Fin!

Hello fellow airplane nuts. This is an exciting entry, because the vertical fin is now assembled and riveted! The vertical fin was mostly done, except for bending the skin. I’d been putting that off, because it seemed a daunting job. With some help from Liz, it turned out to be pretty easy. Now let’s get to some pictures, shall we?

Here we are setting it up to bend the skin using the vacuum method. Liz was making a point of being silly for the picture, making some kind of “ta dah” sound. Or maybe it was “Look! I have tape!” 🙂

We used boards and clamps to keep the pipe in place along the proposed bend line.

The next step is to pull the skin together at the trailing edge and tape it. There are no pictures of this process because it was a two person job, and I haven’t figured out how to get Ducky the dog to take pictures. Then it was time to gather up all the plastic and start taping it in place to seal it for the vacuuming.

Here it is taped up as best we could, shop vac ready to go.

And the fun begins! The vacuum is turned on and it starts shrinking…

And in seconds it’s pulled as much as it’s going to go!

You may notice extra tape around the vacuum nozzle in the picture above compared to the rest. Yep, it pulled those adapters right off. What you can’t see is a piece of 3/4″ pipe taped on the end to get the vacuum in past the plastic, to keep it from sucking the plastic into the hose and cutting off the airflow. We had several false starts before we figured that out! Anyway, once we got it pulled down, it was time for the reveal.

 

It worked great! Onward with the rest of the fin assembly. Next it was time to fit the ribs to the spar and start fitting the fin.

The Zenith assembly manual shows how to build a couple of wood jigs to help keep the fin skin held to the right shape to fit to the skeleton. It works well, and would be really difficult to do without using them. You also need to make some spacers to keep the spar assembly up off the bench. This lets the skin extend past the spar (it gets trimmed later) and also allows you to level the spar to check that the fin is being built straight. Here’s the first fit of the skin to the skeleton:

From here, it’s a matter of getting it to fit the top rib, marking where the rivet rows go, and getting it drilled. First is the top rib, making sure your skin is lined up properly.

Then you level the spar and scoot the skin around until a plumb line hung from the center of the leading edge hits the center of the spar. Close enough! 😉

After you get this, you clamp the skin to the spar and back-drill the bottom rib using a 90 degree angle drill. It’s a fiddly step (and requires a helper) but it works.

I was disappointed that I couldn’t get the leading edge of the bottom rib to fit all the way forward into the skin while also keeping it at a 90 degree angle to the spar. However, after seeing a few other builder pictures (made with factory kit parts) that look much the same I felt better about it.

The skin then gets marked where the spar flange ends and the excess trimmed off. I used the Olfa knife to score it, then snapped the section off with seaming pliers. Worked great!

Before riveting everything up, the last thing I needed to do was make the cut on the bottom edge of the skin to clear the horizontal stabilizer. The problem is, the dimensions for these cuts are not shown on the plans! A plea for help in the Zenith forum got me quick help from fellow builder Michael Chesney. Thanks again Michael, you are da man!

With the last excuse out of the way, it was time to start drilling the spar-to-skin rivet holes.

While drilling these holes I had one of those “oops” moments. I realized I had not taken the end of the spar doubler into account when laying out the rivet line on the spar-to-skin joint, and one of the rivets was too close to the end of the doubler! Two were, actually, the other side had the same issue. As you can see from the red line, I decided to just add an in-between rivet. If anyone ever asks why there are two rivets that close together on the fin I will just smack them. 😉

Here is that same area after it was all done:

Let the riveting begin! After riveting the rudder with the hand riveter, I ordered and received a pneumatic riveter from Zenith. My hands are grateful for the money spent, that’s for sure!

One side done:

Other side done:

And I had to attach the rudder for a photo, before even peeling off the plastic from the fin!

Plastic peeled, sitting on the bench to show the nice leading edge radius:

And here’s the obligatory photo of me holding the finished assembly:

All that’s left to do is make the fiberglass cap for the top of the rudder, which will have a few challenges that will need to be addressed. But that’s a story for another day. As always, you can browse all the photos in my 750 Cruzer album.

A Riveting Experience

As the holidays approach, things tend to take up my spare time, so there hasn’t been a lot of progress on the plane. And that’s OK! I’m not complaining. This airplane thing is just a hobby, after all. 🙂

I did get the time to rivet together the rudder skeleton, which marks the somewhat momentous occasion of the first rivets being pulled on the project!

There have been volumes written on whether to prime the internal parts or not, and much like religion or politics everyone has their own opinions and preferences. I initially was planning to prime the mating surfaces with a self-etch primer, but I stumbled upon discussion of using CorrosionX instead. It’s not advised if you plan to paint, since the product can leak out around the seams and rivets over time. However, I do not plan to paint the plane so that’s not an issue. I cleaned the parts with Scotch Brite, wiped them down with alcohol, then sprayed on some CorrosionX and wiped it to an even sheen with a towel. I then riveted the parts together. If the product description is to be believed, this should provide all the corrosion protection the already corrosion-resistant 6061-T6 aluminum needs. Time will tell, I guess!

I also spent some time correcting a slight issue I had with the hinge angles on the vertical fin spar. If made to the length specified on the plans, they are 5mm shorter than the overall length of the spar. This doesn’t seem like much, but it means if you split the difference top and bottom, the edge distance on the rivets that go at the top and bottom are too close to the edge of the hinge angles. If you make it flush at the top (which I chose to do), the rivets basically hit the edge of the angle at the bottom. Rather than make new parts, I decided to trim them back and install a doubler at the bottom. This gives the bottom attach bracket the double layer of .040 to attach to (as designed) and also adds a bit of reinforcement to the bottom of the hinge angles, at the point where they will be most loaded (where the rudder is driven by the control cables). I’m pleased with the results.

And finally, I got the itch to fly some RC stuff again. Since I really don’t want to take the time to drive all the way to the RC field, I needed something small that I could fly in the yard, or even in the garage at a moment’s notice. After some research, I picked up an XK K110 micro 3D helicopter. So far it’s proven to be fun, and a remarkably good flying heli. Here’s a photo, and a couple of videos.

You might notice my vertical fin skin and rudder skin in the background of that second video. 🙂

That’s all till next time! As always, you can browse all the photos in my 750 Cruzer album. Thanks for stopping by!