Elevator rigging

So today I picked up where I left off last night, starting with getting the forward elevator push tube loosely in its place under the seat floors. Then I got to spend some time reviewing the annoyance of getting this whole system together. For whatever reason, the manual tells you to 1) slide the forward tube into place, 2) bolt the bellcrank to the forward tube, and 3) slide the bellcrank into place. Problem is, the bellcrank can’t go into place from beneath, which is how it would have to be inserted if this procedure was followed. So instead it has to go from above, and then the attach bolt has to be positioned and tightened in the very tight space between the baggage ribs. This was not much fun before the turtledeck was in place, and will probably be even worse now.

Anyway, before I could do any of that, I needed to take a look at the autopilot pitch servo and see how that would fit in with the rest of the procedure. Turns out that the way the servo mounts, it needs to be installed before the bellcrank. I also needed to drill the hole in the bellcrank for the servo linkage, as well as assembling the linkage itself. Finally, there was the consideration of the optional bracket on the servo to limit movement of the arm. Limiting the range of motion is important because if the servo linkage can go over-center, it’ll lock up the controls, which would be bad for fairly obvious reasons. Generally, the control stops and linkage setup should primarily prevent this, and the bracket is a backup.

After thinking all this over, I concluded that I was going to have to install all this stuff twice if I was going to get the limiting bracket set up correctly – that is, installing the servo, bellcrank, and aft pushrod, moving the elevators full down (putting them closest to the over-center position), and checking the alignment of everything. This led to the first of many trips in and out of the tail today. The real fun with this is that the backboards can’t go in place because they block access to stuff I’m working on, so I was left to work using a few random pieces of scrap wood placed across various ribs.

Now, the first problem was with the interference between the limiting bracket and the servo mount bracket. The install kit warned of this interference, and I figured the first temporary install would help me decide how to maybe trim the limiting bracket to fix the problem. Well, turns out the interference was way more than I expected, to the extent that I’d have to basically destroy the limiting bracket to make it work. So I decided not to install it – realistically, given that the elevator stops are beefy structural pieces, any event that allowed the controls to move past those limits would probably already be catastrophic.

The good news here was that I didn’t have to fit up everything, but I still had to pull the servo again to remove the limiting bracket. Then I got to climb in again, reattach the servo, and then start to really think about getting that forward tube and bellcrank put together. Well, that latter part was what broke me for the night. The rod end bearing on the tube installs with a thin washer on either side, which makes for some really fun coordination. Back when I did this before, I glued the washers inside the bellcrank to simplify this, but whatever I used (I think it might have just been superglue) gave up the ghost today. I made one brief attempt to just get them inserted manually, but there was just no way that was happening with the tight confines.

So I pulled the bellcrank out again and embarked upon gluing the washers in place again. This time I used epoxy, in the hopes that it’ll hold a little better. The fun part was figuring out how to clamp the washers in place while they dried, without also epoxying the clamping stuff in place. I ended up putting a short #10 screw through each side of the bellcrank, with a nut to clamp it all in place. Judicious application of the epoxy kept there from being a ton of squeeze-out that might glue everything together. If this was a real structural bond I’d have wanted to be more liberal with the epoxy, but here I just need those washers to stay in place while everything is assembled.

So that’s where it sits tonight – tomorrow when the epoxy’s dry, I should be able to finish getting the put tubes and bellcrank installed, and hopefully confirm that the aft tube length is right and the servo arm lines up as it should. Then I guess I’ll be gettin the rear avionics shelf installed again as well…maybe. Not sure if I should wait on that or not. In any case what I’ll really be moving on to soon is getting the vertical stab attached and then probably looking at the fiberglass work back there.

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