces. In order to really make that bulkhead stable, the baggage floor has to be in place too. So a bit of busy work there, but once that was done, it was the moment of truth: trying to install the shelf. I probably didn’t need to worry, it fit just fine.

Here’s the shelf clamped into its stowed position (also giving me my opportunity to mark where the shelf edge should go, using the angles as a guide):

And then in the lowered position, as I’d see it if I needed to swap out a fuse or service anything else here:

So we’re getting there. The big remaining thing is going to be fitting the actual quarter-turn fasteners. These things came with no instructions or drill templates or anything like that, so while they’re not exactly complicated, I’ve still got to get this hashed out. Maybe I should check the McMaster website and they’ll have some dimensional drawings I can us for drilling.

I’ve also got to get those angle pieces primed before I install the fastener bases and rivet everything in place. I’m leaning towards just using MSP blind rivets here; bucking under that brace might be interesting, especially with the bases installed. But the way I figure it, this should be wrapped up tomorrow.

Posted in Electrical, Fuselage | Hours Logged: 2