Windmills frequently have TWO mechanisms that keep them from getting destroyed by excessive wind loads. First on is a brake, the other, is a furler.
The brake holds the turbine in a stationary position.
The FURLER either turns the blades sideways to the wind, or releases the pitch of the flights, to stop motion.
The FURLER does all the work... the brake just keeps it from rattling and jogging the gearbox.
There's some windmills that use variable pitch control on their flights... they'll actually change the ratio, in order to manage working speed and torque... as wind speed increases, they reduce pitch to maintain constant speed, but in doing so, they're able to provide higher torque.
There are some windmills that don't use a variable pitch, but rather, just have two positions- working, and feathered. In the feathered position, wind will not cause the turbine to spin.
Other things to know about windmills:
The wooden pump rod is wood, so that in the event that the well's hand-jack or sucker rod becomes bound, that the windmill gearbox won't become damaged... it will simply break the wooden rod.
There are 'clutches' in many varieties... that can be used to stop the well from pumping. Typically, when water isn't needed. I've seen floats rigged to the furler (to knock down the turbine's operation when a water tank was full), and I've seen some that just disengaged the sucker rod, while the turbine kept spinning.
The coolest setups, are when a windmill lifts from well to an elevated tank, providing running water in a farm. My grandfather's farm had such a system- cistern was actually buried in the top of a hill, about 40 feet above the farmhouse. They had running water in the house... since 1880... and a copper heating loop around the jacket of the woodburning stove... so hot and cold running water... and drains in the house to the septic tank down the hill another 30 feet...
Old tech rocks! ;-)
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