Building an airplane – July 21–25

I’ve gotten way behind on my blogging about the airplane build, in part because on the days I’m doing it, I tend to work until late (after 10pm in a couple of cases) and on the days that I’m not, I’m too busy catching up with other essential business, like reading student theses.

The short version is that I worked Friday, Monday, and Tuesday (yesterday) for anywhere from 4 to 10 hours each, with Jonathan helping out for several hours each on Monday and Tuesday.

The completed wing ribs. It took me about a day and a half to make all of these, with the first few taking the most time.

We are now most of the way through the fuselage and wing assemblies, and Jonathan has done most of the engine mount assembly and has started to look at the struts. Our plan is get as far as we can on our own before Chip rejoins us to help wrap up.

The wing assemblies with ribs attached. Metal straps on each end were wrapped around the spars, epoxied, and riveted at the top of the ribs. Half-ribs still need to be attached between the main ribs.

A couple of technical notes for others who might be tackling a Zigolo build:

  • The wing ribs are trickier than they look, at least until you get the hang of them. The pre-drilled holes in the ends of the top and bottom tubes don’t perfectly line up with the pre-drilled holes in the steel end brackets, which means you often have to drill through to get the 3×16 rivets inserted. But those 3 mm diameter rivets are extremely sensitive to the size of the hole on the far end – if it’s even a little too large, the mandrel pulls all the way through to the near side of the bracket before breaking off rather than on the far side where it should. You can tell when this happens, because the rivet “pops” only after the second or third pull rather than on the first. Sometimes a pulled-through mandrel doesn’t make a noticeable difference in the strength of the joint; sometimes it does, because it can break up the aluminum sleeve between the bracket sides. In any case, the way to avoid this problem is to first start with a true 3mm drill bit, or at worst a #31 bit, rather than the more readily available (in the U.S.) 1/8″ bit, which is about 6% too large. Then, be very careful not to widen the hole more than necessary once you get through to the far side of the bracket.  It took me several ribs and a few ruined rivets that had to be drilled out again before I figured out the right technique.
  • Another “gotcha” with the wing ribs:  there are sheet metal straps that get riveted to the bottom of the ribs on the leading and trailing edges – these eventually get wrapped around the spars and epoxied into place. I made the mistake of thinking the pieces were all the same for both leading and trailing edges, not noticing that some had center holes and some didn’t.  The ones with the extra hole go on the trailing edge. Don’t do as I did and attach them indiscriminately!  Naturally, about half turned out to be wrong, and I had to drill them all out and re-rivet the correct pieces to the correct ends, all after I thought I was completely done making 26 beautiful ribs!
  • If your riveter stops pulling the rivet mandrels for no apparent reason, you probably have a piece of debris stuck between the internal jaws, preventing them from clamping down.  Simple enough to cure once you know to partly disassemble the head, but puzzling and frustrating for a newbie when you don’t know what’s going on.  It happened to me with two riveters in the space of a half hour, and only the next morning did Jonathan and I figure out how to fix them.

Before we can do much more work on the wings, we need a fresh supply of 3×16 rivets, as we ran out prematurely and need them to attach the half-ribs. Still looking for a U.S. supplier!  In the meantime, we’re on pause again, and I’ll take Thursday and probably Friday to catch up on other things.

Note: I originally had some incorrect information about bit sizes in the item above about 3mm rivets – thanks to Clay Stuart for pointing out my error!


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