The Rudder

Although the rudder “spar” layout is shown in the tail section of the plans, I found that the drawings of the rudder “post” in the fuselage portion of the plans just as valuable. (For definition, the rudder spar is the leading edge of the rudder. The post is what the rudder spar is hinged to on the fuselage.) There is a difference in the two drawings for the dimension of the base of the unit. The base of the spar is shown as 2” while the base of the post is 2 1/8”. I decided to make my spar match the dimension shown for the post, 2 1/8”. I cut two pieces of ply to rough dimensions and nailed them together with ½” nails along the edges. These pieces are the front and back of the rudder spar. I drew the rudder layout on the top piece and then sanded to the lines so that both pieces would be alike. Next, I glued on the flange stock. I put a small nail through the ply on the inside of the bend point of the flange material to help hold it in place until the glue was dry. I fabricated and placed the hinge support blocks into the spar. Not knowing exactly how far down to move the top hinge (see note in the plans) I decided to fill the top 16” of the spar with spruce. This area is so narrow that there is virtually no weight penalty for filling this much area and it will make sure I have support material for the top hinge, wherever it may end up.

After gluing on the top of the spar I drilled the ¼” vent holes in what will become the aft side of the spar. I centered the holes in the “open” bays of the spar, not remembering that the ribs will be attached at different points along the spar. Well, as luck would have it, one of the vent holes is pretty close to where one of the ribs will be. This is a relatively easy fix. I’ll plug the hole with ¼” dowel and sand it flush with the aft face of the spar. Then I’ll drill another hole for the vent in that bay.

I laid out the grid for the rudder bow directly on my flattest workbench. After covering the table with waxed paper I placed nails along the inside radius of the bow. Then, with the help of a few friends, we were able to mix and spread T88 fast enough to glue up half of the required laminates for the bow in one session. We glued up the other half the next day. Using a combination of nails and clamps to hold the laminates in position worked well.

I notched the top of the rudder spar to accept ¼” plywood gussets that attach to the bow. Making sure the bow is straight and square to the spar took a little effort. I marked the center of the spar from one end to the other. I drew lines on each side of the centerline that represent the 5/8” width of the bow. I also marked the center of the bow width with a mark inside each end of the bow. With the spar laying on the bench, I used a framing square standing vertical on the bow edge line to keep the bow straight over the spar and matched the mark I put on the inside of the bow to the centerline of the spar to keep the bow centered on the spar. I was able to keep the bow in this position by clamping the top gussets in place as I glued it all together. There may be an easier way to accomplish this task but this is what I did.

I used balsa wood to serve as filler on the bottom of the bow. The balsa is very easy to shape and will get very hard once it is sealed. I then used the measurements of figures 3-1 and 3-4 to mark the locations on the spar for the rib locations. Positioning the framing square against the marks on the spar for the ribs, I marked the bow for the notches to receive the rib ends.

Next comes fabricating and gluing in the ribs. I drilled ¼” vent holes in the body of the ribs with 1/8” holes at the aft ends for moisture drainage.

As I mentioned earlier, I used ¼” ply for the top gusset between the spar and the bow. I notched the spar for this ply but not the bow. After looking at this, I realized that the step down would be rather drastic over the short width of my gusset so I decided to add a filler along the sides of the bow to allow a smoother transition.

I decided to have the trailing edge of the bow be a bull nose shape. A ¾” hole bored thru a piece of 2x4 and cut in half makes a good sanding block for this task.

Here is a shot of the rudder awaiting final shaping of top and bottom, hardware and covering.

Here are some pictures of the process of mounting the rudder to the tail post. The only real trick here is to make sure that you position the upper hinge so that it doesn’t interfere with the diagonal spar of the vertical stab when it is installed. Still have to add the rudder horn and the tail wheel steering horn.

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