Horizontal Stabilizer

After work, and before kids went to bed, I spent about half an hour setting the last 10 rivets in the Horizontal Stabilizer. I had to use a double offset set to get clearance, but it went easily enough. The small rib flanges needed some finessing to get them to line up, but eventually everything came together no problems. Here’s one side, the rivets in question are the 5 in a row closest to the lightening hole.

The black marks on and around the rivet heads are from the electrical tape I’m using on the bucking bar to prevent scratching.

Now that it’s finished, I need to put it somewhere so I can start working on the Elevators. I already have a plan, and tonight I installed hooks and eyelets as a first step, can you guess where it’s going?

Tonight I finished riveting the skins to the rear spar. This was a breeze with the squeezer, and everything ended up looking good.

I took the whole thing out of the cradles and started setting the last 10 rivets, which connect the inboard nose ribs with the front spar and inboard in-spar rib. Unfortunately the squeezer doesn’t fit, so I need to buck these 4-7 and 4-8 rivets. It was too late to make all those loud banging noises, so I’ll leave them for tomorrow after work before the kids go to bed.

Here’s how it looks sitting on the bench:

Not much progress today, but I managed to squeeze the rear spar and rib rivets. For one rivet, the rib pulled away slightly, leaving a small gap. I’m not planning to drill and replace, but will get a second opinion. After that experience, I used a clamp for the rest of them and had no issues.

As I moved to riveting the skins to spar flanges, I noticed the skins are not sitting completely flush with the rib flanges, at least in some places. Given that the holes line up, I suspect my spar flange countersinking may be to blame. If the counter sinks are not deep enough, or otherwise incorrect, the skin dimples won’t fully seat in the holes. I set around 10 rivets before I stopped riveting so I can figure out a plan. It’s pretty frustrating, as fixing this would require replacing around 40 rivets, which is always risky. Here’s a picture of the gap on one side. The nearest rivet on the flange marks the first hole, which is sitting correctly, skin flush to spar flange. The rest of the holes are not flush, with a gap of around 0.025 inches (0.5 mm).

I emailed Vans to get an opinion on whether it’s a structural issue as-is. The interlocking of the countersink and dimple is designed to add strength. It’s possible this may also create stress points resulting in possible skin cracks in the future. I’ll see what they say.

Today I was able to finish riveting the HS skins to the ribs, then rivet the rear spar to the ribs. This took longer than I planned, because of a couple of issues.

As I squeezed the rivets around the edges of the skin, I found one side of one of the the in-spar ribs which I had forgotten to dimple. Lucky it was the inboard rib, and I was able to squeeze-dimple the holes using my pneumatic squeezer. I ended up drilling out a rivet in the process, which wastes some time.

The second issue was that a few of my countersink holes on the spar flange were not quite deep enough. This was creating a gap between the skin and the spar, and needed to be addressed. I experimented with some scrap material and switched my countersink cage. The cage that I was using had some slop in it, and was unpredictable. My other cage is a different design and is much better. I increased the depth of a number of holes, then primed the newly cut holes.

Here’s one side done:

Riveting the skins to ribs:

View of the shop heads. Most of my rivets set perfectly, none were in need of replacement:

Rear spar in position and clecoed to ribs and skin:

Pop rivets set, binding the rear spar to the in-spar ribs:

The inboard and outboard ribs get Universal head rivets, which I will probably squeeze. Then the spar flange will get riveted to the skin, and it will be done!

I was able to spend some time last night and today getting the front spar riveted, then the in-spar ribs and stringers. I was happy with my riveting, although I did end up drilling a couple where the bucking bar slipped and malformed the shop head. By the end of the day I think I’d set about 300 rivets, with about the same number to go to finish the Horizontal Stabilizer. This has been very good riveting practice, I’m definitely producing more consistently good rivets, and I’m moving much faster. Most of the remaining rivets are around the edges and for the most part, can be squeezed. I’ll probably squeeze them, because it’s faster and quieter, which helps when it’s late at night.

The black scuff marks in this picture are from black electrical tape on the bucking bar, rubbing on the spar and ribs. The tape is to stop the bar from scratching the aluminum.

Slowly the clecos are coming out and the rivets are going in. Each time I lift and turn the whole assembly, it’s noticeable how much lighter it’s getting. Clecos are much heavier than rivets!

I applied some primer to the countersunk holes on the flanges of the spars and stringers. This is to provide a barrier between the spars and the dimpled skin where the skin will sit inside the countersunk hole. I sprayed some rattle-can primer into a plastic cup, then used a cotton bud to apply it to the holes. The primer color is olive drab, but it will be completely covered so I’m not worried about it not matching the white primer I used on the rest of the parts.

Then I inserted the forward spar into the skins, and riveted the spar to the nose ribs, joining the whole forward spar and rib assembly to the skins. I couldn’t get my pneumatic pop rivet tool into the rather narrow gap between ribs, so I used my hand squeezer to set the rivets. Everything came out nicely.

Here’s the clecoed skins, ready for the next step of setting the 600 odd rivets.

I also applied some thread paint to the torqued bolts on the rear spar. This will provide a visual reference to identify if the nuts ever loosen up for any reason.

I finished up the riveting of the nose ribs, and then drilled and removed one particularly ugly rivet. My riveting woke up one of the kids a couple of times, so I’ll need to finish the one final rivet tomorrow.

Didn’t make much progress over the weekend, but I set up the cradles and skins, then started riveting the nose ribs to the skins. It’s been a while since I bucked rivets, as most of the rudder was done with the squeezer, back riveting, or pop rivets. I made a practice piece to remind myself how to do it, and to ensure I had the right air pressure at the gun. Access is a bit awkward, especially for the forward most rivets. The skins are deep enough where it’s a stretch getting a hand down inside, and near the leading edge, there’s not enough room for a hand, a bucking bar, and a rivet. I finished this step on one skin, getting the three nose ribs in (the 4th one is attached to the spar and gets riveted in later), and started on the second. I’ve got a few rivets that will need to be drilled out and redone, but I’ll worry about that once I have the whole step completed. I may end up using flush pop rivets in the forward rivet holes, since it’s hard getting a bucking bar on those rivets, and I managed to mess up a few of them.

The forward-most rivets in this rib are both bent and not fully formed. I’ll drill out and replace:

I riveted the stringers to the in-board in-spar ribs and stringer web.

Then I clecoed and riveted all of the in-spar ribs to the front spar, and the two outside nose ribs. I got everything done with the pneumatic squeezer, which was easy given that I have a sheet with all the settings. Just twist the adjustable set the right number of turns and then squeeze away. These were all 4-4 rivets except for 8 4-5 rivets where the rivets go through the spar, spar cap, and then the rib.

Next step is to start riveting the nose ribs to the skins.

I finished up the Spar and stringer countersinking work tonight, everything went quite well. The only issue I had was when I tried to use the drill press for the stringers. After a lot of setup time, and lots of clamping, the piece moved slightly and I ended up with a lopsided hole. I switched back to using the drill after that mistake, as it’s easier to feel what’s happening and stop or adjust if needed. The enlarged hole will need to be drilled out to fit a larger rivet, which shouldn’t be a problem. Given that I countersunk over 400 holes, I’m ok with one error.

Then I riveted the inboard inspar ribs to the stringer web, and clecoed the stringers to the stringer web. I decided to stop there, as it’s getting late.