There may be more than one way to skin a cat,

...but I'm not sure there's more than one way to skin a vertical stabilizer. And, just like skinning an unsedated cat (or so I would imagine, anyway), it's not particularly easy to skin a vertical stab.

The final steps actually began last night when I found myself back down in the shop just before midnight pulling blind rivets on the two stiffeners in the vertical stab rear spar. As Rick and I were riveting in the ribs yesterday, we found it odd that the plans didn't have us take care of those dozens of rivets at the same time. Rick suggested reading further forward into the plans to see if maybe it was taken care of later, but in previous forays into the depths of pages not yet reached I had seen nothing of the sort. Later in the evening it was still nagging at me so I went down to look again; still nothing. It wouldn't make any sense to drill all of those holes and not fill them, so I knew I must be missing something.

I was.

There it was, hiding right there in plain sight:

See in the upper right corner where it says LP4-3 TYP and points at one rivet hole? 'TYP' is short for 'typical,' and 'typical' is apparently Oregonian (home of Van's Aircraft) for "do this to every hole that we haven't told you to so something else with." This is not the only case of the Oregon taciturnity that makes reading the plans such a challenge, as we'll see in a minute.

I lost count of how many rivets there were to pull, but during the grueling process I re-learned something I had learned years ago when I was new to kart racing. I had overheard a couple of guys talking about how sore they were after races, and I thought it odd that I never seemed to be sore at all. Then, after a few weeks of experience, I realized that I wasn't sore because I wasn't doing it right. Once I get more competitive and started going home with aching muscles and big bruises on my back from racing so much harder, I realized that when I had heard those guys before, I simply had not yet learned how to do it right.

Fast forward to pulling blind rivets, a topic upon more than one person has suggested using a pneumatic rivet puller. I have one of those, but it's in the hangar along with the air compressor needed to feed it compressed air. "Too much hassle to bring home," I thought, "especially when it's not all that hard to pull them with a hand puller." Well, that was before I had to do a couple of dozen of them by hand. I didn't think I was going to be able to finish the last few, but I toughed it out.

And I'm sore from it.

The weather this morning had been forecast to be very nice for flying so I had planned an 0900 meeting with Co-pilot Rick. I wanted to fly down south to Portsmouth to have breakfast partially because it's a nice change of pace from the usual Urbana breakfast and partially because the fall colors are nicer down that way than they are up here in the Pool Table Flats region of Central Ohio. The problem with Portsmouth, though, is morning fog. Which they had plenty of, but then again, so did we. With a departure delay in effect, I went down to the shop to do a little work. This morning it was to be dimpling.

The front of the vertical stab has a fairing that screws onto it. The screws that will hold that fairing in place will use nut plates to attach to rather than nuts. The nutplates are attached to the inside of the skin that will cover the vertical stab frame (the Xmas tree). The skin is too thin to countersink to make room for the flush rivets that hold the nutplates, so it has to be dimpled instead. The hole where the screw will go in also has to be dimpled so the screw will sit flush against the skin. This is accomplished by using a dimple die on the rivet squeezer. There is a nipple side and a receiving side to the dimple dies:

Sounds easy enough, it in all actuality, it is. But I had another run-in with Oregon taciturnity. Here are the directions in the plans:

"FINAL DRILL, DIMPLE, FLUSH OUTER SURFACE, 26 PLACES."

Final drill is easy, and the concept of dimpling is well within my grasp. But "flush outer surface??" I hadn't a clue. Near as I can figure, it's Oregonian for "dimple this hole so that the attachment part going through it will be flush with the outer surface." Which, because that's so patently obvious anyway, seems to cause more confusion than it abates. Once I got over that mental hump, the actual dimpling was quite easy. Here are some dimpled holes:

Too bad it's not quite as easy as that. You see, the nutplates have to be dimpled too so that they will fit snugly against the skin. That's a bit tricky because the receiving end of the dimple die is too thick to sit close to the hole without getting caught on the threaded part of the nutplate. Fortunately, this problem wasn't just invented when they put together my tail kit; others have dealt with it before. Rick provided a cut-down/ground-down receiving piece for just this purpose:

You can see the difference between the two of them in the 3/32" column. Here's what it looks like in action:

Man, am I ever glad to have his help! If I was trying to do this completely on my own, I don't think I'd ever get it done.

With the dimples done, it was back to squeezing rivets to attach nutplates, something I'm familiar with.

 Here they are all riveted in:

 

With that done, I was just about ready to put the skin on the Xmas tree. All that was left to do was deburr all of the rivet holes and the edges of the skin. But before I could do that, I had to do the most onerous part of working with aluminum: remove the blue vinyl protective layer. It's not that hard to do on the small parts, but on large sheets like the skins it's an enormous pain. I had already pulled off the layer on the outside of the skin, but had put off doing the inside because it was an even bigger pain. I think it took at least an hour to get it all off of there:

 

Finally! Time to cleco the skin to the Xmas tree. It started out well enough as I was able to easily get the first few holes to line up, but as I worked my way across the skin it got harder and harder. Until the skin gets put on, the skeleton (the Xmas tree in this case) of an airplane is surprisingly fragile and floppy. It isn't until the skin is put on that the frame develops any rigidity. This is called a "stressed skin" construction, and I'm here to tell you that today is the day that I put the stress into stressed skin. The last corner of the first side that I clecoed put up quite a fight. You can see where I had to amass the most troops in the battle:

Once I got it that far, I mistakenly assumed that the battle was won. Just when I thought it was all over but the ticker tape parade, I ran into a couple of pockets of resistance:

Hey look! No hole!! Where is it??? Well, the tip of that rib was reluctant to move up into the fold of the skin, and I had no way to persuade it, or so I thought. I eventually realized that the other side wasn't clecoed yet so I could simply lift up the skin and reach up inside there to push it into place. That turned out to be harder than it sounds (mostly because I couldn't be on both sides of the skin at the same time) but I got it done. There was another hole in the same situation, but even when I'd get it lined up with the hole in the skin, I still couldn't get a cleco in. Eventually my attempts just caused the tab inside the skin to simply bend down. I had to reach in there and straighten it back out, and as I was doing so I'd swear that I noticed that the hole in the tab was only drilled to a #40 size, not a #30. It was the same on the other side too. I just lined them up real nice and ran a #30 bit through them and all was fine. Thus was the battle finally won:

Does that look like a triumphant warrior with a splitting headache? Well, it should - that's exactly what it is!

The stab was ready to be riveted, but that would have to wait until I could haul it up and out to the hangar in order to use the pneumatic rivet puller. That, and until the headache went away. I wish I had gotten my morning coffee sooner... stupid fog:

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!