Author: Dale

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CAW2 brackets

Over the past couple of days I’ve gotten all 14 of the CAW2 brackets shaped. I had drilled all of them already, but the ends needed to be rounded off. One end of each will be hidden inside the wing, but some will have one end exposed so I wanted them looking decent.

I designed a radius guide to help with the bandsaw and sander. It’s just a 1″ diameter disk, with a short 1/4″ button on the center of one face. Stick the button into the hole on one end of the bracket, and the guide is there to show a 1/2″ radius all the way around. My original idea was to use them to scribe a line to follow when finishing the ends. I had 3D printed a couple of them, and found it was just as easy to just leave it in place and work around the edge. Inevitably, of course, you end up nicking one so I printed up a batch of 9 more. I used 3 of them to finish off the CAW2 brackets.

Given that there are a bunch of other brackets to finish, I’ll definitely try the scribed line approach as well. Overall, though, I’m pleased with the results. I used the bandsaw to lop off the corners, then shaped the ends with a disc sander and finished them on a Scotch-Brite wheel. I had planned to paint them, but I may not. I’ve still got a batch of metal etch and Alodine (Bonderite 1201, to be precise), so if it still works I’d like to just give them a conversion coating that weighs nothing; that way they are protected from corrosion but only the exposed parts get paint. I’ll probably try a test piece to see if the Alodine still works; if not, I’ll get some self-etching primer and use that instead.

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Miscellaneous work

Today came and went without mixing up any glue. I sorted out the nose plywood, then went through all of the aileron pieces and got them cleaned up, marked, and re-taped for the three remaining ailerons. I got the aileron spar web and marked it for the notches to clear the ribs, then brought it home and started cutting those notches on the bandsaw. I pulled a wingtip bow down and checked its fit; it looks like minimal trimming will be needed.

I also collected all of the aluminum pieces I had at Stu’s shop and brought them home, and cut the ends on the bandsaw. They’re all CAW2 pieces, I think — I need to dig out the rest of the pieces and get them all drilled and finished off. I’ll finish them on the belt sander and Scotchbrite wheel before priming them. My little 3D printed guide button worked great for this. I don’t recall if I described it or not, but it’s just a 1″ diameter by 1/8 thick disk, with a 1/4″ diameter by 1/8 thick nub in the center. Put the little piece in a 1/4 bolt hole, and the larger piece gives you a perfect guide for shaping the end of the bracket with a 1/2″ radius. They’re disposable if you nick or break one, and only take a little while to print up. I’ll probably print a few more in case I destroy any while using the belt sander.

I spent some time trying to determine whether the wing walk pieces will be of any use to me or not. The plan sheet and plywood supports all seem to be made for some earlier version of the wing. The notches on the supports don’t work (or even come close to working) with the root blocks on the main spar or rear spar. The forward plywood bits are too long, and even if cut off don’t match the curve of the wing ribs. There are supposed to be three installed forward of the spar — but that would only work if I removed one of the false ribs. I still don’t know what I’ll do for the wing walk. I do know that 1/4 plywood for the rear portion would need some curve in it, and I’m not sure about that. The plan notes say to nail it in place until the glue dries… ::shrug:: This is why I’m considering a laminated layup with some wood and maybe a layer or two of carbon fiber.

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Nose ribs glued

Got the nose ribs glued in place, clamped, and taped to keep them stable. As I write this, I remember my earlier idea to cut another nose rib from slightly thicker plywood to use in the center of the span where the 1/32 plywood will have a butt joint. Oh well. I don’t think I did that on the other wing, so I’ll just have to get a look at that to see what I did there.

I did take a quick look at what I’d need to do to get started on the aileron, but didn’t really have time to spread the plans out and re-familiarize myself with that area. I’m kind of debating the order in which I’ll do the steps to complete this wing. I’m itching to tackle the aileron, but the more I think about it the more I think that would best be done later on. I think probably the best idea will be to wrap the nose with plywood and finish out that in order to protect the nose ribs. Once that’s done I think I’ll move on to mounting the wingtip, as it will be better to get that in and completely blocked in and reinforced before cutting out the aileron. Then there’s the wing walk to deal with. The plywood wing walk support pieces FFP packed in this kit are nowhere near correct, so I’ll probably just end up making new ones — unless I take a page from a guy who’s building a Tiger Moth and just make a new cantilevered wing walk from a sandwich of wood and carbon fiber.

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Wing down, new bandsaw blades

Wednesday afternoon I went over and worked with Stu to get the wing down off the rack and onto the bench. I grabbed the nose ribs and, since they weren’t cut out for the false spars, took them home with me. Before I did, I carefully marked where they need to be notched.

Stu has gotten out of the cabinet business and has sold off much of his wood shop equipment. The thickness planer, jointer, band saw, edge banding machine, and some other stuff is gone. Wait — the band saw is gone? Crap, if I’d known I’d have bought it from him on condition that I could leave it where it was. Oh well. I have one at home, a cheap little 10″ tabletop model.

While cutting the notches in the nose ribs, it was immediately apparent that the saw blade was toast. I’d wanted to replace it anyway, as it’s a 1/4″ wide blade and not really great for keeping a straight line. I removed and measured it, then tossed that and the equally worn out metal blade I had for it that couldn’t make it through 1/8″ 6061. I ordered a 62″ x 3/8″ x 6 TPI wood blade, a 10 TPI wood blade, and a 1/2″ wide 24 tooth metal cutting blade.

A few days’ delay was inserted here, while dealing with another issue unrelated to the airplane..

The blades arrived over the past few days. I put the 6-tooth wood cutting blade on and got the saw adjusted’ it works great. I can cut a 1/16 slice off the end of a 2×2. I think I still need to get the saw table squared up a little better with the blade before trying to do any re-sawing, but it’s close enough for the time being. The metal cutting blade slides through that 6061 like butter, so I’ll be able to finish off the AL fittings for the wing and get the tubing cut for the bushings. Then I can order the bolts I need and get the fittings installed.

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Engine thoughts

I haven’t made any decisions about what engine I’ll hang on the front of this thing when I get to that point. In a conversation with Dave Hertner, former owner of Fisher, I recall him saying that the engine weight needed to be at or below 200# — which would limit my choices somewhat. Small Continentals (A65 through C85 or O-200) are obvious choices, though the smaller ones are a bit less power than I’d like and the bigger ones are rather expensive. Of course there’s always a Rotax 912 ULS, or a Verner or Rotec 7-cylinder radial, or Aero Momentum, and so on. Corvair? Maybe, maybe not; I have yet to see a straight answer to the simple question of, “What does a complete Corvair engine weigh?”

While I have flown a lot behind a Rotax and like it, I’m not wild about the idea of building all of that into the plane, and I’d like something that “sounds better” – or more appropriate for a classic looking biplane. The Rotax sounds great on an RV-12, but it’s just not the experience I want for the Celebrity. Ditto Aero Momentum: I like their engines, but don’t really want to use one for this project.

A few days ago I was exchanging messages with a guy on POA. He’s about my size, and flies a Celebrity — with a Lycoming O-235 up front. He says the weight & balance work out fine, and he’s still got 200# of load – though he didn’t specify the conditions there, so maybe it’s full fuel, maybe just him and no fuel, I dunno. I’ve asked what his plane’s empty weight is.

So, I’m adding the O-235 and O-290 to my list of engines to watch for. The O-235 seems to be pretty well supported for parts; the O-290 less so – seems like new cylinders are not available — but they’re available pretty cheaply and weigh about the same as the O-235. And of course either one could be switched to electronic ignition, vacuum pump deleted, lightweight starter, and so on.

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Reflections on fuel tanks

I’ve been thinking about fuel tanks for a while now. The Celebrity normally has a 12-13 gallon fuselage tank, located just forward of the front cockpit Cub-style. In fact it may use a Cub tank for all I know, or a Champ tank. It’s enough fuel for flights as long as I suspect I’ll ever really want to make in the plane, but I’m interested in adding some capacity. I can envision a scenario where I fly somewhere and want to fly home without refueling, or fuel simply isn’t available where I land. Dirt strips, busted fuel pumps, whatever. A couple of wing tanks for some extra fuel capacity would be a welcome addition and give me some added flexibility.

Since the sale of Fisher to CKD.aero, I doubt very much I’ll be buying the tank or tanks from them. I got a price for wing tanks — over $400 each. Nah. They’re simple welded aluminum box tanks, which are mounted in the wings by means of some stainless steel straps attached to the main and rear spar caps.

Welding aluminum isn’t really in the cards for me, I don’t think. I considered building the tanks out of sheet AL, riveted and sealed with tank sealant. I have experience building those for the RV-7 and RV-12, but of course I’d need to design and build these from scratch. That option is not off the table yet.

Lately I’ve been thinking more along the lines of fiberglass. I could mock up the tank using cardboard and then foam board, to get the exact size and shape and work out the mounting attachment details as well as the location and details of the fill, drain, and sump. There are several construction methods possible including making a mold, building it over a Styrofoam plug and dissolving the foam once cured, or building a foam or balsa structure and glassing over the inside and outside for a sandwich construction. I could make it all internal or could make the top surface match the top of the wing, include a flange to attach it to the ribs, and either just paint it or cover with fabric.

Once I get back to work on the wings I’ll do some more exploring. Right now Stu’s got some stuff going on in the shop so the wings are still on the rack. Once he’s ready for me to get back to work, I want to accelerate the pace of construction so this thing is done before I die.

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False ribs in

There was a delay of a few weeks in construction progress. I had a horrible respiratory thing for a couple of weeks, and didn’t want to pass that on to anyone. We’ve got a rental house we’d been prepping for rent, a wedding, and a short amount of time given to clear a bunch of stuff out of the hangar, including my Vespa which I’ve been doing some work on. So, things sat for six weeks.

I did get over and glued in all of the false ribs. This actually went pretty easy, maybe easier than doing it the “other ” way of gluing them in before the false spars. I was able to just mark up the main and false spars to make sure the false ribs were aligned, then glue and pin them in place.

Next up: Leading edge plywood.

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Bottom geodetic and false spars

Yesterday I got the rest of the compression member gussets glued in, then cut and glued in all but two of the bottom geodetic braces. Those two I couldn’t get in because of a clamp holding a gusset in place. I also got about a quarter or so of the geodetic intersections glued and clamped before running out of epoxy.

Today I finished up the geodetic members, and had enough glue left to install the false spars on the front of the ribs. I think I may have actually used all of the spring clamps I had over there… in fact I know I did, because today I took over another dozen I’d gotten for Christmas a couple years back, that had been sitting in a gift bag in the basement. I think there were a couple left today, but certainly less than a dozen.

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Top geodetic glued in

Yesterday I went over and cut all of the geodetic braces for the top of the wing. Unfortunately, I’d neglected to take over any epoxy – and I’d finished up the last pair of syringes earlier in the week. I remedied that today.

My strategy of using the geodetic braces to shim the rib cap to spar cap joint worked a treat, as the Brits say. It saved me time and trouble. Most were a close fit, and a couple pieces needed sanding to slip in snugly.

I thought I was going to use a record number of clamps, but then I remembered the wingtip bow laminations. Still, it looked like a lot of clamps.

Everything glued and clamped in place. Joints that aren’t clamped are a snug fit and don’t need it.
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Compression members in (lower left wing)

Over the past few days, I have gotten the rest of the ribs glued to the rear spar. I’ve left them unattached to the top of the main spar, as I’m planning to just run the geodetic braces between the rib cap and spar rather than use a separate shim between the cap and spar.

Today I got all four of the compression member assembles cut, fitted, and glued in place, and glued plywood gussets on some of the joints. I ran out of time before I could get the remainder of the gussets cut and glued in.