Riveting the horizontal stabilizer10h
May 21, 2022
Time to rivet the horizontal stabilizer together!
I started with clecoing the nose rib into the left skin. I used the painter's tape to keep skin from opening (it kind of worked, but this tape is not very strong, it tears very easily)
Then I proceeded with the riveting. On my test coupon, I used 40 PSI. Here I set my pressure to 30 PSI, just to be on the safe side. With 30 PSI it takes a few seconds to get a rivet fully compressed -- feels about right.
The foremost flanges of the rib would not sit tight against the skin, so I used a piece of wood to spread out the flanges and make them tight against the skin (and of course this photo is staged post factum).
The nose rib was, perhaps, the hardest part to rivet with the rivet gun. There is very little space and it is hard to see anything without very bright light (which I had!).
Riveting with the gun was the part I was concerned about the most. As it turned out, for no reason. Working on a 3/32" rivet with the gun set to 30 PSI is not too hard and the process is very controllable. My first rivets came out a bit slanted, mostly because they were the first and also because of the difficulty to keep the bar square against the rivet given the spacing and curvature of the rib.
Then I squeezed the tip rib to the front spar assembly. The manual suggests inserting the front spar assembly into the skin first and then riveting the tip rib to it. However, I was determined to avoid riveting -4 universal rivets, so I decided to change the order.
With the skin spread apart, there is no issue at all to insert the front spar with the tip rib attached to it.
After that, I installed the blind rivets.
Then there was a time to rivet the spar to the skin. It was not a particularly hard process. As I've mentioned, the gun is very controllable. The swivel mushroom set I used does not slip too easily on the skin, so getting it exactly square to the skin is not critical (although, there were times where my gun would slip off the rivet -- but given how big is the "mushroom" it left no damage).
Holding bucking bar square is important, though. I used my tungsten bucking bar -- works really well (okay, I've never used any other bar to be fair)! I covered it with multiple layers of the painter's tape, leaving only small windows for bucking. To keep it aligned with the gun, I would look into the part such that one eye would see the bucking bar and the other eye would see the rivet gun.
To make it square, I would rest the bar on the fingers and the palm. By varying the pressure, I can tilt it both in a "lateral" direction ("roll" it) or a "longitudinal" direction ("pitch").
To my surprise, I did not have to drill out a single rivet. Okay, I did drill one partially set rivet, but it was because I tried to use my rivet gun in the left hand and the rivet did not set properly (I think I was not pressing the gun enough, so the rivet set above the skin surface).
Then, finally, some help arrived: two younger apprentices came and helped me to cleco the rear spar to the stabilizer.
Then I started squeezing all the perimeter rivets. Surprisingly, this is where things did not go as planned. When squeezing the rivets, I forgot to press hard enough on the squeezer so the rivet would bounce up and set above the skin surface. I have installed about 10 rivets when I realized my mistake and saw that almost every single one of them needs to be drilled out 🤦🏻♂️. I carefully drilled them out (just out of an abundance of caution, I used a #44 drill bit instead of #40), and luckily, have not damaged any of the holes. I would drill the head a bit, break it off, then adjust my drilling based on where the hole in the stem would be. Drill a bit more, then pull the rivet with the flat cutters.
When I was reinstalling them, I pushed on the squeezer to make sure the rivet is pressed enough against the skin. I have reduced pressure to 60 PSI from my "standard" 90 PSI, and I think, this helped, too. Also, I pressed the trigger more carefully so it would not run with great force. All of that helped to avoid other bad rivets, and everything went smoothly.
In the end, there were a couple of rivets that were not accessible well via the pneumatic squeezer (other than by using the "trigger feathering" technique), so I switched to my manual squeezer.
Pulling the pins from it is such a pain (although, seems like rubber o-rings wear on the pins and they now are easier to insert/remove)! While removing the previous yoke, I found that the pin head is exactly the size of a cleco and I can use the cleco plier to pull the pins (after pushing them a bit from the other side so their heads sit a bit proud).
Finally, after squeezing all of the rivets, I got the horizontal stabilizer complete!
One thing to note here is that I left 10 holes (5 on each side) on the top open, to be used for the fairing attachment. I saw on the forum that with good quality fairing, you don't really need 5 holes, but I decided to just follow the plans.
Also, I haven't installed the central bearing as am still debating if I want to disassemble it and re-prime it.
Next, I am going to redo the front spar assembly for the vertical stabilizer.