Matt's RV-7 Project

With all the preparation steps completed, I once again recruited my long-suffering friend to spend a day putting the wings back on the plane, this time for good:

This time I installed the close-tolerance NAS bolts, eight per side. Even with a generous application of LPS-2, these were a challenge to install due to the tight fit. All the NAS bolts had to be tapped slowly into place – I used a combination of a plastic-tipped mallet and a brass rivet set with the gun turned down to 20 psi. I also installed the two AN4 bolts per side that were the subject of a service bulletin.

Following the plans to the letter, I put a washer under the head of each of the bottom bolts:

In retrospect, I think the plans are wrong here, at least for the RV-7 taildragger. On the top I ended up with two washers under each nut to keep them from bottoming out on the bolt shanks, and on the bottom there are no washers between the nuts and the F-7114 gussets due to lack of extra threads. It would have been better to put a washer under the heads of the top bolts, not the bottom ones, which would have allowed the use of a single washer under the nuts on both top and bottom. However, the bolts are so tight in the holes I decided it would risk damaging the spar to remove and replace them, so I just made it work and torqued everything down.

I installed and torqued the six 1/4" bolts in the front side of the center section on either side of the fuselage. For the lower ones I had to torque them from the bolt side since the nuts were way down in the bottom of the center section, where I could barely thread them in place or get a wrench on them.

This is a closer view of the area inside the center section. I discovered that the wiring bundle that passes through the center section comes very close to the spar web, which is aggravating. I used the factory-provided holes, which you'd think would be engineered to provide adequate clearance, but apparently not. I put some nylon edge grommet on the sharp edge of the spar web, but I'll have to come back and do something with RTV here to make sure the wires don't chafe through.

I torqued the nuts at the aft spar, and installed the required cotter pins:

Fuel tank brackets installed and everything torqued:

Here's a reverse view showing how the bolt is safety-wired using a small hole I drilled. This bolt is tightened just enough to keep the washer from rotating, so the fuel tank can theoretically pull away from the bracket in the event of a crash. Hopefully not something that will ever be tested.

Inside the fuselage, the fasteners that attach the tank brackets were a real pain to torque, due to the way everything fits (or barely fits). The design of this whole apparatus seems like an afterthought, but at least it's all finished now.

Getting all those fasteners tightened to spec took every torque wrench and most of the socket extensions and adapters that I own:

Underneath the fuselage, I installed all the screws that attach the bottom skin to the wing roots.

Happy to have achieved this milestone at last.

The plane looks great with the wings on it, although I must say it's a lot less convenient to walk around the hangar now. Suddenly this thing takes up about three times the space!

Continuing to accomplish everything I can do inside the wings while they're still in the jig, since working on the wings while lying on the ground will be worse in the future…

The chrome finish on my old Gretz pitot mast was peeling and the underlying steel was rusting, so I threw it away and ordered a new one. It seems you can no longer order these in chrome, just bare steel. Here's the new one as-received:

I still wanted a chrome pitot mast, so I took the unfinished piece to a local metal plating shop. A few weeks later, it came back with a reasonably nice satin-chrome finish on it. This actually matches the satin finish on the GAP 26 pitot tube fairly well, so I'm happy with it.

I made this little plumbing bracket out of scrap aluminum:

This is a pair of AN816-3D nipples connected to 90-degree air fittings, which is my solution for adapting the 3/16" aluminum tubing coming off the pitot tube to 1/4" nylon tube that I could run through the wings. I couldn't find any satisfactory bulkhead fittings for this application, so I just captured the bracket between the blue AN fittings and the female NPT portion of the air fittings, using some O-rings to make it all secure.

This is mounted to the top of a wing rib directly over the pitot mast:

The aluminum pitot plumbing is a straight shot through the mast to the fittings above, no complicated bending required. The nylon tubing will go outboard from the 90-degree fittings (to the left in this photo), do a gentle 180, come back inboard through the plastic snap bushings at the forward end of the rib, and then run down through the wing to the fuselage.

The pitot's aluminum tubing has a minimum length of 8" for heat dissipation reasons… mine ended up being almost 9", so no problem there:

My helper and I pulled the wings back off the plane so I could take care of a handful of things before installing them back on the fuselage for good. I swear I'm having a good time in this photo:

One of these tasks was to install all the countersunk nutplates for the the wing root fairings, over fifty nutplates in total. This took basically a whole work session – I just turned up the music and cranked them out:

Squeezing the rivets for some of these near the tank leading edge was a bit tricky, but I got it done:

The aftmost hole on the top skin was too close to the wing walk doubler for the nutplate to fit properly. Not sure if this was a plans error or a quickbuild assembly error, but I'm stuck with it now. I solved this by making a little shim to give the nutplate a flat place to live:

With the shim under the nutplate, it sits flat like it's supposed to, which means the screw will go in straight:

Since I've removed the old AFS AOA system in favor of a Garmin GAP 26 pitot/AOA probe, I had a few small holes in the left wing skins that needed to be plugged with flush rivets:

I roughed-in the wiring through the conduits for the wingtip lightning, and also ran wiring through the snap bushings for the roll servo (right wing) and pitot heat (left wing). The two sets of unused bushings in the left wing will be used for the pitot and AOA plumbing.

I left the wires extra-long and will cut them to a more manageable length later. This is a bit wasteful of expensive milspec wire, but still cheaper than having to replace every wire because they're all an inch too short.

Long ago I followed the factory guidance for installing plastic wiring conduits in my wing ribs. Now that I'm working on attaching the wings, I've realized that the end of the conduit is nowhere close to the prepunched wiring hole in the fuselage (which you can even see in this photo). Since I need to accommodate a pair of 1/4" pneumatic tubes as well as a thick bundle of wires, I was going to need to add more holes in the fuselage anyway, so I decided to use the existing hole for the pitot/AOA plumbing and create a new hole for the wiring.

After checking for edge distance and clearance issues, I decided I ought to be able to put the new hole exactly in line with the end of the conduit. But how to locate the hole accurately? The gap between the wing and fuselage is too narrow to get an angle drill into, and even marking it with a sharpie seemed problematic. Then I thought, what if the hole could be drilled starting from the other end of the wing? All you'd need is a ten-foot drill bit!

I'm sure very long drill extensions exist somewhere, or you could daisy-chain a bunch of the 18" ones together, but those ideas sounded expensive. Instead, I fired up the lathe and made something that did the job, using nothing but stuff I had laying around anyway.

I turned down a piece of aluminum rod into a bullet-shaped thing. One end has an 8-32 stud, and the other end has 1/4-28 threads, into which I screwed a #40 threaded bit:

This I screwed to the end of my electrician's fish stick:

Then it was a simple matter of running the resulting contraption in from the wing tip to the root, chucking the outboard end in a drill, and having at it. It's not totally unlike snaking a drain:

Result, one pilot hole exactly centered on the wing conduit. The space between the fuselage and wing aft of the spar is so tight I could barely take this photo, but you can see (via the reflection) that the "drill snake" has exited the conduit and gone straight into the fuselage skin; only the camera angle makes it look crooked. When the wings come off one more time, I'll enlarge these holes and install plastic snap bushings for the wires.

With the wings temporarily fitted to the fuselage, there are a handful of tasks to accomplish before removing them one last time. Careful planning will prevent too many on-off-on efforts – let's hope I didn't forget anything!

First up is the wing root faring, which will be screwed to nutplates all along the inboard edge of the wing. I was pleasantly surprised that the pre-punched holes lined up pretty well, although there is still some fiddling required (and watch the edge distance on the tank skin!).

The gap here is not perfect yet, but it's good enough to drill the fastener holes, which is my main concern. Once the wings are on permanently, I'll scribe and trim the edge of the root fairings to achieve a uniform gap into which I can install a rubber trim strip.

I drilled all the wing root fairing attach holes up to #19. The job of dimpling the holes and installing the nutplates will have to wait till the wings come off again.

I fitted the tank attach brackets, which required a few small tweaks to the bend angles, and drilled the bolt hole in each tank's mounting ear. When the wings are off I'll install a nutplate where this temporary bolt is: