Root Connections

[paul330]

At the risk of re-starting another "never-ending debate" I would like some advice on connecting wires at the wing root. And, yes, I've done the forum search, read the stuff and have decided I need connections. I don't have the luxury of working in a hangar. I have a good size double garage and plan to complete all sub-sections, wiring, plumbing, panel etc before going to paint and airfield for final assembly.

The obvious solution would seem to be Molex connectors for the higher power stuff like lights and pitot heat and D-sub for the autopilot and aileron trim. How do you then secure them to stop them rattling around? Could you use the nylon wire-mount bases that Avery sell and secure with Ziploc?

For the shielded wire for the strobe, is it OK to simply pigtail and insulate it and put it through the same connector? Will this cause a noise problem?

Since the wings will probably never (or very rarely) come off again, should I simply use a service loop and butt splice the heavier wires and solder/heat-shrink the lighter ones? Just seems a little inelegant and untidy! Probably more secure and reliable though - hmmm.......

Any thoughts greatly appreciated.

[Jeff R]

If the wings will "never (or very rarely) come off", then why bother with connectors? Why put in a potential failure point? I am just going to stuff an extra foot or so of wiring in there, and if I ever do have to remove a wing, I can cut the wires and there will be plenty left to splice the wires back together again several over. Or, put another way, I will run the wires and if I ever have to pull a wing, THEN I will do the cut and splice or add connectors.

[kevinh]

Originally Posted by Jeff R

If the wings will "never (or very rarely) come off", then why bother with connectors? Why put in a potential failure point? I am just going to stuff an extra foot or so of wiring in there, and if I ever do have to remove a wing, I can cut the wires and there will be plenty left to splice the wires back together again several over. Or, put another way, I will run the wires and if I ever have to pull a wing, THEN I will do the cut and splice or add connectors.

Exactly - I built my RV in a one car garage and had a big loop of wires hanging out each side of the airplane until I was finally able to go to the airport. Pull the wires through the wing conduit and attach landing lights/antennas/pitot heat and auto pilot in a few hours. Done and done. Worked great and no connectors in the root that will get skungy in a few years.

It worked totally great and it was less work - a rare combination. Even if I need to remove the wings - no biggy. Though as an RV builder friend says:

"The only way the wings are coming off is with two appropriately spaced trees" ;-)

[paul330]

Were it that simple. There is a lot of wiring in the wings which would be difficult to fit at the final stage. I know hundreds of people have done it, but I don't like the idea of the conduit. I would rather use bushings so that I at least have some limited inspection capability. The thought of electrical wires hidden away in a conduit for years leaves me a bit cold! Besides which, it's not as simple as pulling the wires through - branches have to be made to lights, pitot, autopilot, stall warning and trim!

I appreciate your comments but, as I said, the decision has been made. What I would like is some advice on how to best achieve the aim.

[Bob Brown]

I have no conduit in my wings...and I have no connections at the wing root. I just built a service loop should I have to ever disconnect. I installed pull strings through all the bushings to where I needed to go (aoa tubing, autopilot, navs, strobes, landing-taxi, etc. No big deal. I just used the access plates to reach in "for access" and installed a few ties to keep the wires snugged together in between the snap bushings. No reason to have connectors at the root unless you REALLY WANT CONNECTORS.

[apatti]

Like you said earlier, I plan to use Molex connectors for the higher power items. I like that they lock together. For the low power lines I have been envisioning D-sub's and debating on whether to use panel mount D-subs mounted to the root rib. I am leaning against that, though. I don't trust those little screws to hole the D-subs together given all the vibration. So, I am thinking I will make mid-air connections and heat shrink the connectors together. Then, I will use a couple of adel clamps to hold the wiring and the connector against the root rib. That is the plan in my mind, anyway. When I really get at it I may find some new constraints and capabilities that alter the design.

On the shielding, I just spoke with a guy who does aviation wiring harnesses for the military about this. He said it is standard practice to break the shield at the connector and carry it through on one of the pins in the connector. In my case, I had 4 shielded cables coming together at a D-sub connector. It was OK to tie those shields together and carry them through on one pin. Just remember, though, the shield should only be grounded back at the source and nowhere else. He also suggested that if you have a mix of power wires and signal wires, use separate pins on the connector to carry the shield through rather than tying them all together.

As far as noise, I suspect any run length of unshielded wire increases the possibility of noise problems. So, the shorter you can make the unshielded section the better. Also, physically separate the noisy wire connectors (i.e. strobe connector) from the other wires as much as possible.

[Brantel]

Originally Posted by apatti

In my case, I had 4 shielded cables coming together at a D-sub connector. It was OK to tie those shields together and carry them through on one pin. Just remember, though, the shield should only be grounded back at the source and nowhere else. He also suggested that if you have a mix of power wires and signal wires, use separate pins on the connector to carry the shield through rather than tying them all together.

If you are going to do this, I would use separate pins to carry through shielding no matter what. The method of connecting them together at one pin and also grounding at the source will create an opportunity for ground loops of various degrees depending on how far away these sources are from each other.

[apatti]

Brian,

Good point. I think this is why he suggested separating any power runs from signal runs. Also, in my case, the four shielded cables are all from the audio panel (Mic, HP, Music, Cell). So they are all grounded at virtually the same point.

[jdeas]

Originally Posted by Brantel

If you are going to do this, I would use separate pins to carry through shielding no matter what. The method of connecting them together at one pin and also grounding at the source will create an opportunity for ground loops of various degrees depending on how far away these sources are from each other.

Treat your shields as just another signal line in the connector. While much debate exist on connecting the sheild at the source or destination, as long as it is passed through all connectors and only tied on one side you will have a good loop free shield for just about any control signal you will find in an RV.
We call this a telescoping shield in my industry.

[paul330]

Thanks for all the info.

Had another look at the AeroElectric site and found what looks like a good idea for AP wires etc. Bob shows connections using the D-sub pins and then wrapping in heat shrink. Gets rid of the problem of how to secure the shell.