Wednesday, November 17, 2010

"You wanna box for that?"

This will come as a shock, but I have an admittedly well-earned reputation as being a bit (just a bit??) of a wise ass. "Tis true! And as sure as "two bits" follows "shave and a haircut," I simply cannot resist answering "No, but I'll wrestle you for it" when a cute waitress asks me if I want a box for my leftovers. She has to say it just right, of course, or it doesn't work. It has to be kind of informal and run together like in the title of the post. "Do you want a box for that?" won't work.

What brings this up, you ask? What, suddenly I need a reason? Well, here's the deal. As much as I love my RV-6, it's kind of like an early model car. Think back a few decades. Remember when we didn't have electric windows, cruise controls, two dozen cup holders, 6-way adjustable power seats, seat heaters, adjustable rate intermittent windshield wipers, and power moon roofs? The RV-6 is kind of like that. Unrefined, if you will.

The RV-12, on the other hand, is a fresh, new design that in many, many ways has benefited from an aggregation of refinements that have shown up "in the field." With over 7,000 built and flying, there had been a lot of opportunity for better mousetraps to have been developed. Here's an example: there are two long hinge pins that hold the top cowl in place where the back edge of the cowl meets the front edge of the fuselage. The RV-12 has that too. In fact, I just installed the hinge strip last week. The hinge pins are pushed into the hinge strips at a gap in the middle of the hinge area. The ends of the hinge pins need to be secured once they're in place to keep them from working their way back out from the vibration of the engine. On my RV-6, that is accomplished, with great difficulty, by using safety wire. One the RV-12, there is a better way. A little panel will be installed at the top of the cowl/fuselage joint that will have a little latching mechanism to hold the hinge pins in place.

I built that panel last night.

It starts out with just a couple of small, innocuous looking flat bits of metal. That, and a fairly rudimentary drawing in the plans. I spent some time looking at that drawing and developing a plan, finally realizing that all I needed to do was put a 90 degree bend in the little sliver of metal, followed by two 45 degree bends at marks roughly 1/4" each side of the center.

Trusting neither my math nor my skill, I tried it first with a piece of scrap metal.

The second one was for real.

Two rivets, two dimples, and done.

Next I needed to bend a curve into the front edge of the panel that will cover the area between the firewall and control panel. This too is a huge improvement over the RV-6. While my plane has a tip-up canopy that allows a little more behind-the-panel access than the slider style canopy, it is still the case that it is an enormous pain in the back (quite literally, as most work has to be done while laying on the cockpit floor and reaching up behind the panel) to do anything in that area. The RV-12 has a screw-on panel covering that area. For that panel to sit flush on the top flange of the firewall, the front corner has to be bent down a little built. How much is a little bit? Dunno. Trial and error is the only way to figure that out. I made a bend and fitted the panel temporarily to the fuselage. There are two interesting things in the next two pictures: one that you can see, and one that you can't. You can see where the hinge pin clip panel will fit, and you can't see a gap between the covering panel and the top of the firewall. Success!

You can also see that the panel shelf is not yet riveted down. It's supposed to be, but I've been deferring it. I was actually supposed to do it before building and installing the battery box. The reason that I haven't done so is that I have heard that having the shelf riveted in too early makes the installation of the map box very difficult.

Oh, have I mentioned the map box? Remember that old car I was talking about before? Imagine that it didn't have a glove compartment either. That's the state of my RV-6. It's so tight and cramped that the only place I have for maps is the tight area between the seat cushion and the sides of the airplane. The RV-12 has the benefit of a large expanse of unused control panel space resulting from the use of space-efficient computerized flight instruments. That space is used to provide a map box.

While a wonderful convenience, the map box is a bitchy little thing to build. It needs to have two holes match-drilled into from underneath the panel shelf, and they are located in an absolutely horrible place to have to find without being able to see. There is also a lot of trial & error that goes into getting the map box door to fit just right, and that too would be a lot harder to do with the panel shelf installed in the fuselage. It seemed easier to just wait until after the map box was built and installed before riveting the shelf into the fuselage.

And it would have worked, too, if it hadn't been for those meddling battery box rivets. Remember the ones I riveted in from the inside of the fuselage out through the firewall? Well, about ten of those were supposed to also rivet in the front flange of the panel shelf. Those had to be drilled back out. Luckily, drilling out LP4-3 rivets is as easy as can be. Once that was done, I was able to get everything test fitted. This is the panel that will support the map box.

The box comes in two halves. One of them needs to be clecoed in for the drilling.

The holes that would have been match-drilled are way down there under the panel, where the rudder pedals would be if they weren't still sitting down in my basement.

Assured that everything would fit, I removed the shelf and returned it to the workbench.

Access to the holes was so much easier this way! You can see how hard it would have been to do this if the shelf was nailed to the fuselage!

The door uses the same type of hinge used for the cowl attachments and seat backs. This is, though, one of the few cases where it is actually used to hinge something. Getting it fitted was a little tricky. I decided to do the piece that sits inside the map box first. I started by drawing a line 1/4" from the bottom of the hinge.

That got clamped into the map box, positioned so the line would split the center of the row of pre-drilled holes.

A similar line was drawn on the door. Hole locations were measure and marked. The measurements provided were in increments of 1/32" which is always amusing to be, given that I'm lucky to get within an inch of a measured spot when it comes to drilling.

Having learned a valuable lesson last week, I ensured that my drilling of these holes would be more accurate by starting with a #40 pilot hole and following with a #30 final hole. With the holes drilled, I could clamp on the second piece of hinge and match drill it.

I was then able to cleco the hinge and door to the map box. That's when I found that the door wouldn't open. It was too long and the bottom edge was hitting the panel.

It had to come off and be adjusted. The adjustment was to shave 1/32" of an inch off of the bottom using the band saw. It's amazing how much more precisely I can cut with the band saw now that the blade twisting problem is solved. Still, it wasn't quite right.

Another pass through the saw did the trick!

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