07-02-2020 Aircraft Wiring

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During a brief vacation in late June I had opportunity to focus on the “learn” part of the EAA motto “Learn, Build, Fly”. I was at a spot in my CH750 STOL elevator build where it made sense to study up on aircraft wiring — which I knew next to nothing about. This was essentially motivated by the need to wire up my Ray Allen trim tab servo. This book Aircraft Wiring and Electrical Installation is great, but it has also helped to see this video for clarifying what’s hard to explain using drawings and text alone:

Soldering connections is typically considered a bad idea in aviation applications due to the potential for the solder to crack during normal operation (vibrate, vibrate, vibrate — crack!). There are specific aviation applications where soldering is used. Zenith and Homebuilt Help instructions in the case of the electric trim tab servo are to solder the lead wire to the longer 5-conduit shielded wire that leads to the empennage center section. Required? Not really. This happens to be an application where I just didn’t want to solder — though I have no hard data to contra-indicate soldering for the trim tab wires. Still, I wanted a way to disconnect the wires without having to cut them (for eventual servicing / replacing the servo). Mostly, I wanted to learn.

I asked for suggestions and got some great answers on zenith.aero.

I liked the D-Sub connector suggestion as outlined in this video best, but a Deutsch-style connector would work too. However you don’t read about Deutsch connectors in AC 43.13 (or in the book mentioned above). Pure Mil Spec would be some kind of MS straight plug (or complex junction). I could have gone Mil but thought D-Sub would do the job as per my reqs (no wire cutting disconnect) and would teach me cool things I’ll use in the future.

D-Sub is the closest method to the Zenith / Homebuilt Help method of soldering that does NOT use soldering or crimp splicing. D-Sub doesn’t use a connector body like Deutsch or Molex but can be disassembled without cutting wires or trying to remove solder. Heat shrink tubing is cleaner and more resistant to the elements than electrician’s tape — and it won’t ever unwind. More expensive? Barely.

Now for the crimper tool. I prefered American made (this is my personal bias toward supporting decent paying jobs in America): Daniels Manufacturing Corporation makes top of the line crimpers, and for the middle size range (16 to 28 AWG) MH860 tool the D-Subminiature positioner should be 86-30-1 (for the 20 to 32 AWG AFM8┬áit’s K13-1). Here’s a vid from Jan Eggenfellner of Viking Engines on the importance of using aircraft quality wiring in the homebuilt: