Building Small Ribs

Santa Claus, in the guise of Roger the UPS Man, brought me two big boxes of Bede BD-4C pieces on Friday so I was finally able to start construction of my plane. I quickly learned that there is a world of difference between assembling pre-made parts, which I had done in September when I spent three days in the Bede Corp shop, and translating a drawing on paper into a three dimensional aluminum object, which I did this weekend in my home.

I started with this

And ended up with this:

I was feeling my way like a snow-blind Floridian in an Arctic snowstorm, since this was my first attempt to fabricate anything out of sheet metal (if you don’t count the speaker shelves in my freshman college dorm room which destroyed the dry wall when we removed them at the end of the year but that’s another story all together). This was also my first attempt to actually work in my new shop / airplane factory full of lots of new tools.

My first challenge was to transfer the pattern for the rib to each piece of 2024-T3 0.020″ aluminum stock. I ended up photocopying the section of the drawing with the rib pattern and sticking it to the piece of aluminum with a bit of rubber cement. I used a spring loaded center punch to mark the metal through the paper. Then I pulled the paper off and drew from dot to dot, er, from dent to dent, recreating the pattern on the metal.

I made the HS-7 ribs, which will go in the anti-server tab on the back edge of the horizontal stabilator, on Saturday. This entailed trips to Harbor Freight and Home Depot for a few tools which I still needed, most importantly, a Dremel tool and accessory kit. I tried cutting the HS-7 ribs out with the Dremel tool and a tiny cut-off wheel. It worked pretty well but boy was it slow!

Once I had the ribs cut out and the edges deburred, it was time to figure out how to bend them. My first thought was a sheet metal bending brake but I quickly discarded it because there are three bends and the brake could only have done one. Thanks to a phone conversation with my friend Karsten (I would never get through this project without advice from friends my EAA chapter), I decided to make a bending jig and hammer the flat metal over the top of the jig, forming the finished rib.

Since I could not figure a safe way to cut the jig on my table saw, I headed to Sears and picked up a small band saw. Quick as a wink, I had my jig cut and working. It had been so many years since I had used a band saw, I had forgotten what delightful tools they are.

I broke the top half of my jig after forming three ribs but realized that I could do quite nicely with just a straight piece of wood. That worked to fashion the fourth HS-7. When I built a jig for the HS-9 ribs, which will go into the non-moving trailing edges of the horizontal stabilator, I made only a lower portion shaped like a wedge and used another straight piece of wood for the top.

I learned that it is very important to properly center the flat aluminum stock in the jig before bending it when I messed up the first HS-9 rib. Since the stock was off-center, one flange ended up too wide and one too narrow near the pointed end of the rib. It might work but I think that the rivet hole will end up too close to the edge of the flange so I will rebuild the part. Better safe than sorry, particularly since this part will be difficult to inspect after the plane is flying and pretty difficult to replace if a flange cracks.

I spend a day and a half making just eight small parts but I feel like it was time very well spent. My shop is better set up, with a power strip securely fastened where I need it for the band saw and the Dremel tool. I have some real experience with a bunch of new tools: Dremel tool with a cut-off wheel and with a sanding disk, 12″ disk sander, band saw, a couple of files, drill with new 110° TiN #10 drill bit, and the Scotch-Brite deburring wheel on the bench grinder. I am learning a ton, too. I was much faster on Sunday than on Saturday.

Best of all, my friend Gale looked at the pictures of the parts, talked to me on the phone about how the ribs fit into the anti-server tab skin, and opined that it sounds like I built the ribs correctly!