Sunday, May 20, 2012
Stabilizer Leading Edge
Waco originally used 1005 steel, then 1010 steel and by the time most of the drawings were last revised they were using 1025 steel. Today I'm using 4130 steel because that's what is readily available in a seamless tubing and it is stronger. The disadvantage of 4130 is that it is an air hardened steel which means it will cool fast enough in the air to harden it. Even a slight breeze will cool it fast enough to harden it more than desired. It's easy to get it hard enough to make it brittle. Low carbon steel, like 1025, doesn't have this problem but it is weaker than 4130 so you can design a lighter structure with 4130, which is why we use it today. I have no desire to re-engineer the plane so I'm just using the same sizes of steel originally used .
I made this piece of tubing 14'-6" long. That's longer than needed but I needed enough extra at each end to be able to easily form the bends. I think you could still do this with a piece 14'-0" long. I started with the center of the tube (mark on blue tape) at the center of the stabilizer. The blocks clamping the tube to the lines on the jig are the standoff blocks, turned upside down, I made for holding the tubes in place. The blocks were made so the centers of the spars and leading edge are on the same plane, far enough from the board so the bottom ribs can fit under the spars.
As an alternative I clamped some blocks to hold the tube from over bending as I moved along the tube.