Saturday, October 16, 2010

Lap Dancing

I only got out to the hangar once during the week, and that was only to make sure that everything was ready to go for the final riveting of the tailcone. There were two lower side skins that needed to be installed. That sounded easy enough, but as with all things tailcone-to-fuselage, the devil is in the lapping. The parts were to "underlap the side skins, overlap the tailcone, and underlap the belly skin."

Wow! That's more laps than the Coca-Cola 600! These particular skins had stiffeners molded into their edges in the same way the tailcone skins did, so it was no simple matter to get them to fit in underneath the edges of the other skins. It took a bit of finagling to get them in and get all of the disparate rivet holes aligned.

As I was working on them, I couldn't help nervously casting glances at some of the other areas of complex lapping where two or three different skins were layered. At one point I talked myself into removing some clecos and changing the order of things, only to have to go back and return the skins to their original order after yet another consultation of the drawings. This was all just a case of nerves, typical behavior for me when the next step to be performed will immutably lock into place large chunks of airplane. When there's no turning back, I tread lightly forward.

Unable and unwilling to put it off any longer, I had Co-pilot Rick come down and help with the final riveting. Large riveting jobs are immeasurably easier with two, especially if, as in this case, the assembly is too big to manipulate alone. In this case, the bottom rivets would be much easier to do if the fuselage could be rolled onto its side, and it's now far too heavy and unwieldy for me to do that alone without running the risk of dropping it on the floor.

It was also beneficial to have someone experienced with building these things to bounce ideas off of when the plans left us wondering about some glaring omissions. The relatively large riveting job was summed up in one sentence in the plans: "Rivet the areas common to the tailcone and fuselage." Fair 'nuff. That's what we're here for, after all. But lacking in that cogent, concise, and comprehensible edict was any mention of the holes left open that weren't common to both parts. In other words, one of the C's was missing from what I call The Four C's of Good Communications: Complete.

A complete directive would have mentioned something about the status of the holes that had been left open in the areas surrounding the common bonds. In the case of both the tailcone and the fuselage belly skins, a half dozen or so holes had been left open at the edges to allow the skins to move away from the main framework to allow the required over- and under-lapping to occur. We could see no reason at all not to go ahead and rivet those holes, but we could also see no "permission" to do so.

What to do, what to do.

We finally went with our analysis that there could not possibly be any reason for those holes to not be riveted as part of the overall joining operation. I can always drill them out later if I have to, but I don't see that happening. After you been building these things for awhile, you get a pretty good sense of these kinds of things. Well, right up until the point when you don't, anyway. I feel pretty confident about this one, though.

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