Tail Kit

My work schedule picked up a little in the last week, and I haven’t been able to make much progress. After a few sessions of bending and forming, I was able to cleco the bottom section of the rudder leading edge, and tonight I riveted all 3 leading edge sections. In the middle of the bottom section I had difficulty getting the holes to line up enough to get the fine tolerance pop rivets in. I made a tool to help support the skins from behind while I worked to align the holes and get the rivets in. This worked out quite well in the end, although the whole process took much longer than I had anticipated.

Clecoed and ready to rivet:

The tool:

Part way through:

The finished product:

With the rudder done, I had to get a picture with it next to Vertical Stabilizer. Once I have the aft fuselage done, I’ll be revisiting these parts and fitting them together.

After what seemed like a straightforward exercise, I quickly ran into some difficulty getting the leaded edges rolled correctly. After carefully reading the instructions and doing some research, I bought two lengths of 3/4 inch steel pipe from Home Depot. I traced the cross section templates onto some cardboard, and rolled the top section. Everything went well on the right side, so I flipped the rudder over and did the left top section. Alignment was good, and I could easily cleco the three holes.

I moved to the middle section, and rolled the right hand side. In hindsight I made the mistake of using the short length of tube, which meant I couldn’t get the torque I needed to make the bend as cleanly as I needed. I didn’t fully realize the issue, so instead of fixing it, I moved to the bottom section on the same side and rolled that section. This made it harder to fix the middle section problem, due to interference, which I didn’t realize until later. I flipped the rudder over and rolled the middle section on the left side, but didn’t match the bend radius or location, and ended up with a gap between the two sides.

Squeezing hard, I could make it work, but there’s too much tension, and I’m concerned that the thin skins will crease at the edge of the spar, which is not good.

I stopped there, and decided I needed to experiment some more before proceeding.

Here’s the one bend side on the bottom section, which is not quite the right shape.

Using some string and the template, I marked out locations for the start and stop of the bottom section bend, and transferred it to a scrap of 0.016 aluminum (same as skins). Then, experimenting with where I place the pipe, I made some bends.

The bend on the right is close to the shape I need on the bottom section. This was made with the pipe about 1 inch from the edge of the skin. The bend I made in the bottom section on the rudder was done with the pipe almost flush with the edge of the skin, which is the bend on the left. It’s easy to see the difference between the bends on this test piece, and there is definitely going to be an alignment problem. A secondary issue is that the bottom section bend radius is larger than at the top. For the bottom section, I probably need a larger diameter pipe, perhaps 1 or 1.25 inch instead of the 3/4 I’m using.

I need to fix the middle section first. The primary issue is that the distance between the spar and the start of the bend radius is too large, on both sides, with the left side being worse than the right side. Since the left side overlaps with the right, I’m planning to fix the right side, then the left. Using a string, I’ll mark on the skin the locations I need the bend radius to start and finish. Then using my test piece, I’ll carefully place and tape the long pipe into position and torque. The edge may end up slightly over-bent, but shouldn’t be a problem. Then I’ll switch to the left side, and repeat. It will be harder since the bent right hand side, and the bent bottom sections will be in the way. Hopefully I’ll be able to get enough of a bend to make it work. Once the middle section is aligned, I’ll worry about the bottom section.

After a few day’s break, I spent a couple of hours working on the rudder today. I started with a practice piece to get the feel of a new rivet set, and the double-back riveting process. Then I set up the rudder and riveted the trailing edge. The instructions call for partially setting the rivets initially, then going over again to finally set the rivets. All the while checking for any waiviness or distortion. After the initial setting, everything looked good, so I went back and finally set the rivets. I was happy with the results, very straight edge, and skins nicely mated. There is probably some amount of warp, but nothing worth worrying about.

Tonight I set up and practiced with my pneumatic pop rivet gun. I cut and drilled some scrap aluminum and then set half a dozen pop rivets. The gun is so easy to use, I can’t believe I bothered with the hand riveter. Instead of two to three squeezes, a single trigger pull sets the rivet and pops out the stem. Within 5 minutes I set the remaining 8 pop rivets in the top of the rudder, all of them set perfectly. With that done, the next step is back riveting the trailing edge, then rolling the leading edge, and the rudder will be done.

Just a couple of hours in the garage today, but I managed to complete several more steps in the plans. First I riveted the skins and spar on both sides. This was fairly straightforward, with my 3-inch squeezer yoke reaching 90% of the rivets. I bucked several towards the bottom, and the top three, where access was a little more challenging.

Then I set the middle rivet in the forward skin overlap, and was disappointed to see the skin lifting a little. Looks like the break I put in the left skin was insufficient to pull the edge down completely flush. Here’s a picture of the overlap once I had all the rivets in place. There’s not much I can do about this now, without some major disassembly, or drill, increase the break, then pop rivet the end back together. I don’t think that would be worthwhile, and in any case, I’m going to leave it as-is for now.

I then riveted on the top rib, except for the pop rivets. I’m going to figure out my pop riveting issue before putting any more rivets in. There are pop rivets in the aft 3 holes on each side, and two more attaching the top rib to the spar.

Today I riveted in the rudder horn brace. I was able to squeeze all the rivets. I did run into one issue, when I inadvertently squeezed the wrong length rivet. Rather than a 3-4, I used a 3-3.5. The rivet had set nicely, but I decided to take it out and use the correct length instead. I was able to drill and pop the top off easily, but getting the shank out was a challenge. Mostly it was an access issue, as I had to reach in through a little access hole, and couldn’t get anything to really grip the rivet. Eventually, after a lot of uncomfortable pressure, I was able to pop it out. The hole and dimples remained intact, so I set the correct rivet and carried on. In hindsight, I should have checked the dimensions, and I may have just left the 3.5 in there.

I finished riveting along the bottom rib, and noticed how tight the tolerance is where the skin goes around the protruding rudder horn. The skin isn’t touching, but the slightest lifting of the skin, and it rubs against the horn. It’s perfectly symmetrical, with the same gap on both sides of the rudder.

Next I clecoed and riveted the counterweight rib.

Then it was time to fit the counterweight. With the rivets in position, I had to trim a little off the sides of the front section of the counterweight. After a few iterations it fit snugly in place.

Then I countersunk the attach plate, riveted on the nutplates, and screwed the AN509 bolts into place. Everything fit nicely, and I was pleased with the result.

It’s getting late, so I’m going to stop there for today. Tomorrow I hope to get the top rib done, and time permitting, make a start on the trailing edge.