Matt's RV-7 Project

How was your labor day weekend? I drilled two big holes through my airplane's wing spar:

Relax, I got approval from the factory first:

Matt,

Yes, you can provide additional holes within reason. Use the same diameter as we have, and also keep in mind the proper edge distance (2D). Also keep clear of other structure such as seat ribs, spar bars, flanges, brackets, etc.

Joe Blank
Builder Support
Vans Aircraft Inc.

Since doing this incorrectly would basically ruin the airplane (or at least be extremely time-consuming and painful to repair) I spent a lot of time measuring and contemplating various locations. I eventually picked a spot outboard of the F-716 seat ribs and inboard from the F-783 cover support ribs.

Vertically, the new holes are equidistant from the upper and lower spar reinforcing bars, and have more than enough distance from the existing holes I've been running wires through. I had to pull the wire bundles out of the way to drill the new holes, and I had to use an extension to keep the drill chuck from grinding up the ribs, but it all went just fine.

You can bet I deburred the heck out of these holes.

I wasted no time putting the new wiring holes to use… this is the coax for the transponder antenna, which runs down the right side of the forward cabin floor, goes up through one of the new holes, and then turns inboard before running down the right side of the center tunnel.

After passing through the rear spar, the transponder coax jogs outboard again and runs down the F-727 rib before passing through a bushing in the baggage bulkhead.

This is as far as I got before I had to go mow the lawn. Later on I'll figure out a way to secure the coax to the floor, and put on the BNC connector. By the way, this particular piece of coax is actually the same one I had previously cut and run to go to the nav antenna connection in the left wing root. Subsequently, this thread on VAF convinced me that it would be a better idea to instead use a V-shaped dipole antenna under the tail instead, so I ripped that cable back out. By happy coincidence, it was the perfect length to use for the transponder, so nothing is wasted.

I ran a few other wires this weekend too. The tail and each wing got power wires for the nav and strobe lights, plus a wire to synchronize all three strobes. I have decided to go with LED nav/strobe lights, although since I am an inveterate bet-hedger I made sure to size the wires for the strobe lights so they'd each be sufficient to run a single-output power supply for a more traditional certified light head, should I have a change of heart and decide to go that way instead. I also ran a spare wire to the right wing with an eye towards eventually using it to power an APRS tracker (someday).

Many feet of wire are ready to be run back to the tail too, although not everything is in place yet.

New game! Whenever you drill a hole in your spar, you have to take a drink. Tonight's beverage was a summer seasonal from Blue Moon, which was not half bad.

One of the things that always annoyed me about my last RV was that the electric elevator trim was incredibly sensitive at normal cruise speeds… trying to trim out control pressures would always turn into a game of "how fast can I press and release the trim button so the airplane doesn't get out of trim in the opposite direction". So to improve that situation with this airplane, I bought a Safety-Trim two-speed trim control unit, which gives you the ability to slow down the trim servos when flying faster than a preset airspeed threshold. It also provides some protection against trim runaway due to a stuck switch, which is nice.

To mount it, I made some little standoffs from scrap alclad:

I attached it to one of the ribs under the pilot-side baggage floor. It's a pretty short run forward from there to the control sticks, and the wires to the servos can go fore and aft through the center tunnel. I'll run the wires to it later – right now I'm just trying to get all my boxes mounted where they need to go so I can plan my wire runs.

In the photo above, you can also see that I've riveted a bunch of plastic tie wrap anchors to both sides of the left and right tunnel ribs. They'll get put to use soon when I start running wires through the tunnel

I bent a doubler for the transponder antenna out of 0.050" alclad and drilled a bunch holes for rivets and mounting studs and antenna connectors through it:

Then I crawled into the fuselage and match-drilled the doubler to the belly skin and the F-729 bellcrank rib, about a foot behind the baggage bulkhead. In terms of the length of coax needed to reach this location, I'm right at the limit of what the Garmin install manual allows, but I couldn't find a better place to put it. Not to mention, I hope the transponder-rays won't do anything weird to the pitch servo. Also, I shortened the doubler slightly between these two pictures, since I'm thinking about moving the ELT back here and I wanted to be sure to leave plenty of room.

A view from the outside. I need to deburr, dimple, and alodine the mating surfaces, and then see if I can coax Mary into helping with the riveting duties.