Now for the most fun/scary part of the whole rudder construction - the trailing edge!
Leading up to this point was stressful. The trailing edge needs to be back riveted to ensure a flush head on each side. You can't backrivet with clecos in, so you can use either tape or tank sealant to keep the trailing edge locked in place between the rudder skins. The tape method is what's recommended by the latest Van's documents since it's a lot cleaner (no mess) and faster (no waiting days for it to cure). The tank sealant method was the method originally recommended, and a lot of builders still prefer it over the tape. I debated back and forth over which method I wanted to use, and I eventually decided to order both the special 3M double-sided tape and some tank sealant and decide later on.
Regardless of which method is used to keep the trailing edge together, it's recommended to use an aluminum angle to ensure the edge stays straight while your adhesive of choice cures. I took care to find the straightest piece of aluminum angle I could find at Lowe's, and I match-drilled holes into the angle along the length of the rudder so it could be clecoed in place after gluing the edge. I did this after I had already dimpled the rudder skins causing a couple of holes to be slightly enlarged, so I recommend match-drilling the angle before dimpling the skins.
When the day came to do the deed, I decided to try the tape method first. I wiped down the wedge and the trailing edges of the skins with acetone to clean the mating surfaces. With the rudder in place on the bench, I took out the tape and began peeling off the protective paper. Immediately the tape itself began pulling apart in shreds. No matter how carefully I peeled, I couldn't get a clean, smooth strip of tape. I couldn't be confident that this tape would work well, so I decided to use the tank sealant instead.
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| Yeah, this stuff does stink. Time to break out the odor mask! |
Tank sealant definitely isn't the nightmare goop a lot of people make it out to be. It actually turned out to be mostly painless, but smelly. The best way I can describe it is "garbage being burned in hot, fresh asphalt." I ordered the sealant in the caulk-type container on purpose to make mixing and applying easier and cleaner than with your standard tubs.
With the sealant mixed, the container fits nicely into a standard caulk gun. This makes application so much simpler than just using popsicle sticks.
I went to work applying the sealant to one side of the wedge. I worked in sections, shooting a line of sealant down about a third of the wedge at a time then using a wide popsicle stick to spread it evenly over the width of the wedge. This stuff is super thick and takes considerable effort to spread, so patience is needed here. The viscosity also means that any excess won't easily squeeze out when both skins are pressed together, so I had to be careful to make sure the coating was thin and even along the entire length to avoid any major bulges or waviness along the trailing edge.
With one side coated, I flipped the wedge upside down and carefully set it in its place on the bottom skin. I applied sealant to the other side and lowered the top skin in place, then clecoed the aluminum angle in place on the bottom of the assembly to hold everything straight.
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| I temporarily put some weight on the trailing edge to help hold it tight, but the clecos provide enough clamping force on their own that this isn't really necessary. |
The next step is patience, since the tank sealant needs time to cure. I ended up leaving it for about a week before coming back to it since it was starting to get cooler in the garage and the sealant sures much more slowly in cold temperatures. When I came back, I unclamped the angle and immediately checked how straight the edge turned out.
It has just a slight bow along the entire length, but it's well within the .1 inch limit the manual recommends. Which means, it's time to rivet!
Backriveting the trailing edge was one of the most stressful experiences of the empennage thus far. I wanted to avoid having to redo the dozens of hours of work I had sunk into this particular control surface, so I made sure to take my time and follow the instructions to the letter. I set the rivet gun pressure lower than normal so setting the rivets into their recess would be slower and more controlled, then I started at the middle of the trailing edge and set every tenth rivet to lock things into place. From there I partially set the rivets halfway between the last ones, then repeated this process until every hole was filled with a partially-set rivet. I then went back over each rivet in the same order and set the rivets almost fully. Throughout the process I kept check to make sure the small amount of bow wasn't getting any worse.
Since I couldn't get the rivets fully flush using the rivet gun alone, I flipped the rudder over and used the mushroom set to buck the rivets against the backrivet plate. This set each rivet flush into its recess and left me with a finished trailing edge.
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| The trailing edge isn't bowed quite as much as it looks here - the counterweight on the horn tends to lift the trailing edge when the rudder is laid flat on the workbench. |
With the trailing edge out of the way the penultimate task prior to rudder completion was to roll and rivet the leading edge, which proved to be a bit frustrating as things progressed. I used the pipe and tape method to start the bends. The smallest section at the top seemed like it would be the easiest section to bend, but getting it into its desired shape required a lot more force than I had anticipated.
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| In hindsight I probably should have used duct tape instead of masking tape, but I didn't have any issues with it here. |
