Saturday, April 24, 2010

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.

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