Saturday, October 24, 2009

Building the Xmas tree

Today was the day when I hoped to have something that looked like an actual piece of airplane to work on. Having spent a fortnight preparing all of the parts that would make up the Vertical Stabilizer, I thought that a full day in the shop (this being first time that I had a full day to devote to it) would be enough to get it all assembled. At a minimum, I wanted to get what I call the 'Xmas tree' built up. It's the framework that supports the skin of the vertical stab:

The first step was to radius the narrow ends of the VS-1204, VS-1205, and VS-1206 ribs. "As shown in figure 1," was the promise. As it appears is often going to be the case, the drawing doesn't convey nearly as much information to a novice builder as Van's seems to think it does. I know what it means to radius something, that being somewhat academic if you know what the word 'radius' means, but I wasn't sure how much material they wanted removed, or why it needed to be removed in the first place, for that matter. Once I took a look at the narrow end of the VS-1204 rib, though, I could see what needed to be done and why.

The "why" is that the process of folding the front of the aluminum rib over to form flanges on the sides causes the bent over metal to extend past the most forward part of the rib. It's hard to describe; a before and after picture might help:

The one one the left has not been touched. See how the side flanges extend past the front of the rib? That will cause problems when installing the rib flush against another part. In the case of a skin being formed around the rib, that problem would be an unsightly bump in the skin.

The one on the right has been 'radiused' (def - verb: to abuse with a grinding wheel) to remove the extra metal that would have caused the problem, The plans suggest that a fine file is a great way to remove the unneeded metal, and I'm sure it is. But a ScotchBrite wheel is even better:

The VS-1204 and VS-1206 were a piece of cake, but I ran into some confusion with the VS-1205. You see, it had a tab on the front, where as the VS-1204 and VS-1206 didn't. What's more, the drawing of the VS-1205 in the plans didn't show a tab either. After an unwarranted period of wondering how the plans could be so wrong, it struck me that maybe it wasn't the plans there are at fault at all! Could it be possible that I was looking at a part other than the VS-1205? Easy enough to find out: just go pull the blue vinyl that had been covering it out of the trash can and double check the identifying tag. Ah, mystery solved. I was attempting to work on the HS-1205. Makes all the difference!

With that mystery solved and all three of the ribs ground down to fit, it was time to 'flute' them. Surprisingly, this doesn't involve holding them up to your mouth and blowing across them to play Jethro Tull music. No, fluting means making little indentations in the flanges of the ribs to straighten them out. The bending of the flanges around a curved rib causes it to bow. Fluting the flanges takes up some of the excess metal to remove the bow. Again, it's easier to show than to explain.

This rib has not been fluted and you can see how the end of it bows up:

To flute it, you use fluting pliers (aptly named, eh?) to put small creases in the flanges. Here is the business end of the fluting pliers:

All it takes is a very light squeeze in the flanged part of the rib between each of the rivet holes. It's something that is very easy to over-do, but if you start small and just increase the flutes a little bit at a time, it's pretty easy to quickly flatten a rib:

I did one of them, and as I was patting myself on the back for a job well done, I realized that something was amiss with that rib: it hadn't been deburred. Why, you ask, would I have not deburred it? Well, I reply sheepishly, because no one told me to. You see, Van's figures you know that it needs to be done by this time and they figure that you don't want or need to be nagged about it. We're all adults here, right? I did two things: I sat down and deburred the rib, and I made a note for myself in the plans to remind myself in the future that I should deburr everything first:

It takes awhile to deburr those things! Maybe that's why Van's is so quiet on the subject - why be the bearer of bad news? You have to deburr all of the rivet holes, then the flange edges, and finally the edge around the lightening holes in the middle of the rib. As you can see in my note, I quickly realized that doing the deburring before fluting is a lot easier:


This drawing in the plans is interesting for another reason. This is the first drawing that I had to work on to see it in the correct perspective. When I first looked at it, I thought it showed the vertical rib from the front and the ribs attaching to it going diagonally to the rear of the picture. That made the flanges look all wrong, though, so I kept staring at it until I realized the it shows the vertical rib from the rear and the ribs attaching to it angling towards the front of the picture. Again, perspective it makes all the difference!

I was just finishing up the deburring when Co-pilot Rick arrived to provide some much needed QA inspecting and to provide an extra pair of hands in the building of the Xmas tree. It's hard to hold all of the pieces in place and rivet at the same time; it's been one of my biggest challenges. With him holding stuff in place while I riveted, it didn't take long to get the ribs attached to the front and rear spars:

Oh yeah, the box helped too.

Here it is all put together:

The time just flew by, and before I knew it, it was quitting time. With the skeleton built, the next step is to install the skin. That's a non-trivial job since there will be a lot of prep work required, but once it's done I will have an actual aerodynamic airplane part done.

Here's a preview:

It was a chilly, blustery, cloudy day today and would have been wholly unsuited to flying. In other words, it was the perfect day to have something fun and interesting to do in the basement. I'm loving every minute of this!

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