Riveting the Tail Fuse Frames

The first two and a half were easy. Blind rivets - not too much can go wrong.

The third frame, however, has a very beefy structure on top. That can mean only one thing: it is going to have a very important job to do, and will therefore require big, fat #4 solid rivets. Ok, it means two things. It will have a very important job to do, it will require big, fat #4 solid rivets, and they will be a bear to squeeze. Ok, it means three things.

So, what's the critical function that will be the responsibility of the upper half of the smallest frame? Funny you should ask. That extension coming from the top of that frame is where the four bolts that hold the vertical stab and rudder will go. Given that the plane probably can't fly without the vertical stab, keeping a tight grip on it is an important role indeed!

There are 18 rivets to be squeezed, and they are a bit tricky to get at. There are. as seems to often be the case, flanges that get in the way. After attempting multiple contortions and invoking any number of profane incantations, I came across an angle of attack (so to speak) that allowed the access I needed, although it still required quite a bit of facial scrunching and bulging arms to get them squeezed:



I know I make it look easy, but really, you should consult your physician before trying this yourself. Facial contortions lasting longer than four hours should be considered a medical emergency.

In addition to the circus act needed to get the squeezer into position, there was also a special pattern required to work around the clecos. Here's the order that I found to work best:



Here's the ugly side that no one will ever see again once the tail is buttoned up:



After all of that effort, the frames ignominiously joined the tail skins back on the parts shelf while other parts are prepared. The first of those is the piece that a threaded O-ring will go into to provide a tie-down hoop at the back end of the airplane:



There's a template that provides directions on holes to be drilled and corner to be cut:



The manual calls for a 3/8 x 16 (3/8" diameter with 16 threads per inch) tap to be used to thread a one inch deep hole that the tie down hoop will screw into. My tap set has two 3/8 taps, one labeled 3/8 x 24 and the other simply labeled 3/8. My assumption that the plain old 3/8 tap assumed a thread per inch count of 16 was proven with this side-by-side comparison:




There's a rather cryptic command on the drawing that says "Cut To Tangent of 1/4" Hole." I'm not sure exactly what it means and will research it before proceeding, but my initial guess is that a line drawn from the tangent of the holes will intersect the two little semi-circles on the edges, and that I am supposed to remove the metal from the part underneath the template that resides under that line:



Note also the 5/16" drill bit that will be used to pre-drill the hole into the part. The masking tape marks one inch of depth.

Finally! Done with all of that deburring

The tough slog of preparing tail cone skins is finally done! The next step, which I had been deferring because the "full scale" drawing wasn't, finally came to the fore. I decided that it didn't really matter that the "full scale" drawing didn't actually match the scale of the defining object; all that was required was enough fluting on the part to get the slight bend in the four-hole flange to match the barely discernible bend in the "full scale" drawing. That was easy.

So, with a long period of deburring done, it was on to.... another bunch of parts that needed deburring.

Not so bad this time, though, since these parts are small enough to be deburred with the Scotchbrite wheel. That didn't take long, so it was on to the next step: flute the formers. Aw, crap. More fluting. If you remember, the fluting for the ribs in the vertical or horizontal flight surfaces was very easy. Just a few light squeezes flattened everything out nicely. This was not the case with the tail fuselage formers, as you can see here:



In fact, it seemed like the more I fluted, the more "bent" the parts got. I posted the picture above to the Van's Airforce forum and was told that the part appeared to be "over fluted." I was also told that it wasn't super critical to get the part to lay completely flat; the part is pliable enough that I will be able to pull it into alignment with the skins when I go to assemble the cone. Ah, cool! I de-fluted the over-fluted part and pressed on with using the clecos to test fit everything.

In an interesting (but probably meaningless) twist (so to speak), two of the formers are assembled with the right half overlapping the left, but the third former does the opposite:





Oddly enough, it now appears that the "less is more" fluting advice was absolutely correct:



Except, that is, when it isn't. It took quite a large amount of fluting to get that minimal curve into the flange:



There's still a little more deburring to do on those formers, then they will be riveted together. These formers will eventually provide the basis for the tail cone skins to be formed into the "too big for the shop" tail cone. The clock is ticking on the time I have left to work in the comfort of my indoor shop.

Tail cone skins flying off the shelf...

... so to speak.

There's not a lot of variety to this part of the job. Grab a skin from the shelf, remove the blue vinyl, deburr the holes, wave one form of abrasive or another in the general direction of the edges in a Kabuki performance of deburring them as well, and break the edge.

The vinyl removal got a little easier once I adopted a tip that I saw on the DReeves site:



Of course, you then need to remove the tightly wound from the little pipe so it's not exactly a free lunch. It still nets out to easier, though.

I also found a piece of scrap metal in the hangar that I could use to practice the usage technique of the edge breaking tool. The first few tries were horrible, but once I got the hang of it I got a pretty nice edge:



I'm down to three skins left to prepare. It looks like this next one is going to be tricky because it doesn't have a 'J' bend molded into like the others. That means it has the rigidity of a jellyfish. It's going to be hard to work on something this big and flaccid:



It's also far too wide for the little piece of PVC pipe that I've been using to remove the blue material to work. I'll need something bigger. And that will be the story for a later day.

Here's the problem: I'm doing it wrong

In the ultimate case of barn door closure in a post-equine escape scenario, I decided to do a little more research on the topic of edge breaking as it pertains to making a big, stinking mess out of it. What I found is that, well, I'm doing it wrong. The edge breaking, that is, not the making of a big, stinking mess of it. I'm excelling at that, thank you kindly.

So, here's the right way to do it:

"To use this tool, open up the set screw and close the jaws. Then put the tool on the edge of the piece to be broken with the rollers just barely on the edge. Then tighten the set screw just enough to get the rollers to touch the metal. Then open the jaws and close them with the tool set with the edge guide against the edge of the material. Then just pull the tool along the edge without twisting it down. The tool does the work and only bends about 3/16ths inch of the edge down. If the tool does not pull along easily, you have it too tight. Remember, you are not putting a large bend in the edge, but just a 2 degree tilt on the very edge. The tool does that without twisting the tool at all. If you twist the tool down, you will put a crease about 5/8ths inch in from the edge where the inner edge of the tool is. That is not where the break is supposed to be."

That whole "without twisting it down" thing? Got that covered. I was twisting it up!

But yeah, even though I twisted up rather than twisting in the verboten downward vector, I have that whole "crease about 5/8ths inch in from the edge where the inner edge of the tool is" thing going on. The big question now is what to do about it. It's possible that it will flatten out as I rivet the skins down, but it's possible too that some unforeseen genetic mutation resulting from cutting-edge bacon research will result in us all sharing uncontrolled airports with aviating pork-flavored barnyard livestock. I'm not sure I can, or should, count on that.

At least it's the bottom skins. Even if it ends up ugly, it will be on a location on the airframe that only another RV builder would be rude enough to inspect. Guess I won't ever be flying in to Oshkosh if I can't get this cleared up.

"So, how was your day at the office?"

I can only imagine what a bad day at the office for a plastic surgeon might be like:

"You wouldn't believe how many tail skins I deburred and broke today."

It's not all that much more pleasant as an RV-12 builder, truth be told, although it sounds a bit less gross.

I've been working on the bottom tail cone skins, my thought process being the same as Van's: make your messes on the bottom where they're less likely to be seen.

The mess I'm making is from deburring the holes - that's pretty routine stuff by now. No, the problem I'm having is in "breaking" the skins. The tool that I'm using apparently requires the asceticism, diligence, and patience of a Stavrophore monk to master. There appears to be no limit to the ways I can find to create a wavy or buckled edge. I'm hoping that the contrition inherent in the riveting of the skins will flatten everything out enough to at least partially mask my errors, but if it doesn't, well, at least my sins will be apparent only to those willing to crawl underneath the plane. Judging by the coat of oil and grime that routinely builds on the bottom of my RV-6, it's not like I will ever be under there!

This does not address the issue of top and side skins, though, and I don't think I'm going to suddenly tap some new reserve of innate ability before the completion of those pieces comes due. Instead, I'm going to try a different tool. Co-pilot Rick has one of these:



My hope is that it's easier to keep a grip on and it won't slide off of the edge like the puck shaped tool does. As with my hypothetical surgeon, tool slippage can (and does) leave a very, very ugly mark.

Starting on the tail cone

It's been awhile since I've worked on the RV-12, primarily due to competing demands from my other (still broken!!) airplane and a smattering of Xmas preparation chores. I'm also slightly reluctant to start on the part of the kit that will inexorably take me down the path of working out in the winter elements when the assembly gets to big to keep in the basement shop. That may not be too bad, at least until January and/or February. I've spent quite a few hours out in the 30-ish degree hangar working on the RV-6 and, while not completely comfortable, have not yet lost any digits to frostbite.

The two most daunting prospects in the construction of the tail cone, at least from where I'm standing, are the preparation of the skins and the preparation of the skins. I mention the skins twice because these particular skins require a relatively particular preparation. Sure, there's the normal drudgery of removing the blue vinyl and deburring dozens and dozens of holes, but there's the new wrinkle (cue José Jiménez (2:40): "Oh, I hope not!") with these skins: the edges have to be "broken."

Broken?? Again, "Oh, I hope not!"

My 'broken' they mean that the edges need to be bent down a few degrees where they will join or overlap other edges. By bending the edges down, the tightening caused by pulling the rivets will not curl up the edges as much. Or so they say.

The breaking of the edges requires a specialty tool (presumably called an edge breaker) which, clever fellow that I am, I ordered at the same time I ordered the 120 degree countersink bit. It's an odd looking little device:



But that would come later. First, the blue vinyl has to go. I used the same "cut it into boxes" methodology introduced in the peeling of the horizontal stab skins, but this time I added a sophisticated step that I hear all of the pros use: I let the soldering iron roll off of the heat-proof stand on rest on the side of a rubber glove left lying around after some of the fiberglass work that I had recently done on the RV-6 cowls:



Naturally you're wondering how that simplifies the job of removing the onerous blue vinyl. Well, it doesn't. But golly, it sure does generate an awful stench! What's the benefit of that, you say? Nothing. Nothing at all. In fact, you force me to admit it: I had no deliberate intention of burning the rubber glove. In retrospect, though, I wish it had been the least of my careless moments...

Anyway, on to deburring:



That took awhile. These skins are huge!

Finally it was time for the step that I have been stewing about for weeks. You see, the correct tool and method for breaking the edges has generated quite a bit of discussion on the forums. I've read every available opinion on which tool to use and exactly how to use it. I've seen the horror stories. In short, I've worked myself into a state of nerves over the whole thing.

The rectification for that is, of course, careful study of the plans and instructions, followed by an introspective visualization of the process. Concentration is key. There's no room for a mistake here. Caution is of the utmost importance.

Which is why I could have just screamed when I was a third of the way down the edge of the first skin and realized that I was bending (breaking) it in the precisely wrong direction. Out, not in. Twisted down, not up. One hundred and eighty degrees off course.

Well then.

What to do.

As it turns out, all you have to do is start over and bend it in the correct direction and all is forgiven.

Phew, that's a relief!!



That was enough stress for one night, so I set the tools down. Besides, I have another problem to figure out. As I was reading ahead in the plans, I ran into a little confusion:



If you can't read that, it says "align the holes in the four-hole flange of the angle to the full-scale illustration in Figure 2."

Sounds easy enough, but if you look closely you will see that the holes do not line up. And what have we learned about this kit? If it doesn't look right, it probably isn't. What I need to determine is whether the holes are supposed to line up after the fluting. It's hard to believe that they will, but I've learned that fluting can make a pretty big difference in a lot of ways. To be safe, though, I'm going to do a little forum research and see if anyone else has mentioned anything about this before doing anything to this part.