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Bushings

On Wednesday I went over and tried cutting some of the bushings used for the bolts that hold the brackets to the wing.

I’ve cut a couple with a chop saw, but one got away and ruined a saw blade and almost took my thumb off. I think I could fix that problem, but after ruining one nice Freud carbide blade I’m not really inclined to pursue that method again. I’ve been using my small (9″) band saw with a metal cutting blade, and it’s been a bit of a struggle. I’ve had no success getting the miter slot aligned to the blade, so I made a custom miter gauge with a slight angle to get straight cuts. I wrapped masking tape around one end and made test cuts until I got a square cut. After cutting, I typically need to take a few thousandths off with sandpaper before I get the correct length.

Until now I’ve been scribing a line with a micrometer and following that with the blade. I think I’m going to switch to clamping a fence down on the table and using that for repeatability. I have three sizes of tubing — 5/8, 1/2, and 3/8 OD. Bushings are made with one, two, or three pieces of tubing nested together, so I need to cut identical length pieces. The 1/2 and 5/8 tubing is a snug enough fit that I can cut them together, but the 3/8 OD is not a snug fit, so I end up having to cut that separately or it spins and moves out of position. I’m going to just try a different approach, as making these bushings is taking forever.

I’ve been using a 1/2″ wide, 24 TPI metal cutting blade on the saw. I think it’s too fine for the AL tubing; I’m going to try a different blade. Of course I’ll have to order it. I have the 24 TPI, as well as 6 and 10 TPI wood cutting blades. I think I want to try 14 TPI.

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Wing metal parts

Over the past couple of days I’ve been collecting, drilling, and prepping the aluminum wing attachment parts. These are a collection of pieces cut from 6061 and 2024 AL bar stock. They will be used to attach the wing spars to the fuselage, attach flying and landing wires, and attach the N struts, and connect the upper and lower ailerons. Each one must be cut from the raw bar stock, drilled for bolts, and some of the ends rounded. I’ll do some sort of finish to prevent corrosion. I have some Alodine left over from when I was building the RV-12; if it’s still usable I’ll use it. If not, I’ll most likely buy some.

More than once the instructions have caused a little bit of panic. For example: Yesterday I drilled all of the holes in the attachment brackets to their final quarter inch (0.250) size. I remember that I’m short some pieces, but didn’t remember which ones or how many. I’m also unsure of which ends of which brackets need to be cut and sanded round. This morning I looked at the plan revision sheets that show the drawings for the parts… and saw that the drawings call out all of the holes to be 0.1875″. Panic!! Holy moly, did I just ruin all of those parts and waste all of that work? Oh, wait. I’d made little 3D printed pieces to help mark the ends for cutting… and those have 1/4″ bosses to fit the holes, so I planned 1/4″ holes before. And a 3/16 hole would fit an AN3 bolt. I’m pretty sure the plans call for AN4 bolts everywhere, and there’s no way in hell I’d be comfortable with wings held on with AN3 bolts…

Back to the wing spar plans… Yep. AN4 bolts and 1/4″ ID bushings everywhere. The supplemental drawings are incorrect or out of date, no big surprise. Back to work.

I did manage to badly mis-drill one of the CAW9 brackets, so that’s scrap — but it really doesn’t matter in the long run. I came up a little short on the 3/16″ 2024 stock needed for some of the parts, so I’ll need to buy another 12′ length anyway. It’s an odd size that is difficult to find on line, but fortunately my local supplier can get it for me even in single piece quantity. Even they don’t list it in their catalog. Most places only carry 2024 in 1/4″ thickness or more.

After inventorying my parts I need another 60″ or so of 2024 stock, and I only have about 3′ if that. Fortunately the parts I have on hand are enough for the two lower wings, so I can cut the bushings, buy hardware, and attach all the pieces on the two wings I have built and get them finished before moving on to the upper wings.

I got over to the shop to make sure the bolt lengths called out in the plans were OK. I’m glad I did. IN each case I decided to bump the bolt up one number to get the next longer grip length; the exception was the three bolts on each wing that attach the CAW-4 landing wire brackets. Those were specified nearly half an inch short; I had to go from AN4-20A to AN4-24A to get the right grip length. I’m glad I checked. I also ordered a couple dozen standard and half-thickness AN960 washers to get everything done up right. The hardware is ordered, now I just need to get the bracket ends done and get them prepped for installation.

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Scallops and metal work

Today I had Stew help me mark the leading edge for the scallops, and got those cut. After getting home, I spent an hour or so rounding up and drilling all of the aluminum wing brackets I have cut so far, which is most of them — all but a couple, I think. I seem to recall I ran out of 2024 with one or two left to go. Anyway, I figure I should get them all done up. I’ll need to cut bushings, mount these, and get the fabric stiffeners cut and fitted — along with varnishing the wings — before calling these two wings “done”. Oh, and I’ll need to get the final torque tube bushings milled out and mounted.

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Some detail work

So many little things left to do. Today I made a little jig to mark the leading edge plywood for the depth of the scallops that need to be cut, and marked the center of each bay. I did some sanding on the wing walk to bring the rib caps down flush with the plywood skin — it’s not much to remove, just a few thousandths, but I want it smooth. I glued the LE plywood to the wing walk plywood, since that hadn’t gotten clamped well enough and the edge was loose. I’ll sand a tapered transition on that later.

I’ve got a dozen or two micro pins that I tried to use to stick down some 1/8 spruce to hold down the leading edge plywood. That failed, leaving the pins sticking out, They need to be driven in so they’re below the surface, so I got a few of those done with a center punch. I have a small pin punch I’ll use to do the rest tomorrow when I get back at it.

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Finishing out the aileron bay

Last session I cut and sanded everything to get the top of the aileron bay closed out. Well, not everything; after gluing in the CW37 piece I realized that there were some additional supports I hadn’t cut. As I was running short on time, though, I had to leave them for another day.

The fun part (and it actually was kind of fun) was cutting notches in CW37 for the ends of the rib caps. After marking the location of both sides of each rib. I cut a shallow slot with he razor saw, then used an X-Acto knife to gradually fit the depth of the notch to fit. In the end I got it in and clamped, then had to leave.

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Aileron skin

Over the past couple/few days I’ve glued the bottom skin on the aileron, then attacked the top nose skin. Trying to get the lower and rear edges of the skin glued down at the same time is, I have concluded, a fool’s errand. I ended up gluing it to the flat front portion, then doing the top edge separately using a long piece of flat board to clamp it to the tops of the ribs and the aileron spar. The front edge I’ll do separately as there’s not a good way to clamp it in place.

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A couple days’ work

Saturday: Ripped the CW37 parts down to the proper 1/4″ thickness. These are the strips with one beveled edge that go in the top and bottom of the aileron bay. The parts I got are 1/2″ thick, which won’t work anywhere. Ripped them all down to 1/4″ so I don’t have to do that again for the other two wings. With them cut to the right thickness, I cut one to length and glued it into the bottom of the aileron bay.

Then I discovered (or confirmed) that I’m an idiot… there were a couple of missing aileron pieces that I found in the bottom of the parts crate. Had I installed them in the first place, the little triangular braces would not have been needed. It’s no big deal; I was able to slot the nose skin support spar and get them glued in.

Today: Got the nose skin plywood glued onto the front of the wing. I think there are now about 70 or more clamps on the wing. I had planned to glue the top aileron nose skin in place, but that’s going to take some more work. I see no way to get that ply to stay attached all the way around without some sort of clamping jig. Stu and I figured out a good arrangement, but I’ll need to get some MDF, ply, or pine scrap to cut them out of. I need seven sets of clamping blocks for the nose and trailing edge, then I can use bar clamps to hold everything in place.

I also found that a few batches of glue I mixed up over the past week or two were probably not the greatest. My T88 had started getting cloudy — a sign that the resin is starting to crystallize. Some of my test pieces failed at the glue joint, albeit with a lot of force required, instead of the wood failing before the joint. I’m not really concerned about this. All of the affected glue was used for either the wing walk or adding corner blocking and gussets to the wingtip bow. The wing walk pieces are fully supported and there will be no bending, twisting, or pulling loads applied. The glue is strong, just not AS strong as what I’ve used everywhere else.

I have since tossed the syringe of clouded resin, warmed the rest of my resin supply until it’s crystal clear, and verified that test pieces now all break well into the wood rather than at the glue line. I’ve tried spruce to spruce, which tore apart well into the wood, and spruce to plywood which ripped the plywood apart.

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Bracing and gusseting

I got all the clamps off of the aileron this afternoon. Everything looks pretty good. Due to the way I had to cut the thin nose skin spar, I felt it best to install some bracing for it. These are just little half inch right triangles that I glued in to keep it straight.

With that done, I removed the clamps from the wingtip bow and sanded down the gussets I’d installed last time. I won’t know if they require any “fine tuning” until I have a chance to get some fabric on it, but I think they’re good to go.

I flipped the wing on its top surface and added some more blocking under the ends of the wing walk. These are just regular corner block stock to tie the plywood to the spar caps. I think everything looks pretty sturdy there now.

With some time and glue left, I sanded down the corner blocks on the underside of the wingtip bow supports. I cut, glued, and clamped the gussets in place and called it a day.

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On a roll!

Today I did some work with the razor plane and a new sanding block to get the aileron spar and other bits to their final dimensions. I got the top side geodetic braces cut and glued in place on the aileron. Then I glued the lower aileron nose skin in place – the aileron now has, I think, the maximum possible number of clamps on it.

With that done, I got the blocking sanded down on the wingtip bow supports, and cut and glued the top gussets in place. Only eight clamps there, but I think it’s still feeling the love.

And if you’re a Star Trek: Voyager fan, this makes Seven of Nine days in September that I’ve worked on the plane.

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Aileron work

I removed the clamps from the wing walk skins; all looks good. Once I have the wing flipped upside-down again I’ll have a look at the underside and see if there are any additional opportunities to put in more support for the structure, but I think it’s about as good as it’s going to get.

I cut and installed the lower geodetic braces in the aileron, as well as the aileron skin support (not sure if the plans refer to it as a spar or not). I’m pretty happy with how this one is coming together, especially considering the angst the first one caused.