Tag: Wood

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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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Aileron progress

It’s been an on-and-off couple of weeks. I’ve had a persistent cold/bronchitis that has kept me away from the shop for days at a time. On days I do feel like working, I’ve got a house cleanup project that’s been sucking time as well.

This evening I got over to have a look at the aileron. I’m not thrilled with the plywood, to be perfectly honest, but I believe it will be OK. I re-glued a couple of the geodetic braces and glued down a couple of corners of the thin plywood that were loos and/or slightly de-laminating. I think the fabric would probably have been sufficient, but I want to make things as close to perfect as practical. I’ve got a list of things to do differently on the next three ailerons.

I got a few corner blocks installed to make sure the plywood stiffeners don’t flex or bow. The pans don’t call for them, but I’ll feel better knowing they’re there. I also got the ends of the aileron nose plywood trimmed and sanded flush with the ends of the aileron. There’s one more round of gluing to do, then I can use a router to put a radius on the lower front edge and it will be done. I did check the aileron travel; 22 degrees up and down will not be a problem.

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Aileron progress

Building this aileron has definitely been a learning experience. Some things that I didn’t think would make a big difference early on in the process have come back to haunt me… and of course I’ve learned how the whole thing goes together, which isn’t always 100% clear when comparing the plans to the parts received in the kit. The end result will be fine, but the next three will be a lot less hassle to build.

Lessons learned: All of the plywood bits need to align perfectly with each other and with the wing ribs. That means CW36 needs to be shortened and the hole moved, and CW35 needs the hole moved. I will also pay more attention to getting the aileron spars perfectly flush with the rib caps — otherwise there’s planing and sanding to be done. Ditto for the stringer on the leading edge; I’ll want to make sure the notches I cut for that are exactly the correct depth.

As my CW35 pieces were about 3/16″ high on each end, I glued a couple strips of the 1/8 lamination stock along the bottom edge to fill the gap. Once that was dry I planed and sanded to match the profile of the ribs. I had to sand the top down to match the ribs and CW34 contour, and finish getting the bottom of the spar flush with the ribs. There wasn’t much hanging down, but it was still fussy work. With that done I was able to glue the bottom layer of plywood to the aileron. Once that’s dry I can go to work on the rest of the plywood — of course the angle cut in the spruce piece at the bottom of the aileron doesn’t match the angle of the CW34/35 plywood pieces, so I’ll just have to sand a good profile for a smooth transition. Then I’ll be able to figure out the rest of the aileron bay.

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More aileron work

With a week or so off in there due to both my wife and I having COVID, things have been progressing. I got one of the torque tubes measured and cut for the wing. The plywood bits for the nose of the aileron ribs all got drilled out. Looking at how to do the aileron build brought up some issues, though. The plans say to glue and clamp those in place — the challenge is in how to do that, exactly. The clamping anyway.

In order to make the job a bit less complicated, I glued up the plywood sandwiches for the two ends and the middle, where the locking pins will install. I spread some epoxy and threaded the pieces onto the cutoff piece of torque tube to get them all perfectly aligned – and they were tight. With everything aligned perfectly, I shot a few 1/2″ 23 ga. micro pins to keep everything stable, then added spring clamps and took them off the tube so they wouldn’t end up glued to it.

Next day I ran those and the 1/8″ ply pieces on a spindle sander with a 3/4″ drum on it to enlarge the holes a bit. I wanted a slip fit on the tube for the thicker pieces, and a more “roomy” fit for the 1/8″ pieces. Those were supposed to get 1-1/8″ holes in the first place, but I missed that part in the instructions and we drilled them to 1″.

Realizing that the wing now can’t sit flat on the steel rail due to the trailing edge of the wingtip bow not being tapered to match the wing, I took care of that as well. Only the last couple inches of the bow need to be tapered. I started with a little razor plane that Dad used for model airplane work to shave the bow lamination and corner block down very close to the contour I wanted. I then finished it up with a sanding block, and I’m quite happy with the result.

Everything is ready now to get the plywood pieces glued into place. I’d have done it today, but as I was about to mix up the glue I was reminded that it was time to go pick up the grandkids, which turned into dinner and a late arrival home.

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Lower left wing assembly

I chose the lower left wing to start with since it is the simplest of the four. The lower right will get the wing walk, and the upper wings get a diagonal cut on the inboard bay.

This morning I pulled the first two wingtip bows from the forms; they look pretty good. I mixed up about 40cc of glue and started gluing up all of the strips for the second pair of bows. Had to mix another 10cc, so if I ever do this again I know it takes 50cc per pair of layups. I got them clamped into the forms and slid the table as far out of the way as possible.

The plans say to nail or screw a block of wood to the top of the bench, square with the trailing edge to set up the wing. Since we’re not building it resting on the bench, Stu and I squared up the first rib with the TE (which is clamped to a steel rail) and marked & clamped it to the other rail. After some debate, we decided to pull the main spar out temporarily. I needed to pull the TE of the rib from the notched TE stock to glue it, and with both spars in place it was nearly impossible to do so. The rear spar is a pretty snug fit in the ribs, btu the main has about 1/8″ of clearance so it’s relatively easy to slide out and back in.

Rather than a continuous piece of trailing edge material long enough to do a complete wing, this kit had four 8′ long pieces and four pieces roughly 4-1/2′ long, I cut the longer piece just inboard of the first aileron rib, and started one of the shorter pieces at that point. We got them aligned and clamped well enough that you can’t tell where the joint is if you sight down the trailing edge.

Stu cut a rectangular block about 6″ tall by 11-1/2″ wide, since that’s the distance in between each pair of ribs. With the first rib glued in and squared to the TE, it was then just a matter of using that gauge block to seat each rib exactly where it needed to be on the rear spar. Each rib was glued to the TE and rear spar, and a couple of 1″ micro pins shot through the rib cap to hold it in place while the glue cures. Working that way we got the entire set of ribs in place. We’ll let the glue cure and slide the main spar back in place tomorrow, glue the ribs to it, and attach the false ribs

I did some other work today, including trimming the false ribs so they’re ready to install.

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Building the Wingtip Bows – and more

It’s really nice working in Stu’s shop with lots of room and plenty of work surfaces. One of those work surfaces is a 48″ square low table, with a 3/4″ melamine laminate top. It’s just the size needed for laying out thew wingtip bows. I started out by laying a large piece of cardboard out and taping the plans page over it. Then I used a sharp punch to poke through each of the nail locations on the plans to mark on the cardboard where they should be. Since I wanted to get two bows done at a time, I then rotated the plans page and marked a second set of nail locations.

Rather than hammer nails into the tabletop, we taped some poly sheet and then the cardboard down onto the surface and drilled 1/16 pilot holes. Stu has a bunch of trim head screws, so we sunk those using a block of wood as a depth gauge so that the heads are just above the 3/4″ mark – since we’re laying down 3/4″ lamination strips. With all the screws in place we pulled off the cardboard, leaving the poly sheet and screws.

Knowing that I’d need to spread a lot of epoxy in a short amount of time, I bought a small silicone glue roller and tray. The tray is about 6″ long by 3″ wide, and the roller is a bit under 2″ wide and is grooved to hold more glue. Since it’s all silicone rubber, the cured epoxy just pops right off after use.

After getting all the screws in place, I wanted to see whether I would need to soak the wood laminating strips to get around the form. I had no trouble whatsoever getting the strips bent around the forms without any soaking, so that was good news. With that bit done, we trimmed 20 of the laminating strips (4 wingtip bows, 5 layers each) down to the right length to clamp down to the forms with a few extra inches on each end. With that done I went home for the night.

Friday morning I was back at it. Mixed up some epoxy in the silicone tray and used the roller to evenly coat 4 of the 5 laminating strips with glue. It worked wonderfully well, I’m glad I bought it. I then just stacked the strips and clamped them to the first form, then repeated the process with the second set of strips. The entire process was so much less complicated than I anticipated — I’m not the least bit worried about repeating it for the other two bows, or for the tail. Of course we’ll see how those bows come off the forms tomorrow…

With the bows curing, Stu and I drilled the holes for the bolts and bushings that will attach all of the fittings to the wing spars. Stu’s got a set of Forstner bits, which cut nice clean holes. I’ve got to get a set of those… been meaning to anyway, but that really drove the point home, so to speak. One big advantage is that with the drill press running, you can clearly see the point on the bit to precisely put it right on the mark. Then we cut the 3 degree angle on the lower wing main spar root ends. No pressure at all, just taking a chop saw to a nearly irreplaceable bit of very expensive spruce and aircraft plywood…

Now it’s time to start actually assembling the wings. We started by attaching a steel rail to the side of the bench to support the leading edge of the ribs. The idea is, rather than supporting the trailing edge material with an angled block to let the ribs sit on the bench tom, we’ll clamp the TE flat to one bar, then use the other to support the leading edge at the proper height to match the angle of the TE. If you’re building one of these, I wouldn’t recommend trying to do it this way without a similar setup. Stu’s got a pair of 12′ long square steel tube rails that bolt to the edges of the bench and can move up or down from slightly above the level of the bench top to about 5-6 inches high. It’s pretty unique. The method outlined in the plans is a solid alternative, though personally if I had to do it without this setup I’d bevel the edge of a long block and use pocket screws to attach it to the bench.

We got the first half dozen ribs in place but were unable to go further, since I had taken all of the aileron ribs back home — I just grabbed the stack of ribs that needed modification, and it didn’t occur to me that the aileron ribs could stay.

So that was today — a lot of progress. By the end of the day tomorrow we should have something that starts to look like an airplane wing, and two more laminated wingtip bows.

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11/11 update

How many mistakes can one man make? Enough… thank God I’m building this out of wood, so things can be fixed!

With enough of the aluminum bits cut and drilled to get the spars drilled, I started laying out the hole locations for drilling. Along the way I found a couple of places where I’d gotten blocking in the wrong places for various reasons. Fortunately, in each case I was able to simply add some well fitted wood blocks to get the support where it’s needed. So far I figure the plane will be about two ounces heavier for the extra wood and epoxy. I can live with that. Still, it’s caused a bit of angst.

As of this morning, the next step is to cut the slight angle on root ends of the lower wing spars, drill the holes for all of the bolts, then start actually assembling a wing. At last.

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11/5/23 updates

Went over this morning to see what remaining tasks I could knock out before starting the first wing assembly, and to do some planning and figuring stuff out — like, how I was going to jig up the trailing edge and other stuff for the wings. Stu came in and had a fantastic idea for using the existing steel rails on his workbench to hold the TE flat and perfectly straight, then supporting the front of the ribs with the other rail. It’s a 10′ bench with 12′ rails, so plenty big enough. It’s a significantly different method than that suggested in the plans, but it’s a pretty unique setup. I’m sure a 2×4 shimmed for the correct angle is a lot easier solution for most people than adjustable 12′ long steel square tube rails. I’m just glad he had them built out of square tube and not round.

Next I gave the main and rear spars a once-over to make sure everything was right. It wasn’t. One of the upper wing main spar tip bow supports was off by 1/2″, the result of not having the two spars oriented the same way when I installed those parts. Or, maybe it was something else. Those supports have been a real pain in the rump, and I have a sneaking feeling I’ll run into issues there again. Anyway, the easiest fix was to cut the offending tip support off with a razor saw, put a slight angle cut on the root end, and re-attach it with appropriate splices. Right now part of the re-assembly is drying; I’m hoping to complete the assembly tonight after the epoxy cures.

I got the ten ribs that I have over there trimmed fore and aft, so they’re ready for assembly. I’m planning to start with the lower left wing, just for the sake of simplicity. The lower right wing gets the wing walk. The two upper wings may or may not get fuel tanks, so I’ll do the lower wings first while I work that out. Therefore the lower left is the simplest and a good place to start, I think.

Stu and I discussed building the wingtip bows. He’s got a 48″ square table with a melamine top. It’s big enough to lay our two bows. I’ll wax it thoroughly and use a glue roller for gluing up the lamination strips. This will be good practice for the tail surfaces, which will need to wait until after the wings are done as they’ll need a 4 x 8 work surface. Now I just need to order a glue roller and about 40 or 50 more spring clamps. Given the size of the stabilizer & elevator assembly, more is better… I’m pretty sure there is no such thing as too many clamps.

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Spar update 10/29

Work continues on the spars. Over the past few days I’ve put the wingtip bow supports on all but the upper main spars. Hopefully I’ll do those today or tomorrow.

I’ve been looking for the aluminum stock to make all of the wing attachment fittings. I need a mix of 6061-T6 and 2024-T4, in two different thicknesses. The 6061 isn’t too difficult to find, but as yet I haven’t found anyone that has the 2024 in stock. In fact, Wicks is the only place that even claims to carry the size I need, and they’re out of stock. I’m ordering the 6061 and bushing material. Irritatingly enough, the instructions call out the size of tubing used for the bushings but not the material. I’m fairly sure it’s 6061 AL tubing, and fairly sure it doesn’t matter if it’s AL or 4130 steel.

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Workshop assessment and kit inventory

I met with Stu over the weekend to figure out where and how we’d set up the spar assemblies. I was concerned about the lack of any long workbenches in his shop. He’s primarily set up for building cabinets, and most of his work tables are smaller, low to the ground, and on casters. As it turns out, one of the tables has folding extensions that make it 9 or 10 feet long. The top is very thick, heavy, rigid, and very flat — he uses it to mount rails and a sled for a router to flatten large slabs of wood. He put threaded inserts on the edges of the table where a set of heavy welded steel rails can be attached. With those installed, there will be a built-in straight edge for blocking and clamping the spar caps. It’s not something I would have thought of; the “normal” practice is to lay out a chalk line and nail wood blocks to locate the spar caps during assembly. I think, however, that this setup will be more than adequate for spar construction. I may need to build a matched-height extension for the wing assembly, but that’s a decision for another day.

The wing kit contains no hardware at all. Fortunately it looks like all of the hardware required is made from readily available material and requires simple manufacturing. It’s all flat aluminum stock, some 4130 tubing for bushings, aluminum tubing for aileron torque tubes, and so on. No brake, lathe, welder, etc. required yet. Some of the material I may already have on hand, in fact. The rest can be ordered or even found locally.

While I was there, I grabbed a few pieces of rib capstrip so I could finish off the last of the false ribs. I made two on Sunday, and set up two more this morning.