The second windmill model that I'm building is based on a 1910 design for a 10 foot blade diameter with automatic feathering on the sails.. The original rating of this windmill is about 1/4 hp in a 16 mile per hour wind. The rule of thumb for wind calculation is that a " 16mph wind blows 8 hours a day on 2/3'rds of the days in a year." (from Windmills and Wind Motors, F.E. Powell, 1910, reprinted by Lee Valley Tools (AT LEAST IN 1910!)
watch for pictures coming soon.