Time: 12 Hours
This blog post is for several days of work since it is mostly about wiring. After the last post on the start of the VP-X power connectors I finished up the remaining two connectors with all their power wires. I started by cutting and crimping all the pins in place.
I was getting a good rhythm on prepping the wires and crimping before too long. The tool that they loan out works really well and I had the remaining plugs done pretty quick.
So that finished up the power connectors so I packaged up the crimper and ran it to the post office to ship back to Vertical Power, thanks Chad Jensen for the great customer service. After getting that done I moved on to the Dynon harnesses. I will have to build one for the autopilot panel, intercom and both com units. I started with the autopilot panel and orginized the wires, labeled, cut and crimped the d-sub pins on.
I followed this up with inserting the pins into the housing and put the d-sub backshell in place. I repeated these steps for each of the com units and finished their harnesses.
I decided to skip the intercom for the moment and moved on to the ADSB and transponder. Both of these have a power wire, and ground wire and two data wires that are orange and purple. These data wires are what the system uses to transmit and receive data. The Skyview screens have a 37 pin harness which has 5 sets of data transfer wires. Each is a different color with a matching purple and orange stripe. So you pick a color or port and match the orange wire from the equipment like the transponder to the colored wire that has the orange stripe and repeat with the purple. I used port #1 for the VP-X so that it can communicate with the Skyview system giving all kinds of information like how tha battery is doing and other electrical draws. Port #2 was used for the transponder and port #3 for the ADSB. Since I’m having dual screen, a 10″ and a 7″ I have to split the wires from the items, transponder, ADSB etc., to both screens so that they both receive the information. I hung the two 37pin harnesses on the back wall of the avionics area so that the length of the wires would be at a good distance to make the harness reach the screens.
Since I started with port #1 I finished up the last d-sub connector for the VP-X which houses the data wires as well.
So on to the intercom, the worst one. So for the record I am not a avionics guy and have no training on this stuff, with that said this is the hardest harness for me to build and this is why. From reading all about avionics specifically the communications parts the biggest problem is for noises to come through your headset like buzzing or static. To prevent these noises you use shielded wire, or wires that are encased with a braided cover under the white tefzel coating. This braided shield is to prevent other electronics like servos or motors from introducing noise into the communication wires. Makes sense to me that having these shields is a good thing. Here is the second thing that you have to do to prevent that noise introduction, grounding. So this shield needs to be grounded or connected to the airframe so that electrical charges can be dissipated. The biggest cause of noises in the system come from ground looping. Something new to me but the idea is that if you ground each end of a wire run there is the possibility that there is a different charge on each end of the shielding and could create a bad situation. So you leave one end ungrounded and ground the opposite one. Dynon wants you to have the ground come into the intercom and then to the ground block. So here is the fun part, I have 8 shielded wire bundles that need to be grounded. On top of that there are 6 of the wires that are inside those eight bundles that need to be grounded too. So what I have is 8 shields, 6 internal wires, a wire that will go to the pin in the d-sub and a wire that will go to the ground block that need to be connected together. This basically brings all grounds to one point and prevents any chance of ground looping. With all this chaos I had to really plan out my attack on them and figure what I wanted to do.
Here is what the block view of the d-sub looks like from the manual. You can see my chicken scratch on it helping me to understand what I was doing.
I used solder sleeves, like I have in the past, to terminate the shielding. I used one wire to figure out the best length for the harness and cut the wire. I then measured back 3″ to and removed that covering, trimmed the shielding and connected the solder sleeve.
So now I had the 8 shields terminated and a lead off of them. My plans was to solder these together and fold them back over so that a single wire could be added going towards the d-sub and a single wire back to the ground block. I also needed to add the 6 internal wires to tie into this bundle. I zip tied the ends together to hold them in place so I could solder.
I didn’t think that my solder iron would heat up this large bundle so I used my small torch to heat the wires and solder them.
I added the wire that will go to the d-sub pin, each time I added wires I used a strand of wire to wrap around the bundle to hold them in place and just soldered over it.
Now that I had all the shield wires, the ground wire and the pin wire soldered I needed to add the 6 wires from inside the shielded wires. These wires are directed towards the d-sub connector so they needed to be bent back to be able to connect to the soldered part, and I didn’t forget the heat shrink before soldering them.
So now I had all 23 wires completed with their pins installed and needed to insert them into the d-sub housing. Before doing that I slid a large piece of heat shrink over all the wires to finish them off when done.
I then spent some time straightening out the wires so they looked good and zip tied the harness and added the backshelll.
So that was a very tough harness to make and took a lot of thought and planning. I’m real happy with how it turned out and think that it will work just fine. I would say I’m probably 85% done with my wiring which makes me happy thinking that all I need to do is screw in the avionics and connect these harnesses and I will be good to go, keeping my fingers crossed as I say that. I few more items left for me to then I’m off to connecting the wings to the fuselage which is a really cool thought.