G3X Avionics Wiring

Worked on more wiring the LRU (line replaceable units) or blackboxes for the G3X avionics.

So far, I've just wired up the signal wires (which are the hardest parts). The power wires will come later when I get the actual instrument panel painted and install the switches into places. But these boxes connect to sensors and other boxes that will then display all the information on a screen (Electronic Flight Instrument System - EFIS - if you want to be fancy about it)

Once all this is done, just add the front panel and screen and the panel will  be finished.

Mounted subpanel, wiring work

Installed the subpanel and old instrument panel to see where the G3x black boxes and avionics would fit. As expected, the GTN 650 is longer than the space between the instrument panel and subpanel, so I'll have to cut out a section so it can fit.

I also kept going on the wiring. So far, most of the wiring has been point to point, meaning you simply put a wire on one end and connect it to another. I've been putting off wiring the CAN bus, which allows the avionics to communicate with another. Unfortunately, it's odd how it is depicted in the wiring diagram.

You can see that here I have to make some sort of splice, so that two wires come together and only one wire comes out (actually 3 in 2 out for the CAN lo pin and CAN termination pin). How you physically do this is beyond me. I suppose you can use solder sleeves that make a soldered joint for the wires. I suppose a butt splice would work too, but the idea is to avoid a method that increases the size of the joint too much. The solder sleeves shrink when heat is applied to them, not so much for the butt splice. 

Anyway, here's my first attempt - which I screwed up. 

The method for doing this came from the G3x install manual and this VAF post. Anyway, I'll need some help before I continue on with the CAN wiring. 

Magnetometer bracket, FAB, and subpanel

I made a bracket for the Garmin magnetometer. Apparently you can purchase one for $75 or make it yourself. No surprise, the guy who makes his own plane will make a bracket. Like anything else, I screwed it up the first time.

It came out OK, but was too thin with 0.025 in aluminum sheet. So, I remade it with 0.040 in sheet. Also, this time I used a 2.5 in hole saw to make it appear a little more professional.

What's crazy is the G3X manual specifies that you have to "Align the GMU 22 mounting rack’s forward direction to within  0.5° of the longitudinal axis of the aircraft".

So, I tried to make it as square as possible.  0.5° is a pretty small tolerance, but I think I got it. Here's how it came out:

Next up was the forward airbox. Yes, I had been putting this off. Basically, I shifted to bottom plate about 0.75 inches toward the copilot side so it would clear the mixture arm. I had to trim off the top of the filter because the captive bolts were poking the filter. Design is a series of compromises, I guess. I hate to hack up the filter but I was tired of fucking with it and something had to give.

Finally, I've been working on the subpanel now that I've started wiring the cockpit. The center section was the first up, and it came out well. I'm planning to install the cockpit instruments on the bench rather than in the actual plane (I'm not good at yoga).

The spotty green paint is zinc chromate primer. It's supposed to be a light coat, so while it looks stupid this is what you get. The factor claims you don't need any paint at all because the aluminum has an alclad layer that protects it from corrosion. Oh well, better safe that sorry.

Overdue update

It's been a while since I updated the construction log. Most of the heavy lifting gets done on weekends, but the last few weekends have been busy: Chapel Hill, NC; Orange County, CA; Atlanta, GA; Austin... so. Lots of excuses. But, some progress:

PMag installation:

Simple and straightforward, plug and play.

I was not too pleased with the adapters. Plane spark plugs are 18 mm, but "regular" spark plugs with larger gaps (and better performance) are 14 mm. So, there EMag air sells adapters that can convert the size for you. Problem is, they are brass, or some sort of soft metal. The fit and finish is terrible - the threads were full of burrs and I had a really hard time getting them to thread into the cylinders without cross threading them. Anyway, I'd go with another vendor's if I had to do it again.

Also, I installed the engine temperature sensors for the G3X system: exhaust gas temp, cylinder head temp, and oil temp:

Avionics and Panel wiring!

So I've mentioned before that I'm putting in a Garmin G3X avionics system. Over the last few weeks, the boxes have slowly been rolling in.

Putting it together has been kind of fun. Here is what the wiring diagram looks like:

Simple, right?

So, the crazy part is how these things are connected to one another. Think of each rectangle as a "black box" and the lines are the individual signal and power wires that go to each box. They are connected with DSUB pins. These are the kind of connectors you see on older monitors and printers. The only difference is, I am making the connections myself instead of just plugging a monitor cable into the end. 

Another intersting note is that the wire is pretty small - 22 gauge is typical. To put that in perspective, that's about 0.025 inches around. Kinda small. Typically, you would solder these connections. But since this is an airplane, we need a better connection. The answer is a crimped pin. 

Someone on vans air force was nice enough to let me borrow their military-spec crimper. This thing simply crimps down a pin or socket onto the wire. My avionics dealer has a series of videos on the tools, wire, crimping, etc. It's been very helpful. 

I put some Styrofoam models of the black boxes into the plane (this is before I had the real thing, and wanted to avoid damaging the real things moving them around) and planned out where all the wires would go. Then, I used the spaghetti diagram shown above to connect them all together using the tool and wires I was talking about earlier. 

 What's crazy is how precise the crimping is. In the second photo, you can see the slight difference between the top and bottom set of wires. The top set has too much insulation stripped off. The tolerance is 1/32 to 1/64 of an inch. Not much to work with there. The ones on bottom are within spec. 

Anyway, just do wires like that 70, 80 times and call it done! 

So, not much to show here other than I'm wiring away... 

FAB, mixture arm, cowl

Worked on the mixture arm again.

Finished up fabrication on all the subcomponents for the subpanel. Then I primed all the parts, which takes a couple days to dry. I'll have to wait until then to rivet it all together.

Getting the throttle body to work has been a pain in the ass, to say the least. Van's calls the air intake a forward air box (FAB), and it attaches to the bottom of the throttle body. On the other end, the cowl has a snorkel that provides ram air. In the middle of the FAB, there is a filter like you would find in a car. Of course, this means it has to line up with the cowl. On top of that, the captive bolts that connect to the throttle body cannot interfere with the filter. On top of that, the levers and cables for the throttle and mixture have come from either side and can't hit the side of the FAB. On top of that, each cable and lever has to be aligned at a certain angle to give enough torque so that the throttle body can go through it's full range of motion. And on top of that, the fuel servo sits off center on the engine, so it is shifted to one side.

So, all this bitching and moaning is about the fact that there are a lot of variables to account for with the throttle body..and when you mess with one it messes up all the other ones too. The good news is I came up with a solution. First, put the cables and levers into place. Make sure they are aligned correctly so that the throttle can go from the full range from open to closed, and the mixture arm can go through the full range of rich to idle cutoff. Then, go get a clear piece of plexiglass and cut it into the same shape as the aluminum top that serves as the mount to the FAB/throttle servo.

This way, you can see where the filter is and avoid positioning the FAB where the bolts would hit the filter, while keeping clearance for the levers that operate the throttle and mixture.

Even with all this, I'm going to have to make a cutout in the cowl. The end of the bolt is less than 0.25 inches from the side of the cowl, so the solution is to cut out that section and make it balloon out a little. You can see the minimal clearance here

I also fitted on the cowl just for grins to see how it would fit. Not too bad, need to make a few adjustments so everything is square and symmetrical.

The next steps are to get the servo sorted out, figure out the cowl, then start busting out the avionics. After that the wings and tail will go on, and hopefully some flying!

Subpanel and avionics choices

Continued with the subpanel.

Got everything test mounted and installed. Now just priming it before final riveting takes place.

I'm not going to rivet it into place just yet though because it will be a lot easier to install the avionics on the bench instead of inside the plane. But my plan is to have it ready to final-install after the wiring and avionics are complete.

Speaking of avionics, here's the current plan:

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That's the Garmin G3x Touch. It's basically the same thing that business jets have, except with more features like touch screen, angle of attack indication, and an infrared camera inset capability. Here's the expensive verision in a business jet. 

I have to say, this is pretty exciting. I'm hoping for a clean, functional, and capable flight deck and this seems to fit the bill. Other things I'll need to get or want to add are: 

• FAA-approved IFR GPS navigation radio
• Autopilot
• backup instrument (with backup power supply)
• lighting

Of course, all this comes with a pretty hefty price tag so it might be a while till those get added. Anyway, waiting to secure some cash so I can put my order in and install this. Should be fun