Vertical stabilizer complete! Dimpling and riveting VS parts

Based on previous experience working on the horizontal stabilizer, I decided to finish the vertical stabilizer first. The VS is a lot easier to work on and will be done a bit faster since it's a smaller part. I still needed to dimple the understructure and the skin since I had elected to wait until after priming to dimple everything. The AKZO is pretty much bulletproof now that it's fully cured, so dimpling now wasn't an issue at all. I was able to get most of the holes using the DRDT-2, but the ribs and the very ends of the spars had to be dimpled with the hand squeezer since the DRDT couldn't reach them without deforming the parts.

I ended up having to re-countersink the bottom holes on the spar doubler since the primer had increased the thickness just enough to start showing a gap between the spar and the doubler when they were put together. The countersink cage was still set from the first time I did this, so this task went by quickly. I clecoed the parts together and started squeezing the flush rivets first, then moved on to the round headed ones. Most I was able to reach with the squeezer, but the rivets on the hinge brackets had to be bucked since the squeezer couldn't fit into the limited space. I was a bit nervous at first since this was my first time bucking rivets on the project itself, but I was both relieved and emboldened when they turned out looking nice.

I did end up having to drill a couple rivets out, namely the long -7 rivets that are really easy to fold over instead of squashing straight down. Using a #40 drill as a pilot hole then removing the rest of the rivet with the #30 bit worked well without enlarging any of the holes.

Those two empty holes at the bottom used to contain some pretty poor rivets. Not anymore!

I had one minor slip-up with the rivet gun when I didn't hold enough pressure on the round rivet head and the gun slipped. I have a couple of minor smileys in the spar now, but I doubt this is going to bring the whole airplane down.

A short while later I had a completed rear spar.

Apart, these pieces are flimsy. Together, they're pretty darn strong. ...there's a metaphor in there somewhere. 

With the rear spar done, I began work on the front spar by riveting the ribs to the spar itself. Attaching the 706 and 707 ribs were easy enough, but the only real challenge is keeping the spar still while putting so much force on the rivet gun and bucking bar. The assembly is so light that I ended up having to clamp it AND put weight on it to keep it from moving when I used the rivet gun.

My makeshift VS spar jig. 

When it came to joining the bottom 705 and 704 ribs at the same time, I was forced to use the offset attachment for the rivet gun. Having to indirectly apply pressure to the rivet head while keeping it square and also having to hold the bucking bar steady while the ribs themselves are in the way the whole time is difficult. Still, I powered through and got it done.

I hadn't yet dimpled any skins at this point in the build, so my DRDT-2 wasn't really set up for it. I've seen builders build tabletop shelves to elevate the skins to the level of the DRDT itself, but my impatience made me decide to build a stand that lowers the DRDT to table level instead.

Just a few spare 4x4s joined with some extra 2x4s. Simple, but sturdy. 

I made the stand at a height that brings the lower dimple die on the DRDT level with the table with carpet on top. This should support the skin while still making it easy to maneuver it around to dimple each hole.

Dimpling skins is where the DRDT-2 really comes into its own. Once it's set to the correct pressure, dimpling is way more easy and consistent than with your typical C-frame/hammer setup. There's no listening for that "right sound" to let you know the dimple is deep enough – just push down on the handle and you're good to go.

The DRDT is also supposed to help prevent a known issue with the C-frame – making extra, unwanted holes in the skin should the skin slip off in between hammer strikes. Of course I, being the rebel that I am, decided that no one could tell me what I can and can't do with my DRDT, so I accidentally punched a hole in the VS skin when I pushed the handle down without looking.

My actual reaction: "Wha– NO."

I had just made a mistake, using a tool designed to avoid making that very mistake.

I immediately rushed to the forums for advice. Did I just waste dozens of hours of work, or will I still be able to salvage my poor VS skin?

Thankfully this seems to be a common issue (one that happens more often on the thin rudder skins than anywhere else). I followed the steps others took: flatten the offending hole, drill/ream it to #40, deburr it, and then re-dimple it and put a rivet in it.

The offending hole, after clean-up.

Since this rivet won't be structural and only needs to fill this hole, I chose the absolute shortest rivet I have: an AN426AN3-3, normally reserved for attaching stiffeners to the thin rudder skins.

The rivet in place.

It's a good thing I didn't punch that hole any closer to the edge of the skin since the shop head was almost touching the rear spar. Any closer and I probably would have had to replace the entire skin. Luckily there was no interference between the new rivet and the spar and no deformation of the skin itself. It's not too noticeable as is, but I should be able to put some filler over it just before painting the aircraft and no one will ever know it's there.

This is later on after all rivets had been set. The extra rivet looks out of place, but at least it doesn't cause any issues.

With that catastrophe avoided I finished dimpling the skin and clecoed it to the skeleton. It was time for the fun part – riveting on the skin. The plans recommend starting in the center of the skin at the intersection of the front spar and the VS-707 rib, then working your way up toward the tip. I ended up drilling out my first attempt at setting the -4 rivet here since I easily flattened the shop head. A -4 rivet honestly seems too short for the 3 overlapping pieces of dimpled aluminum at this hole and I considered stepping up to a -5 length rivet instead, but I was able to set it better the second time so I didn't bother.

The rest of the rivets set with the rivet gun and bucking bar went by a lot easier and faster than I had predicted. Once you get the correct placement of the gun and bucking bar and have a feel for how much you need to feather the trigger and for how long, it's actually easy to get consistent shop heads down the row.

These are looking nice. In pictures there appears to be a slight gap between the rivets and the skin, but they do actually sit flush in the holes.

At first I was pausing to check the shop head of every rivet with the rivet gauge, but as it's been said (and I was skeptical at first) your eye is actually pretty accurate once you know what the proper shop head thickness and diameter are supposed to look like. I quickly got to the point where I would only have to recheck a shop head after shooting multiple rivets, and this helped the process go by much faster.

The bucking bar was scraping off primer in a few places, so I wrapped it in tape to protect the spar.

With the skin riveted to the front spar and the 707 rib I clecoed on the rear spar. The skin is riveted to the rear spar first, then to the top and bottom ribs to close everything out.

I wanted to make squeezing the rivets as easy as possible, so I set the VS with the spar horizontal to make everything easy to get to. I got the idea from one of Jason Ellis's videos. I couldn't use the squeezer on every rivet – the hinge brackets actually don't allow the squeezer to fully contact the shop head of the rivets in that area. I was forced to use the rivet gun and bucking bar, which really wasn't an issue now that I had a lot of practice with it.

While the part was horizontal I went ahead and set the blind rivets that connect the rear spar to the 707 rib. It's a good thing there isn't an abundance of blind rivets in this build since I only have a manual pop rivet puller. It takes a surprising amount of force to get the mandrel to break free of the rest of the rivet, and it ALWAYS makes a super loud, startling pop when it finally does break. I'd consider getting a pneumatic blind rivet gun if there were a lot more of these, but the hand riveter should suffice for this build. If I decide to build an RV-12 down the line (which uses blind rivets for almost everything) then I'll pick one up.

Some of those scratches are from the rivet puller bouncing when the mandrel suddenly breaks. It just happens too quickly to react.

I set the piece vertical for riveting the top and bottom ribs. The forward-most rivets on either side of the top rib were challenging. That area is too small for my bucking bar, and the squeezer didn't seem to be fitting in the limited space. I pondered how I could solve this without ordering another, smaller bucking bar. I then realized that I could take the flatter, wider flush set and put it inside the rib on the shop head while putting the thicker head outside on the factory head. That juuuust barely allowed the squeezer to fit, and I was able to squeeze all of these rivets without any deformation.

And just like that, I have a finished airplane part sitting on my workbench!

Well, technically it'll be completely finished once I get the fiberglass tip installed, but I'm going to wait and take care of all the fiberglass parts at the same time. For now it feels great to have a chunk of my airplane pretty much complete, the first milestone of this long journey. 

The horizontal stabilizer is next...