So, I've studied this windmill type, after getting home, and this is a 'sectional mill', early 1800's. Note-this one may not be that old. However, if I understand the description meant for an engineer correctly, the sections could fold 'back' upon itself depending on the wind speed (you've seen umbrellas do that in a strong wind). Web says this was one of two main styles of mills used during the nineteenth century. See also: http://wind.nrel.gov/public/library/shepherd.pdf Page 31.
This one is located on the grounds used for the NowThen Threshing Show.