Time Away = Mistakes!

Friends,

After what felt like forever, I was able to get back out to the shop over the past couple of weekends to work toward finishing up the elevator. One of the things that first stalled me out so many months ago was that I was trying to "build a better mousetrap" when it came to the access panels for the trim tab motor/servo. Zenith's typical access panels are just panels that are over-sized for the hole they cover and then riveted in place. I have seen some nice flush panels that use screws and rivnuts, had been interested in doing something similar.

After messing around with a rivet squeezer and some scrap a aluminum a couple times, I wasn't able to get my rivets to squeeze properly. I've watched several videos on this and I'm certain there's something simple that I've overlooked. But, I couldn't make them work some months ago and set that (and the whole project) aside due to other distractions. I finally just decided to go with what the blueprints specify (the simplest of solutions, to be sure), because I can always retrofit later. 

Enter Fall 2018: It's been 9 months since I last touched the project, and over a year since I had any kind of progress tempo going. I was dreading cutting the access panels and actuator cut-outs on what was otherwise a near-perfect elevator. Well, with my time away and perhaps a little too cavalier an attitude, I made a few mistakes when I started cutting.

I have no idea how I ended up doing it, but I cut the access panel on the top surface of the elevator instead of the bottom, right where the trim servo is supposed to mount:

What a beautiful access hole & cover panel! But, it's pretty clear in the blueprints:

My only solution was to rivet the original cover plate I made (the very first part I made for the airplane!) over the hole and then rivet the trim servo to that & the skin:

This turned out okay and has plenty of strength, but I got very lucky with the placement and spacing of rivet lines. I also had to drill an extra hole in the left (hidden from view above) mounting flange of the trim servo to accommodate an extra rivet where there's an existing hole in the skin. Again, very lucky that this all lined up properly under the circumstances.

Here, you can see the access panel cut-out in the proper location on the BOTTOM skin, actuator rod sticking out the back and ready to trim to length and mate to the elevator. A keen eye will notice the rivet hole that's too close to the actuator rod port. This was because I laid out & drilled my rivets before laying out the actuator port. Another rivet approximately 12 mm from the edge rivet will keep things structurally sound. If it develops a crack at the edge, I can simply widen the cut-out enough to remove the crack & rivet hole.

As if all that wasn't enough, I accidentally drilled & mounted the trim tab bracket to the trim tab backwards:

These 4 extra holes are from where I'd had it mounted on the wrong side. I originally thought I formed the bracket as a mirror image to what is shown in the plans, and therefore thought I would need to mount it on the outboard side of the trim tab arm. However, because I failed to do a simple test fitment of these parts before drilling, I failed to see that I had formed the trim tab bracket properly, thus requiring it to be mounted on the inboard side of the trim tab arm. This isn't a complete disaster, since four A4 rivets in those holes will seal them up and only 2 of the rivet heads will be in the slipstream. But still...dumb mistake!

Finally, although this isn't a mistake so much as a modification, I added some of Zenith's "Standard  L" to my nose and tip ribs to stiffen them up. When Zenith forms these, they have a little more flange material around the radius of the nose, allowing for a 3rd rivet to be installed on the skin toward the nose of the elevator. I had to trim away material bit by bit to get the radius to form on these ribs without cracking the material. As such, I felt they were a little too flimsy, and added some stiffening angle to them:

Ordinarily, you would install a 3rd rivet on the top and bottom radiuses, just head of the 2nd crimp around the nose. But I don't have enough flange material. These nose ribs really only provide a little shape structure for the curvature of the nose skins, so they don't need to be super strong, but the stiffening angles will certainly ensure they don't flex or crease under any kind of pressure.

As to why I made the errors in the access panel and brackets, I can only speculate that it's largely because I've been away from the project and remembered things incorrectly. Once you break the cycle of productivity, it's really hard to get it back. Moving forward, I'll keep reminding myself to check and re-check the locations of things and do test fits BEFORE I drill holes. At least I have the elevator completed, and just need to disassemble, prime and re-assemble with rivets. I filmed a lot of these issues  and will present them in my elevator build videos. More to come!

Cheers,

Greg