Well, for wing ribs at least. 30 false ribs down, 8 to go. It looks like I may be able to get some more building done, at least temporarily, at the EAA Chapter 80 “Able Ace” build space. The chapter has leased a storefront in a shopping mall that’s dying a slow and pitiful death. There are a couple of good sized workbenches there that I may be able to use for wing spar and tail assembly.
Got a couple more false ribs glued up, now I’m waiting for the epoxy to cure. I also unrolled the plans to get a good look at the wing layouts, and re-read the instructions for building wing ribs. The instructions say to make 42 main ribs (I have 43) and 37 false ribs. These two make 20, or it could be 21 if I cut down the extra main rib. I’ll just keep making them and see what happens. I really need to get that second jig back on the bench so I can do 3 at a time.
I glued up two more last night, and will do two more tonight. That will make 18 down, with
20 19 more to go. I’ll typically take some time at lunch to cut out the cross brace pieces and get everything set up. Then after work I’ll mix up some T88 and glue the ribs up, then let the glue cure overnight. By the next morning I can pull them out of the jigs and start again.
I’ve run out of cross-brace stock that’s been sanded down to 3/32″, so I’ll have to stop while I retrieve the small shop vacuum from the project house where it is now and run some more 1/8″ stock through the drum sander. It’s a pain, yes, but it has to be done.
I’m already debating where to go from here, once all of the false ribs are finished in a few weeks (maybe). I could start on the tail, but that will require a 4 x 8 work surface. The wing spars will require a longer bench, at least 12′ long. I may instead start working on cutting out the large number of nose ribs that will be needed, and the other high volume plywood parts. It’s awfully tempting to set up my CNC router again for that part, but I doubt that I will. I’d have to translate the outline from the printed plans into G-code for the router, and quite frankly I think by the time I got that right I could cut them all out by hand. I’ve seen a couple of guys use a router and a flush cutter to route the nose ribs from a pattern. I’m a little concerned about the radius on the inside corners where the nose rib glues to the false spar. I figure I could either sand a matching radius there, or touch up the corners of the nose ribs with a bandsaw or something. I’ll cross that bridge when I get to it.
Another false rib glued up today.
Believe it or not, I have not abandoned or stopped building this project. I haven’t done much (OK, much of anything) over the past… good lord, has it been THREE years? Oof. That’s horrible. But, other things do take priority. I also don’t really have a place to go any further than completing wing ribs at the moment. That said, I have gotten back into things in a limited fashion by testing the epoxy stock and completing another false rib. I want to at least get all of those finished and start figuring out where I can set up a 4×8 work area to start on the tail.
For anyone else who might be in the same predicament, the fine folks at Homebuilt Airplanes came up with a couple more sources. B&D International carries 5′ x 5′ sheets of Finnish birch aircraft plywood, and will cut and ship UPS. Boulter doesn’t carry as wide a variety, but might be good if you’re closer to the east coast than the west.
The price at B&D is higher than Aircraft Spruce. If you price it by the square foot, it’s not terribly higher. 13%, on the 1/8″ sheet I need. Not terrible.
The plans and BOM call for plywood spar webs, cross-cut, 60″ long. The webs are butt-spliced mid-wing, with what seem to me to be fairly narrow blocks of spruce on either side.
Problem is, you can’t buy 60″ wide sheets of aircraft plywood in the US. Aircraft Spruce has ONE size, and not a size I need. Everything else I’ve found is in 48″ wide sheets. And since the web needs to be crosscut, it’s not as simple as just buying a 4′ x 8′ sheet. I’ve contacted Fisher Flying Products as well as another supplier in Canada. Fisher’s tab will be roughly $340, the other place was pretty reasonable for the plywood but wanted over $500 for crating and shipping. To put that in perspective, ACS will sell me the plywood I need for about $100, delivered.
The question is, can I make 48″ long spar webs work in a way that is at least as good, or preferably stonger and better, than the original design? I am no engineer. Especially a mechanical engineer. I’m certainly not qualified to make such a call. Fortunately, I have someone local who is an engineer, and is qualified to help make that decision and recommend another way to do it — if there is one. I’ll be taking the wing plans to the February EAA chapter meeting to go over them with him and see what we can figure out.
If that doesn’t work out, Spruce does sell 5/32 ply in 61″ x 61″ sheets. The spar webs are specified as 1/8″ for the main spar, and 1/16″ for the rear spar. I could just make both webs 5/32 with a slight weight penalty. The plywood would weigh 3 to 5 pounds more, but I’d probably also need to trim 1/32 to 3/32 from the spruce stiffeners, so that might make up for some of it. Again, I’ll need to consult with a real engineer to see if that wold work or not. Ending up with a plane that’s a couple pounds heavier but significantly stronger is OK. Ending up with a plane that is in any way less strong or less safe is absolutely not. And if the ribs need to be modified a little to clear a beefier spar — I’m OK with that.
Another year draws quickly to a close, with what feels like not a lot of progress on this project. I have a tall stack of ribs, but really nothing else. I had hoped to have a good start on the tail surfaces by now, but haven’t even started on them. We’ll need the basement for a family Christmas party, so no laying a 4×8 sheet of MDF over the island down there to start laminating pine. No worries, though. I have located some nice clear pine boards at Menard’s that will rip down nicely into 10′ long lamination strips. I have an order of Finnish birch ply queued up on Aircraft Spruce’s web site, ready to place the order once I’m sure I have all the stuff on there that’s going to be expensive to ship. As soon as we’re finished with the post-party cleanup, I’ll have the basement available to work in through the rest of the winter since the garage will just be a bit too cold for epoxy.
I also got a great idea from one of the guys on the Biplane Forum. I’ve been pondering how to store the wing ribs. I think I’ll build short pieces of main and rear spars out of pine and non-certified plywood, just to assemble all the ribs and clamp them together. That way I can surface sand them all together, and maybe if I’m lucky use that assembly to run them through the table saw for trimming as well. Maybe.
Reluctant to toss a fair amount of epoxy, I mixed up a larger batch of about 8 CC, just to make sure I got a good mix ratio. The first batch I had mixed to test the suspect glue was very small, and I figured I may have just muffed it. No such luck.
I mixed 8cc, then glued two pieces of capstrip together with a totally unscientific scarf joint. I then glued in two short pieces of geodetic brace stock, ends cut at roughly the angle of the braces in the ribs. After 24 hours of cure time, all three joints came apart at the glue line, not the wood. Into the bin it went, all of it. I’m glad I didn’t use any of it for construction. Fortunately I have another quart of epoxy here, unopened, and some new syringes. I’m now set up with fresh glue in new dispensers.
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.