Sunday, November 29, 2009

Overall, a fairly easy day to complete the horizontal stab

I know, I already said it was done. I thought that it was close enough to fudge a little, figuring that the final steps of installing the control horns and counter balance arm would be fall-off-a-log simple. The parts were all match drilled, so how could they not fit, right?



It wasn't quite that easy when it came to doing it. The top control horn went on with no problem, but the bottom needed a little convincing. When you do the match drilling on these, the stab spar box is not yet riveted closed. Apparently there can be tiny changes in it as it gets riveted together. The match drilling isn't super precise to begin with because the horns can't be held in place with clecos. You temporarily slide bolts in the holes that have been drilled. Either or both of these situations led to a bottom control horn that didn't quite line up. A clamp was enough to coerce it into position, but I still had to deal with the nerves that come with knowing that cross threading a bolt into one of the nutplates would cause weeks of heartburn. The entire stab would have to be disassembled to replace the nutplate.

The counter balance arm also was off by just a thread. On bolt went in fine, but the other hung up on a tiny little lip inside the bolt hole. There was no hope of getting a drill in there to remove that tiny little ridge, so I put a bunch of tape on the front of the arm to protect the powder coat while I tapped on it with a mallet. The bolt slid right in after putting an appropriate amount of fear into the assembly.

The part that I thought would be the most difficult was the drilling and bolting in place of the actual lead weights. That was actually the easiest thing I did all day:

I spent the rest of the day working on the RV-6 cowl and watching The Battle of Ohio. The right team won.

Oh, I also mocked up a picture of the sponsor decal that will ride on my brother's NASCAR modified next season:

As if I needed another reason to look forward to next year! That is so cool!

Friday, November 27, 2009

Mixed feelings

Certainly there is a great sense of accomplishment to be had from finishing the horizontal stab. It was, after all, the most time consuming and challenging piece yet. But as I was out in the 35 degree hangar riveting the last few pieces together, I couldn't help thinking that it was the end of an era. That era being The Era of Building an Airplane in the Comfort of My Basement. From now until February, most of the work is going to be in the hangar.

On the plus side, 35 degrees was comfortable in my Walmartts:

I'm estimating that there are close to 500 rivets in the horizontal stab, but it went quickly enough with my brother-in-law manning the Cleco pliers and placing rivets while I followed along with the pneumatic rivet puller. Still, that's a lot of rivets! I remember 35 years or so ago being jealous when my brother came home from school with a little toolbox or something that his shop class had put together as a project. It was held together with pop rivets, and I was fascinated by the whole concept of metal work and riveting. I pursued a different tack in school so I never got to take that class. Now, 35+ years and a couple of thousand rivets later, I am finally ready to proclaim myself as no longer being fascinated by pop rivets.

That said, riveting on the skins continues to be the big pay off after hours of deburring, fitting, and general shop work. It takes a week or more to get to the point of riveting on the skins, but then it's all over in one or two short sessions:

You can see why I wanted to get it done, though. This is the stab crammed into a full size SUV:

I don't think it would have even fit in the bed of a pick-up truck. The Subaru Forester never stood a chance of moving this thing. Yep, the work is going to get a lot tougher as I move into the tail cone stage!

Thursday, November 26, 2009

My Blue Vinyl Epihany

I really wanted to get the horizontal stab skins riveted on today for a couple of reasons:

1. It's too big for me to move to the hangar in any vehicle I own, but my sister and brother-in-law are visiting with their gigantic SUV. Actually, it's so big that you could drop the 'S' and just call it a utility vehicle.

2. The CEO is coming to visit and this is the biggest chuck of airplane yet; it would be nice to have it in a presentable form.

Counter arguments were limited to one: I hate pulling the blue coating off of the large pieces. The coating material has no "grain," by which I mean that there is no direction in which it will easily tear. That means you can't just tear off strips of it. It all wants to come off in one big piece and that makes it hard to pull off of large sheets.

I decided to compromise. One of the evangelical arguments in the community is over the question of removing all of the blue stuff at once or leaving as much on the metal as possible to protect it. I think this is similar to what you see in NASCAR when the cars are behind the pace car zig zagging back and forth on the track. If you ask the first guy why he's doing it, he'll say that it clears built up rubber from the tires. If you ask the second guy, he'll say he's trying to get heat in the tires. If you ask the third guy, he'll tell you that he's doing it because the two guys in front of him are doing it. I decided to give it a try for reason number three.

The areas that need to be cleared are the lines of rivet holes and the edges. Cut Lines are made in the plastic by using a soldering iron to cut through the material. This is supposedly safe for the metal, but I have my doubts. It doesn't take long, although the smell can be somewhat nasty. Once you've done it, though, the lines of material peel right off, easy-peasy:

Here's the epiphany part: I could also cut lines to make the plastic on the inside of the skins easier to remove! I did, and it did! Cutting it into a few big rectangles made it much easier and faster to get that stuff off of the skins.

That done, I soon found out why we had put masking tape over a couple of places in the hange; both the left and the right side hinges get temporarily clecoed onto the right stab skin to have some holes match drilled:

For once I didn't stop to try to figure out why Van's had us do it this way. Schedule to keep, you know: VIP visit in the offing.

The skin halves are then to be clecoed into place. I wriggled the skeleton around in the fold of the skin to try to work the tips of the front ribs into place. Just like they did with the vertical stab, they often found it easier to just bend to the side rather than snug themselves up into the leading edge fold. A little poking and prodding get them more or less into position:

The bottom of the skin gets clecoed first so I had to roll the stab over. As you are positioning the skins, Van's suggests that you make sure that the rear flange of the upper skin overlaps the rear flange of the lower skin. It was easy to see what they meant by that sentence of near gibberish because the skins pretty much wanted to do that anyway:

Half way done and it's half skeleton, half horizontal stab assembly:

My brother-in-law would be going over to the hangar for a riveting session so I gathered up tools and supplies to be ready. As I was grabbing handfuls of rivets to take along, I remembered that measuring out rivets is like making spaghetti: you never know if you are making too much or not enough. I loaded up what I thought was plenty of rivets, then threw in another two handfuls for good measure.

I still didn't bring enough. We were about fifty short. Still, it's good enough to show:

Tuesday, November 24, 2009

The Saga of the Torque Wrench, etc.

Having skeletonized the front of the spar box, it seemed that the next step would be to add the ribs to the back side. I thought that would be a simple matter, and I had reason to believe so: the front ribs were easy. It took very little time to learn that I had been overly optimistic. So little time, in fact, that it was the very first rivet that demonstrated the flaw in my thinking. The problem was that the rivet puller wouldn't fit inside the rib because the raised part of the lightening hole punched through the web of the rib was in the way.

I knew what needed to be done: the very first step of the RV-12 construction, which I had skipped. I figured I'd do it when I needed it, and now I needed it. That step involved taking a little wedge shaped piece of aluminum, grinding off some extraneous material (which is why I didn't do it - I didn't have the Scotch-Brite wheel yet), and cutting it into 1/2" lengths. Each of these lengths would then have a #40 hole drilled through it 1/4" from the fat part of the wedge.

All of that work was intended to create a little wedge that could be put over a blind rivet in a tight spot and provide an angled flat surface for the rivet puller to work against. If the nail part of the blind rivet was appropriately bent, the rivet puller would be angled out away from the obstruction but the rivet itself would still be flush against the surface. I think one of the videos linked over in the right sidebar demonstrates this technique.

It's a simple matter to bend the rivet:

Here's the whole contraption in place and ready to be pulled:

It results in nice, flush rivets. For all I know, that might have been the result anyway if I had simple pushed the rib over to the side out of the way, but even if it was just a feel-good technique it worked pretty well:

It was slow going compared to "normal" riveting, but an hour or so of riveting resulted in a fully skeletonized horizontal stab:

I still had to finish the fabrication of the little aluminum tubes that I had let sit over night while I hoped for a flash of brilliance (or, at least, a brief moment of lucidity) to strike me. I was still worried about getting the ends of the tubes flush across without getting them too short. I finally decided to just lightly brush them across a file. If I had it to do over, I'd just cut them 1/32" too long in the first place. They would already be in tolerance at that length, and I'd have a little buffer to allow me to clean them up if needed.

I was forced to tackle that job because the next step was to bolt on the hinge supports and install the metal tubes. It turns out that they are not used as hinges as I had originally thought; they actually act as 'stops' to limit the travel of the stabilator. I installed everything finger tight to see how it all fit:

At that point I needed a torque wrench to tighten them correctly. Van's provides a chart that indicates that the appropriate torque value for bolts this size is 25 inch-pounds. They caution against over torquing and quite definitively state that 25 inch-pounds will not feel like much torque at all. They also are very clear about their feelings regarding torque wrenches that measure in foot-pounds: throw them away, they have no utility in this job. As you can imagine, my torque wrench is measured in foot-pounds.

None of this was a surprise; I had started the process of acquiring the correct type of wrench weeks ago. Harbor Freight even had a 1/4" drive, inch-pounds torque wrench on sale! Now I know at least half of you just rolled your eyes in disgust at the idea of using a Harbor Freight torque wrench on anything more complex than the assembly of an Ikea footstool, but I had done a little research on this. Or, more accurately, read a second or third hand account of a little research done by someone else. What they allegedly founds was that the Harbor Freight torque wrench was accurate enough, but much like a pet hamster, you wouldn't want to get too emotionally attached to it. In other words, good enough to warrant spending $20 instead of the $150+ that it would cost at Sears.

Thinking myself clever, I came up with a scheme whereby I would take the CFO to dinner at a local sub shop which purely by coincidence was right next store to Harbor Freight. And, what with it being right next door, I'd pop in and buy a torque wrench while she went to the sub shop and placed our dinner order. The perfect crime, except for one little thing: Harbor Freight was completely out of the $20 torque wrenches. Not all was lost, though, since I still needed a set of 1/4" drive sockets to go with it, so I'd go ahead and get those while I was there. That too would have been an at least adequate crime, except for one little thing: two registers were open, and both had long lines of impatient customers waiting. It seems that the connection to the credit card verification service was on the fritz. No worries, I thought, I'll just pop back in after dinner.

All thoughts of clever machinations thrown to the wayside, I had my dinner and confessed that I needed to go back to Harbor Freight when we were done. If not the perfect crime, at least still an efficient trip, right? Well, when I got back to Harbor Freight the long lines were gone. In fact, there was only one register open and just a single customer in line. Ha! My patience paid off! Well, it would have, except for one little thing: we waited ten minutes behind that guy as he argued with the cashier over what a $3 discount that he believed he qualified for, while she steadfastly held that it was $1. When she decided that she had to find a manager to resolve the conflict and he was nowhere to be found, I put the sockets back on the shelf (again!) and left.

I simply gave up on the torque wrench and looked for an alternative that was better than the Harbor Freight tool but not as expensive as Sears. I found one on for $48. Chances are that it's the exact same tool as the $20 tool at Harbor Freight, but the extra $28 dollars makes me feel that it's surely both more accurate and more robust. Consider it $28 worth of piece of mind.

But I still needed sockets. Having been fooled once, I know it would take a much more elaborate scheme to trick the CFO into trying again. This time I used the argument that we should try the new chinese buffet that had opened conveniently close to Harbor Freight for lunch, the compelling argument being one of sound economics: if the food is horrible, let's find that out at lunchtime prices. So, off we went.

It was a pretty good lunch and we were soon on the road to Harbor Freight. Then an inspiration of the two-birds-one-stone variety struck me: we could forgo the inevitable Harbor Freight hassle by simply continuing down the road a bit to Sears, where we could also shop for a new Xmas tree. The former tree, which we liked because it had lights already installed and we didn't have to mess around with untangling and stringing lights every year, had gone dark last year. Sure, a $4 string of lights would have kept it on hospice for a few years, but I needed sockets and I had a 100% confirmed report that Sears had Xmas trees. Easy sell, that. On we went to Sears.

Reports of the availability of LED lit (LEDs are supposed to last a long, long time and I'd really like for this to be the last time I have to buy an Xmas tree) trees were proven accurate and we selected an attractive 7.5 foot model with multi-colored lights. Decision made, I went through the formality of walking back out to the car to see if it would fit. It would not. Not even close. Someone would have to hoof it back to the house and return with a more capable vehicle. I nominated the CFO as I still needed to shop for sockets. That took awhile because I didn't want $30 worth of sockets. If you look long enough, you will eventually find the cheaper stuff Sears sells hidden back in a dark, musty corner.

That took long enough that I was starting to get worried that I wouldn't have the tree bought and ready for pick-up by the time the larger car arrived to pick us up. There was no line at the register, though, nor was there anyone else waiting at merchandise pick-up. This was going to be easy! Well, except for one little thing: when the merchandise pick-up guy went to pick-up the merchandise, he found that I had cleverly purchased an empty box. The tree that had ostensibly habitated the box that I bought had been promoted to floor model.


A group of employees gathered to determine what could be done to rectify this situation. I had a suggestion: "Box the floor model back up and sell it to me for $50 off."

That idea was immediately shot down: "We need that tree as the display model."

"Oh yes," I replied, "You definitely want to keep a model of a tree that you don't have any of on display. That's bound to work out well."

There was a counter proposal: "Just pick out a more expensive tree and we'll sell it to you at the same price."

The perfect solution! Well, except for one little thing: I had already bought the most expensive tree.

We finally settled on the expedient of nullifying the transaction and us buying a cheaper tree at 10% off.

Finally, I had my sockets!

And used them:

Van's was right: 25 inch-pounds feels almost finger tight. It's not very much torque at all and I can see how it would be easy to over tighten them without the appropriate wrench.

With that finally done, I went on to the next step which was to retrieve the trim tab hinges that I had cut to length on page 08-03. That would have been quite simple had it not been for one little thing: I hadn't done it. Figured it could wait. It's pretty easy, after all. And it would have been, except for one little thing: the piece of hinge that I hadn't cut to length on page 08-03 had come with a piece of duct tape on the end of it. That duct tape left a sticky residue on the hinge pin (the wire that holds the pieces of hinge together to make it, well, a hinge) and it was buggeringly hard to get that damn wire out. Once done, however, it really was easy to get the hinge cut:

Certain spots on the hinge apparently don't get drilled until a later step. Van's has us mark them to make sure we don't mistakenly drill them:

Drilling the holes was pretty routine work, especially since I remembered that the drill guide fits better if you lightly file the inside edges of the tabs.

With the hinge pieces ready to go, they need to be matched to the horizontal stab skins. Those skins are, unfortunately, still clad in the blue vinyl coating that I hate hate hate removing. It will wait for tomorrow, I suppose.

It should be pretty easy. Well, except for one little thing....

Monday, November 23, 2009

Just like a butterfly

Or more fittingly, I suppose, a schmetterling.

Right before your eyes and without the privacy afforded a caterpillar by a cocoon, the Horizontal Stab box is transmogrifying into the Horizontal Stab skeleton.

Well, it will.


But first, I had to fabricate the inner pieces of the hinges that the stab will pivot on. And by "fabricate," an overly lofty sounding word, I mean "make." And by "make," which in this case is also overly aggrandizing considering the nature of the actual work involved, I mean cut a little tube of aluminum into smaller tubes of aluminum. 21/32" long tubes, in fact. With a tolerance in size of plus 1/32" and minus 0. Zero. None. Nada. (As is "nada smidgen shorter." Oh, you thought I knew Spanish? Nope.)

You'd think my first step would be to find a ruler graduated in 1/32" increments. And, well, you'd be right. But I haven't got one. So my second step was to pull out my precision calipers. Which quite naturally led to the third step: go back upstairs and get a calculator to find the decimal equivalent of 21/32. Which, as I'm sure most of you already knew, is .65625 inches. My calipers are only useful down to .656, though.

It would have to do.

Cutting the tube with a hacksaw was easy enough, but doing it well was a completely different story. The saw leaves a rough edge that has to be deburred, and the deburring is not easy. In one case, I deburred a piece to below the minus zero tolerance. You can pick it out easily enough:

You can also see that the remaining pieces will still need to be cleaned up a bit. I'm letting them sit over night while I think of a way to get them nice and flush in the ends without chasing them down to below the allowable size. I'm thinking it's going to be something not involving the Scotch-Brite wheel. The great thing about the wheel is that it removes a lot of metal quickly. Of course, the bad thing about the wheel is that it removes a lot of metal quickly. It's a lot like working with fiberglass that way.

With that part back-burnered, it was time to move onto something more gratifying. Something like a little helicopter flying:

Unable to put it off any longer, I started attaching the parts that would hold the ribs that in turn would support the skin of the stabilator. This is another of those situations where Van's made sure that the parts could only (correctly) go in one way:

If you tried to install them incorrectly, the holes in the flange wouldn't match up with the holes in the spar box. That's what drills are made for if you're the type to insist on having things your own way, but I found it easier to just turn the part over so it would fit:

Those little parts will have the ribs aft of the spar box riveted to them. Eventually. Not tonight. For tonight, I was concentrating on the stuff forward of the spar box. That involved the preparation of eight ribs. The preparation included the normal deburring, plus some fluting to straighten them out and some grinding away of material on their noses. Just as with the vertical stab, the noses of the ribs are going to have to nestle into the bend at the leading edge of the skin. To allow for that, some of the material that got pushed forward of the leading edge of the rib when the flanges were bent needed to be ground away.

This is a before and after picture:

Grinding that much material off of eight ribs takes a toll on the relatively spendy Scotch-Brite wheel. After enough time watching the wheel shrink, I started to feel like it was billing me by the minute! Here's the spar box, half way to becoming the horizontal spar skeleton:

I hope to get to the back half tomorrow, but I'm on vacation. It seems like that would be a great time to get airplane work done, but my time seems to be getting soaked up honoring all of the "I'll do it when I'm on vacation" commitments that I've been piling up for three or four months. Plus there's RV-6 cowl work to do, although that's going to be on hold while I wait for a few little bags of appropriately sized rivets to arrive from Van's.

Saturday, November 21, 2009

Spar box done

I spent most of the day working on the RV-6 cowl. The weather today was simply gorgeous and here I am without a functional airplane to fly in it. Time to get it fixed! But that's a story for another blog.

While the epoxy that I had injected into the holes from the drilled out cowl rivets set, I went back to work on the RV-12. There wasn't much to do, really: a total of 24 rivets needed to be pulled to seal up the spar box. Being rather the over-achiever at times, I pulled 25. Oops! You can see the 25th rivet here:

It's the flush blind rivet at the top that doesn't have a '120' written next to it. That means that the hole wasn't countersunk to 120 degrees. In fact, it wasn't countersunk at all, for the very obvious reason that no rivet should have gone in that hole. Yet, anyway.

So, my first attempt to drill out a blind rivet. It's actually quite easy, but it did have the unfortunate side effect of bending down the flange that it had been riveted into. You know, a flange inside of the spar box that I had just riveted shut. And to add insult to injury, it is very likely that I will now be one rivet short in my inventory, a fact that almost certainly become painfully apparent at an extremely inconvenient time. That's just the way these things go...

Rather than drill out all of the rivets, I found that I could reach up inside one of the lightening holes in the spar box with a long, thin rod and bend the flange back into place. Hopefully I got it straight enough such that whatever rivet ends up inhabiting that hole will go through it rather than just push it out of the way. These are the loose threads from which the fabric of sleepless nights is woven when building an airplane. I'm virtually guaranteed to wake up in the demon filled hours of the night worried about that flange, with the only way of getting back to sleep being to go downstairs and look at it again to assuage my doubts that I got it bent back where it belongs.

Here's the ostensibly completed and equally restless spar box recumbent on pair of borrowed saw horses, no doubt wondering if my arthroscopic surgery has obviated the need for a far more invasive procedure:

Only time will tell. And I'm likely to have plenty of it: I got a letter from Van's yesterday telling me that I won't be seeing the fuse kit until at least Feb 1, 2010.

Thursday, November 19, 2009

Hey, remember I'm a part-timer!

It's not that I haven't been working on the plane; I have. I haven't written about it because I've only been able to squeeze in a little rivet squeezing and hammer a little rivet driving into my schedule this week.

On Tuesday I hosted a shop visit with Kyle and Don, a father and son pair that are contemplating building an RV-12 to replace their Cessna 152. I think that's a terrific idea, but I'm clearly biased in favor of the more sprightly and capably Van's airplane. I was able to squeeze in the rivets that hold the nutplates on the fore and aft spars of the spar box. It went swimmingly, but I will pass along a tip: there are two different rivet sizes to be used, depending on which nutplates are being riveted. I used the wrong length on one of the nutplates before realizing my error.

The shop visit was fun. They both had a lot of the same questions that I had when I was considering the kit and I think I was able to answer most of them accurately based on the smattering of experience I've gathered so far. There were a few times when I had to caveat my answers with a cautious "as far as I know" or "at least with regards to the tail," of course. As with any RV, there were a lot of questions about riveting, and a lot about the quality of the plans/instructions. Riveting: well, blind rivets are super easy. Squeezed rivets are too, for the most part, although some can be hard to reach with the squeezer. Driven rivets? Well...

Last night I was ready to rivet the counter balance brackets onto the spars. Those require the thicker #4 rivets and are therefore a little harder to squeeze. I was going to squeeze them anyway, but the yoke on the big squeezer wouldn't clear the flange of the spar. I had to load the two spars into the little Subaru and take them up to the hangar to drive the rivets with my rivet gun. I brought co-worker Egg along to hold the spars in place while I devoted my two-per-customer hands to the riveting. I'm still quite the novice at driving rivets and it showed. Five or six needed to be drilled out and re-done because I let the rivet set (the part attached to the rivet gun, as opposed to the bucking bar on the other side of the rivet) slip off the rivet head and completely mess it up. I also think I had the air pressure a bit too high as a number of the rivets were slightly over-driven. After I got back in the groove, though, it went as well as could be expected considering that I hadn't had a particularly pleasant day at work (nor on either of the commutes, for that matter) and that was being reflected in my hands. They just didn't want to behave themselves.

With the counter balance brackets in place, it's time to do the final riveting on the spar box. Once that's done, the ribs get attached and the skin goes on. That will take a few days as the parts for the broken RV-6 have arrived and I need to devote some attention to that. I'm off work all next week, so there should be a whole lot of progress to report on both fronts.

Sunday, November 15, 2009

Still working on the spar box

With the spar box all clecoed together, the next steps involve fitting, drilling, and generally massaging the powder-coated steel parts into place. These parts are relatively hefty when compared to the light aluminum of the spar box itself and require more substantial hardware to attach.

The control arms get clecoed in first. There are two of them: a top and a bottom. These are the arms that the cables used to control the horizontal stab in flight. The plans said to cleco them in place and then final drill with a #12 size bit. The problem I had was that the holes were too small to take a cleco, so I had to drill them out with a #30 bit first.

Just to the left of the top control arm is the socket/bracket that will hold the big steel counter-balance arm. It gets clecoed in place turned 90 degrees to its final orientation. This provides access to the holes that will be drilled through the arm for an attaching bolt to pass through:

You can see the two open holes at the top of the counter-balance arm brackets; those will be covered when the bracket gets permanently installed and is turned back 90 degrees. It was clever of the Van's designers to make enough of the holes common in location after the 90 degree turn to allow the bracket to be clecoed in either position. That allowed for easier access to drill the holes for the attach bolt. Always thinking, those guys.

Here it is looking at it from the front of the spar box:

This is the back side. The control arm is pushed in from the front until the back edge is flush with the back edge of the support bracket:

The directions have you match drill with the #30 bit, then final drill with a #12. They then have you push a bolt through, ostensibly to make sure the arm doesn't turn while you're drilling the hole on the other side of the spar box:

You do pretty much the same thing with the control arms:

Drilling through the steel takes a little more effort than drilling through aluminum!

Once all of those holes are drilled, all of the steel parts get removed for deburring. While they're out of the way, some doublers get installed on one of the spars:

These doublers will end up having nutplates installed on them, and those will eventually support the hinges that the stab will pivot on. There will be quite a bit of force applied to those hinges, hence the need for doublers.

The bolts that hold the control arms to the spar box will also be screwed into nutplates. The installation of these particular nutplates was somewhat unique (so far, anyway) for the RV-12 in that the holes for the rivets were not drilled for us by the factory. Instead we had to do what builders of "real" RV airplanes do: use a bolt screwed lightly into the nutplate to hold it in place while the first rivet hole is drilled by using the nutplate as a template. A cleco then uses that hole to hold the nutplate in position while the second hole is drilled:

All of this drilling results in parts that will be happier and line up better if they are returned to the exact same position after removal for duburring, so everything gets marked so it can be returned to the same location:

I couldn't write legibly enough on the tiny tabs the of the nutplates, so I used symbols.

To cleco everything back together after deburring, I found it easier to use one cleco down through the top of every piece, then flip the spar over and cleco from the other side:

Here's everything all clecoed in and ready to be riveted:

Can you find the nutplate that I got oriented incorrectly? Here's hoping that doesn't make any difference!

The riveting will have to wait for another day. There were plenty of pre-winter preparation chores to be done and the oil change on the RV-6 still hadn't been done. The cowls are still broken, but that's no reason for not finishing the oil change. I was able (and this is very rare indeed!) to get the old oil filter off of the engine and the new one on without spilling a single drop of oil. Not bad for a routine oil change that has been anything but routine.

Saturday, November 14, 2009

Taking a stab at the spar

Or sparring with the stab. I can't decide. In either case, I spent a beautiful Native American Summer day down in the Schmetterling shop working on the spar for the horizontal stab. This spar is different from those in the vertical stab and rudder in that it is built up from pieces to form a spar box.

As you may recall, there has been a bit of a delay in building the spar box as I waited for the 120 degree countersink bit to be delivered. It finally showed up a few days ago, but I've been spending some time working on the broken RV-6 cowl. Now that I'm waiting for parts for the cowl, I can get back to the RV-12.

Given the near miss on drilling the countersink holes with the wrong bit, I was very cautious with marking the holes to be countersunk and to what degree, so to speak. The drawings on the plans are a little out of the ordinary in that they "flatten" the spar pieces and show the flanges next to the webs:

Once I figured out the code, I marked the holes:

I also marked the new 120 degree bit since (other than a coat of rust) it looks nearly identical to the 100 degree bit:

Then it was drill baby drill:

With that finally done, I went on to prepping some of the other parts that I would be using in building up the spar box. This is the work I would have done while waiting for the 120 degree bit if it hadn't been for the repair work needed on the RV-6. Some of the parts were to be separated from an aluminum sheet that was far too wide to cut with snips. Out came the trusty hacksaw:

Not so trusty, as it turns out. It's a relatively harsh tool, and at times it can be a little obtuse when it comes to delicate parts. Snips can be like that too, but to a lesser degree. In this case, it was a simple matter to just bend the part back to where it belonged:

Here are all of the newly separated parts all lined up and ready for deburring:

The lightening holes in the bigger pieces needed to be deburred by hand:

NOTE: I have returned from the future with a warning. When it came time to test fit the horizontal stab to the aft bulkhead, I found that the AN4-12A bolts wouldn't fit through the holes in the HS-1213A brackets. It appears that they need to be final drilled to 1/4". What you should do RIGHT NOW is go find the AN4-12A bolts and ensure that they will fit through the holes on the HS-1213A brackets. Only the threads of the bolts go through the HS-1213B brackets, so those should be just fine as-is.

Because all of the parts on the relatively complex spar box have to be positioned perfectly, I laid everything out before I even thought about starting to cleco things together. The nice thing about having the holes countersunk in advance was that it made it easy to catch the fact that I had one of the little doubles in the wrong place. After all, it wouldn't make much sense to wait a week for a special countersink bit just to cover the countersunk hole with another part, would it? I'm rapidly learning that with this kit, if it doesn't look right, it isn't right. After re-checking the drawing, I got the little doubler in the right position:

With all of the parts having been verified to be in the correct position, I started clecoing parts together. The plans are very specific about the orientation of the in-spar ribs. They use two holes in each rib to determine the correct positioning. This is the rib on the left side:

This is the right side:

If you get them oriented correctly, the large lightening holes in the ribs will all be in alignment:

You can look down through it like a telescope to make sure they all line up:

What you can't do, apparently, is take a good picture of it.

Just before starting to rivet it all together, I realized that I had made a pretty serious mistake in positioning two of the ribs. See if you can see the difference.

First, the wrong way:

Here's the correct way:

What tipped me off that I had it wrong? Same thing as before: countersunk holes that didn't appear to have a purpose.

I got it all straightened out and put back together, then marked the holes for the correct rivet size since two different lengths were to be used. I also marked the holes that were to be left open with masking tape:

The rivets were all painfully easy to squeeze. Why painfully? Because the only reason I could come up with to use the flush blind rivets that caused such a delay was if it would be too hard to reach the rivets to squeeze them. I think I could have reached them easily. The flush blind rivet is the one in the middle:

It's possible that it would have required a bigger yoke on the rivet squeezer to reach it, though, and those cost about $100. Maybe it was just to moot the need for another expensive tool.

Here is the spar box with the top and bottom pieces riveted into place:

Then it's just a simple matter of clecoing on the forward and aft spar pieces.

Easy, that is, except for one thing: the holes in the ribs didn't line up with the holes in the spars:

That made No. Sense. At. All. With the precision with which this kit was designed, it was inconceivable to me that these parts could be that far out of alignment. After all, if it doesn't look right, it isn't right. I went back through every step of building up the spar box and could not find anything I had done wrong. I thought I was going to have to post a plea for help on the Vans Air Force forum and wait for an answer. That's when I noticed that the positioning holes in the in-spar ribs weren't where they were supposed to be; I had somehow managed to get the inner part upside down. All I had to do was de-cleco the fore and aft spars, turn the inner part over, and cleco it all back together:

Voila! If you put it together correctly, everything lines up! Again, I am very, very impressed with the thought and expertise that went into the design of this kit.

By the time I had the spar box clecoed together, I had spent the entire day in the shop. Being a Fall Saturday in Central Ohio, it was time to call it a day and watch some Ohio $tate football!