Nothing new, but last night I gathered up all 47 full ribs and stacked them up, carefully aligning the cross pieces for the main spar, aft spar, and nose spar. I was a little concerned about the amount of variation I might find, considering the ribs came out of two jigs over a period of 20 months. I was very happy to see that there’s no more variation than could be attributed to wood thickness. Less than 1/64″, probably under .025″ anywhere along any of the ribs. Then I stacked up the dozen false ribs I have done so far, same story.
Wait – 47 full ribs? Yes, it seems somewhere along the line I must have lost count and built one extra aileron rib. I’ll either keep it around as a wall hanger/test piece, or maybe stick it under the wing walk for a little extra support. I’m not sweating it.
This exercise has also reinforced my idea to build a sled for the table saw to lop off the ends of the ribs for the leading and trailing edge pieces. They are very highly consistent, as they should be, so I think that will save time and make subsequent assembly steps easier.
The bad news is — my T88 epoxy is junk. I refilled the dispensing syringes and the resin looked a little “off”, not perfectly smooth and clear as it usually is. Maybe a little cloudy and with a different texture. I mixed up a small amount and glued up some test pieces. Where I glued the flat sides two sticks of capstrip together, the joint held well and pulled apart well into the wood. However, where I had glued a couple pieces of geodetic brace into the slots, the glue joints failed allowing the braces to pop out without breaking. The glue also was not clear and hard, as it should be, but had an almost grainy or mealy texture to it. I don’t have any trust in the remaining glue in those bottles. I’m certainly not going to risk using substandard adhesive to save about $20 worth of epoxy! Into the trash it goes. I have two new bottles here, and half a dozen new 60cc syringes on the way from Amazon.
I haven’t been doing much on the biplane recently, but I did manage to score an altimeter for it. I’ve been watching the for sale ads on line for decent deals. Someone offered an altimeter that worked, but failed an IFR certification due to out of tolerance leakage at 15,000′. Well… if I ever do finish the bipe and fly it, it certainly won’t be at anything over 10K, let alone 15K. So for fifty bucks it was a no-brainer. It’s a pretty nice altimeter, not one of the super cheap imported junkers that’s being sold now. It’s really more altimeter than I need…
So… I have an altimeter, and a quad oil temp / oil pressure / CHT / EGT gauge for monitoring the engine. I will still need an airspeed indicator. Most that I see for sale have speed ranges not appropriate for the Celebrity — I really don’t need or want a 200 knot ASI. Then I’ll need a compass, of course; a slip/skid ball; a tachometer. Whether I need a fuel gauge or not depends on what I decide to do for fuel tanks. I’m thinking no electrical fuel gauges, all float or sight type.
I could just ditch all of it and go with a single instrument from Dynon or Garmin, but I just think such a thing would look out of place in a classic biplane. I’m not sure what I’ll do for the front cockpit, though. It would be nice to at least have airspeed and altitude there for passengers, but I’m not sure I’ll be able to score a deal like this again. There’s always UMA…
Five down, eleven to go. Cutting the geodetic braces individually is really not as much of a chore as I thought it would be. I am finding that I’m going through the 6′ lengths of stock quickly, though — I figure I have enough shaved down for the next 3 ribs, maybe 4, then I’ll have to fire up the drum sander again and make some more. Not that it’s stupidly tedious work or anything, mind you.
In hindsight, it would have been a whole lot less work and actually less expensive to have bought 3/8″ thick spruce spar stock and just ripped it down to 3/32 strips, losing half the board to saw kerf. I am at a loss to explain why that little bit of math didn’t make itself obvious. Of course, I thought at the time that shaving 1/32″ off those strips would be quick and easy. Not so much. So… if you’re building a Celebrity from plans, you’d be better off doing that.
It’s a little early for this debate, but given the long lead times for ordering wood… not too early. I could possibly be done building the wing ribs in a month or two, if I get on it with a purpose. If I’m going to need a bunch of spruce, I probably need to get the order in now. So the question becomes — what next?
I could build the wings. It looks like the wood for the spars will cost me around $8-900, plus substantial shipping. I’d also need to extend my workbench by at least 4 feet, so that’s another project in itself. But I’d have wings, man, which would look bitchin’ cool hanging in the garage or hangar.
I could start on the fuselage. It’s a big piece that would be a huge leap forward. I haven’t calculated the wood cost yet, but it’s a significant amount of birch ply and spruce. Again, I’d have to build another workbench to extend what I have by 8 feet or so (and rearrange the garage).
I could start on the tail feathers. I could do all the work on my existing workbench. After looking at the parts list, most of the wood specified is pine; I’d need some aircraft ply as well. The elevator & stab. spars are specified as spruce, but I could source suitable quality Douglas fir locally and substitute that. I’ve seen boards at Menard’s with growth rings and grain slope that meet specs, with enough defect-free wood to be usable. That means all I would need to ship from Aircraft Spruce or Wick’s would be a couple sheets of plywood. Plus, building the tail would give me some valuable experience with large/long glue-ups that I’ll need to do for the wing spars, and if I screw it up it’s relatively cheap pine instead of very expensive spruce.
So… tail feathers it is. Now I just need to consult the plans and see what size sheets of plywood I will need to order.
Yesterday I glued up the last full rib (#26) and the first aileron rib. I’m going to call this a milestone. 🙂 I now have 15 more aileron ribs to go, then 34 false ribs. I suppose I should pull out the plans sheet for the spars and see exactly what I need to order for them. I have the BOM, but it doesn’t really tell me what I need to know without looking at the plans too.
I had to look at the plans a few times. It looked like the plan sheet was calling out just one geodetic brace to omit for the aileron ribs, but the locations to mark for eventual cutting didn’t make sense. I finally realized that the text read, “Omit this X-brace for aileron ribs”… as in, BOTH braces, not just the one. Great! That’s two less pieces to cut and glue.
I’ve been wanting to get back to building ribs. The garage bench has been piled too deep to get anything done, and now it’s been below zero for over a week solid. Insulation or no, it’s damned cold out in the garage. Too cold for epoxy to cure, and too cold to work.
So… there’s a perfectly good work bench down in the basement. 8′ long and rock solid, built by Dad back in the 1960s. It’s been pretty much completely covered up for the past several years with a collection of parts, partially-disassembled or -assembled prototype projects and assorted debris from the side business I was running, plus a CNC router that took up about 3′ of it. I have cleared most of it off (much of it into a trash can). The CNC machine is shelved for now; I’ll maybe resurrect it when needed at a later date. It will probably come in handy for cutting the instrument panel and/or nose ribs.
The next issue is containers for the geodetic rib braces. There are 24 braces used in each rib, all of which are of course slightly different. Just enough so that none are interchangeable. I was using paper cups to hold them in the garage, but it’s a completely unsatisfactory solution. In the basement I think I’m going to try stapling taller plastic cups along the back edge of the bench and see how that works.
I’m not moving power tools down there from the garage, so new geodetics will be cut with a razor saw. We’ll see how that works out… it’s one of those jobs I wish I could set up a machine or fixture to do. It’s 24 different lengths with over 40 different angle cuts, so I’m not sure how I’d make that work. Even cutting them out in batches on the band saw meant fine-tuning each one with a sanding block before assembly. It’s fiddly work and tedious as hell. Classic gusseted ribs would be a whole lot faster and easier to build. If I were starting this over I’d probably just depart from the plans and build them all that way; I’d probably have them all done by now.
Just so I could feel like I’m not totally stalled, I built rib #15 this weekend. 6cc of glue turned out to be just about right, with no skimping and very little excess. The new method of mixing and applying the epoxy with an acid brush worked out well. I think I will go back to an earlier idea I had, of pre-wetting the groove with glue before putting the top and bottom capstrips into the jig. It will be easy to do with the brush, and will save some assembly time. I have a template with pencil marks defining where the glue should go; I think I’ll mark the glue lines along the bottom and top of the jigs to make it easier to apply the glue.
The other night I finished up the steam box and made a set of little standoffs for the bottom. I wanted to keep the wood off the bottom of the box to allow air circulation, but also allow water to run back to the low point at the rear. I got a little lazy and didn’t put in dowels like most plans show.
Tonight I loaded it up with eight cap strips and let it run for 45 minutes while I went out and hung some outdoor lights on the deck. When I came back I found that the door had developed a pretty good curl — concave from the outside – and was venting a lot of the steam past the door seal. The spruce inside was fairly pliable, so I clamped three pieces in my bending form and put four more in the rib jigs. They would only fit partway down in the jigs, since the wood is swollen. While the wood cooled down I got all of the geodetic braces ready to install. I’ll glue these two ribs up tomorrow night.
I did email System 3 about their epoxy. Some of the ribs were assembled with the capstrips not pre-bent. They’re fine, but the wood will spring out of shape if it gets hot enough for the epoxy to soften. I don’t want that to happen. so I was thinking about clamping them in their current shape and steaming them to relieve some of the stress in the capstrip. Of course that will soften the epoxy, and I wanted to know what that would do. Their answer is that T-88 will begin to soften at around 120 degrees, but once returned to room temperature will be at full strength. That’s great news.
I’m definitely not in love with the geodetic rib bracing design. 24 braces, no two alike, and I’m having to hand-fit them all. It takes for-freaking-ever. I have to wonder how much heavier 3/32 plywood would be with suitable lightening holes. A guy could pop sets of them out on a CNC router in no time, save a ton of time and effort on the ribs, and probably end up with much stronger ribs too. But, I don’t think I’m going to re-engineer the ribs right now.
Last night I ran another 20 sticks of geodetic capstrip stock through the sander. I had to adjust one of the guide boards for thickness; due to temperature and humidity changes it was too close to the drum by about .014 or so. So, 20 more down, a hundred or so to go. Sounds like a lot, but if I can do 20 in a night it’s another week before they’re all done. Then it’s just measuring, marking, and cutting them in stacks on the bandsaw. Over lunch today, in fact, I ran another ten through the process. It took about 40 minutes start to finish.
I can totally understand why people like plywood ribs. I could be knocking out plywood pieces, or more traditional braces for “normal” non-geodetic ribs. Would it be less work? Probably not. I’d still have to make precise cuts and no two pieces in a rib would be identical. There might be fewer of them, but with this method at least I have a very small amount of leeway on the exact length and angles. If a piece is 1/64″ or 1/32″ longer or shorter than the next, I can adjust the angle or position to make it fit without causing problems. I think wing ribs are just going to be a lot of repetitious work no matter how you do it. My only regret here is not calling Wicks or ACS on the phone to see if they would custom cut my capstrip to 1/32″, that would have saved a lot of work and waste.
An update on the oil pressure sending unit. I had found exactly one of the correct sending units for sale, a NOS Honeywell part that was listed on eBay for a couple hundred bucks. I didn’t buy it, but I was watching the listing. They dropped the price, I made a lower offer and they accepted. I ended up paying roughly what a normal oil pressure sending unit would have cost from a source like Aircraft Spruce. And, it’s got the exact output that the Westach quad gauge needs. Now I won’t have to build a conversion unit but can just wire this one up directly. These transducers are no longer in production, and if you can find one you’ll pay 8-10 times what I got this one for. If it ever fails, I’ll probably replace it with a cheap one and a converter board — now that I have that figured out.
Update 5/4/17: Transducer arrived, NOS as advertised with a nice sealed electrical connector. This thing will likely outlive me.