Avionics Wiring Question

[mswain]

I am planning on the Garmin system for my Bearhawk, so I created a mount inside the right wing to hold the Magnetometer and would like to run the wire now. It uses a 9 pin connector (2 pins are unused). There are 3 different grounds shown on the pinout, so my question is......does every ground need its own wire or can I tie the grounds together at the plug and run them all back on a single ground wire? I need 7 conductor cable if they all get their own wire, 5 if they are tied together at the plug.

[aerolite]

My customer had Stein do up our main harnesses and this is how he did the 44 which seems to be identical wiring to the 22.

[tailwind]

Stein wired my system also. The Wiring was built with the pins crimped. I made provisions for the wires at the trailing edge. Landing lights and other wiring in the leading edge. When the wings were installed I was able to run the wires and install the pins into the connector.

[mswain]

Thanks for posting that Steve. So am I reading the diagram correct, it looks like they used 2 wires.....a 2 conductor and a 3 conductor for a total of 5? Using the shield on each wire for signal grounds?

[aerolite]

Yes, you're correct. I just had a look and confirmed that there are two shielded wires coming to the 44.

[mswain]

Steve, that is very helpful to know. This is my first foray into avionics wiring, trying to get my bearings.

I am thinking about adding another inline connector at the wing root, so the wing could be disconnected and wing removed without having to touch anything behind the panel. As much as I hate to add a potential failure point, it seems prudent to make the plane more serviceable? If anyone knows this is a bad idea, let me know.

[bestbearhawk1231]

I have been going back and forth with that idea also. Pros, you can run spares and have them pre terminated at the root on both sides, shorter sections for your runs, easier once you get to the airport and do final assembly, can wire your wings before your fuselage is complete if you know what you are going to use or have an idea of how many of what type you will need.
Cons, added weight and cost, one more failure point, one more place to screw up your pin out, can be easy to forget to hook it up and cause headaches trying to figure out why stuff isn't working when you are tired and stressed (since nothing is working right and it worked great in the shop before you got to the airport), added structure to support the connectors depending on what type you go with.

IF I go with them I will probably use the CPC series from AMP. They are round plastic connectors that come in various sizes and current carrying capacity pins...but I also have the crimper in my toolbox from my aviation days. Molex also makes some plastic connectors that would work well and are light weight. If you are already set up for d-sub connectors (k13-1 positioner if I remember correctly and a small blue daniels crimper) then that would be the way to go, be aware however that d-subs are limited in their current carrying capacities. Not a big deal unless you are planning on running a heated pitot probe and/or taxi/landing lights. Never run connectors at their full rated capacity since their life will be limited and will give you problems in the future. Also, when you are planning the # of pins needed, that you will need to carry all shields through the connector and it isn't a bad idea to run power wires in a separate connector or at the very least on the opposite side of the connector as your signal wiring with space between the power and signal wiring. That helps keep noise to a minimum.

Also, RayChem makes solder sleeves that make terminating shielded wiring much easier. I prefer the ones with the pigtail poking out one side since it makes it easier to daisy chain sheld ground together to reduce the # of shield ground wires going to your ground block. The small size works well for single shielded wiring, medium for 24-20 shielded pair and triples, large for 18 and larger shielded twisted pair and triples. An 18 shielded twisted pair may fit into a medium size but I don't remember for sure off hand. I don't have the part numbers handy.

Hope this helps.

[aerolite]

I always do some form of a disconnect at the wing root, most of the time a Molex connection. I have used anywhere from a four pin to a 12 pin connector. They are easy to make up, and it's not like you're pulling them apart very often, so they work just fine.

[rodsmith]

Where have people been mounting the Garmin magnetometer. Looking at the instructions there doesn't appear to be any good location in the wing. I'm thinking in the last wing bay to keep it away from steel, but worried my led strobe may affect it.

[mswain]

Where have people been mounting the Garmin magnetometer. Looking at the instructions there doesn't appear to be any good location in the wing. I'm thinking in the last wing bay to keep it away from steel, but worried my led strobe may affect it.

I copied Dave (DesertBearhawk) and built a bracket to go on the inboard side of the center rib that is 2nd in from the tip. There really is no place that meets all of the criteria in the Garmin manual....especially if you have Aux tanks and pumps.....but it seemed to be the best place. I am hoping I can calibrate any errors out. I am using all shielded wiring, so I hope that helps too. I found some non-ferrous nutplates to go on the access hole I put there.

[DesertBearhawk]

Two things:

I checked the installation spec's for the GMU22 magnatometer in the Garmin installation documents and the amount of ferris metal is < the maximum amount allowed within the critical distance. Also, a respected builder friend of mine who is building an RV8 has installed this system in his aircraft as well as several others tells me Garmin's spec for ferris metal is very coservitive and I will have Zero issues with my chosen location. I also spoke directly with a Garmin factory rep for the G3X and the G1000 (the both use the same magnatometer) and he says my location is a non-issue.

Secondly, I plan on wing disconnect plugs on both my wings, as well as my panel which will have two or three disconnects and the panel will be off and on your hand. This is how every production aircraft I've ever worked on does it. If it works for them it will work for us!

[rodsmith]

That's encouraging news. Mswain, where did you find the non-ferrous nutplates.

[mswain]

That's encouraging news. Mswain, where did you find the non-ferrous nutplates.

I got them from B and B aircraft.

http://www.bandbaircraftsupplies.com

The 68NA21-J-62 are aluminum and the same hole pattern as the K1000, so that's what I ended up using since I had the drill jig. The MS21076-06N are 660 Stainless (I believe silver plated?) and smaller (I assume its the same as the MK-1000?). Both are non-magnetic.