Wire Chafing

[N941WR]

When building my -9 I took great care FwF to make sure the wires, hoses, etc. were secured and didn’t touched anything I didn’t want them to. This has paid off in that after 150 hours the FwF section of the plane looks as good as it did the first day I flew.

However, the same can’t be said for the tail cone. I’m in the process of installing a two axis autopilot which required access to the tail cone.

When I installed my wires and manual trim tab I glued zip-tie pads to floor with automotive trim adhesive from Goop rather than relying on the self stick pads they come with. This seems to have been a good plan as they are holding up well.

With 150 hours on the plane I notice that in some places the wires running down the tail cone were touching the floor and had rubbed the primer off. It was simple enough for me to add another zip-tie pad or two under these wires, since I had access.

What I’m point out is that I thought the wires would be just fine, lying on the inside of the skin like that. Boy was I ever wrong. Over time I, suspect those wires would have either worn through the skin or the wire insulation would have been compromised (I’m betting on the insulation), either way, it would have been a pain to correct the problem had it not been caught.

The advice for you builders is to secure all wires and make sure they do not touch any part of the structure.

[Rupester]

I've been wondering about that issue all thru my build to date. i.e. Just how fussy do I have to be in keeping wires away from everything? Your observation and advice is much appreciated, Bill. Good to know it now.

[osxuser]

As a rule, if it rubs, whatever is more expensive or structural will be what gets worn.... I'm betting your skin would have gone.

[deene]

Yes, chafing is a major deal...I dealt with this on my first homebuilt, a BD4 which I flew for almost 25 years. I found that fiberglass and stainless steel hose surfaces were the worst and the closer to the engine the more the wear.

On my 8, I making a very concerted effort to tie down and/or isolate where ever possible not only wiring but any potential rubbing surfaces.

And don't overlook the effects of long term engine operation with the associated oil contamination of the engine compartment. Adel type clamps do work much better that plastic cable ties, although I do use ties selectively inside the fuse where lacing is impractical.

Also, SCAT tubing is expensive and will quickly wear thru if rubbing. Use a bead of RTV to isolate from any rubbing surfaces and make sure to carefully place and secure the internal wire of the tubing.

[BuckWynd]

Some general advice on securing wires/hoses:

I would only use nylon zip ties where I could easily get to them every few years to replace them. The tail cone, under-floor areas, etc. -- anywhere you won't be able to inspect often -- deserve Adel clamps. Plastic ties and glue will eventually weaken over time, especially when subjected to the kind of vibration a recip aircraft engine puts out. The engine compartment, especially, is brutal. On my airplanes, all the plastic ties under the cowl get replaced during every annual. I've never had one break. (The previous owner of a Citabria I once had, however, had never replaced them. When I bought the plane, it had several broken tie-wraps.)

I'd also suggest using heavy-duty, UV-resistant tie-wraps rather than the standard Cheapo brand you can buy for $4.99 per hundred at the auto parts store. As always, you get what you pay for.

As far as securing tie pads, I've seen a few airplanes with wiring bundles secured with tie wraps and attached to tie pads, but using the pad's adhesive back alone to secure it to the structure. I think this is a big no-no. These pads are not made for this kind of duty. At the very least, you should remove the sticky pad and use some kind of super adhesive. Goop is pretty good stuff, and I think it would probably outlast both the tie and the tie-pad.

JMHOs.