If the flour is to make bread, why not use the cooked sweet potato as the first ingredient, then add the other things to it, no need to dry? Just an idea, and I'm sure it would not be practical for all recipes.

I would need this as a replacement for grain flours and not a supplement.

I guess what I'm saying is sweet potatoes store pretty well whole. Flour maybe less so.
There is a site I have seen thru Google where George Washington Carver's research on sweet potato is all listed, including how to make flour from them. I will look for it but you might find it faster.

On google, type carver+sweet potato. It's the first site, Texas A&M. How to make flour is down toward the bottom.

The site about George Washington Carver and how to make sweet potato flour is:
http://plantanswers.tamu.edu/recipes/sweetpotatoes.html

if you try this, please post your results. This is very interesting. Purdue University is doing a great deal of research on alternative flours andhas developed a really good bread recipe (yeast) but I don't have it. Our state fair also has a category of baking with alternative methods/ingredients.

I did try this way back when I first posted. I borrowed a friend's dehydrator and dried the sweet potato slices, which I think were par-boiled. I can't quite remember. It took forever to dry them and they shrunk up quite a bit. The only thing I had to grind the pieces was a blender and this was less than satisfactory. A flour mill would have made this task easier and more successful. From four trays of sliced sweet potatoes I think I got about 3/4 cup "flour" which was rather coarse. (Again a flour mill would have helped with texture.) I think I made some muffins using just this flour and they were edible, though not what I would have liked. I might try this again now that I have a better dehydrator and I'd get a grain mill in place of the blender.