Elevators

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.

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.

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.

With the bushing in place I drilled the left elevator hole

Then I removed the elevator and step drilled it up to 1/4 inch, and deburred the holes.

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.

With the experience of the left elevator, the right elevator went quicker. A couple of tweaks and I was happy with all the measurements.

Just a couple of tries and I had right elevator set. I made sure this was securely fastened to the bench as we will be away next week at Lake Tahoe

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.

After backing off the rod end bearings approximately 1.5mm, the elevator can deflect down 25 degrees without contacting the spar flange.

I used a 9V battery to test the trim tab servo, and everything worked perfectly.

I also made a new shelf for storing the elevators while I build the tail cone.

https://mytwings.com/wp-content/uploads/2020/02/img_4732.mov

I received a shipment of electrical supplies today from steinair.com, which enabled me to finish the left elevator. Instead of using a molex connector, I went with Stein’s recommendation on using dsub pins, and heat shrinking the wires. I picked up some crimping tools and a decent wire stripper, along with the dsub pins and some heat shrink.

I crimped the male and female pins, then slipped on the heat shrink, and pushed the pins together

Then slipped the heat shrink over the pins and used a heat gun to shrink the wrap making a nice tight seal.

Then I installed it in the left elevator, using some Velcro to hold the wires securely inside the elevator.

With that done, I hooked up the trim tab, and then installed the counterweights, putting some thread marker to ensure I can tell if the nuts ever back off.

Here’s the finished product:

Today I attached and safety wired the trim tab to the left elevator, trimmed and applied silicone to one of the trim tab molex connectors, and fitted the counterweights.

The trim tab fits perfectly, and the hinge is snug against the rear spar. I safety wired the hinge pin into place. I ended up redoing the safety wire after I took this picture, getting a tighter fit and a few less turns

Next job was to trim the corners off a molex plug, then seal it with silicone. This will be exposed to moisture, so the sealant is important. I bought some electrical-grade silicone sealant to ensure it doesn’t react with the wiring in any way.

Then it was onto the final step in the elevator plans, attaching the counterweights. I drilled out the holes to #12 using my drill press, then deburred the holes. I marked and trimmed the weights using a hacksaw and emery file. This was easier than I anticipated, and I soon had the weights ready to attach.

Starting with the right elevator, I bolted on the weights, then torqued them to 28 inch pounds. I used some thread marker to ensure I can tell if these ever back off. With that, the right elevator is finished!

Installing the left elevator weights was more challenging. After some trial and error, I realized that there is an alignment issue with the holes on the tip ribs. These holes are 0.03 inches too far apart, which is causing the bolts to splay out, and preventing them from being able to attach the inboard weight. I carefully filed the bottom hole to allow the bolt to pass, but ran out of time to secure the weights.

Today I flush riveted the trailing edge of the right elevator, and then rolled and riveted the leading edge.

I used a new tool, the safety-pin angled squeezer dies from Cleveland tools, and squeezed all the right elevator trailing edge rivets. These were partially set previously, and I was really happy with the way the edge came out. It looks perfectly straight, and there is less surface scratching than I was getting with back riveting. I should have bought these earlier, and would recommend them. It’s a shame this is the only place I can use them on the aircraft.

Then I set the aft 3 rivets along each edge of the elevator, too and bottom. The last two on each side are pop riveted because of the lack of clearance.

Then I rolled and riveted the leading edge. Having done the rudder and left elevator, this seemed to be much easier. I used my highly specialized tools from earlier (popsicle stick on a piece of tube) and was able to get good rivets into each hole.

I did make a mistake unfortunately, and placed the bottom skin over the top skin on the very outboard section. This is a bummer, because fixing it will be very hard without making a real mess. I guess this will be a distinguishing feature on my plane. It won’t be very visible to the casual observer.

Last night I rolled and clecoed the left leading edge, and tonight I riveted it together. I also drilled a 1/16 inch hole for safety wiring.

Rolling the skins was generally easier than it was for the rudder. The experience from the rudder helped, and the process went faster. I used a 3/4 inch pipe and duct tape to get a good grip and a nice even bend. Using a couple of pipe wrenches helped, and I was pleased with how it turned out. It’s definitely a non-precision exercise though, and it seems like there should be an easier way.

I made up a couple of tools to assist with the riveting, by attaching some popsicle sticks to lengths of tube and aluminum channel. These were helpful is holding the bottom skin (the inside skin) against the top skin, which forms the outside of the join. Without any pressure from inside, it’s hard to keep the two skins close together when setting the rivets.

I’ll be interested to see how much adjustment will be needed once the elevators attach to the horizontal stab.

Just a few minutes in the garage tonight, so I riveted the close out tab on the left elevator. These pop rivets were easy, but the last squeeze didn’t remove the rivet stem, so I carefully cut it off using some cutters.