The what??

I had a little time to head back down to the shop after mowing the lawn (it didn't rain, but there were some light sprinkles) to build the "flaperon mixer arm."

"The what?" you say?

Beats me. I went all the way to the end of the plans that I have and while this thing does get installed, nothing gets attached to it.

Let's think about it, though. First, you may be wondering what a flaperon even is. Well, the word itself is a conglomeration of the words "flap" and "aileron." Most of my readers will know what a flap and an aileron are, but if nothing else, I'm inclusive. I'm reclusive too, but that's not the same thing at all. Anyway, here's a quick paragraph or two from Explaino the Wonder Donkey:

Ailerons are hinged control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll. The two ailerons are typically interconnected so that one goes down when the other goes up: the downgoing aileron increases the lift on its wing while the upgoing aileron reduces the lift on its wing, producing a rolling moment about the aircraft's longitudinal axis. The word aileron is French for "little wing".

I didn't know that last part. And now that I do, I realize that I didn't know because I don't care. On to the flap:

Flaps are hinged surfaces on the trailing edge of the wings of a fixed-wing aircraft. As flaps are extended, the stalling speed of the aircraft is reduced, which means that the aircraft can fly safely at slower speeds (especially during take off and landing). Flaps are also used on the leading edge of the wings of some high-speed jet aircraft, where they may be called Krueger flaps.

Extending flaps increases the camber of the wing airfoil, thus raising the maximum lift coefficient. This increase in maximum lift coefficient allows the aircraft to generate a given amount of lift with a slower speed. Therefore, extending the flaps reduces the stalling speed of the aircraft.

Extending flaps also increases drag. This can be beneficial in the approach and landing phase because it helps to slow the aircraft. Another useful side-effect of flap deployment is a decrease in aircraft pitch angle. This provides the pilot with a greater view over the nose of the aircraft and allows a better view of the runway during approach and landing.

Wow, all those words and Explaino missed one of the most pertinent things: where ailerons move in opposite directions, flaps move concurrently in the same direction. If one flap goes down, so does the other. The same goes for up.

As long as the donkey is on a roll, here's his take on the flaperon:

A flaperon is a type of control surface that combines aspects of both flaps and ailerons. In addition to controlling the roll or bank of an aircraft like conventional ailerons, both flaperons can be lowered together to function much the same as a dedicated set of flaps would. Both ailerons could also be raised, which would give spoilerons.

The pilot has separate controls for ailerons and flaps. A mixer is used to combine the separate pilot input into this single set of control surfaces called flaperons. The use of flaperons instead of separate ailerons and flaps can reduce the weight of an aircraft. The complexity is transferred from having a double set of control surfaces (flaps and ailerons) to the mixer.

I added the emphasis - he's just a donkey, he doesn't know HTML for crying out loud.

My guess, then, is that I just assembled the mixer. I have no idea how it works - all it does is provide a pair of arms that swivel back and forth a few degrees.

But why does the RV-12 have flaperons in the first place? None of the other Van's airplanes do.

I've found that when I come across a "why did they do it this way" question with regards to the design of this airplane, it pays to start looking for an answer in a "follow the money" kind of way, but by replacing "money" with "removable wings."

For example, one would ask if the design element in question benefits the removable wing feature.

In this case, the answer is yes.



One of the most frightening things about removable wings is the fear that you will forget to re-attach the control surfaces when the wings are put back on. To counteract this (and most assuredly to reduce liability), most manufacturers of removable wing aircraft will make the connection of the control surfaces automatic. This is the case with the RV-12. The flaperon has a tab that fits into a slot on the side of the fuselage when the wing is installed. The control stick moves the slot, the slot moves the tab, and the flaperons do what flaperons do. With this type of control linkage, it would be very difficult to provide a separate slot/tab for the flaps and ailerons. With flaperons, only one slot/tab is needed.

That's one slot/tab per side, for you lovers of symmetry and/or pedantry.

With all of that complexity, then, this mixer seems woefully simple.



It's actually pretty easy to put together, too. It starts out just being a simple box.



I thought that this would be a nice break from installing nutplates, but it wasn't to be. There are two that get installed. Then there is a lengthy easter egg hunt for a collection of bolts, washers, nuts, and bushings. The search for the bushings would have been easier if the measurements hadn't been truncated on the inventory sheet.



I'm just being churlish. There are only three aluminum bushings in the entire kit, all three are in the same bag, and the measurements are plainly written on the drawings. It was easy to find the correct pair. I laid everything out prior to assembly, mostly because there are six washers that are the same diameter, but two are thinner than the other four and I didn't want to get those mixed up with each other.



I probably won't know how this thing actually works until next year when I'm doing the finishing kit. I have a couple of pictures of the slot and tab, though, from a nearly finished plane.



Below the flaperon control tab, you can also see the tab that goes into the receptacle I was working on a few days ago.

The threat of rain

Saturday morning and the immense lawn of my palatial estate requires mowing. Again. Seriously, in my opinion grass is nothing more than the weed that had the best PR department when suitable lawn coverings were being decided. But, the threat of rain! Granted, it was about the same level of threat as a Chihuahua giving you an irritated glance, but I latched onto it like Wile E. Coyote when a new Acme Products catalog shows up in his mailbox. No mowing today, might as well head down the shop!

Having deferred the installation of the last two baggage floor supporting riblets the last time around, I knocked those out pretty quickly. With those in place along with all of the other ribs that will support the baggage floors, it's not surprising that the next step is to rivet the baggage floors onto those ribs. A few different rivets get used; the first are regular LP4-3 blind rivets which go into all of the undimpled #30 holes in the baggage floors. I clecoed about half of the holes and pre-placed rivets in the rest.



The next set of rivets are flush blind rivets - those go into all of the dimpled #30 holes. I chose to do the ones that are in the same row as the non-dimpled holes first.



That just left the holes that run along the tunnel section. I used the silver clecos in the #40 holes since there are only three of the #30 holes and the baggage floor skin was curling away from the baggage rib flanges. I needed a bit more than the one or two #30 clecos I would have been able to use.



I think the most defining factor of the work I've been doing lately is installing nutplates. It seems that every other step involves dimpling and installing nutplates. And the K1000-08 nutplate in particular has achieved a level of ubiquity rivaled only by GEICO commercials. That's why it came as somewhat of a surprise to notice (and I'm glad I noticed! This would have been very easy to miss) that this particular batch of nutplates was comprised of two variants.



The blue indicates K1100-08 while the red shows K1000-08. The numbers are so visually similar that it would be easy to miss the distinction. Conversely, the rivets themselves are quite distinct.



The K1000-08 is on the left. The K1100-08 on the right will be used in the holes under the right side baggage floor. As I've surmised before, those holes will eventually be home to screws that will sit flush to the floor to make room for the fuel tank.

With the rivets selected and positioned near their ultimate resting places, all that was left to figure out was how exactly some of the nutplates were to be put in position, considering that access to the holes was blocked on all sides by the bulkhead and floors. See the back row of nutplate holes and how there's no access to the bottom of the baggage floors? Yeah. Bummer, that.



The trick is to flip the whole assembly up onto its side and install them from the bottom.



Note how I managed to focus the camera on my emerging bald spot instead of on the nutplate I was clecoing into place. Nice. I'd have been better off mowing.

With one cleco in each of the rivet holes, it easy to rivet them into place. Note that these are the CSR flush blind rivets, not the normal LP4-3 blind rivets.



The remaining four nutplates were accessible from the sides of the floors, so they were installed with the normal AN4263-3.5 flush rivets and the rivet squeezer. Once those were done, I wiped the whole deal down with MEK to remove the Sharpie writing and my grubby paw prints.





So, do you remember those bearing brackets that I put together last time? The ones with the gap between the plates that I was worried about? The ones that I was wondering why I was putting together at that stage in the first place? Well, here we go. The next step is to install a plate between two of the floor riblets to provide support for them.



This was another of those cases where it was going to be easier to get at the riveting by flipping the whole thing over and coming at it from the bottom.



Having grown accustomed to working inside these parts to rivet through the flanges, I just automatically bend the rivets and grab the little close-quarters wedge thingy right away. Doing it that way helps get sufficient clearance to get the rivet puller down in there. This is probably the best picture I've been able to get that shows what a difference the wedge thingy makes.



The bearing assemblies go in with the heads of the flush rivets up against the skin. That shouldn't surprise anyone - can you imagine how poorly it would fit the other way around? Here's some good news: look at how the cleco in the back pulls the plates of the bearing assembly together! I was worried that the gap between them was going to be a problem. It looks like it won't! Unfortunately, having that cleco there made the rivet inaccessible enough that I had to use the wedge thingy again, and it is the wedge thingy that I blame for this:



Can you see the part of the mandrel sticking out? It seems to have broken in a different spot, probably because of the way it got pulled when I used the wedge. I doubt that it would have made any difference to just leave it that way, but I thought it would be easy enough to file away that I might as well take a couple of minutes to do it.



Ok, everyone that thinks filing that mandrel off with a tiny little file was likely to be really, really boring and take way too much effort, raise their hand.

[My hand is raised.]

I quickly tired of it and found a faster way.



I swear, if the Roman Empire had had Dremel tools and duct tape, it would never have fallen. There's nothing they can't do!

It cleaned up right purty, iffn' I does say so myself.



There was only one more little thing to do on the page, so even though I was ready for a break (I have this little known malady called "coffee hands," the primary symptom of which is a rapid decrease in manual dexterity as my morning caffeine jolt reaches its second half-life) I decided to get it done. It's basically "go find three parts on the shelf, band saw one of them into two parts, and rivet it all together."

Voila! We'll figure out what it's intended to do next time.



Here's where we are so far:

Back on track

I was able to go visit the almost-done RV-12 to check the fit of the semi-circular wing spar tab receptacles today. Normally it would be somewhat of a burden to ask a guy to remove the wings from a plane that is nearly complete and ready for its airworthiness inspection but in this case one of them had to come off anyway. It's kind of a sad story, really. He and a friend had moved the plane to his hangar and were reassembling it when a gust of wind grabbed the right wing off of the trailer and threw it against some immovable objects. The net result is that he will have to strip off and replace the skins of the damaged wing, along with at least one of the inner ribs.

The only thing I could think to say was "at least it wasn't painted yet."

I'm not particularly adept in situations of personal loss.

Thankfully I did have sufficient tact to refrain from pointing out the benefits to me from his misfortune. So there is that.

It was interesting to be involved in removing a wing, and I have to say that it is every bit as easy as advertised. Remove the pins, pull the wing out, and ensure there is someone on the root end to catch it as it comes out of the plane. Not necessarily in that order. In fact, the third step works better as the second step. Just, you know, for future reference.

With the wing off, I test fitted the semi-circular wing spar tab receptacle to the aft wing spar tab. It fit like a glove. Now, I could have stopped there and simply assumed that the left would fit as well, but... I'm losing enough sleep over this thing already and don't need to add new chapters to the horror novel that is on my current stuff-to-worry-about-at-three-AM shelf. And really, the wing would only need to come out a few inches - what's the big deal?

Well, it's not a herculean effort by any stretch and I'm sure it gets easier with practice, but it is inarguably harder to put the wing back in than it is to take it out. Lesson learned. Naturally after all that effort, the left receptacle fit just as well as the right. Neither will need any filing or trimming at all.

Oh, and I got to sit inside a nearly-finished RV-12 too. I liked it! It's wider and seemed to have a more comfortable seating position than the RV-6. The visibility is great and the control stick falls readily to hand. I will have to adjust to the new throttle location, but that's a nit.

Now that I'm sure the receptacles are ready to be installed I can finish up the aft bulkhead on the center section. That's a simple matter of riveting the receptacles into place with a few handfuls of LP4-5 blind rivets. Interestingly, this is the first time the manual has asked that all of the rivets be put in place before driving any of them; the work of holding the parts together and in alignment is normally left to the venerable clecos.



Bada, bing, and boom. All done.



In what appears to be a pretty random ordering of steps, I then was tasked with assembling a pair of aileron hinge brackets. The four parts used to make two brackets are completely identical, a situation that I have learned requires caution. In this case, it would be very easy to countersink all four of the bracket sides, but only two of the parts need it. The other two sides will have the non-flush shop head on them. The plans clearly state this, of course, but I still caught myself thinking that I'd be countersinking both sides of the brackets. Taking a breath to think things through saved me from that. As a reminder, I marked the holes that I would countersink.



Once the parts were clecoed together, I saw a potential problem: there was a notable gap at the ends of the brackets where the bearings were inserted. I put a clamp on one of them and it closed the gap down, so the problem wasn't a mis-fit of the bearings. I figured I'd just leave the clamp on while I did the riveting to keep the parts tight.





Which worked, more or less. Now there's a gap at the other end. I suspect that I've only managed to kick that can down the road. There's nothing I can do about it now. I'll just have to burn that bridge when I get to it.



With that diversion out of the way, it was back to getting the aft bulkhead attached. This was another step that had a potential pitfall in it that I successfully circumnavigated. At first glance, it would appear that all six of the ribs get riveted directly to the aft bulkhead, but a closer reading shows that the first step only involves the two outer most ribs on both sides. The innermost ribs get riveted on the next step after having a couple more little ribs put in place. I went ahead and clecoed those little riblets into place so I so I wouldn't forget and rivet the inner ribs prematurely.





It turned out to be a better position for the riveting over on the saw horses rather than on the work bench. I'm going to miss being able to move this thing around easily when it gets bigger.



As long as I was riveting, I went ahead and riveted the riblets too. Those rivets were down in the flanges and pretty hard to get at, but the articulated rivet puller made it possible. This seemed like a great time to quit for the night. Have you noticed the way that I'm humped over in every picture of myself that I put up on this blog? It's not because I'm bending over the work; I think my back is taking a permanent set from all of this riveting and stuff.



It doesn't look like much, does it? Just to give you an idea of where this will eventually end up: