Electrical Plugs at Wing Roots

[Cherrybark]

I thought a fuselage mount would be great for the magnetometer but the Garmin G3X system came with their GMU 11, solid state magnetometer that is very sensitive to magnetic fields. The manual specifies a minimum of 10' from electric motors and relays, including servo motors. Using Kitfox factory mounts for the autopilot servos put my AP pitch servo near the elevator bell crank towards the rear of the fuselage. So a wing mounted magnetometer is in my future.

Can you tell me more about how you wired the lights? AeroLED says the braided shield can be used as the "Black" negative/ground wire without any radio noise. Seems odd to have varying current running in the shield as the landing lights are wig / wagged but I know just enough to be dangerous.

Again, showing ignorance of wiring, what is a "bare shield"? And what type of wire did you find that offered 6-conductor 20 AWG? I'm only finding 3-conductor in official TEFZEL aircraft wire. Whether or not that grade of wire is really necessary is probably worth a separate thread that would go on and on.

[jmodguy]

Cherry
I am using DB9 (computer serial port) connectors at my wing roots. These are very affordable (cheap) and easy to put in small places. You can get a bag of 10 for a few bucks at Frys or similar electronics store. Be sure to use mil spec machined contacts. We use these on mil aircraft. The rolled contacts can be iffy at times and it is harder to get consistent crimps.
I am using a 4 wire unshielded cable in my wings. This allows for wingtip wires for nav, strobe, ground, and sync.
I used a 3/8" OD polymer tube from Lowes as a conduit to route the cables to the wingtips. I cut a small hole where the OAT and magnetometer wires head to the fuse. Plenty of room for the quad cable and 4 wires from my magnetometer.
As for using the shield in a cable (term for a multi wire jacketed "wire") as ground, I would NOT recommend this. The shield is designed for noise mitigation (EMI), not current handling. Some of the tefzel cables use a silver plated braid that corrodes rather easily and you would not want that to be carrying any current.
Do you need Tefzel wire? nope. a lot of your car wiring is not tefzel, even in the engine compartment. The reason mil aircraft use teflon based jackets is the noxious fumes PVC puts off when it burns. Tefzel is pretty nasty too, it just has to get hotter.
I have been wiring military and civil aircraft since 1980. I currently work for a DoD contractor in the wiring and interconnect department and can go on for a bit about wiring best practices and techniques...

Oh - the connector on the fuse should have female contacts so you do not inadvertently short any pins (there will be power on one or more).

[efwd]

Thanks Jeff. I never understood why the instructions instruct what end of the wire the female and male connectors go on. Now While wer on the subject Ill hijack Carls thread since he will want to know as well. Without spending $150 on a crimper, where or how would one get the 6AWG battery cable connector crimped onto the cable. I bought a really nice multi head ratchet crimper but it turns out that it wont handle 6AWG
Eddie

[Cherrybark]

Jeff,

Thanks for those comments. Being retired software, I've been surrounded by DB9 connectors, just never thought of them in this context. When using shielded, do you solder or connect the braid to the cases?

I saw your idea of using the 3/8" OD polymer tube in an earlier thread. Promptly returned my unopened bags of official conduit and bought a nice length of poly for a fraction of the cost. Great idea, and I like the smooth walls.

Do you know offhand if the magnetometer is doing the analog conversion at the unit and sending digital in the wires? I would think digital transmission would be less subject to noise. If digital, I would be less hesitant to use non-shielded, 4-strand for the lights and run the magnetometer wires through the same spar.

I'll be happy to move away from Tefzel and enjoy the wider variety of color choices. Would you go so far as to use Tray Cable or is tinned better?

[Cherrybark]

Floog,

I really appreciate that specific recommendation for wire. Excellent to have rather than spending hours digging through on-line catalogs.

[Dave S]

Carl,

I thought about making a junction at the wing root; but ended up going simple and cheap while reserving enough of a service loop at the root to permit the addition of connectors or a junction block if I some day needed to remove a wing or two. So far, 8 years of flying and I haven't found any reason to remove a wing...but there is enough wire in the service loop to cut and install connectors.

[Floog]

The cable is:
Nova Electronics Strobe Cable Made is USA

The bare stranded wire (grounded at ONE END ONLY) is in contact with a metal shield under the insulation. I used one of the (6) conductors as aircraft ground. The other (5) are for position, landing/wig-wag, and strobe lights.

[Floog]

If memory serves (iffy), I got 42 feet of the cable gratis from GS-Air. Hope this helps, Carl. You'll need another run for your ADHRS.

[PapuaPilot]

I choose to use Tezfel wiring throughout my plane. Yes, you can use other types of wiring, but there are good reasons why there are standards for the wiring that goes into certified aircraft.

How often do you think you will need to remove the wings? After lots of thought and advice I decided not to put connectors at the wing root. Every connector is a potential source for problems (poor connections, corrosion, etc.) and EMF (noise) if it is a shielded wire. I have lots of experience finding corrosion in connectors, including wing root connectors. I really didn't want to put a connector in the magnetometer wiring, it is a very sensitive sensor. I made my wing wiring so it could easily be disconnected and pulled out of from the spar tubes if ever need be. It would only take a few minutes to do this after opening the wingtips. I bet it will take far less time to do this than to troubleshoot and repair a problem in the wing root connectors.

Per the Garmin criteria there isn't a good place to put the magnetometer in the entire plane. I ended up mounting mine on the outboard rib of my left wing. I used shielded wiring for the nav, strobes and landing lights and all of their grounds returned in the same wire so that there would be minimal EMF. I also used stainless steel screws for my wingtips (certified planes use brass or SS).

Don't use the spar or airframe as the ground as it could lead to EMF that could affect the magnetometer. Doing so can turn the spar or airframe into on big EMF antenna.

The G3X will self test for problems with the magnetometer; they have you turn on circuits one by one while the unit is checking for interference (it is pass or fail). Initially mine failed when the landing lights were turned on and I had to reposition the wingtip connection farther away from he magnetometer, then it was fine.

[Cherrybark]

Connectors at the wing tip...sigh. Sometimes I get fixated on a solution and don't consider all of the alternatives. The Garmin magnetometer already requires a connector and I intended to have connectors at the lights as part of the tip removal. Pulling wires through the spar with a cord is dead simple. I'll skip the root connectors but appreciate all of the inputs.