Charles,
Once again you have me wanting to build one of these. I have all the materials for this one, although I will have to wait for spring to dig up the clay. It's frozen as hard as iron right now.
Quick question: what is the functional difference between this design (hole in clay) versus a Viking style side blast? The Viking style seems to be more horizontal for the fire. Yours looks more like a bottom blast tuyere. Is there any difference?
Also, if you are using that much clay and you use a thin walled pipe for the air supply would it even matter that the pipe will wear away? Or should you put a couple fire bricks in to block some of the heat? I understand the reason for water cooling, I just don't see its necessity. Am I wrong?