My UH12R : Control Surfaces

Building the control surfaces

The plans required me to make 3 rudder pivots made from 3/4" x 1" x 40" strips of pine and 1 trim wing pivot made from 3/4" x 1" x 46" strip of pine. The problem is that 3" on each end had to be rounded to 5/8". I don't have a lathe, so I had to do it the hard way. First, I marked where the 5/8" peg was to be located and marked the edges of the peg.
Next I cut down the previously marked lines which made a square 5/8" x 5/8" square peg.
Finally, I held a peice of 50 grit at each end like a shoe-shine rag and sanded the corners off making the final rounded shape until my calipers told me that I was around 5/8". Not precision, but it'll do.
Each of the 3 rudders were constructed from 2 pieces of 1" thick styrofoam cut to 34" x 3" and 34" x 12" joined together by the rudder pivot discussed above. The trim wing was constructed in the exact same manner except the foam pieces were 40" long. The template sitting on the rudder was to be used as a template to cut the rudder shape with a hot-wire and is a cross-section of how the rudder will be shaped.
Since the above template was made of light cardboard, it was too flimsy to cut the pointed end of the rudder and so it was replaced by 1/8" plywood templates which gave a much better result. This is an end view of how the rudder looks after being cut. The curved lines you see indicate that the hot wire was too loose and drags behind in the middle during the cut. This was remedied for the other 2 rudders and the trim wing. The lines sanded off and didn't result in problems.
This is a view of the rudders and the trim wing after being cut and coated with the first coat of glass cloth and epoxy resin. The trim wing is the longer one on the left.
After glassing the rudders, I made a mark 3" from the top on the trailing edge and made a cut from the top of the pivot to the mark. This resulted in an angle that would allow the trim wing to clear the rudders. Finally, I rounded the top of each rudder to allow moisture to run off and glassed 'em.
The three rudders and the trim wing are fully glassed and ready for the control horns to be installed. Then they'll be painted and mounted.
After constructing the trim wings and rudders, I soon discovered that I had placed the trim wing pivot point too close to the rear of the duct. I hadn't even considered this when I was building the trim wing mounts as I was just happily building the craft to the plans which offered no dimensions for the location of the pivot point in relation to the duct. I measured the plans to get the position (and converted from 1/12th scale) rather than actually think about it. The result of my folly was that I had to hack off the existing mount and reattach an extension using a 3" overlap dovetail joint and epoxy.
I filled the imperfections and drilled the hole and after it's painted, you shouldn't be able to see my mistake.
The next job was to make the aluminium lower rudder mounts shown here two phases of construction. The lower unit has been marked and drilled and not yet angled and the the other two have been angled. I cut the shapes out using a hand-held jigsaw with a metal cutting blade.
The tough part involved drilling a 3/4" hole in the business end of the mount. This was tough since I didn't have a 3/4" bit that could chew through aluminum. I solved the problem with my jig-saw and a narrow blade. Only took a few minutes to make each hole. Next, I had to press a 3/4" diameter by 3/4" long piece of EMT into the hole and epoxy it in place. The extension you see attached to the bottom of the mount is due to another miscalculation on my part as well as an ambiguity on the part of the plans. It ensures the mount is far enough out to allow the rudders to clear the back of the thrust duct.
Here's one of the lower rudder mounts mounted to the back of the craft.
The next job was to make and attach the upper rudder pivot/mounts to the trim wing which also acts as the upper rudder support.
This is how the trim wing and a rudder look when mounted.
This is a close-up of the upper rudder mount in action if you're curious.