Priming wing ribs

Prepping and priming all 38 wing ribs was the biggest priming job I've done yet. I ended up having to split the work into two days. Day 1 was all about scuffing and cleaning each rib individually, while Day 2 was spent cleaning each rib with acetone and actually spraying them.

It was a loooooong day scuffing and washing each rib one by one. I normally keep the garage door open so I can scuff and immediately rinse each rib with the hose, but it gradually dropped into the 30s outside. I set up the propane heater to make it bearable and keep my wet hands from getting too numb. As long as you're within 6 feet of it and don't mind the constant propane fumes, it's actually quite nice!

The heater saves the day!

Each paint rack would only fit about seven main ribs with enough room to comfortably spray them from all angles, so I actually ended up painting about five racks worth of ribs on Day 2.

To keep things organized I had labelled each rib with its number in sequence from inboard to outboard - blue sharpie for the left wing, red for the right (it's not a politics thing, I swear).

"Red 5 standing by."

As expected it took a LOT of primer to cover everything. I mixed up around 48 oz of primer total just to be safe, but I ended up using just over 38 oz to cover every rib. I should have around 50-60 oz worth of primer left in the cans, which should roughly be enough to spray all the inside surfaces of the wing skins.

I managed to get a rhythm going - I would prep and arrange the ribs on the rack while waiting for the primer to induct, then shoot primer as soon as it was ready. Priming each batch only took around 15-20 minutes, after which I'd start prepping the next batch while waiting for the ribs to dry enough to move them from the racks to some cardboard for drying. Replace the primed ribs with some fresh ones and repeat.

That right there is around 22 hours of work. I think I'll take a couple days off to recover...

Match-drilling wing ribs to the spars, attaching tiedown brackets

Time to see just how big these things are gonna get. 

Starting with the left wing, I took the now-straight ribs and set to work attaching them to the spar one by one. Just to be safe, I made a checklist of which rib should go in each position on each wing and double checked things as I went.

One potential "gotcha" I noticed was that the outboard W-712 ribs and the leading edge ribs have identical hole spacing on the spar. The leading edge ribs are meant to go on the INBOARD set of holes at each attach point. Even if the main ribs are in the wrong set of holes they can still flex to meet the rear spar in the proper location, so it'd be really easy to get it backwards.

After all the appropriate ribs were set in place, I attached the rear spar and took a step back to admire my RV-7's left wing. Compared to most of the other planes I fly, these wings are relatively small and easy to handle.

Oh yeah. It's all coming together.

The #30 reamer made quick work of things. I ended up removing the nose ribs to gain easy access to match drill the main ribs. Once everything was match drilled I took one last look at things and started removing the rear spar and the ribs. I went ahead and deburred the holes on each part as soon as I pulled it off to streamline the whole process. I reattached the nose ribs to match drill them to the spar, then disassembled everything and moved on to the right wing to repeat the process.

Getting all of this match drilling done went by surprisingly quickly. Once I was done with all that I laid both of the spars back on the workbenches and set about finally attaching the tiedown brackets. I've had them done for a while now but never got around to actually installing them.

I had matched drilled each bracket with the spacers flush against the insides of the spar doublers so I knew it was going to be a very tight fit. The left wing bracket slid into place with only a little resistance, but the right wing bracket was way too tight to force into place without damaging the anodizing off the spar doubler. Most likely, the spacers shifted a tiny bit when I used the squeezer to set the rivets. I ended up taking a file and shaving some material off the spacers to allow the right wing bracket to slide into place without having to use too much force.

When bolting everything down I came across a small issue. The hardware list next to the diagram has the necessary parts in the order of bolt, AN960-10 washer (1/16" thick), AN960-10L washer (1/32", thinner), then nut.

The drawing itself appears to show the opposite, with the thicker AN960-10 washer being next to the nut and the thinner AN960-10L washer being under the head of the bolt.

I'm probably overthinking this; it probably doesn't matter all that much which washer goes where. I went ahead and installed the washers the way shown by the drawing, with the thinner AN960-10L under the head of the bolt. The tiedown bracket itself is an extra layer of material between the bolt head, washer, and spar doubler so I can probably get away with the thinner washer on that side. There's only the nut and the washer on the other side before the spar doubler, so it makes sense to have the thicker washer on that side.

I didn't fully torque the bolts just yet; I didn't want to put any torque sealant on anything in case I have to remove the brackets for some reason before I close up the wings. I'm making a list of all the bolts I'll need to torque before the first flight, and these will be added.

Another small job down, a few hundred more to go.

Fluting wing ribs

With the edges finished and the flanges straight on the wing ribs, I only needed to get the webs straight before I could finally move on to the next major portion of the wing build. Time to break out the fluting pliers.

Before and after.

Using my trusty metal ruler, I went along the flanges of each rib and placed flutes where they were needed to line up the holes. Compared to the empennage ribs, the wing ribs are pretty severely distorted. I only had to place a flute every couple of holes at most on the vertical stabilizer ribs for example, but most of the wing ribs required a flute between nearly every hole to get them straight.

The difference in straightness is pretty noticeable after just a few ribs. There's an equal number of ribs in each pile here.

...and this is after half were finished. One wing down, one to go.

The leading edge ribs were the worst offenders. Even on the main ribs I would have to put a very big flute in any one place, but the leading edge ribs each required some DEEP flutes toward the forward holes to bring the curved area in line with the rest of the rib.

With the fluting finally done, I organized the ribs by type and put them all back on the shelf. Next step: get them on the wing spars.

Clean and finished. Finally!

You may notice that I haven't touched the fuel tank ribs. I'm going to save work on the fuel tanks until I get the rest of the wing done, mainly because it's a little too cold out in the garage to make working with tank sealant practical but also because I'm sick of working on wing ribs and I'd very much like to move on for now.

Building wing stands

Now that the new year had come and I finally had some time to breathe, it was time to get back to work.

I finally managed to build some wing stands so I'll be able to get the wings assembled. Van's instructions specify using upright 4x4s for mounting the spars, but being in a garage instead of a basement means I don't have any exposed 4x4s to use.

Instead, I put together some free-standing wing stands by squaring up some 4x4s with some 2x4s and fastening it all together with deck screws. Once I put everything upright I added small wood shims under the bases to make sure everything was as close to perfectly upright as I could get.

I needed to reorganize things a bit to make these things fit. It's starting to get a little tight in this single bay...

I don't quite need these just yet, but I needed an excuse to get back in the shop and back in the groove. There's still quite a bit of work I need to get done on the wing ribs before I'll be able to get the skeletons assembled and mounted to these things.

On a semi-related note I've pretty much decided that I'm going to be ordering a quickbuild fuselage instead of going with the slow build kit. It's definitely a premium over the standard kit but I'm trying to set a completion goal for myself: getting this airplane flying within the next two years. We'll see how realistic that is, but if I can keep a steady pace and a steady income then it may still be doable.

As far as the fuselage goes, I'm going to need to either get REALLY good at working in tight spaces or I'm going to need to store the wings and empennage somewhere else once the fuselage arrives. Probably the latter.