S

SteveHRV7

Member
I am ready to start wiring my wings and would like feedback on the contents of my wing conduits. I will be installing a Tru Track AP, dual GRT Horizon EFIS and Aero LED lights. I plan to run 3 conduits in each wing with the following wires in each conduit:

Right Wing
1. GRT magnetometer wire
2. Power for LED nav and LED strobe lights, power for the autopilot servo, marker beacon antenna coax
3, Return ground wires (I am using separate return grounds for anything with power)

Left Wing
1. GRT magnetometer wire
2. LED nav and strobe power, pitot heat power, Archer VOR antenna coax
3. Return ground wires

The strobes are LEDs so they should not cause RF interference as a non-LEF strobe might. Any obvious conflicts here?

Cheers!
 
I was planning my wiring runs today for my -7A wings. My runs are similar with slight differences. I've heard A LOT of mixed reviews of the Archer VOR wingtip antennas. Some love them, some hate them. I can't tell you how many calls our avionics shop gets from customers who have issues with those. I wanted to install one in my -7A because they are hidden, but its going to be full IFR and I need something reliable, so am going with cats whiskers. Just my .02.

As an avionics installer, I would recommend you not run those ground wires. You can eliminate them completely. If you look at manufacturers install diagrams, most call for local grounding. This is especially true for lighting and pitot heat. However, you will want to run all the grounds to the GRT Magnetometers, as they are likely signal reference grounds. It won't hurt anything adding all those extra grounds, but honestly its dead weight you don't need.
 
Steve,

This is not a thorough review, but a couple of general comments:

1. Do not separate the power and ground wires for a given load. By separating them you make a big ol' loop antenna. Run the power and ground wires for a given load together in the same bundle. Or better yet, if you're worried about EMI, run them as a twisted pair for added immunity.

2. EMI-wise, the objective of splitting your wiring into separate bundles, if you find that that's necessary, is to keep highly EMI-emitting circuits away from circuits that are highly sensitive to EMI. In your case, the magnetometer and antenna cables are probably the most sensitive to EMI (although likely sufficiently immune to be run together with the rest!). The LED nav/strobes are actually probably your worst EMI emitter. Yes, they're LEDs, but they use switching regulators that can generate EMI (though likely not enough to cause any problems). The heated pitot may be an EMI emitter if it is one of the newer designs that switches power to the heating element to regulate temperature, i.e. Dynon or Gretz/Angus (though likely not enough to cause any problems). The autopilot servo will be an EMI emitter and may also be somewhat susceptible to EMI itself. Specifics will vary from one product to another, so see manufacturer's guidelines for your specific products.
 
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Don't over think!!!

Keep it simple. Trevor is correct in his assessment, especially with regards to the ground. Run all wires, coaxes etc. in one run.

To make a very simple and effective local ground, get one of the B&C grounding trees. Get the 48 tab version.

http://www.bandc.biz/grounding-supplies-battery-cables.aspx

Cut the tree so you have small tree of 4 tabs. Drill a hole in the base of this tab. Scuff an area of tip rib and mount this tab on the tip rib. Put a "fast on" connector on your ground wires and attach to tabs. For a bit of added security, put heat shrink over each one. Confirm continuity. The photo shows the terminal strip for Landing light power, taxi light power, position power, strobe power and strobe sync. These have ring terminals connectors from the source. The grounding tree is brass and can be seen to the right.

img2604g.th.jpg
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For your power and sync wires for the lights, you can also make it simple for removal by purchasing a terminal strip from Steinair with fast on tab adapters and using this for the remaining wires. For this build, I purchased one of those printers that prints on heat shrink.

For coax you can purchase bulkhead connectors and mount them to the tip rib for any tip mounted antennas.

Simple, effective and works great.
 
more wires...

The a/p servo obviously needs more than just power.
Where's your OAT?
How 'bout landing lights?
Run a spare/unused power/ground for that future upgrade, like aprs or something else.
 
TCONROY said:
As an avionics installer, I would recommend you not run those ground wires. You can eliminate them completely. If you look at manufacturers install diagrams, most call for local grounding. This is especially true for lighting and pitot heat. [...] It won't hurt anything adding all those extra grounds, but honestly its dead weight you don't need.
Click to expand...

For what it's worth, I believe there are some avionics manufacturers that recommend you avoid using the airframe to ground your wing lighting, since it can cause problems with wing-mounted magnetometers. For instance, here's what one manufacturer says in their install manual:

Consideration for Wing Grounded Lighting Fixtures

The following installation practices are recommended if the required (magnetometer) mounting bracket is located in the wing.

1. The wing tip lights should not have a power ground referenced to the chassis of the light assembly that would then be referenced back to the airframe ground via the light assembly mounting.
2. A dedicated power ground should be used and returned as a twisted pair with the power source back into the fuselage for a wing mounted (magnetometer).

These installation practices will prevent magnetically interfering currents from flowing in the wing skin that encloses the (magnetometer).
Click to expand...

Food for thought.

mcb
 
Great input!

Thanks everyone. In reviewing the various threads on wing wiring the only commonality is that there is no consensus on how to bundle the wires. I like the idea of running a ground block out into the wing. I also think the twisted wire pair makes sense. In reply to some of the questions, the AP has a wiring harness so it contains all of the necessary wires; the OAT is going into the tail under the HS. I will give GRT and AeroLEDs a call and see how they recommend I handle the wires for the magnetometer and lights. I will post an update when I finally decide how I will do it. Thanks again for all your advice!
 
roee said:
Steve,

This is not a thorough review, but a couple of general comments:

1. Do not separate the power and ground wires for a given load. By separating them you make a big ol' loop antenna. Run the power and ground wires for a given load together in the same bundle. Or better yet, if you're worried about EMI, run them as a twisted pair for added immunity.

2. EMI-wise, the objective of splitting your wiring into separate bundles, if you find that that's necessary, is to keep highly EMI-emitting circuits away from circuits that are highly sensitive to EMI. In your case, the magnetometer and antenna cables are probably the most sensitive to EMI (although likely sufficiently immune to be run together with the rest!). The LED nav/strobes are actually probably your worst EMI emitter. Yes, they're LEDs, but they use switching regulators that can generate EMI (though likely not enough to cause any problems). The heated pitot may be an EMI emitter if it is one of the newer designs that switches power to the heating element to regulate temperature, i.e. Dynon or Gretz/Angus (though likely not enough to cause any problems). The autopilot servo will be an EMI emitter and may also be somewhat susceptible to EMI itself. Specifics will vary from one product to another, so see manufacturer's guidelines for your specific products.
Click to expand...

Very good advice! I recommend that the power and ground wires be twisted together in pairs to help null out potential near-field coupling into adjacent wires or antenna coax, and it is a good idea to run any power wires and their grounds in separate bundles from signal wires to avoid noise coupling. It is best to bring the ground wires back to the ground block in the fuselage to provide the lowest ground resistance path for higher current power devices, lights or otherwise. Relying on rivits and skin panels for your ground path isn't always the best way to go, especially since you can't guarantee that the ground "image current" flows right next to the positive wire the whole way. Separation between the positive current and the ground "image current" in a metal wing is what leads to RFI since it does create a loop antenna. Twisted pairs are the best option because they alternate the electric and magnetic fields created by the current flowing in the wire with each twist, effectively nulling out emmissions when you get more than a few inches from the wires.
 
Here is a wiring diagram that represents the recommended installation for a wing mounted Pulsar NS90 or a tail mounted Suntail from AeroLEDs: http://www.aeroleds.com/LinkClick.aspx?fileticket=ytfG_ZoIwB8=&tabid=2181

There are a couple of ways to go about making the twisted pairs. You can go DIY and twist individual Tefzel wires with an electric drill, or you can go to the EDMO website and order shielded/twisted wire. This is a good choice for running the nav, strobe, and power wires: 18G 3C TEF M27500-18TG3T14 TEFZEL SHIELD This is three conductor twisted, shielded wire. The synch wire can be run as a separate individual wire since it doesn't carry any current.

http://www.edmo.com
 
I Guess Im trying to bring back an old thread as this one hasnt been touched for a while. I am pretty much Dumb when it comes to Electrical so I am wondering if you have a block in the end of the wing, could you run one common power and one common ground to the block from the fuselage and then run your landing lights, nav lights etc off of that.

I have alot to learn.......
-david
 
Flyguytki said:
I Guess Im trying to bring back an old thread as this one hasnt been touched for a while. I am pretty much Dumb when it comes to Electrical so I am wondering if you have a block in the end of the wing, could you run one common power and one common ground to the block from the fuselage and then run your landing lights, nav lights etc off of that.

I have alot to learn.......
-david
Click to expand...

You could do it that way, but then you'd have to put relays out there, with another control wire from the panel to each relay....not to mention circuit protection....more complicated! Wiring the extremities of a small airplane like an RV is incredibly simple, well understood, and well documented. Bingellis or Knuckoll's are good sources for the straightforward "distribution" stuff.

Paul
 
David, you can have a common ground but I think what you are forgetting is that you want to be able to switch your lights on individually. That's why you don't want a common +12 block.

You'll use 1 switch to turn on the Strobes and 1 switch to turn on the Nav lights. There are a couple of different switch options that you can use for your landing lights.

I'll show you how I have mine when we go flying tomorrow.
 
Keep it simple, as the more complex you may want to design it the more issue you may run into.

I would keep the two magnetometers in the same wing, separating them could give you much hassle.

Here is what I have and have had zero issue with RF or functionality. My GRT magnetometers are installed up above the bell crank behind the baggage compartment. VOR antenna along with marker beacon are in the wing tip and the monthly test for IFR shows zero error with great reception while enroute. The Strobe and Nav (LED) lights to the wing tip are on a different path then the main conduit which contains all my coax and other antenna cables. Two GPS antennas are in the opposite wing tip. Also highly recommend the B&C ground block. Be cautious in choosing dimmers, they can be a good source for RF noise I am using Maxdimmer and it is working great.
 
Thanks for the replies, Rick I totally wasn't thinking about switches yet but that wouldn't work at all as you pointed out. Thanks a lot
-david
 
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