Tag: Glue

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More left wing work

I’ve been over working on the wing a couple of times since the last post. Stu and I worked out what seems to be the best way to fit the wingtip bow. Yesterday we glued, stapled, and clamped the leading edge plywood to the top of the ribs and the top false spar, but left it at that stage. Wrapping the ply around the leading edge results in the upper edge pulling loose, so we decided to leave it as is and do the rest later on. I was planning on today, but may hold off on that until the wingtip bow is installed — I want to get the corner blocking glued in behind the LE ply, and that may be difficult with the plywood fully wrapped. Don’t know, I’ll need to look at that today.

We spent an hour or two yesterday trying to work out the aileron bits and pieces. The factory cut and drilled plywood bits (CW32, CW34, CW35, etc.) have been both a blessing and a curse. Most of the confusion seems to come from the fact that the CW36 pieces, which attach to the ribs just inboard and just outboard of the aileron bay, are apparently drilled WAY off. The pieces are too long for the wing to begin with — they seem to be sized for a rear spar built with the original 1/2″ thickness. non the current 3/4″. Then there’s a hole marked “more or less” on center, but the actual hole is drilled about 1/8″ or so low, or high, depending on how the piece is flipped. There is no orientation we could find that matches up with the holes drilled in the CW35 pieces that are used to attach the aileron to the torque tube. Fortunately, it really doesn’t matter. I’ll be cutting 1/2″ UHMW end bearings that will attach to those plywood pieces, so we can enlarge those holes as much as needed as long as there’s enough room left to attach the bearing pieces.

What we did get done was to cut and glue in the aileron spar web, and some of the 1/4″ stiffeners before the glue left over from the leading edge ply got too thick to work with. I glued up a test piece with that; the epoxy is a bit thicker than I would normally use, but I may have just been too conservative on that. I can’t think of any reason it wouldn’t give a full strength joint; the test piece will tell me for sure.

For the most part, I’m waiting for my aluminum for the torque tubes to arrive at Millard Metals, and sheets of 1/16 and 1/8 ply to arrive from Spruce. I need the ply to cut gussets for the compression struts, and we don’t want to get much farther into the ailerons without full length torque tubes to keep everything perfectly aligned.

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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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11/5/23 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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The easy way to manage T-88 epoxy

I’ve seen all kinds of methods people use to mix up their T-88 epoxy. The manufacturer says to mix the resin and hardener (Part A and Part B) 1:1 by volume, or 100:83 by weight – which are the same thing. Plenty of videos on YouTube and EAA Hints for Homebuilders show various methods, and I’ve read some pretty involved threads on various homebuilding message boards. Some squeeze out equal lines of the two parts. Some cut the bottle tips to different sizes and squeeze out for a measured amount of time. Some have built scales to measure out by weight. Some do it in graduated mixing cups, like the little medicine cups that are easy to find. Some just use “TLAR” – or, “That looks about right”. You can buy T-88 in twin dispensing cartridges that automatically dispense and mix the glue — but it’s something like six times the cost of buying it in bottles, and of course you’re going to waste some each time when you throw out the mixing tube.

I have a bit of an aversion to not measuring epoxy accurately, and estimating and hoping for the best didn’t seem to me like a good plan when building an airplane. I know the precise ratio isn’t super critical; even System Three says that. Still, though, why guesstimate or get “close enough” when it’s so easy to get an exact amount?

I bought some 60cc catheter tip syringes through Amazon. They’re cheap and disposable, though I’ve reused mine a number of times. I fill one with Part A and one with Part B, and usually use a permanent marker to mark the cap for the Part B (darker) syringe, just so I don’t accidentally mix the caps up and ruin some epoxy. I’ll fill them just past the 60CC mark, then stand them tips-up overnight to let all the trapped air bubble up to the top, then squeeze a little back into the bottle or jug until the plunger is exactly on the 60cc mark. Pull the plunger back just a bit to get a little air in the tip, and cap it.

By doing this you can very accurately measure both parts to mix up any desired quantity of glue, from 2 cc up to 120 cc. Gluing plywood spar webs to spar caps? I’ll mix up 20 cc at a time, 10cc from each syringe. Building ribs? About 8 or 10 cc of glue will do two wing ribs, so 4 or 5 cc from each syringe. When the syringes are empty, you can either be a cheapskate like me and refill them, or just toss them in the trash if they’re too grungy to re-use or if you’re Daddy Warbucks and don’t care about the cost. I’ve got two pair of syringes that I use, and each has been refilled probably six or eight times. I just ordered some more syringes, since these are getting a little sticky and I want to keep fresh ones on hand. I use them for other things as well, so it’s never a bad idea to have some around. You also don’t want to run out of glue before you’re done building for the day, so I try to always have at least two sets filled.

Note: Pay attention to the quality of the syringes you buy. The first few I bought were made by B-D (Beckton-Dickinson) or Brandzig, are nice heavy duty plastic, are marked with 1 cc graduations, have good caps, and are generally high quality. The next batch I bought are thin, lightweight, shorter, marked with 2 cc lines, and are generally cheap Chinese crap. I’ll toss these after the first use and chalk it up to a lesson learned. As is almost always the case, it’s better to spend a little extra for good quality.

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Progress, up to a point

During two working sessions today I got most of the assembly of the lower main spars complete. “Most of”, because when it came to laying out the plywood blocks for the landing wire attach points… well, after a while studying the parts and the prints and the spars, none of it makes any sense. The upper wing spars were not exactly straightforward; a few of the parts didn’t match the plans, but the end result looked correct in that the location and final layout of the blocks matches the print, even if the parts making up those blocks are a bit different. I’ll need to spend more time studying the plans for the spars, as well as the plans for the N-struts and landing wires to figure out what needs to be done.

I also ordered a gallon of T-88, hopefully I’ve got enough to last me until it gets here mid-week.

Edit: After looking at print #15 of the plans, things are quite a bit clearer. That drawing shows the flying wire, landing wire, and N-strut attachments, with part of the spars shown. Tomorrow I’ll be able to glue in the blocks for the lower main spars and, hopefully, get them finished. Well… “finished” is a relative term, I suppose. I haven’t started attaching the parts for the wingtip bow support, but I may just hold off on that for the time being.

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Main spar progress

It’s been a busy week. The two upper main spars are essentially complete. Spar caps, stiffeners, and all of the filler and reinforcing blocks are assembled. The only thing not done are the outboard ends, where the tapered pieces for the wingtip bow attachment need to be assembled. The two lower main spars are under construction now. Both have the caps and web glued, and one has the stiffeners on one side. I’m planning to finish as much as I can today on the main spars, and hopefully get at least one of the rear spars glued up.

It’s been a real joy working in a place where there’s plenty of room to work. The availability of a large number of bar clamps – in addition to the 40 or so spring clamps I have – really helps as well. I took the day off work yesterday and was able to get over there once in the morning to set up a spar, then again in the afternoon to take that one off of the jig and glue up the next one.

Stu is anxious to get enough pieces built to start getting wings assembled so they look like wings — I can’t say I’m not in agreement. I was a little tempted to build a rear spar after the first main so we could assemble one complete wing, but I’m convinced that this way is a lot more efficient. For one thing, after the first spar we’ve both figured out enough ways to make the process better that each spar is taking less time than the one before. Just as an example, my process for getting epoxy into the grooves in the main spar caps has evolved and gotten much more efficient with each spar. It’s almost a shame there aren’t any more to do. On the last couple I would get some glue on the long edge of a popsicle stick and use that to spread it into the groove. After doing a foot or so, I’d slowly follow through with an acid brush with the bristles trimmed down to about 1/4″ or so, to make sure it was evenly distributed and get any excess out of the groove. The result was the cleanest glue joints of all the spars.

I’ve been going through T-88 like crazy. Gluing 9 and 10 foot long pieces of wood uses a lot of epoxy, and I know the laminations for the wingtip bows and tail surfaces will use a lot as well. Given the price increases since the last time I bought glue, I think I’ll just order a gallon.

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Started on the second spar

This morning I went over to Stu’s and finished gluing the root attach blocks and the blocks for the N strut and flying wire brackets to the spar. Other than the tapered extension for the wing tip bow, that’s all of the wood for the first spar. Once the glue is cured, I can start locating and drilling the holes for the attachment bolts and bushings.

With that done, Stu and I started on the second upper wing spar. The bench has threaded inserts set into the edge, and he’s got a long steel rail that bolts on. It’s 2 x 2 inch square steel tubing with mounting brackets welded on. The rails were designed and built to bolt to the table, then he’s got a steel sled that sits on them that he can use to flatten a large wood slab using a router. We bolted one rail to the edge of the table, overhanging the work surface. Now there’s a long work bench with a straight, level steel rail on one edge.

We glued the groove in the spar cap, inserted the plywood web, then glued the other spar cap. One spar cap is clamped against the rail, then the assembly is clamped in place to hold it straight, flat, and properly spaced at 5-3/4″ total spar height along its entire length.

I think about 10 ml of epoxy is plenty to glue one spar cap groove. I mixed two batches today. I’ve been using 60 ml syringes ordered from Amazon to hold and measure the glue – it works wonderfully. I can very precisely measure out even very small quantities.

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First spar, continued

It’s been a bit of a learning experience building this spar. The amount of glue required, of course, is one thing – about 45 ml or so, I think, for the whole thing. There are still a few pieces of plywood that need to be glued, most of them for the flying wire and N-strut attachment brackets. Yesterday Stu showed me his pneumatic pin nailer, which I plan to use. It’s not unusual to use staples or small brads to hold wood together while glue cures. This thing shoots ridiculously small wire pins — 22 or 24 gauge, I think — with no heads. They’re just enough to hold the wood in place, and won’t need to be removed.

I also found that the spar has about 1/8″ of gradual taper toward the tip end. That was a builder error; it’s supposed to be a constant 5-3/4″ across the entire length. When I assemble the other three they will be correct. It’s not a critical error; I can fix it with shims when the wing is assembled. It’s even noted in the plans that ribs may be shimmed where they attach to the spar. It’s just been an inconvenience. Before I found that taper we’d cut some reinforcing blocks that fit between the spar stiffeners to a constant length. Some needed to be sanded, some needed to be re-cut because they were too long. That’s when I measured the spar height more carefully. I had just measured one end and a spot partway down the spar before — I guess it didn’t occur to me that it would have a taper to it. Everything else is good, there’s no bend, twist, or warping, so it’s good to go.

Other minor things — the plans call out 120-1/4″ for the spar length, but the main caps are 120″. Obviously the quarter inch at the tip isn’t going to make a difference, I’ll just make sure both spars are exactly the same length.

I’ll go over tonight and finish the assembly of this spar, and hopefully get started on the next. I also need to find my box of 4130 steel tubing and see if I’ve got the stock I need to make the bushings for the wings. There are bolts through the wing that hold the attach brackets for the fuselage, struts, and flying & landing wires. All of the holes need steel bushings through them. Simple enough to cut and file to size; I just need the right size tubing. I bought a “grab bag” assortment of random tubing cut-offs from ACS a while back to see if I could learn to weld. If I’ve got a couple feet of the sizes I need, I can use them for this.

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Gluing up a wing spar

Yesterday I headed over to Stu’s to glue up all of the pieces to the aft face of the upper right wing spar. There are two full length spruce spar stiffeners, four pieces of plywood at the wing root, spruce blocks placed at each rib location, and four plywood pieces for the flying wire attachment brackets. Then I’ll get to flip it over and do the same on the other side.

When I was building wing ribs, I found that a total of 8 ml or so was about right to make two ribs. Since I did that a lot, I got used to mixing up small batches of T-88 epoxy. Yesterday was the first time I have had to mix relatively large quantities — I went through two 20 ml batches, which is about the most I can do in the little medicine cups I bought for this. Even that left me slightly short. There are a couple of plywood attachment pieces that I didn’t get installed yesterday. System Three makes auto-mixing dispensing cartridges, but they’re substantially more expensive to use. As in, over six times the cost. I think I’ll be sticking to mixing cups. I may need to get some larger ones, though — mixing up 20 ml at a time isn’t going to work for a lot of this stuff.