Matt's RV-7 Project

You might recall I was displeased with the way the audio panel wiring was impinged upon by the crosswise brace at the top of the radio stack. This weekend, I fixed that particular glitch by drilling out the rivets in the piece of angle across the top of the cutout in the subpanel, and very carefully enlarging the cutout by another half-inch. At various times I was going after the subpanel with a unibit, a cutoff wheel in a dremel, various files, and a scotchbrite wheel in a die grinder… luckily I managed to avoid nicking any of the hundred or so wires back there.

New reinforcement pieces were cobbled together out of various pieces of scrap I had laying around. Since I was working around a bunch of existing structure that couldn't be moved, it was kind of a puzzle figuring out the best way to get everything attached securely together.

Here's what the finished product looks like from the aft side. Compared to the previous version, the new brace is substantially higher. There is a 0.032" spacer between the angle and the subpanel, which is bent around underneath to form a kind of cable guide.

A little piece of scrap angle ties the new horizontal brace to the existing vertical piece. It's kind of cheesy, but it's plenty strong. There's plenty of room now for cables and connectors to pass through. You can also see that I had to use another screw and nut in the inboard hole, since there was no way to get a squeezer in there and I didn't want to risk smashing something delicate with the rivet gun.

I also changed the desiccant material in the engine dehydrator plugs again… the dark blue one is filled with fresh silica, and the other one is old. Later on I baked the old silica until it was the same color and the new stuff, and dumped it back into the container.

I ran wires and installed connectors for the rudder trim switch (lower center) and its associated speed control (upper center).

I used some miniature connectors for the 26-gauge wire on the Ray Allen trim components. I used the size of pins and sockets that are rated for 22-26 gauge wires, and doubled the wire strands back on themselves before crimping… worked great. I also bundled all the small wires together with a piece of double-wall heatshrink to provide sort of a strain relief.

Same thing on the rudder trim switch side. Also: Dear Ray Allen company, what's up with you guys and 26-gauge wire? Would it kill you to use something slightly heavier than can be used with normal tools and connectors?

Since I have a habit of only posting extreme closeups, here's a few overview pictures to show how the wiring is progressing. First, a wide shot of the whole panel. The glare is due to the garage door being open to let the extremely nice weather in.

Big fat bundles of wires surround the main bus fuse blocks, but it's all relatively tidy.

Wire bundles running back through the spar and out to the wings. I'm starting to run out of room in the snap bushings that go through the F-704 center section. You only get a total of four half-inch diameter holes to pass all your wiring through, which may be enough for a simple VFR airplane but is totally inadequate for an intergalactic spaceship like I'm building. I know some people have drilled extra wiring holes here, but since the spar is so critical I think I will wait to get blessing from the factory before I go poking any more holes in it.

Looking aft towards the tail… I do have two extra snap bushings in the lower F-705 bulkhead web, which were approved by the factory. I had originally intended those to be used for running wires to the ELT and strobe power supply, but now I'm thinking of moving the ELT somewhere else (yes, again) and switching to LED strobes, which don't need a power supply. However, I have enough other wires and antenna cables that need to get back to the tailcone that I'll probably end up using these for other purposes. You can see in this photo I've already started running trim wires for the passenger stick through one of them.

Big coils of wire are starting to pile up aft of the baggage bulkhead, in preparation for some future date when I get around to crawling back into the aft fuselage to run wires to the empennage and aft-mounted antennas. Not to mention retrieving whatever else has fallen in there.

I ran wires for the autopilot autopilot and got it powered on and talking. Lucky for me it fits perfectly in the panel, so I guess my CAD drawing of the cutout was accurate.

Here's a closer view. Notice that my panel has an on/off switch for the autopilot, so if it tries to kill me I can return the favor.

The autopilot is too deep to use a standard D-sub connector (it hits the subpanel) but I was able to make it work by using an expensive right-angle D-sub backshell. It was pretty dicey to get the two halves of the backshell clamped together and the thumbscrews inserted without pinching any wires.

All the fuselage wiring for the autopilot is in, but I haven't installed the connector for the pitch servo or the wing root disconnect for the roll servo yet. I'll do that later.

I've been thinking for a while that I'd eventually like to add rudder trim to this airplane, similar to what other builders have done. I may not actually get around to putting a servo in the rudder any time soon, but if I at least install a switch in the panel and run wires back to the tail it will be a lot easier to retrofit later. If I decide to fly the airplane before installing rudder trim, I'll just placard the switch "inop".

I had a Ray Allen rocker switch left over from a previous project, so I located it and dusted it off. There's a spot just below the radio stack, next to the flap switch, that's just about perfect for it.

I measured and marked cut lines, then used a unibit to hog out most of the material:

Then I used a hacksaw blade (held with leather gloves) to make a roughly square hole:

Then I filed away at the edges until the switch fit through the hole. It's not the kind of perfect cutout that I'd have had if I'd thought to include it when the panel was being CNC cut, but the switch bezel hides all that.

Test fitting in the panel:

To allow me to adjust the sensitivity of the rudder trim, I attached a Ray Allen servo speed control to the lower flange of the center subpanel rib.

Here's another view. I'm sure this thing is nothing but an LM317 and a trimpot, but it's easier to buy one of these than to roll my own.

Anyway, at least I can run all the wiring now and make the airplane ready for a future upgrade. Maybe some winter when it's too cold to fly I'll build a new rudder with a fancy trim tab… it would be nice to have a choice between building and flying! The airplane that I'm sort-of partners in has been down for maintenance since March, and of course the RV-7 is still in pieces in my garage.