Tag: Parts

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Boy, I’m bushed!

Today I took the wing brackets over to the shop, sorted them all out, and re-marked them so I could tell one part from the other. There are seven (I think) different bracket types. The acid etch solution had removed all of the markings, along with other stuff.

I sorted out which brackets are needed for the right lower wing that’s on the bench, and checked all of the bolt sizes for proper fit. All are acceptable, if not perfect. I have AN4-24A bolts (1-15/16″ grip length) for the main spar root attachment brackets; I could have used AN4-23A (1-13/16″ grip length). It’s not a problem; a couple of AN960 washers do the trick and are a perfectly acceptable solution. On the rear spar N-strut (outer end) brackets, the AN4-16A bolts are a tad long; I could have used -15A. Two AN960 and one AN960L are fine. As a mental exercise I calculated the weight savings if I ordered the shorter bolts. The shorter bolts would weigh about half an ounce less (total per wing); the washers would bring that up to just a smidge over half an ounce — .53 ounce, or about 15 grams per wing. I can live with that.

But I digress. I got all the remaining bushings cut. Once I wrapped my head around that fact that the bushings do not need to be cosmetically and dimensionally perfect, but just need to be “flush or slightly below” the face of the wood per the plans, things went a little quicker. I pulled the 24 tooth per inch metal blade from my bandsaw and replaced it with a 10 TPI wood blade, which is fine for thin wall AL tubing like this. I set up the miter gauge and fence for the length I wanted. The tubing cut-off end was snagging the blade teeth; Stew suggested a spacer on the rip fence that extends just shy of the blade. That did the trick! Now the cut-offs roll out of the way. I cut one piece and tested for fit in the hole; once that was verified I was able to set the fence once and cut as many pieces of each diameter tube as I needed. Easy peasy. That will save hours of build time.

Now I need some etching primer for the brackets, and spar urethane for the wood, and I can get everything installed and call this wing done.

Oh, after I cut the bracket for the aileron connecting rod.

And get the bearing block holes drilled.

And… whatever else I’ve forgotten.

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More bracketry

Today I got my bag of bolts, washers, and nuts from Aircraft Spruce. Wanting to make sure I had all the correct lengths and all, I headed over to the shop to try them out. As you might guess — especially if you know me — all of the brackets were at home, so no joy there.

I did order a 14 TPI bi-metal bandsaw blade, it should arrive tomorrow. The 24 TPI metal blade is just way too fine for cutting this tubing. Stew says the 10 TPI wood blade I have would do fine — but I want something I can use on the 2024 stock without worry.

Once back at home, I treated all of the brackets with Alumiprep (now known as “Bonderite C-IC33 Aero”). It’s a phosphoric acid etching cleaner, does a bang-up job of cleaning up and etching aluminum parts prior to conversion coating or painting. Well, as it turns out, my Alodine is no good any more. No surprise, really. I left a set of brackets in the bath for an hour and could barely see a tinge of tan or gold color, not enough. Too bad, I was really hoping to use that. I’ll need to pick up some good self-etching primer instead, I’m not spending close to $100 for a quart of Alodine that I’ll then have to dispose of later on.

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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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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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Wing walk extension

This morning I went over to check on the work I did yesterday. The main portion of the walk structure looks good. I still needed to get the extension (front portion) ready for the skin.

The center plywood support is glued to the first false rib, but of course the plywood skin sits between the ribs. That meant I needed to shave about 1/8″ from the top cap of the false rib. I used the razor plane for most of this work but needed to use a file for some of it like the front edge. I cut the cross supports and used them to gauge whether the top of the middle support/rib was level with the other two. In the end I used a DA sander to “fine tune” the high spots until it was all level.

I also wanted to make sure the front and back edges of the thin plywood are fully supported and level with the thicker ply on the rear portion of the walk. I ended up just cutting a couple of support strips to attach to the top of the spar; I use da cutoff scrap of the wing walk for this as it was the perfect thickness. I also cut a couple of pieces of rib capstrip (I’ve got a lot of it left) to glue to the false spar to support the front edge of the walk extension. The plans don’t call for it, but I’ll feel better with a little added structure there.

I can probably remove half of the capstrip on the center one. if it’s not going to provide any strength, there’s no need for the extra weight!

The plans call for using nailing strips and brads to nail down the plywood skins while the glue dries. That’s one way, but I’m thinking another way would be longer clamping strips and long clamps. One strip would hold down the aft end of the main walk and get clamped to the rear spar. One would hold both the forward end of the main walk and the aft end of the extension and get clamped to the main spar. A third would hold down the forward end of the extension… I’m not entirely sure how that one would get clamped, but since it’s 1/8″ plywood it won’t need a lot of clamping force. I’ll find a place, I’m sure.

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Wing walk work

Today’s session was pretty much all wing walk. I got the notches for the cross pieces all properly fitted using a large file. I got the nose walk supports similarly modified to fit the cross pieces, and cut to fit the spar. Then I glued on all of the long supports as well as the cross braces under the main portion of the wing walk. The front extension portion will have to wait until I figure out exactly how I’m going to deal with the false rib in the center.

Along the way I also glued the top of the root wing rib to the top of the spar. The root rib is angled slightly to accommodate the dihedral, so the wing walk skin will need to be cut in an irregular shape to fit, of course. It has to be; cutting a simple rectangle would be far too easy.

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Aileron freedom – and wing walk work

Today I located and temporarily screwed the bearing blocks in, and cut the aileron free from the wing.

With that done, I decided to have another look at the wing walk situation. I don’t know why the support bits were the way they were, but I decided to just get on with making them work. When I look at the plans, especially the oblique view, indicate that the parts may have been cut in an attempt to match a much earlier version of the wing without much of the reinforcement at the main spar root. Anyway… Two of them had the aft end cut well enough to work at the rear spar. The inboard support needed to be trimmed at both ends. All had to be modified to fit the main spar.

In the end I got all three to fit, though I’m not terribly thrilled with the lack of good options for supporting and blocking the ends.

Next up were the notches for the cross braces. Most were too shallow and look to have been cut out with an end mill or router; the corners were rounded. I used a file to square up the corners and deepen the notches to fit the 1/2 x 3/4 pieces.

I figure I’ve got another hour or so of work to get all of the blocking and support in place before mixing epoxy. Probably more; I still haven’t figured out what I’m going to do about the extension of the walk forward of the main spar. If I build it to plans I’ll need to remove or hack up the first false rib. And of course the plywood pieces require significant modification.

On the bright side, the plywood skin for the wing walk curves nicely and won’t be a problem to get glued down. I’d been worried about that, and had visions of needing to make my own laminated piece there, but it’s fine.

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Aileron spar and parts fitting

Today I got the aileron spar web cut and glued in, along with the top pieces of 1/4″ spar cap. I couldn’t get to the bottom side to clamp those pieces without some significant effort, so I left those for the next session. I also got the CW32 pieces cut and sanded to fit between the rib caps. I trimmed and clamped the CW36 and CW34 pieces in place to locate the aileron torque tube, then marked the CW32 pieces for the holes that will need to be drilled for the torque tube.

The wingtip is nice and solidly in place, so now I just need to sand the blocking and trailing edge flush so I can start installing the gussets and additional bracing.

This time around I plan to NOT screw up the same way I did the first aileron, by assuming that the holes in ANY of the parts are drilled in the proper place. As I did before, I’ll index everything off of the CW34 parts, using those to locate the torque tube, and drill or sand everything else to match them. And of course I’ve already 3D printed a pair of torque tube bearing blocks for this wing. The final parts will be milled out of UHMW or something similar, not 3D printed, but these are great for getting all the holes located without the risk of messing up a flight part.

The more I use it, the more I like my little razor plane. This thing was bought back in the 70s, I think, by my father for use on R/C airplanes that we (mostly he) built in our basement, usually from scratch. It’s a plastic body with a blade that resembled a heavy duty, oversized razor blade. The key thing I found was to use light passes, and hold the plane at an angle to the wood. It’s quite effective for shaving down spruce, plywood, and even the odd bit of end grain. It’s usually quicker than sanding.