Electrical

Just a brief session tonight. Earlier today I sola fantasized about getting all the ground terminations done tonight and powering things up before the weekend, but it didn’t take much looking out in the hangar tonight to realize that was hilariously optimistic.

I got the newly-laced bundle pulled down into the gear tower and through the hole towards the firewall – kind of a pain really since all the masking tape tags made it impossible to just feed the bundle through as a unit. Between that and feeding a snap bushing over the end of the bundle to put into that hole, the result was a pretty tangled bunch of wires that needed some attention.

Next I sat down with the label printer and went through all those wires, putting in the labels for them. Kinda fun keeping track of which of 30-some wires I have and have not typed in already. Plus there were a couple tape labels that I was no longer sure what they referred to, so I ended up referring back to the schematics a couple times, just to make sure I was labeling things properly. Then I printed out a loooong string of heat shrink.

Before I trim anything to length, I want to get an Adel clamp mount point into the auxiliary longeron, since this bundle will need securing. That’ll let me get the general routing of the bundle down pat, and then I can start thinking about trimming. It’s going to be fun doing this since the area between the gear tower and the firewall is a bit snug.

Another no-photo night, I’m afraid. I decided to work on making provisions for securing the ground bundle. I already knew I’d be adding an Adel clamp on the auxiliary longeron forward of the gear tower, but I was debating also putting one on the forward brace above where the bundle goes down into the tower. The latter would be similar to what I did with the larger bundle coming up out of the right gear tower; on this side, the bundle was much smaller, but eventually I decided I wanted it secured as well.

Getting the nutplate mounted on the brac was pretty straightforward, though it still required the angle drill and some other creativity. The longeron was a lot more fun – initially I thought about just drilling the screw hole and using a nut instead of a nutplate, but I really didn’t like the idea of needing two hands to get the thing secured, so I went with the nutplate mount here too.

Unfortunately I didn’t finish that mount. The aux longeron is kinda fun to work on since it butts against the curved forward side skin – this means getting a tool aligned with a hole can be challenging. I already knew I’d have to make the rivet countersinks by hand, but I couldn’t even use the long shaft with the countersink bit here. Eventually I rigged up a combination of a hex adapter, 1/4” socket, wobbly joint, and a few extensions. That worked but it seemed like it’d take forever. So I added an adapter and my T-handle wrench, which let me put more torque on the setup.

That turned out to be a bad combination – it was hard to keep the bit well aligned, but easy to overcome the resistance from bad alignment with the T-wrench. The result was that I snapped the tip off my countersink bit on the second hole, and that tip remained lodged in the hole. I worked on extracting it for a while but eventually decided that I was getting to the point of causing damage if I kept trying to force the issue. Hopefully revisiting this in the morning, I’ll have better luck.

Started off today revisiting that countersink bit chunk that was tuck in the longeron hole. At first I wasn’t getting anywhere, but eventually instead of trying to drive the thing out, I got a fresh bit and tried using that to push the broken off part out from below…and it popped right out. Should have tried that a while back, I guess.

I still needed to finish the countersinking, but overnight I had a real forehead-slapping moment about this job. Yesterday I was trying to work out some really crazy ways of running the countersink bit by hand. I thought about trying to just run it in the angle drill, but was thinking of threading the countersink into my thread-hex adapter and then chucking that in the chuck adapter for the angle drill, and thinking that would all be too bulky. When I thought of it the way I just typed it, though, I realized my stupidity…I could just thread the countersink bit directly into the angle drill…duh. With that realization, I finished the countersinks and riveted the nutplate in no time, then got the adel clamp loosely attached, just to keep the wire bundle roughly in place.

Then it was time for some terminations. First was the short pigtail for the fuel pump – I’m using handshake splices for this connection. It occurred to me today that blade terminals might be nicer down the road, but I don’t have those in the right sizes, so handshakes it is. I needed to do the pigtail first because the fuel pump ground was the last wire to add to my bundle – I temporarily removed it while pulling the bundle through the gear tower. While working on this stuff, I also went ahead and laced the bundle up to and a bit past where the pump pigtail comes out.

Finally, there was nothing left to do but to start trimming and terminating the actual grounds. I got through eight of them (out of, I think, thirty-some) before calling it a night. These went pretty quickly, so I’m feeling confident about wrapping the rest of these up tomorrow – though there will be some pauses to handle lacing up the bundles. I want to go a little beyond just lacing the big bundle until it splits to individual ground tabs, maybe lace together batches of eight or so just to provide some vibration support closer to the tabs.

But hey, I finally have a photo again:

Got a nice early start this morning before it got stupid hot outside. I managed to finish up all the ground terminations by 8:00, at which it was time to stroll across the runway for Sunday Coffee Club. That was followed by several hours working on a Helio Courier that was donated to the Waller County Aviation Museum. Finally, I got back out and finished up the cable lacing and securing in the ground bundle area:

 At this point, I decided it was time to work towards actually powering up the panel. There was still a decent amount of work to be done before that, mainly from a quality-control (read: avoiding release of the magic smoke) perspective. What I decided to do was to disconnect every avionics connector in the airplane, apply 12VDC to the fuse blocks (with fuses installed, of course), and probe every pin in every connector, confirming that only the ones that were supposed to have 12VDC had it. After all, I figured the most likely cause of magic smoke release was putting bus voltage somewhere it didn’t belong.

That bit of testing took some time and was pretty tedious, and I also did the same testing for good grounds, ensuring everything was kosher. I also built out coax cables for the com radio and GPS-175 – I didn’t want any chance of something being damaged by powering on with no antenna connected. But finally, I had the panel and avionics shelf in, everything in place, and the main bus block tied to the power supply. I looked everything over one more time – that’d be a lot of money to ruin – took a deep breath, and flipped the switch.

What I got was not what I expected at all. A couple units flickered on briefly, and one display showed a splash screen for a moment before going dark. Was this the normal boot sequence? Nope, another flash, another brief splash screen, nothing. This seemed indicative of periodic voltage drops from the power supply, and checking across the terminals with my multimeter confirmed it – the drops were large enough to be noticeable on a relatively slow-responding digital multimeter.

Strange – this was a 12A power supply, and by the book all the avionics together should draw under 6.5. But still, I started pulling fuses – maybe I just needed to shed loads a bit. I eventually got down to just the two HDX displays, but still got the same results.

A this point I gave up and went inside for dinner. After thinking it over, and chatting a bit on a phone call with my parents, I decided to try one more thing – bypassing the fuse blocks entirely, and trying to only power a single display. And here I finally had some success – the one screen was actually able to get through the boot sequence. Even so, the display was still flickering from time to time, so obviously this power supply is problematic.

At least now I know that both displays are functional. I didn’t get the full-panel “it’s aliiiiive” photo I was hoping for, but I guess one display lit up is still something:

So, where to go from here? I may see if a neighbor has a better power supply I can bother. I may also try adding a 12V battery in parallel to the power supply to try and smooth things out a bit – it’s not a perfect solution but maybe it can at least get me through some initial testing.

Well, today I went through several levels of troubleshooting but it all paid off in the end. Working off the idea that my power supply wasn’t performing well, I decided to try adding a battery in parallel. At first I tried the small backup battery for the CPI2 unit; I removed it from the plane last night and let it charge on a battery tender overnight. This morning before work, I tried adding it in parallel – no change. I even tried powering the panel off the battery alone, to no avail.

In retrospect, this should have been a major hint as to what was going on, but I didn’t get it. Instead, I concluded the battery was too small as well, even though that seemed nonsensical since the ignition is going to draw significantly more power than a single EFIS display. So i extracted a battery from a motorcycle, gave it a good charge, and tried that after work. Same result again, which was really weird.

OK, next step is to take the aircraft wiring out of the picture. I took one of the original Skyview harnesses that I never used, removed everything except the power and ground leads, and connected those to the power supply. This time, the display booted up, and for a moment I thought I’d had a breakthrough…but then it started flickering again.

After a lot of head scratching – plus bouncing ideas off my neighbor, who’d come by to take my firewall rotisserie fixture for his -8 project – I really was suspecting the connections. Up until this point i’d been using some test leads I had with alligator clips on either end, since they were easy to install. To make a long story short, I replaced both leads with actual terminated wires, and finally I was in business:

From that point, I started adding things back until I was powering both busses again, and I was able to get the entire Skyview system up and running. I configured all the network devices, got an initial hack at a display setup done, and generally just kind of sat there playing around with things. Lots of stuff isn’t going to be functional at this point – no GPS signal in the hangar, the engine monitoring obviously has nothing to monitor, and so on – but by god, it looks like airplane stuff.

The only rub here was the GPS-175, which didn’t want to power on. I reverified the connector pinout, made sure it had power/ground where appropriate, but still no joy. But when I connected the backshell to the GPS unit outside the rack, it powered up. Clearly there was a connection issue, but only in the rack.

Turns out that when I built this rack mount, I misunderstood how the mechanism for securing the unit in the rack works. I thought it was a simple locking tab, but it also has a threaded portion that mechanically pulls the unit into the rack. Well, even with the bezel of the GPS against the panel, the connector obviously wasn’t engaging. I’m pretty sure that, due to my misunderstanding of how the rack worked, I set it a bit too far back into the panel, so I’ll probably need to re-fabricate the angles that connect the rack to the panel.

I did go ahead and power up the GPS again outside the rack to try some configuration there. A nice VAF person sent me some information about getting the GPS properly talking to the Skyview units, and with his info, I got that setup done in under ten minutes; I was seeing message traffic from the GPS on the Skyview setup menu, and the GPS test mode was properly driving the Skyview HSI as expected.

So all in all a happy day. I guess now it’s about time to set all this aside and start thinking about working with the canopy. Only thing I still need to work out is routing the tail strobe wire out through the aft bulkhead, then I think I need to start getting the turtledeck permanently installed.

As mentioned before, my current goal is to verify as much internal tail stuff as possible before I get down to permanently attaching the turtledeck skin, since that will turn any work behind the rear seat into a sort of cave diving expedition.

First up, I figured I’d see if the tail strobe wiring was OK. I didn’t really have any reason to suspect issues – compared to the wiring for the avionics stuff in the tail, this is dirt simple – but it doesn’t hurt to check. Plus it’s just fun to flip switches and make things happen, especially if I can then go walk out to the end of the ramp and say to myself, “yeah, I should be pretty visible to other aircraft.”

Next up was the more fun thing – trying to get a GPS fix out of the GPS-175 so I could verify it was sending position data to dependent components, specifically the transponder and ELT. At first I was intending to figure out a way to move the entire fuselage out of the hangar to get a clear view of the sky, but I couldn’t figure a method of moving that 1) I trusted to not potentially go wrong and cause damage and 2) wasn’t way too much work for a one-time verification task.

Instead, I worked out an alternative method – move the fuselage as close to the open doors as possible (much simpler than moving it out since I didn’t have to deal with bumping over the concrete lip and hangar door tracks), and then put the actual GPS antenna as far as the cable would allow. Since Garmin requires a minimum cable loss, which in turn means a minimum cable length of 6.5’, this was pretty doable. With this setup, the antenna had a clear view of a little more than half the sky, which I was hoping would be enough for a solid fix – and it was.

So then I went into the Skyview setup menu and went to look at the transponder page, which would tell me if it was getting position data from the GPS-175. Everything was indeed kosher, and the system now believes it is ADS-B Out compliant (this means the transponder can transmit position data accurate enough to meet legal requirements):

That just left the ELT. Here, I had to do some documentation mining – the Artex 345 I have says that it accepts aviation format serial data at 9600 baud, whereas the GPS-175’s serial setup options offer both “Aviation 1” and “Aviation 2,” with no mention whatsoever of baud rate. The Garmin manual provided no clarification I could find, nor did my Google search attempts yield anything, so eventually I decided I’d just pick one format, try it out, and see if it worked – if not, I’d try the other one.

The fun part here is that unlike all the other stuff I’m playing with, the ELT provides no sort of user-friendly UI to get setup info. The only way to check for setup issues is to have the unit run a self-test and see if it reports problems – which it does by blinking the LED on the remote panel switch. Kinda reminded me of checking trouble codes in OBD I cars, where you had to count how many times the check engine light blinked at you.

I was a little surprised that I got no error codes on the first self-test, which seemed too good to be true. So I did a typical software troubleshooting move by intentionally causing the error condition – in this case, powering down the GPS-175 so that the ELT ought to report no position data – and that did indeed get me the error I expected. GPS back on, one more self-test, and once again no errors.

Oh, and I don’t recall if I mentioned it before, but while testing and tinkering with the EFIS, I’ve seen some other aircraft show up as nearby traffic, which confirms that the ADS-B receiver back in the tail is doing its job correctly. So at this point I’m pretty confident that all the tail wiring is in good shape. The only thing I haven’t tested is the elevator trim motor, because I think rigging up a test with that will be more trouble than it’s worth.

So…I guess its really time to pull that turtledeck skin down, finish prepping it (I know it needs to be dimpled, pretty sure I haven’t done any demurring yet either), and get that thing riveted on. Which will unfortunately mean spending one time lying inside a really snug cave in the summer Houston heat, but such is life.