Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater

Tue, 18 Jul 2017

Building a Biplane: Makin' Ribs

With the completion of rib #5 (of 44) last night, I've entered the phase of building where things get kind of boring. It's still enjoyable and gratifying work, but it's hard to describe to anyone else in a way that makes it sound interesting. So, when you get bored half-way through this description, I won't be offended if you wander off to look at cat pictures or something.

I've built up my kit of parts, and am progressing through the ribs. I'm building the -293 (the part number, pronounced "dash two nine three") ribs now, and will be discarding the first two for various technical faults. There are sixteen -293 ribs, and the Skybolt builder I visited in Oregon advised me to have at least one spare built up and on hand, so I have 14 to go.

Each rib takes about an hour and a half to build. I had hoped they'd go quicker with the kit ready, but I guess that's what they take. I don't want to rush, since rushing just leads to mistakes. It's a ten-year project anyway, so a difference of half an hour per rib is absolutely inconsequential.

The procedure I'm following now is as follows. First, I put the nose piece and all the truss pieces into the jig. Some of the pieces need to be trimmed slightly on the sander, but some just drop into place. Then, lay out the gussets for each joint. Mark the gussets' positions with pencil so I know how far out to put glue. Wipe down all the sanded plywood surfaces with MEK to remove dust. At this point the compressor is already at pressure, and the stapler has a full load of staples. The two gussets that overlay the nose piece need to be trimmed beforehand, but the remainder get trimmed with the router once they're stapled down.

Now, mix the glue. I was trying the "squirt out N equal lines of each" method, but kept coming up short on the hardener, as marked by uneven levels in the bottles. T-88 epoxy should be mixed 1:1 by volume, or 100:83 by weight. Since my volume attempts were noticeably off, I switch to weight, and have been happy with the result. The $9 drug-dealer scale on Amazon is perfect for this task.

Once the glue is mixed, you have 30 minutes before it starts to thicken and get hard to work with. That's just enough time to carefully coat each joint in glue, coat each gusset in glue, position the gussets, and staple them down, working one joint at a time. I'm careful to align the gussets such that they don't impinge on the space for the spar (the rectangular openings near the ends of the rib). Any excess glue I see gets wiped up with a disposable rag.

Once all the gussets for a side are glued and stapled, the rib comes out and goes over to the router table, where I trim down any gussets that overlap the outer edge of the rib. Have to wipe the glue off the joint first, so as not to gum up the router blade too badly. The rib is then flipped over, and the same MEK wipe/mark/glue/staple/cleanup/router routine happens again on the flip side. The single rib in the photo above has just come off the router table after its flip-side gussets were attached.

So it's not the most challenging of work to do, but it is definitely satisfying to see the stack of ribs grow one by one. I need to figure out a better storage solution than just stacking them on a shelf, but that's what I've got for now. Before you know it, I'll be swimming in ribs, and trying hard not to damage them.

Posted at 14:05 permanent link category: /charger

Categories: all aviation Building a Biplane bicycle gadgets misc motorcycle theater