Installing a Whelen nav/strobe in the RV-7A tail
by Bob Collins

Yes, I know sticking one of the Whelen combination nav/strobe lights in the fiberglass fairing of an RV airplane is not a difficult task. Why has it taken me three years to get it done? It's a long story but the Cliff Note version is it didn't make sense to do it until the electrical system was installed and the fairings finished and expertly crafted. That's my story and, for now, I'm sticking with it.

But there are some lessons to be learned that can save you some time on this task that I'm happy to pass along. For one thing -- and this has more to do with an overall approach to building an RV airplane, it's possible to overthink yourself into mistakes. To be too careful, one might say.

Well, let's go back to the beginning. The instructions say to epoxy two nuts for a 4-40 screw inside the fairing. But on my fairing, the inside was a mess. There was no way to get a nut to sit anywhere. Why didn't I just take a Dremel tool and clean out the abyss of fiberglass strands. I don't know, but I didn't. Instead I followed instructions on an Internet page that had me adding filler and then just tapping the fiberglass.

It wasn't until last week, after I'd run all the wires and added the connectors, that I realized how wrong this was. I also thought it would be smart to epoxy some conduit on the bottom of the fairing to protect the wires as they made their way to the tail, and I added heat-shrink tubing to the exposed wiring from the time it comes out of the vertical stablizer spar. Both of these turned out to be good examples of over thinking, and getting into trouble.

First, the heat shrink tubing prevented the wires from slowly easy back into the space between the two rear bulkheads when the rudder was fully deflected. Instead, they just sort of folded up. Not good. Second, by putting the conduit in there, I limited the area that the excess wire could be tucked into when installing the light. If I'd just brought the wires in normally, I'd have the whole fairing to hold them when I tucked them back in.

So what happened when I went to screw in the light unit? The large amount of wiring coiled into a small space pushed back at me as I tried to screw the light on, which -- of course -- made the tapped out fiberglass quickly become stripped and useless.

Even worse, the heat shrink tubing prevented me from being able to reach into the access area in front of the bulkhead and pulling excess wire back into the fuselage, relieving the strain. It was a typical "Bob moment." Every decision I made with the best of intentions came back to haunt me.

I had no choice but to (a) cut off all the connectors (and spend the money ordering new ones) (b) shortening the wires on the light assembly to minimize the excess (c) heat the heat shrink tubing and pull it off. Of course, once I cut the connectors, there was no insufficient wire in the fairing. So I had to (d) run new wires from the Vertical Power 50 unit all the way to the back of the plane and into the fairing.

This time, however, I didn't run the ground and power wires for the NAV light through the conduit. Instead, I just ran them loosely inside the fairing.

Next, I carefully ground out the fiberglass buildup where the screws go (making a slight hole in my perfectly finished fairing), until I could get a nut in there. I mixed up a very dry batch of epoxy and flox (so it wouldn't run) and -- thanks to advice from Ted Chang -- bought some 1 1/4" 4-40 screws from a hobby store (the ones that come with the light unit are much too short), screwed them into the holes in the fairing and into the nuts and then smeared epoxy around them.

I was concerned that the epoxy would prevent me from getting the screws back out, but Ted assured me that if I was careful, it could be done. Still, I was glad I used socket-head 4-40 screws when removing them as I'm pretty sure I would've stripped the phillips head. Remember, I have to deal with "Bob moments." Your mileage may vary.

The new connectors arrived, the wire was run, and the VP-50 was programmed, the light was installed and "voila!" Let there be light!

In truth, I didn't remove the big strobe cable from the conduit, so it's still a pretty tight squeeze of wires back there, but it's nowhere near as bad as it was. And the 1 1/4" screws are certainly going to reveal themselves in a preflight if they should somehow back out of the nut.

Having said and done all of this, a product someone gave to me during the Piece of Grass 2009 would've been a better idea. It's a machined mounting ring with -- I think -- tapped screw holes. You could drill extra holes in it, countersink them, and pop rivet the whole shebang to the fairing and be done. It's similar to an idea this RV-10 builder had a few years ago.

Another idea, which seems a bit more complicated to me given the amount of space to work with, is offered up here: Attaching a nutplate instead of a nut. And yet another optiion is one I found on VAF a few years ago -- Make a nutplate and add it to the mounting ring. This method, however, does require you to grind off a significant amount of the fairling flange around the light and I'm not convinced this results in a strong remaining amount.