For hundreds of years, the most important application of windmills at the subsistence level has been mechanical water pumping using relatively small systems with rotor diameters of one to several meters. These systems were perfected in the United States during the19th century, beginning with the Halladay windmill in 1854, and continuing to the Aermotor and Dempster designs, which are still in use today.
The first mills had four paddle-like wooden blades. They were followed by mills with thin wooden slats nailed to wooden rims. Most of these mills had tails to orient them into the wind, but some were weather-vaning mills that operated downwind of the tower. Speed control of some models was provided by hinging sections of blades, so that they would fold back like an umbrella in high winds, an action which reduced the rotor capture area to reduce thrust. The most important refinement of the American fan-type windmill was the development of steel blades in 1870 (Figure 5). Steel blades could be made lighter and worked into more efficient shapes. They worked so well, in fact, that their high speed required a reduction (slow-down) gear to turn the standard reciprocal pumps at the required speed.
Between 1850 and 1970, over six million mostly small (1 horsepower or less) mechanical output wind machines were installed in the U.S. alone. The primary use was water-pumping and the main applications were stock watering and farm home water needs. Very large windmills, with rotors up to 18 meters in diameter, were used to pump water for the steam railroad trains that provided the primary source of commercial transportation in areas where there were no navigable rivers.
In the late 19th century, the successful "American" multi-blade windmill design was used in the first large windmill to generate electricity.
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