I started on the rudder of my Bede BD-4C, again. A week or so ago, I had built two of the ribs that go inside the rudder, the VS-9 rib for the bottom and the VS-10 rib for the middle. These two were made out of 0.025″ aluminum but I could not make the top rib because the plans call for 0.032″ aluminum and I did not have any aluminum that thick, yet.
Fortune smiled on me when it blocked me from making the third rib. I would have had to make it again, along with the other two ribs, and that would have required getting another piece of 0.032″ metal.
When the Bede BD-4C plans were originally drawn, in 1969, the rudder skin was to be made from a single sheet of aluminum. Since it is pretty difficult to find a shop which can cost effectively make the sharp bend in the trailing edge. BedeCorp now recommends that you build the rudder from two skin pieces with a doubler strip between the trailing edges of the two skins. Since the two skins are riveted together at the trailing edge, it pinches the skins and makes the space inside the rudder smaller than originally planned. This means that the ribs need to be both shorter and taper at sharper angles. Because of the change in geometry, you cannot just take an original, long rib and shorten it. Were you to do so, it would be too fat at the trailing edge.
Here is a photo of the parts that I have so far. Click any of the photos to jump to my photo gallery where you can view larger versions of the pictures.
Since the rudder skins are oddly shaped, it is hard to imagine how these fit together so the following pictures should help.
The bottom rib is short enough to let the trailing edges of the skins come together. The middle rib, farther away in the picture, was made from the original plans. You can see that it is too long.
To continue assembling the rudder, we lay the doubler strip, visible on the right side of the photo above, onto the trailing edge and then put the second skin on top.
Here is a picture with the trailing edges clamped together. You can see that the new VS-9 rib fits neatly into position.
How far off, you may be wondering, was the size of the original bottom rib? Quite a bit.
Since there are no drawings for the new ribs, I designed my VS-9 by measuring the rudder. I put the two skins and the spar together with clamps and then used a caliper to measure the thickness by the spar. I wanted the narrow edge of the rib to be 0.25″ so I used the caliper to find the point where the skins were 0.25″ apart and then I marked that point on the skin. Finally, I measured the distance, 10.1″, from the spar/fat end of the rib to the narrow end.
I sketched that, added some more metal around the edges for the flanges, and then drew it neatly onto a sheet of aluminum. I cut it out, bent it, and voila, it fit perfectly.
I have the measurements for the other two ribs so I will spend the next couple of evenings fabricating them.
