The arc of black fabric for the surface of the tornado.
I began work on the top ring.
As I built the top rings, I realized that my illustrations had mislead me. A ten-foot circle was obscene. Even an eight-foot circle was ridiculous.
To get a more accurate idea what would look best, I dropped two strings from the ceiling and fastened them to the floor near my feet. Stacy snapped photos to give me a view into the ideal dimensions of a tornado. The strings are pretty hard to see on film, so I have highlighted them with yellow lines above.
I settled with a four-foot diameter top. The funnel cloud simply looked better when it was tall and thin.
To make the costume fit into our SUV, I needed to make the tornado break down into two or more large pieces. This was a serious engineering concern which had to be considered from the very beginning of the project. I could seperate the curtain from the harness, but I'd have to be able to re-assemble it by myself while I was wearing it. I decided to end the crankshaft in a wooden dowel which could be inserted into the helicopter blade wheel at the top and fastened with a cotter pin.
I reinforced the black fabric with the strongest fabric I could think of, this temporary fencing material made of orange plastic. Tyvek would have also been a good choice, but I wanted the surface of the funnel cloud to be a little more resistant to folding, so that it wouldn't twist up at the bottom.
Some kind of industrial long arm quilting machine would have been useful here, to bind the plastic fencing to the black plastic. Unfortunately, I only had zip-ties and spray glue, so that is what I used.
My high-friction bearing wasn't working well. I stopped production to improve the engineering of the bearing mechanism. I added a lazy-susan turntable.
Next I used self-tapping screws to screw the top edge of the fabric curtain to the helicopter blade wheel. The whole time I was expecting the bottom edge to fall into a cylinder shape, but sure enough, the geometry was correct and I had a real tornado shape developing.
Once the curtain was attached, I slipped into the curtain and connected the harness for a test spin. It didn't want to spin. It wasn't caught on anything, it just had a lot of inertia, and my little auger springs were coming unwound trying to push it into motion. Crap.
I needed to upgrade my auger. I had three options:
I tried all three.
I bought a $33 toilet auger, with a very impressive spring and set of handles, but it was too long for the harness, and I would have had to route the spring into a circle to get it back down to the connection point of the rotor.
I bought a solid wooden dowel and two springs, twisting them together to make my own offset crank.
I explored the possiblity of foregoing springs altogether and using 1/2" sockets to turn my rotor. Harbor freight tools had all the parts available, at ridiculously low prices.