Saturday, October 31, 2009

Riveting battle won, the war proceeds apace

A comment from Wingman Ted on the topic of the ever-bending rivets stated the following:

As for your AD4 rivet, make sure you are using the right length rivet. From the picture it looks too long. When a rivet is too length it bends!

This is true, and I remember it from the sheetmetal class that I took at the local A&P school. But.... how could the rivet be too long when the rivet gauge borrowed from Co-pilot Rick indicated that the rivet was, if anything, too short? Sure, Van's warns us in section 5 of the manual that there will be cases where a too long rivet is called out in the plans and may need to be shortened, but... the rivet gauge! How could it be wrong??

Well, as it turns out, thusly:

Used that way, the rivet appears much too short. This is a sample photo taken later with a different size rivet and different thickness of metal, though - with the rivet in question, the error was not nearly as obvious. That said, here's how the gauge is supposed to be used:

Makes all the difference!! I didn't find that out until later, though. Still working under the impression that the rivet was bending because I couldn't get the squeezer situated correctly due to interference from the flange, I hauled everything up to the hangar and pulled out my Gucci rivet gun:

Would you guess that it hasn't seen much use in the last couple of years? Yep, both the rivet gun and me were pretty rusty - I drove a couple of practice rivets in a piece of scrap to remind myself how to do it. Then I aligned everything on the problem rivet, gave it a few shots with the rivet gun, and.....

bent it.

Drat. Having exhausted my limited knowledge without any commensurate gain, I contacted Co-pilot Rick for assistance. I loaded everything back into the car and hauled it up to his shop where he tried to drive a straight rivet. It bent. "Ah," he said, " it's too long."

"Impossible," I replied, "I checked it with the gauge."

You can guess how it went from there.

We used the bench grinder to shave a little length off of one of the rivets and Rick was able to drive it in perfectly straight. Only to find a completely new problem: a gap was created between the rib and the spar. That poor little rib by then had something like the fifth rivet drilled out of it. The newest problem was caused by trying to form the shop head (the part of the rivet that gets "shrunk" to form the grip) on the very thin metal of the rib. I was doing it that way because the manufactured head (the pretty one that doesn't get all squatted down by being riveted) on the side of the metal that would be visible to the outside world. Pure vanity, that, and completely unnecessary. Turning it around and driving with the shop head on the thicker metal worked perfectly. Rick pounded in all four and I headed back to Schmetterling to do the rest. Those were all squeezable because the called out rivets were exactly the correct length.

You can see the shop heads running down the row between the hinge brackets. Please don't look to closely; one of them is pretty ugly. It'll look nice on the inside where no one can see it, though:

The next step is to create a special rib for the bottom of the rudder. This rib will get riveted onto the big welded control horn/hinge bracket. For that to work, the front flange needs to be cut off:

That rib gets attached using a combination of the #4 solid rivets and a couple of blind rivets. I did the blind rivets first:

That whole deal gets riveted onto the spar with eight solid rivets. I was only able to squeeze six; the other two will have to be driven because of interference with flanges and such that precludes getting a straight shot with the squeezer. Well, that and because I insist on successfully driving a rivet by myself.

Tomorrow the rudder skin will go on, so I went ahead and deburred the remaining three ribs and clecoed them into place:

With a few more minutes before I needed to start preparing dinner, I also pulled the blue skin off of the rudder skin.

I worry that the heated language used while doing this puts me in danger of a deadly no-knock raid from the DEA, (they reportedly use thermal imaging spy cameras to detect the heat of the plant lights used for illicit basement farming) so to distract myself I thought about a fun prank I'd like to pull. A fellow brand-new-to-the-whole-game RV-12 builder asked on an internet forum what he should do about primer. The evangelists came flying out of the woodwork like those flying monkeys in the Wizard of Oz, of course, each having exclusive possession of the only possible right thing to do. I got to wondering what would happen if I replied to his question by saying that my plan is to just leave the blue vinyl skin in place on the inside skins, figuring it was put on there to protect the metal, right?

Oh, that would be a riot!

Friday, October 30, 2009

Another riveting tail (tale?)

Not so good, this one. But we'll get to that.

Building the rudder is eerily similar to building the vertical stab, starting with the preparation of the hinge brackets. Being as these are the brackets intended to attach to the vertical stab brackets, though, we are requested to test fit them. The brackets have to be attached to the vertical stab with bolts, which seems somewhat pedestrian after all of the cutting and riveting and other exotic machinations. The bolts needed to attach the hinge brackets to the stab are lumped into a brown paper bag with a collection of other bolts. As one bolt pretty much looks like the next, I had gotten into the lazy habit of identifying them by separating them into piles and determining their type by comparing the number in the pile to the number supposedly included in the bag. By doing so, I also accomplish an inventory of each bag. It was in the bag of bolts that I found my first inventory error:

It was the AN3-5A bolts that I was after, and it seems that I have one too many. That's all well and good, but the karmic balance was maintained through the exclusion of one AN3-4A bolt. I could pester Van's to send me one, but I'll just order one next time I buy other stuff and save them the hassle. They're not at all expensive. Even with the count disparity, I was able to determine which bolts were the AN3-5A and collect eight of them to attach the two hinge assemblies.

The top hinge assembly bolts into the nutplates that were installed early on in the building of the vertical stab. It was when I went to bolt on the bottom assembly that I realized there were no nutplates to bolt it into. My first reaction was to adopt the jaw-dropped look of utter confusion that I get when I try to use a self-checkout at Wal-mart; my second response was to look more closely at the manual. Oh, we tie it on with string or wire, and it will be permanently attached later. I remembered reading that, but hadn't full realized the import of it. Thought it could wait and all that. Luckily, I had some copper wire left over from the canoe debacle as was able to get a nice, tight temporary installation:

With that done, I needed to cleco the hinge brackets onto the spar that will be at the front edge of the rudder. The top hinge bracket is very similar to those on the vertical stab:

The bottom? Well, it's a bit different. It's powder-coated, welded steel. It needs to be far more robust because it also acts as the pair of control horns that the rudder control cables will attach to:

It was finally time to test fit the rudder spar to the vertical stab. This was again a matter of selecting bolts from the little brown bag and using them to attach the two parts. I can see already that this is going to be a real ugly chore when it comes time for the final assembly; it's tough to get the washers between the parts of the two assemblies. After finally getting the first of the bolts and its accompanying washers in, I realized that I had selected the wrong bolts. It was way too short. It seems that the counting and comparing method is not really the best strategy. After a bit of a search through the book that Van's thoughtfully included with the kit, I found a very helpful page printed in a very unhelpfully tiny little font:

After selecting the correct bolts, I repeated the process. The top bolt was even trickier than the bottom with regards to getting the washers in place and I had resort to using some of the left over copper wire to "fish" the washers into place:

Everything fit great. The manual offered the use of thinner washers wherever needed to improve the fit, but that option was not needed at all.

With the test fitting done, the next step was to start assembling all the little bits that will trail along behind the front rudder spar. The first of these is a rib. It gets riveted in through the spar and through the doublers used to strengthen the area where the upper hinge brackets will be. It gets riveted in with the same big, fat #4 rivets that were used to build the vertical stab hinge brackets. Remember how I said that I had read about people having problems squeezing those big rivets but that I had not had any real difficulty at all? You don't? Good! Because I got my comeuppance, good and hard.

The first rivet that I tried to squeeze in bent:

I drilled it out. Here's the head of it impaled on my drill bit:

That just leaves the shaft of the rivet in the hole:

With the thick parts I was working on before, it was a simple matter to just grab the remainder of the rivet with a pair of pliers and yank it out. It's not quite that simple with this thin aluminum. I had to disassemble all the parts and gently pull the remainder of the rivet out without bending or contorting the rib. That was such a hassle that I was extra careful to get the squeezer positioned correctly when I tried again. Well, the good news is that the shaft of the rivet squeezed straight. The bad news? Well....

The head is canted. Crooked. Not flush. Buggered. Lopsided. Sadly, it too needed to be drilled out.

I won't try to squeeze it again. Tomorrow I'll take it all over to the hangar and use my rivet gun to drive it (and the others) in. That will hopefully work better than trying to use the squeezer in the tight quarters of the inner flange of the rib.

Tuesday, October 27, 2009

Taking a step back: starting on the rudder

Just when you think you can't get any further to the back of the airplane, you finish the vertical stab and start on the rudder. The finishing of the stab was easy: just put in a dozen more rivets at the bottom of the spar and screw the front fairing into place:

When I trial fitted the fairing, it fit horribly. I was afraid I was looking at a long, arduous bend-twist-unbend-rebend process, but once the screws started going in it pulled itself into shape just fine. With that done, I started on the rudder. The rudder, for the most part, is just like the vertical stab but smaller. Even the early steps are familiar: cut a few parts apart with tin snips and (yes, Mr. Gray, I'm still using a hacksaw) the hacksaw. I enjoy using the hacksaw for the incongruity in it - it feels like such a bludgeon when compared to 'delicate' tools like files or more subtle tools like those used in deburring. Of course, for raw power even the hacksaw cannot compare to the pneumatic rivet puller. Rosie the Riveter would have quaked in her pumps if she had to use that monster!

Deburring went far more quickly this time around now that the ScothBrite wheel and I have become good pals. These will be riveted to the front of the rudder so a bolt can be pushed down through them and the rudder hinge thingy on the vertical stab:

Just as with the spar in the vertical stab, a couple of doublers get clamped into place, match drilled, and clecoed. These provide additional strength in the area of the rudder hinge:

In what will surely be the party trick that wows the hot chicks in whatever retirement home I eventually end up in, I have developed the ability to retrieve a cleco and squeeze it into place with one hand:

There is some similarity in their shape...

Still thinking about paint:

Monday, October 26, 2009

A Tail (Tale?) of Two Riveters

Really, it could be 'tail' or 'tale.' There were two of us riveting a tail, and it's quite a tale. And it involved two different riveting tools.

Co-pilot Egg and I hauled the vertical stab over to the hangar for the final riveting of the skin to the skeleton.

After my recent experience with the manual rivet puller, I was keen to try out the pneumatic riveter. What an amazing difference! Even Egg was able to pull rivets with the air puller.

What seemed to work best, though, was having her remove Clecos and place rivets while I followed behind pulling them:

It didn't take her long to learn that pulling Clecos is hard work. She'll be sore tomorrow!

It sure looks good all riveted up, though:

The rivets didn't all go in easily, but there were only two holes that needed a small, quick pass with the #30 bit to convince the recalcitrant rivets to go in.

Next: the rudder.

Sunday, October 25, 2009

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 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: