Sunday, December 19, 2010

Why didn't I think of that?

From the mail bag:

leon said...
seem to me the ribs could travel home where it is warm but maybe it doesn't take that long to justify the possible damage caused by transporting them.
Well, no, it wasn't really a question of difficulty or risk. It was more that I have become so obsessed with finding ways to deal with the cold weather that I never considered the most obvious way: don't go out in it if you don't have to. It was a form of target fixation, I suppose; I was so keen to defeat Winter at its own game that I lost track of the bigger picture. I mean, how hard could it be to gather up a couple of pounds worth of ribs and carry them back to the house?

Not very, as it turns out. although I did have another incident with the car key to the Forester. The last time I had an inconvenient bout of clumsiness with this particular key was on the day of my ignominious defeat at the hands of the sailing gods.

As a reminder, here's a snippet from the whole sordid story:

I ended up pulling the boat around to the other side of the pier and yanking it up onto the bank. I didn't want to have to do that - that side of the pier was filthy with yucky green algae and floating trash, and it smelled horrible. There was no choice, though.

I went and parked the car ("How long was you in fer this time," I heard as I walked by the happily disinterested witnesses) and went back to retrieve the boat. I thought I'd go ahead and get my life jacket on and put my car key in the water proof box before putting the boat in the water. As I was trying to snap the buckle on the life jacket, I heard "PLOP," and looked down just in time to see my car key sinking below the algae.

Great. Just great.

If you think I was reluctant to pull the boat through that crud, how do you think I felt about reaching down into it to fish around looking for my car key?
Today I dropped the key into a pile of snow. You may remember how flush I was with the success of modifying my new gloves to make them more suitable for working with small pieces-parts. Well, as fate would have it that modification also made them completely unsuitable for fishing around in a pile of snow looking for a car key.

Still, it was worth it. Spending a couple of hours slogging through a pile of wing ribs in the relative comfort of the basement instead of shivering in the hangar made it all worthwhile.

The first couple of ribs took the longest. I started fluting them with the idea that with enough effort I would be able to get them to sit flat on the workbench. It took awhile to realize that there wasn't any way to make that happen. They insisted on bending in all sorts of uncomfortable looking directions on the top surface of the rib, and I think it is because of this notch that is cut into each rib:

I may be wrong about this (so don't quote me in polite company), but I think it is good enough to get the ribs fluted such that they will sit flat with only light finger pressure holding them in place. I think the clecos and rivets will pull the ribs into alignment with the outer skins quite easily and without adding undue stress as long as the ribs are willing to comply without resistance.

With that in mind, I soon developed a method that would allow me to routinely get the ribs to sit flat on the first try. Every now and then one of the ribs would need a small correction, but nearly all of them were good on the first try.

My method was to first put light flutes along the bottom of the rib.

Then I'd flip the rib over and start at the notch in the center, moving towards its front leaving ever-deeper flutes as I went. The first few were as shallow as those on the bottom flange, but by the time I got to the very front I was fluting as deeply as the pliers would allow. I knew when to start making the deeper flutes because there are "inverse flutes" in the flanges as the curvature of the rib increases. It makes sense to need deeper flutes here when you consider that the idea of fluting in the first place is to relieve the pressures brought about by bending the flange in a curved surface.

I'd finish the rib by going back to the center notch and running shallow flutes to the back of the rib. I'd check the rib by lying it on the workbench and seeing if I could get it to sit flat with light finger pressure.

Now that I've made you read through all of that, here's a video that demonstrates the technique:

Caveat: I have not yet fitted any of these ribs to the wing. I do not know if they will require further fluting (or, heaven forbid, unfluting) or adjusting.

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