Yesterday I reoriented the HS and attached the elevators so it’s sitting vertically on the bench. This makes it easier to drill these important bottom holes on the elevator horns. I marked and center punched the location for the first hole, then drilled it. The right hand elevator horn is slightly aft of the left, as expected, per the plans.
HS sitting in cradle with elevators attached
Tonight I clamped up the trailing edges, and then spent time shaping up a drill block.
Shaping the drill block with my vixen file
Once I had a perfect fit on the drill block, I clamped the elevator horns and drilled the hole in the left elevator horn. These came out quite well I think.
I found that my trim tab is indeed twisted, which was causing most of the misalignment. I discovered this after removing the tab and setting it on a flat surface.
Sitting on a flat surface, the trim tab shows it’s twist
With the trim tab set aside for now, I clamped up the trailing edges of the elevators, and found I still had a difference of 3/16ths between the counterweight arm and the HS, when holding one elevator counterweight arm flush with the HS. from the research I’ve done, I’m going to leave this as-is, and move on. Provided the trailing edges are flush, it shouldn’t be a problem.
Today was frustrating. My next step is to drill the elevator horns to allow them to be bolted together and attached to the elevator push-rod. The critical part of this step is making sure both elevators are aligned with one another. The plans suggest taping the elevator counterweight arms to the HS, and then going about drilling the holes. Sometimes the counterweight arms are not completely square with the trailing edge, and doing it this way can result in the elevators being out of alignment on the trailing edge. The common practice among builders is to clamp the trailing edges together and use that as the guide instead. I had picked up two 8 foot lengths of aluminum channel to serve that purpose, and with the arms taped to the HS, I laid one across the trailing edges. Unfortunately, there was a significant difference between the trailing edges, almost an inch!
After some investigation, I believe there are two problems. 1. While the trim tab’s trailing edge is very straight, I think the trim tab is twisted. 2. One of the elevators has a slight twist causing the counterweight arm to be out of alignment.
My next step is to remove the trim tab and check it for twist. With it removed, I will also check the elevators to see if I can identify the ant twist. My hope is that with the trim tab removed, the problem will be mostly resolved.
With the left arm taped to the HS, and the trailing edges clamped, the right hand arm is approximately 1/4 inch out of alignment.
Today I drilled the 1/4 inch holes connecting the elevator horns to the bearing on the horizontal stabilizer. This worked out well, and I’m happy with the result. The next holes I need to drill on the horn are perhaps more critical, as they set the alignment between the two elevators.
Clamped up and ready to drill
First I needed to resize the bushing supplied by vans. I put it in the drill press and sanded it down until it fit snugly in the bearing. I also drilled out the center to #30, as the inside diameter wasn’t quite large enough.
Reshaping the bushing by sanding in the drill press
With the bushing in place I drilled the left elevator hole
Drilling the left elevator horn bolt hole
Then I removed the elevator and step drilled it up to 1/4 inch, and deburred the holes.
Using the step drill to enlarge the hole to 1/4 inch
Then it was onto the right elevator, again this went quickly and easily.
Finally, I selected the appropriate number of washers and bolt length (-13), to secure the elevators.
Final product; bolt and washers with a temporary nut.
This afternoon and this evening I spend several hours removing and tweaking the left elevator. The goal is to have free travel from 25 degrees down to 30 degrees up. Starting with the measurements in the plans I had 22 degrees down before the elevator horn contacted the bottom flange of the aft HS spar. It traveled up to around 35 degrees, but there was some slight running of elevator skin against the HS spar. After some careful measurements I calculated I needed to move the elevator about 2mm aft. I also found that the gap between HS and elevator counterweight arm wasn’t quite uniform. After several iterations of removing, adjusting the rod need bearings and reattaching, I was happy with the travel.
Not enough down travelElevator horn contacts the lower spar flange before the elevator can reach 25 degrees down Elevator down deflection reaches 25 degrees after adjusting the rod end bearings
After backing off the rod end bearings approximately 1.5mm, the elevator can deflect down 25 degrees without contacting the spar flange.
The three lower bolt holes are finally drilled to 1/4 inch. This looks like a mess right now, but it’s just dust and some primer touch-up.
Tonight I drilled the last two holes with my new drill bits. The difference was amazing, the new drill bit cut straight through the steel leaving a nice clean and round hole.
Removing the VS after drilling the lower bolt holes.
With the holes drilled I removed the VS, and deburred all the surfaces.
While waiting for new drill bits, I skipped ahead and installed the rod end bearings on both elevators and the rudder. First I made a tool out of PVC pipe, as these are fairly stiff and need some kind of tool. The PVC does a good job avoiding scratching the bearing, while still providing enough torque.
The sleeve fits inside the end of the connector facing the camera. The slot in this little sleeve grips the bearing.Starting the install and checking it’s not cross-threaded before switching to the toolUsing the PVC tool to screw the bearings into the sparElevator bearing installed with jam but finger-tight
Measuring the distance between the spar and the center of the bearing was easy, but not super accurate. I got these with 1/32 of the plans, then finger tightened the jam nuts. These will need to be torqued up once I have some crowfoot attachments for my torque wrench. I’m going to wait on that until I’m sure I have these set correctly.
Rudder with bearings installed
I also made some blocks that I will be using to drill the alignment holes in the elevator horns. Today I also picked up a couple of 8 foot lengths of aluminum angle so I can clamp the trailing edges while locating and drilling the elevator horn holes.
1 spacer and 1 drill block for drilling elevator horn holes. That’s not a swear word, it says “factory end”, which I thought I should label for some reason.
Tonight I drilled most of the bolt holes that attach the VS to the aft-most fuselage bulkhead. I used my drill block, which worked well, but was initially too long to fit within the confined space on the aft bulkhead. A quick trim of material on the block and it worked fine. For the 1/4 inch holes at the bottom, I stepped up drill sizes, starting with #30, then #12, then finally 1/4 inch, all done with a drill block to keep things aligned. This worked well and I’m happy with the results.
Vertical stabilizer clamped and aligned ready to drill
I did run into a problem with the 1/4 inch holes, which I attributed to a blunt drill bit. The 3 holes at the bottom of the VS spar are drilled to 1/4 inch. They go through two steel plates, with aluminum sandwiched in the middle. The drill bit struggled to make progress on the steel, even when running at the appropriately lower RPM. I got 1 of 3 holes drilled, and half of another one before stopping. It’s frustrating to not be able to finish this step tonight, but worth waiting for a new bit so I get the best possible result. I contemplated sharpening the drill bit myself, but didn’t feel like experimenting when these are such critical holes. So I ordered some new bits from Aircraft spruce, and will wait for them to arrive before continuing this step.
First hole drilled and bolt inserted (bottom, just above tailwheel mount). This turned out to be the easiest hole, there is only one piece of steel to drill through on the inside
I have plenty more work to do, so I’m not worried about the delay on this particular step.
Several work sessions; July 30, August 2, 3 and 4, total of 4 hours
July 30: Test fitting the top skin showed a couple of areas where I needed to break the edges a little more. A quick bend with the hand seamer, and then a re-check showed that everything fit nicely.
Test fitting the top skin. Tape is there for when I start back-riveting
August 2: I started by riveting at the forward end and worked backwards, per the instructions. It was easy going bucking these rivets until I was unable to reach comfortably. Then I removed all clecos, and taped up some rivets in preparation for back-riveting.
Bucking the forward rivets, and moving aftJust to prove it really was me doing this work
August 3: By carefully rolling the fuse onto the top skin, and climbing onto the bench, I was able to back-rivet up to the first bulk-head. I ran into an issue on the bulkhead, where the rivets didn’t sit down into the holes in a couple of places. The problem was caused by my positioning of the fuse flat on the back riveting plate, instead of at a slight angle. I moved on, riveting the remaining rivets up to the 2nd bulkhead. This was a lot of fiddling around; starting with the fuse on it’s side, I’d insert around half a dozen rivets on each side of the skin. Then I’d position my back riveting plate, then roll the fuse onto it’s top, and secure with some tie down straps rigged up to the ceiling. By tightening and listening the straps I was able to position the side at just the right angle. For the rivets. A quick check to make sure everything looked right, then up onto the bench, crawl into the fuse, set the rivets, then roll to the other side, check positioning, climb back in and rivet the other side. Then release the straps and roll the fuse onto it’s side to check my work and insert the next set of rivets.
Back riveting the top skin. Note the straps for safety, and to help with the angle Back riveting the top skin
But the end result was worthwhile; nice tight skin alignment, and some good looking rivets. I replaced the bulkhead rivets and wrapped up for the night.
August 4: I finished the top skin by bucking the remaining 30 rivets on the aft end of the skin. I contemplated back riveting these, but decided the risk of crawling that far back into the fuse, wasn’t worthwhile. Too much chance of bending something, or losing my balance and crashing everything onto the floor. By reaching in from the access point on the aft bulkhead I was able to easily buck these rivets, and despite not being able to see the rivets, they came out great. I’m really enjoying my new tungsten bucking bar. It’s about 2 inches square, fits nicely in the hand and seems to do a nice job. Using a couple of pieces of foam on the edges makes it very easy to ensure it’s level.
Bucking the aft rivets
Overall I’m happy with the result, and pleased to be finished with the aft fuse construction. I still need to drill some holes for the VS, but I’m otherwise complete.
