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.

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!