It seems like I say this every time I start writing, but it's been a big week for us. There are just so many milestones as we really start building the plane. Every time we work it seems like we are doing something for the first time. This week we set our first rivets and made our first mistakes. We'll get to the mistakes, but let's start with the rivets.
Those three rivets may not look like much, but they represent a big first for us. Now that those rivets are in place, we will never have to take those pieces apart again. Once we repeat that process about a million more times we will have an airplane. I'm not quite sure what this part is, I think it's a bracket that will eventually connect the vertical stabilizer and the rudder. You may notice that the rivets we used are different than what I've talked about in the past. There are two different types of rivets - flush rivets which is what I've talked about before and universal rivets, which is what you see above. Here's a practice kit Mike worked on that shows both kinds - flush rivets on the left and universal on the right. The vertical stab uses both kind of rivets. I'm not quite sure when and why each different type of rivet is used.
We used the squeeze riveter almost exclusively while putting together the vertical spar. The piece isn't all that big, so all the rivets can be reached with the squeezer. It's also much quieter because we don't have to run the air compressor. The hangar is a shared workspace and when other people are up there we try to keep noise to a minimum. When using universal rivets, you use a die with a little divot that fits right over the domed rivet head. When you squeeze the handles together it squishes the rivet in the right shape. I really enjoy using the squeezer because you can watch the rivet as it changes shape. There's even a little wisp of smoke (or something?) that comes from the rivet as it gets squished.
Riveting is one of those tasks that we've found is MUCH easier with two people. Mike will run the squeezer while I hold the piece steady and make sure everything is lined up. Honestly, with the size rivet we are currently using, I'm just not strong enough to squeeze the rivets anyway. It takes a lot of strength and even Mike gets tired out after awhile. There's a lot to pay attention to while squeezing rivets. The cupped die has to sit just right on the domed head of the rivet. The head of the rivet needs to sit flat against the metal surface of the piece. The rivet needs to be perpendicular to the hole so the shop head is an even thickness and isn't angled. It's very easy for things to move out of alignment once Mike starts to squeeze the handles together. We had really good luck with our first several rivets and then we made our first mistake.
In the picture to the right, you can see that the rivet isn't sitting flat against the metal. This happened because things just weren't quite aligned and that gap was there when we started squeeze the rivet. The problem is that as you squeeze the two ends of the rivet together to form the shop head, the rivet also squishes outward. Imagine an Oreo cookie - if you squish the two cookies together, the filling in the middle compresses but it also starts to squish out from in between the cookies. Even though we had only applied a little bit of pressure, this rivet was already too fat and wouldn't budge.
Once there's a problem with a rivet, the only way to fix it is to completely remove the rivet and start over. We knew this was going to happen (many, many times) during the build so it's not a big deal. Actually, right before this happened I asked Mike if we had the right tools to remove a rivet if necessary. The most amazing thing about the whole situation is that we don't actually have the right tool. I would had sworn that Mike has bought every airplane building tool known to man. So, with my blessing, he gets to order another tool. Now that I think about it, maybe he orchestrated the whole thing so he had a reason to get more tools...
As we were inspecting and discussing our bad rivet, we realized that we had actually been using the wrong size rivets and we were going to need to remove and replace several of them. The construction manual describes exactly which size rivet should be used in every single hole. The particular size of rivet is (presumably) chosen for a good reason, and since the rivets we were using were shorter than they should have been we decided that they needed to come out. You can see our mistakes in the picture below. The rivet that wasn't set properly is the one on the right labeled "bad replace". The rivets covered in tape and marked with an "X" are all the wrong size. We had put several other (correctly sized) rivets into this piece by the time I took the picture - they would be the ones not covered in tape. If you're curious, the clecos with tape on the top are marking holes that won't get rivets at this stage.
This really isn't a very surprising mistake if you consider the drawings we are trying to follow and the way that rivets are named. Here is a picture of the diagram we were trying to follow. The picture below is about twice the size of the actual printed version and only shows about a third of the diagram.
Each shape on the diagram corresponds to a different size of rivet, which is designated in the key on the right side of the page. All those numbers and letters in the "name" of the rivet mean something. The numbers in the middle tell you if it's a universal or flush rivet. The numbers at the end tell you the diameter of the rivet and the length. So in this case we probably should have been using the rivets that correspond to the diamond and accidentally grabbed the rivets that correspond to the triangle. I'm the one that grabbed the wrong size rivets so I've become a little paranoid and have been double and triple checking the diagrams ever since. It honestly isn't a big deal and we just laughed about it but it did make me realize how easy it is to misread these diagrams. Once we get the right tool we will remove those rivets and replace them with the correct size.
Mike also had trouble with one other part this week and we got to order our first replacement piece. He was trying to countersink a small, thin piece of metal that provides reinforcement to another part of the vertical stabilizer. The size of the part made this process pretty difficult and the holes weren't round anymore when he was done. It's kind of hard to see in the picture below, but on the left side you can see that the hole is oblong rather than round. When Mike did some research online he found this is a pretty common problem with this particular part. We'll order a replacement (which thankfully only costs a couple of dollars) and try again.
So, progress is stalled for a few days while we wait for the rivet removal tool and the replacement part. This time gives us a chance to figure out how to avoid these mistakes in the future.
Universal rivet - a rivet with a round, domed head
Die - a tool that is used for cutting, shaping, or stamping a material or an object (definition from the Merriam Webster online dictionary)