Thursday, December 31, 2009

When easy steps aren't...

It should have been an easy day in the shop. Absent on more rivet that needs to be driven, all that was left to do on the aft bulkhead was to add a couple of "wings" that hold the bearings upon which the horizontal stab will pivot.

The two parts get clipped apart and cleaned up as we've done many times before, but not before labeling them as -R and -L respectively so as to remember which side of the plane they each belong on. There's a somewhat dubious drawing that shows how the parts are to be clecoed onto the bulkhead. What it comes down to is that you cleco each part into the flanges on the bulkhead. There's nothing that specifically tells you whether they should be oriented with the angle of the "wings" facing towards or away from the bulkhead, but it's one of those situations where you'd have to go out of your way on some sort of masochistic mission of abject stubbornness to get it wrong. Just in case that actually appeals to you, here's how it should look:

Except, well... that didn't work. The point of this exercise is to rivet only the holes on the tab; the holes on the flanges will get done later when the tail cone skins are all riveted together. Once it's all clecoed together, we have to final drill the six holes on each side, drilling through both tabs and the bearing itself. With the clecos where I originally had them, they interfered with the drill. I moved them to the other side:

Once the holes get final drilled, everything gets taken back apart for deburring, then it gets put back together again. Final drilling works best if the parts are held together as tightly as possible, so I try to only remove one cleco at a time. It's hard to tell if any given hole has already been drilled once you start moving clecos around, so I marked each one just after drilling it:

Because this isn't my first rodeo, I know that disassembling and reassembling can cause issues with the alignment of the holes later if I don't get everything back where it was. Just to make sure the bearing got put back in the same position, I marked each one before removing it:

With it all put back together again, it was easy to squeeze in the twelve #4 rivets. The next step sounded like it would take all of five seconds: press the SB437-4 into the hole shown. That turned out to be a bit more difficult that it seemed it would be. Here you can see the bushing (whose sole function in life will be to prevent the electrical wires running from the instrument panel back to the trim motor from chafing) and the hole where it is intended to live out the remainder of its days:

See the problem? No? Well, here it is. The '437' in the SB437-4 part number indicates .437, which is the diameter of the barrel of the bushing. A consultation of a drill bit size chart (thanks, Wikipedia!) tells me that .4375 is the diameter of a 7/16" drill bit. That's all well and good, you say, but so what? Well, just take a look at this:

Yep, 7/16" diameter. Now, compare and contrast with this:

Count 'em yourself if you wanna, but trust me - it's a 6/16" diameter hole. Or 3/8" for you folks that prefer your fractions reduced. Either way, it's pretty clear why the bushing wouldn't fit. The hole pretty clearly needed to be enlarged to 7/16" since I could think of no easy way of shrinking the bushing to 3/8".

That would require a 7/16" drill bit which, thankfully, I have. But... I have a 3/8" drill, and as we learned just moments ago, 3/8" is less than 7/16". That meant that I'd have to use the drill press. Which, well, is not so easy once the part to be drilled is adorned with all sorts of inconvenient protuberances. It took a bit of trial and error to finally get the bulkhead secured in a useful and accurate position underneath the bit on the drill press:

I have to confess to be a little put out that the plans hadn't had me drill that hole out back when it would have been easy, and I was also fairly sure that a 7/16" drill bit hadn't been called out in the required tools list. Sensing a potential gotcha, I went back and looked:

I was correct in the specific, but incorrect when you consider the requirement for a Unibit. That said, I would not have wanted to use a Unibit for this. My experience with Unibits is that they are too easy to use. By that I mean that it is just as easy to drill to 8/16" as it is to drill to 7/16". The hard part is ensuring that you don't go a step to far. But, with the utmost caution and a steady hand, it could have been done. That doesn't excuse making us figure it out for ourselves, though. There's nothing more frustrating that finding out that something that should have been easy is anything but, especially when the resolution to the problem is something that could have been done with far less difficulty earlier on.

Which, interestingly enough, brings us to the next step.

Rather than build an entire airplane only to find out that the horizontal stab won't fit during final assembly, we do a test fit. This, according to the directions, is intended to have us choose the right set of washers to provide the best fit at the pivot points. The first problem was that it is very, very hard to get the washers between the brackets and the bearing. Both my fingers and my needle-nosed pliers were too thick and bulky. After a dozen or so attempts, all of which ended up with the dropping of a washer and the incumbent risk of losing it, I decided I'd have to make a run to Harbor Freight for more appropriate tools. Here's what I came back with:

Confident that it would be a cake walk now that I had a way to hold the washers, you can probably imagine the emotional letdown when I got a bolt all washered up only to find that the shank was too large to fit through the hole in the bracket:

I went back to the section of the plans where those brackets are prepared for installation and could not find a directive to "Final Drill 1/4," but it's pretty clear at this point that there should have been one. Unless, of course, I'm just missing it.

It's New Years Eve, and while I'm steadfastly avoiding leaving the house because I don't like to be out when I know the rest of the world is tanked up on booze and good cheer, I decided that it might, yet again, be a good time to just walk away from the airplane for a little while.

Monday, December 28, 2009

Aft bulkhead - hangar riveting

I decided to brave the 25F ambient and trek to the hangar to finish up the riveting on the aft bulkhead. It went something like this:

- Put bulkhead gently into vise to hold it still while I use my two-per-customer hands to hold the rivet gun and bucking bar, using only minimal vise pressure to avoid twisting, marring, or in some other way damaging the bulkhead

- Realize that I can't rivet while wearing big, thick gloves. Remove same.

- Realize that the only thing colder than a 25F cold-soaked rivet gun is a 25F cold-soaked bucking bar. Forlornly eye discarded gloves sitting uselessly on workbench

- Drive two rivets.

- On the third rivet, cringe as bulkhead moves in the vise. Grin sardonically at having replaced smiley rivet created with a squeezer, a feat formerly believed to be impossible, with a smiley created the old-fashioned way.

- Re-evaluate my commitment to a smiley-free airplane. Decide that I will only get to build one airplane in my life, and I ought to do it well. Drill out the rivet.

- Immediately reward my conscientious diligence by creating another smiley when the bulkhead shifts in the vise again. Swear a blue streak.

- Drill out the new smiley. Belatedly tighten the grip of the vise using my patented, time-proven JOMT (Just One More Turn) methodology, hoping against hope that for once it turns out as something other than a disaster.

- Successfully drive new rivet. Successfully drive a bunch more rivets.

- Drive the last rivet, one of the two that go through the tail skid bracket. Decide that it needs just one more burst as it is slightly under-driven.

- Create smiley in last rivet. Skip completely past blue, swear azure streak.

- Again question commitment to smiley-free airplane. Again decide to do the right thing. Drill out rivet.

- Realize that I hadn't brought any spares in that size with me.

- Decide that this is enough for today as I have had my fill of education and recreation.

The Aft Bulkhead

Or, if you will, I could also title this post "A New Third Eye." But that comes late in the story.

The aft bulkhead will eventually be installed (wait for it....) at the very aft (or 'back end', you landlubber) part of the tail cone. It will not only seal the back of the tail cone which is, after all, nothing but a big tube (shaped somewhat like a cone, surprisingly enough, given its nomenclature) but will also provide attachment points for all kinds of important things like the vertical and horizontal stabs, the electric elevator trim motor, and all of the sorta complex stuff that makes the Flettner tab work.

With all of that going on with a part that's probably only one square foot in area, it's not all that surprising that there's a lot going on with regards to riveting and the attachment of various pieces-parts. And, with that much going on, it's also not surprising that this particular page in the plans/manual is up to its third revision. And considering that the downloading and reading of revision pages from Van's web site was one of the research methods I employed during the run-up to starting this project, it's equally unsurprising that I have read this page many, many times prior to actually reaching this step.

With all of the different pieces to attach, there are obviously going to be different size rivets used, each depending on how many layers it has to penetrate. The manual has a chart to help you determine which rivet to use for each hole:

There are some interesting things going on with this chart.

First, note the size difference between the third and fourth rivets sizes in the list. AN470AD4-4 is the third down in the list. The '470' indicates that this is a round-top rivet (as opposed to flush), it is a #4 width (which means a tough squeeze), and it is a -4 in length. The fourth in the list is a AN470AD4-6, which is a -6 in length, 50% longer than the -4. The integer gives the length in 1/32s, so a -4 is 4/32" long.

So, why and where do we use the longer rivet? Look towards the bottom of the bulkhead and you will see a couple of brackets are being riveted onto the bulkhead. It would make perfect sense for the longer rivets to be used in the holes that have to pass through the flanges, right? But if you check the sizes used, you will see that it is the shorter rivets that go through the flanges, at least on the left bracket. On the right bracket, the rivets that go through the flanges are different lengths depending on which side of the bracket they go through. This makes no sense until you realize that the longer rivets are also being used to rivet the tail skid in place. This becomes obvious a little bit later in the process.

But what's going on at the top of those brackets? If you look at the top flanges and determine the type of rivet being called out, you will find that it is the LP4-4, which is a blind rivet. Just on the other side of the big hole in the middle of the bulkhead, you will see a collection of eight CCR-264SS-3-2 rivets. Those are #3 size flush blind rivets. So what's will all of the blind rivets? We never see the use of blind rivets in areas where a lot of beefiness is required. My theory here is that those rivets are out of the reach of the 3" yoke of the rivet squeezer, and rather than have the builder spend $100+ for a larger, seldom-used yoke, blind rivets were employed instead. As we will see, though, I'm still going to have ti use an alternate method (which for me will be a rivet gun) to drive some of the more awkwardly placed rivets.

Thus familiarized with that which is to come later in the page, we jump back to the first step on the page which is to fabricate those brackets we see at the lower part of the bulkhead. These require separating from a longer piece in the way we've become accustomed to, and then a quick deburring as has become our wont. But wait! Because we read ahead (it's hard to miss - it's a big, bold-font warning just before the official Step 1) we know not to deburr the larger hole in the middle of each bracket piece. Instead, we rivet the two bracket pieces that have rivet holes in them to create the right side bracket. We then "deburr only enough to locate the bushing."

Ok, that seems odd. I have been locating small parts like bushings by digging through the paper bag inventory list. In all of the deburring that I have done, I don't recollect ever locating a part by performing the act. Clearly we are learning a new Van's term here. Because there is a restriction on where to deburr, my first step was to nominate one side of the two-flanged bracket for deburring and mark it. As long as I was doing that, I marked the appropriate side of the one-flanged bracket to avoid a mistake:

Before locating the bushings with deburring, I located them using the inventory sheet. Test fitting them to the bracket holes helped discern what was meant by the statement "oversize before press fit" in Step 1. In this case (and in most, I wager), the word 'oversize' is not a verb. No, we do not attempt to make the bushing oversize; it already is. So, 'oversize' is an adjective, and an appropriate one to boot. Those bushings were having nothing to do with those holes. In fact, we are informed that a C-clamp and a small socket may be employed to coerce the bushings into the holes.

To make that happen, though, the bushings must be located by deburring. With a clearer picture of what was desired, I realized that what I needed to do was deburr the holes just deeply enough for the newly slanted edge around the hole to guide the bushing into place:

From there, it's (or should have been) an easy process to put a C-clamp on one end of the bushing and use a socket on the other end of the C-clamp to push against:

I say "should have been" because getting all of that in position was a three hand (or two hands and a chimpanzee foot; in either case I am anatomically ill-equipped to the task) job, and even then the bushing insisted on going in crooked. I removed the (Harbor Freight, he said in ominous foreshadowing) clamp to see what the problem could be. Oh, this might be it:

After a short search of the clamp shelf, I found a straight(er) clamp and tried again. Success:

Step 2 took me awhile to figure out. Basically it states that we are to "slightly flute at shallow notches, 4 places" only enough to "reduce the slight pucker in the flange." The drawing showed the notches in question, but it took me awhile to figure out where the slight pucker was, mostly because when they say "slight," they mean "almost non-existent":

Once you find the slight pucker, it's just a matter of squeezing it down with the fluting pliers. That was a little harder than I expected it to be because the fluting pliers that I have are so big that the tiny little pucker was hard to get a grip on. You can see where I had to nibble at it:

With all of the prep work done, we start to cleco things together. Not, as it turns out, in order to start riveting. Rather, there is some drilling to be done. Remember that fancy tail skid bracket that had so much cutting and grinding to do? Well, it's not done yet. The two rivet holes already drilled into it are just starter holes to get it clecoed into place for final drilling:

The plans also have you clamp the part down prior to drilling, but I found my collection of clamps to be lacking in their ability to make any serious contribution at the higher end of the skid. Having seen what can happen when match drilling parts only being held by clecos, I knew to keep a close eye on the fit of the part being drilled into after each new hole. Sure enough, it didn't take long for a chip-filled gap to appear:

Remove. Deburr. Cleco. Drill. Repeat.

It got better as I worked my way down into the area that the clamps were able to reach, culminating in a nicely drilled part:

That is an interesting picture in that it finally shows why we went through all of the rigmarole of cutting corners and slants on the tail skid bracket. It wasn't make-work after all. Now that it's in place, it's obvious that the cuts in the lower flange were to allow the threaded hole to protrude out of the bottom of the plane without interference from the flanges of the bulkhead. But what about that big (ugly!!) slant that I butchered into it? Well, that big hole above the tail skid is where the counterweight bar will pass through into the tail cone. As the bar moves up and down with the horizontal stab, it needs room to move in the vertical plane. If we hadn't cut that slant into the tail skid bracket, it would have interfered with the counterweight bar, which would have in turn interfered with the pilot's ability to use up elevator. And that, my non-pilot friends, is a definite problem.

Once drilled, the tail skid needed to be removed for deburring one more time. As along as I was doing that, I took the whole assembly apart and sprayed some primer on it. As you know, I haven't been priming much of the airplane because it really doesn't add any corrosion protection. That said, it does act as a bit of a talisman (or "Dumbo feather," as I like to say) in situations where the criticality of the area in question is such that a little peace of mind is nice to have. And, just like taking timeouts into the football locker room at half time, primer left in the can has no use whatsoever. Once the primer had dried, I clecoed it all back together again:

NOTE: I have returned from the future with a warning! See those two holes in the lower left corner? There's a big one (3/8", to be exact) and a little one. See them? Ok, good. Go to Step 14 where it tells you to "Insert the bushing into the F-1211 Assembly called out in Figure 3" and retrieve the bushing from the appropriate parts bag. Make sure it will fit into the hole. Don't put it in all the way just yet - just put it in far enough to ensure that the hole is the correct size. Mine needed to be drilled out to 7/16" and it was a lot harder to do at the point I did it than it will be to do it RIGHT NOW!

I started with the blind rivets because they're so much easier than the squeezed #4 solid rivets, then worked on around the periphery. This too was a three-hand operation, but I tried to substitute the edge of the work bench for the third hand. That worked out fine, right up until the point where it didn't. The thing about squeezing a #4 rivet with the robust Cleaveland Main Squeeze is that once it gets past the force-enhancing cam, it has a tremendous amount of "spring-back" potential energy stored. If one were to somehow lose his grip on the part being riveted in just the wrong way, that part (in this case an aft bulkhead with all kinds of sharp-edged protuberances on it) could potentially fly back and hit the riveter (the guy squeezing the rivet, not the actual tool) right in the kisser. How do I know this, you ask? Well, a picture = 1000 words:

Ouch! And, truth be told, not much of a mood enhancer, unless the mood you're trying to enhance is "crappy." A "third eye" like this is a great conversation starter, but it's unfortunately a conversation you'd rather not have. Good thing I'm not going to work this week!

I pressed on with the riveting, though, trooper that I am. But without the good mood that I started with, it start to feel a little like work, a feeling that I have sworn to use as an indication that it's time to quit for the day. I hate being halfway through a job, though, so I pressed on. Through a strange twist of fate, everything went fine until I reached the inner parts of the bulkhead where I found that the yoke on the rivet squeezer couldn't reach all of the rivets. I just left those clecoed (or taped over) until I can go to the hangar to drive them:

Funny thing about that picture: note the two groups of three clecos. You would expect (if you're the type of person that likes symmetry) there to be four clecos in each group. Well, what happened with the fourth holes is something I didn't even thing possible: I got "smileys" on squeezed rivets! That's not uncommon when driving rivets; it happens if you let the rivet gun slip off of the rivet. I was shocked to see it happen on a squeezed rivet. So shocked, actually, that I tried again on other side. Which achieved the same (worse, actually) result:

Between that and my throbbing forehead, it was definitely time to stop. I'll have to carry the bulkhead out to the hangar and drill out the smiley rivets out before driving in the eight (now ten) remaining rivets. Then on to the eight nutplates!

Thursday, December 24, 2009

The Tail Skid Bracket

This must be what it's like to build one of the traditional RVs where it's not uncommon to see a step in the manual that says something concise like "Fabricate the Engine Mount."

In this case, it's nothing quite that complicated. After all, it's just a piece of extruded aluminum that has to have a hole tapped to allow a bolt with a hoop at one end threaded into it. This will provide a way to tie the tail down when the airplane is parked outside. There will be two more of these, eventually. There will be one in each wing. Or so I assume.

There's a little more to the fabrication than simply tapping the hole, though. Not that there needs to be, mind you, as the additional steps seem to be more about the aesthetics of the part than anything else. When you consider that this part will be trapped inside the fuselage where no one but an accident inspector is ever likely to see it, I have to wonder if there is another issue at play. You see, the RV-12 was designed in the midst of a years-long FAA reappraisal of the rules that experimental airplanes are built under. During that time, there was an intense focus on the issue of fabrication. The FAA was trying to put more of the work back into the hands of the builder as they saw a trend towards kits that were so complete that the builder was just assembling a relative handful of parts into a six seat, pressurized business jet.

One of the more frightening proposed rule changes was to mandate that the builder fabricate some percentage of the kit. I believe the value of 20% was proposed at some point. Some wags wondered aloud if builders were going to be tasked with mining their own bauxite to make the aluminum.

This leaves me wondering if some fabrication make-work was built into the design to absorb some of that regulatory burden in non-critical components, should it ever become law. Look at it this way: if you were ever going to fly with me in this plane, would you prefer that I fabricate a tie down bracket or the wing spar? The percentage of fabrication could be made up of meaningless tasks performed on benign parts, or it could consist of parts that are absolutely critical to the flight of the plane. As a designer, which path would you choose?

Motives aside, the fabrication effort is pretty straight forward. As we saw at the tail end (heh!) of the last post, I had tentatively marked a pair of lines that were tangent to the provided holes. What I had not yet noticed was the importance of the somewhat off hand direction to cut tangent to the 1/4" holes. The holes in the template were not 1/4", nor were they actually in the part to be fabricated. So, Step One was to ignore my previous Step One and drill the 1/4" holes, then mark the tangent lines. It made quite a difference:

You could be asking yourself why we need 1/4" holes here. The directions insist on a kind of blind obeisance to the beneficent motives of the designers at times, but eventually it becomes clear as to why you did something. In this case, you can see that the 1/4" holes will be mostly cut away, leaving a nice 1/4" radius on the flange of the skid bracket:

See? It just takes a little faith!

We're also instructed to cut a diagonal off of the main body of the part to create... what? I don't know! This is either a weight saving effort (every .1 ounce matters, I guess) or to provide clearance for an obstruction that we will see later. That, or it's make-work. In any case, it looks like it's going to be a bit of a chore without a band saw:

I decided to save that step for last. I'd concentrate on the most functional step first: the drilling and tapping of the hole.

There's already a hole running the length of the part, so the drilling is simply to increase the radius of the hole to a size suitable for tapping. Even with the existing hole there to help guide the bit, I decided that the drill press would be the safest way to ensure that the hole remained straight:

Section 5 of the manual has a nice paragraph on tapping holes, and one of the suggestions is to also use the drill press for the actual tapping. They have you chuck the tap into the drill press, then manually turn it to tap into the metal. I tried it that way, but it didn't work very well. I needed one hand just to hold the tap down into the hole against the spring action of the drill press that wants to lift it back out, while trying to turn the chuck with the other hand. When the need for a third hand to hold the part steady became apparent, I figured that I was just not correctly configured for the job. And, having no third hand to borrow, well, it just wasn't going to work. There was another problem, too, in that the direction the the chuck needed to be turned to advance the bite of the tap was the same direction that loosens the chuck. I decided to give up on that whole approach and just use the handle that came with the tap & die kit:

The failure of the drill press method of tapping which, to be fair, was probably intended for tapping much smaller holes, didn't dissuade me from using a couple of other pieces of advice. First, they suggest using a lubricant. Second, they advise that you make no more than two or three complete turns before backing the tap back out and cleaning away metal chips. Using that method, it took awhile to get the tap all the way down in the hole:

Here you can see the metal chips that impede progress if you don't remove and clean the tap every few turns:

Here's the tapped hole:

With the intricate machining done, I shifted over to the brute force hacksaw to remove the excess material on the flange:

The hacksaw is the proverbial bull in the china shop and leaves quite an unsightly mess - not exactly what you want when making an aesthetic modification. This is, of course, why we spend $55 on a Scotchbrite wheel. I made both cuts with the hacksaw and then used the wheel to smooth everything out. As long as I was grinding, I added the notch on the side shown on the template (I looked ahead - it's for clearance from another part) and rounded the corners on the end where the flange of the part remains unmolested by the rapacious hacksaw:

Note the beautiful symmetry of the notches on the sides, a symmetry that would be even more beautiful if both of those notches were actually supposed to be there. Unfortunately, one of them is extraneous. The template that provided the radius for the rounded corners only provided it on one side, so I flipped it over to do the other side. I then forgot to return it to the correct orientation before cutting the notch. It won't matter in the long run, but it was a bit of a frustration if only because of how much of the expensive Scotchbrite wheel was wasted in its creation.

There was nothing left to do but to make the final, most difficult cut. This is a perfect example of why I should buy a band saw:

Yuck! The hacksaw is never going to be confused with a scalpel (or me a surgeon, for that matter):

The Scotchbrite wheel was able to clean most of that up, but there are some unsightly gouges that will remain. So, here's the final tail skid bracket, viewed from its good side:

Good thing it will be invisible!

Wednesday, December 23, 2009

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.