The overall history of design of wind turbines is that they started as light, simple turbines driven by aerodynamic drag forces; evolved to heavier (due to more matieral) drag turbines and ten to light, less material, aerodynamic lift turbines.
The first windmills were based on the Persian panemone design which utilized drag as a force (think sails of a ship but in a circular mill with the sails running vertically). These were vertical-axis windmills.
Windmills then evolved into the horizontal axis windmills which is more closely related to the kind we see today. These windmills still used sails to propel them.
Over time the use of horizontal axis windmills was commonplace. But sails were soon replaced with smaller wooden slats and then steel blades.
By the 20th century windmills were actually being used to generate electricity and their designs once again changed to by more aerodynamic (no use of wooden slats) and to use lift rather than drag.
Although there were a few other experimental designs during the 20th century, the use of lighter, aerodynamic materials along with the use of life eventually changed the design to the 3-bladed turbine we have come to recognize today.
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