We had family visiting for Thanksgiving, so not much progress recently. Got the skin-to-rear spar rivets squeezed for the upper inboard skins, except for the rivets that butt up against the rear spar doublers. Those will have to be bucked. Also did edge-finishing on the aileron mounting brackets and flap reinforcements. Sorry, no pictures.

Captain John and I did the upper wing skins today with the mushroom set and tungsten bucking bar. Came out wicked nice!

Upper wing skins riveted

I’ve been stewing over the fit between the fuel tank outboard edges and the inboard leading edge skins; the tank skins stand slightly proud of the leading edges and they “pillow”, or bulge up between the joint plate nutplates when screws are installed. So I started tinkering around with the tank-to-leading edge fit. I used a stick of delrin with a slot cut into one end to edge-roll the tank edges, and although that helped, it wasn’t enough to completely close the gap.

Other builders have had the same problem and pursued a couple of different approaches. My good friend Jim doubled up on the nutplates and screws on the joint plate, and that worked really well. Some folks on VAF recommended shims inserted between the leading edge joint plate and inboard rib. Although that approach require some work to drill out rivets and fit the shims, I decided to try this approach first with the extra nutplate solution as a guaranteed solution if the shims didn’t work.

So I measured the tank-to-LE gaps and the length over which the gap needed to be shimmed, then fabricated a small shim blank of 0.025″ alclad for the right wing and a longer shim blank of 0.032″ alclad for the left. After carefully drilling out all the LE rivets affected by the shims, I slid the shim blanks in place and marked rivet hole locations in them. Drilling, deburring dimpling…and voila, the shims are ready for priming and riveting. Stand by for the completion of this little adventure…

Inboard leading edge shims

I was out of the shop for a week on a work trip to Germany, then I had a bunch of home stuff to do so not much progress in the last couple of weeks. When I did get back in the shop I did some final prep work on the wing spars and ribs in preparation for riveting the upper skins.

At Oshkosh this summer I bought Avery’s 12″ double-offset back rivet set and mushroom back-riveting bucking bar. I had great hopes of back-riveting all the upper skin rivets, so Ellen and I started using this method to rivet the upper inboard skins.

Inboard skins backriveted

I must say that I was disappointed with the results. First, it’s not easy to get that long double-offset set squarely on the rivet and rib flange so we had some “drillers”, as Captain John would say, or poor rivets that need to be drilled out. And once we got the positioning right, it was obvious that the combination of back-riveting and Vans’ rivet length callouts were giving shop heads that barely met specs. Using longer rivets just magnified the problems of getting the set positioned correctly.

After getting a sanity check from Captain John on my riveting results, I decided to abandon the back-rivet set. With the tungsten bucking bar and a little practice with the straight mushroom set on my 2X gun, we were able to get results just about as good as back-riveting by using the normal shoot-from-the-outside approach.

With the leading edge wiring and plumbing done, it’s time to attach the leading edges to the spar. This is one of those “it’s going on for good” tasks so I spent a little time cleaning up the outboard spars – primer touchup, general dusting, etc – before nailing these things on permanently.

One of the minor headaches of attaching the leading edges is how to rivet their ribs to the spars. The plans call for solid AN470-4-x rivets, but access is limited for driving the rivets from behind the spar; even with a ground-down double-offset rivet set, there just isn’t much room to get on the rivet heads without scuffing or denting the spar or main ribs. And my arms aren’t skinny enough to work a bucking bar inside the leading egde. So I opted to use the blind rivets that Van’s says are an acceptable substitute. The only downside is that the limited space between main ribs and rib-to-spar rivets makes it difficult to get a blind rivet puller on the rivet stems.

But that was a problem I could solve. At Oshkosh this year I bought a very skinny blind rivet puller from Avery, it has one of the smallest heads I’ve ever seen on a rivet puller. Even so, I still had to grind down the head quite a bit to get it to fit. Here’s the final product; note that I covered the ground-down upper surface with tape to protect the ribs, and also to keep the guts of the puller in place since I had to remove basically all the enclosing metal at the top.

Blind rivet puller used on wings

After pulling all the rib-to-spar rivets, I squeezed the AN426 skin-to-spar rivets. No problems here, everything came out great! Here’s the obligatory hero picture.

Wing leading edges attached

Over the last two weeks I started wiring the landing lights on both wings and plumbing the AoA pressure probes on the left wing. It was much easier to do this stuff before the leading edges go on the spars for good. The pressure probes were easy – just attach the 1/8″ flexible tubing to the barbs on each probe.

The landing light wiring was a little more complex. I upgraded the bulbs to 100w, and with the length of the wiring run from each light to the fuse block in the fuselage, I upgraded the wiring to 14 AWG. Given that the lights aren’t in an easily-inspectable area, I spent some extra time installing standoffs to make sure that the wires won’t flex or rub against anything that might cause shorts or breakage. The standoffs came from a local supply store, and per a recommendation from Bob Nuckolls of AeroElectric Connection fame, I used Shoe Goo to hold them in place. I’ll let you know in a few years if it holds up.

Here’s the left wing with LL wiring and AoA probe plumbing. Notice the local ground on the outboard rib; using the airframe as a ground path for large-current DC power consumers saves weight and space. There’s a little service loop on the LL wiring that will make it easier to replace the bulb at some point in the future.

Left wing wiring and plumbing

And here’s the right wing LL wiring.

Right wing wiring

Got the wing skins and inspection hole covers prepped and primed today, that’s the last major work on the skins before they get riveted on the wing boxes.

No, I haven’t been doing nothing for the last month. Go look at the Tanks page to figure out what I’ve been up to.

Over the last four days I finished installing the Duckworks landing light kits in both wings. This is one of the last things I needed to do on the leading edges before they go onto the wings for good. Most of the ticklish and potentially expensive stuff got done back in April, like cutting openings in the LEs. What’s left is trimming and fitting the plexiglass lenses, and installing reflectors and halogen bulbs in the light brackets.

If you’re reading this you either (a) are building – or want to build – an RV, (b) don’t have anything better to do, or (c) are my mom. So for the benefit of you folks in group A, I’m gonna give you the gory details of finishing these lights as I learned to do it.

The first step is taking the plexiglass lenses as provided and trimming them to a size slightly larger than the leading edge opening – the instructions give apprpriate dimensions. You gotta provide enough space on the top and bottom for mounting strips, but not so much extra that you can’t get the lens in and out through the LE opening – which you’ll have to do when changing bulbs. To make this a little easier I stuck a drop light in the leading edge and used the illuminated opening to measure and lay out cut lines on each edge of the lens, as well as to marks the opening itself on the lens..

Before working with the lens, I covered it with removable masking tape to make marking easier and protect against scratches.

Marking the LL plexi lens

Once the cut lines were marked on both lenses, I trimmed them with a cutoff wheel in my Dremel.

Trimming the LL plexi lens

Following the instructions, I then fabricated “handles” from fiberglass-reinforced packing tape and coaxed the lenses into the leading egde. Pulling the lens tight against the leading edge, I match-drilled the mounting screw holes through the skins into the lenses. It’s important to keep that lens snug – it directly affects the final fit of the lens – but not to push on the lens from the back. That, apparently, can make the lens too snug and make it difficult to install. It’s also important to use a dull drill bit to make those initial holes in the plexi; sharp drill bits dig into the plastic and can cause it to crack. Here’s the lens with all but one hole match-drilled and clecoed.

Match-drilling the LL plexi lens

The next step was edge-finishing the lenses and drilling the mounting screw holes to their final sizes. Edge-finishing was easy with some sandpaper. I opened up the holes to final size using a special plexi drill bit from Avery, then countersunk the screw holes with a #30 piloted countersink. Countersinking is another opportunity to crack the lens if you go too fast – slow and steady gets the job done nicely.

Lens trimmed and drilled

A few other steps need to be accomplished before the installation is done. First, the reflectors and bulbs must be installed in the light brackets. Duckworks provides automotive driving lights that must be disassembled to provide those parts; the only gotcha here is to make sure you wear gloves when handling the reflector and bulb – skin oil on either can cause them to get too hot. Otherwise, it’s straightforward.

Lamps and reflectors installed

Second, the retaining brackets that hold the lenses in place had to be final drilled and have nutplates installed to accomodate the lens mounting screws. The brackets are match-drilled to the leading edges just as the lenses are. The only real work here is installing the nutplates, and attaching the brackets to the lenses with two-sided tape. One last thing – the skins must be dimpled to accomodate the mounting screws…#6s, I believe. Do yourself and use a real #6 dimple die set. The instructions imply that you can use #30s, but that just wouldn’t look right.

Lens installed

Finally, the light brackets were installed and the lenses attached. Overall, I was pretty happy with the results. The right wing lens fits a little better than the left, but both will get the job done.

One side finished!