Kickin' it old school

I've never really understood what that meant. Kicking what, precisely? And what does 'old school' mean? Is it like "way back when," before the focus of our schools was almost completely centered on teaching to the government-mandated competency tests? Well, it's probably another of those phrases that make no sense if one takes them literally. You know, like "temporary tax" or "can we still be friends?" Life has a way of teaching you how to read between the lines when it comes to things like that.

Back in the early 70's when Van's Aircraft was comprised of one guy and one single-seat airplane (the RV-3), building a kit airplane was nothing like it is now. By "kit" the manufacturer typically meant a box of raw materials, a set of plans, and a few pages of notes about how to put it all together. The raw materials were somewhat more advanced than a few boxes of bauxite ore from which you would smelt and shape your own aluminum sheets, but not by much. Even so, the fact that parts like wing ribs and the like were pre-formed was orders of magnitude better than the previous standard: the "plans built" plane. Those truly were old school. You would have to form every single piece from raw stock. By way of contrast, it is relatively rare while building the RV-12 to even have to drill your own holes.

Every now and then, though, we come across a part that we get to "fabricate" on our own. A case in point:

This is one of the situations where we start from raw, off-the-shelf material.

The fact that there were 70 inches of material remaining gave me pause, but for I set the disturbing thought that there are going to be many, many more parts to fabricate aside and concentrated on the two-inch job at hand. It was very straightforward: measure, mark, and cut.

This part is a brace that will help support the weight of the gascolator.

A Gascolator, also known as a main line strainer, sediment bowl or fuel strainer acts primarily as a fuel drain for water and small particles of sediment and is usually found at the lowest point of an aircraft's fuel system. The gascolator is located below the level of the aircraft's carburetor and fuel tanks and on light aircraft is commonly located on the front of the firewall, as low as possible.

Once formed, it needs to be drilled to support a nutplate. This is done by match drilling through holes already drilled into the firewall by Van's. The brace needs to be held in place while drilling through it, and this is apparently a recipe for drilling into your own (or, preferably, a helper's) fingers. As such, the instructions suggest holding the brace in place with a small wooden block. This is exactly the kind of thing "old school" builders would have had to learn on their own. Once learned, though, I have to think that this is a lesson that would only need to be learned once! If not, I would respectfully suggest that such a slow-witted builder might not be the best candidate for building and flying an airplane. A nice set of Adirondack chairs might be a better idea. Padded, preferably.

Once the rivet holes for the nutplate are drilled, the brace can be held in place with clecos. Then it becomes easier to drill the two holes that will be used to rivet the brace to the side of the tunnel.

This raw stock is not alclad, so it has no inherent corrosion protection. It gets primered before final installation.

Do those two rivets look like they're centered on the flange? No. No they don't. That is why I'm not building an RV-3. I like the new school!

[Insert Clever Title Here]

Usually as I'm working on the plane, there's a background process running in my head trying to come up with a clever title for the ensuing post. Nothing really came to me this time. I'm still working on the lower half of the firewall, but I'm very nearly done with it. Unfortunately, I need another little dollop of firewall sealant. It's a shame that I had to throw away about 200 times the amount I am now in need of. This time I'll order one of the little one ounce bottles.

At the end of the last session, I had just riveted on the bottom skin. The next step was to rivet in the cooler stiffener, which was the part that gave me so much consternation as to whether holes that seemed like they ought to be countersunk but hadn't been called out in the plans as having countersinking required truly ought to be countersunk. As a reminder, I threw caution to the wind and countersunk them. The fun with this part was not quite over; it had three different rivet types required to get it installed.

Once that was done, a half dozen nutplates were clecoed onto the inside surface of the bottom skin. That was one of those reach-around jobs where it's a chore just to get the things in place.

On the plus side, the reach-around jobs nearly always end up using blind rivets.

With the latest batch of nutplates finally settled into their final resting place, we moved on to installing Cowl Attach Plates. These are nothing more than flat pieces of aluminum that host a collection of (see if you can guess.....) nutplates. There's a little twist here, though, in that the plates can't be flush with the edge of the skin. They have to be recessed just a little bit up into what will be the engine compartment so that the skin of the cowl will be flush with the skin of the fuselage. This spacing is accomplished with the highly technical expedient of... spacers. 

The spacers are simply thin rectangles of thin aluminum. They are to be cut from "AS3-020," whatever that is. It took awhile to find because I thought that it would be a smallish piece of metal shipped in one of the brown paper bags. There was such a piece of metal, as it turns out, but there was only one rather then the two required. I finally found the strip of material over on the parts shelf.

The fabrication is quite simple: measure out and cut a couple of 1 1/2" pieces and round the corners.

The drawing showing how it all fits together is easy to follow.

The little spacer plates get placed inside the flange of the firewall:

The part that will hold the nutplates only has one hole already drilled in it. You use one cleco through that hole and a clamp on the other side to hold the assembly in place. The parts are flat but the flange has a little curvature, so there's a gap:

I took it all apart again and bent a little curvature into the spacer and the Cowl Attach Plate, then clamped and clecoed it back into place.

Once clamped in place, two more holes are match drilled up through the flange and through the spacer and the Cowl Attach Plate. When it's all still attached would be a good time to go ahead and machine countersink the rivet holes for the nutplates. That will keep you from doing what I did, which is to countersink the wrong side of the attach plates. I thought I was doomed, but it turns out that even though the plates were match drilled in different locations from each other, they were still interchangeable side to side. The holes matched up every bit as well as every other hole I've match drilled, which is to say they were approximately aligned.

That done, the last step on the page called for the use of a Uni-Bit to enlarge the hole the gascolator fuel line (I think) will pass through the firewall to 9/16". I got a kick out of this: "To keep the hole centered draw a cross hair out from the hole for reference." Why did I think that was funny? Because I knew that there was absolutely no way a cross hair was going to keep that hole centered. All it was going to do was graphically display just how off center my hole was!

I started with regular bits and worked my way up in size. I was able to keep the hole pretty centered.

When I got to where I needed the Uni-Bit, I marked the step at which I wanted to stop. Uni-Bits have a way of just keeping on going well after the spot where you needed to stop.

I then proceeded to use the Uni-Bit to get the hole off-center.

I'll burn that bridge when I get to it.

The next step was band saw work and I usually enjoy that. It's kind of like going someplace warm on a winter vacation and enhancing the enjoyment of the temperate weather by comparing it to the awful conditions back home. I like to use the band saw because I remember what a pain the hacksaw was. 

In this case, it was the simple separation of four Support Channels. These will sit on the shelf that attaches the lower firewall to the upper firewall. They will support the rudder pedals, unless I miss my guess. The plans call fro the aft two holes of each to be dimpled, but fail to give any written direction as to which end is the aft. Placing them on the shelf shows the aft holes.

That's not the side that gets dimpled, though. You have to turn it over.

Some matching holes get dimpled in the firewall shelf and, as it turns out, so do some non-matching holes. I got lost with the dimpler and put dimples in four holes that didn't need them. It's not hard to un-dimple, but it was an indication that my head was no longer fully engaged in the process. Rather than press on and risk a much more permanent mistake, I just clecoed everything in where I think it belongs. I'll look at it again when I'm fresher to make sure that I have all of the nutplates in the right places. 

Besides which, I need some fuel sealant to run between the shelf and the lower firewall before I can rivet it together.