How are wind turbine blades made to face the wind?

[skeptic2]

By noting the direction of the wind, the taper of the blades and the direction of rotation, it is obvious the turbine blades are facing the wind. On the other hand if you blow on a pinwheel while holding it loosely, it turns so the blades are away from the direction of the wind. Does anyone know what mechanism is employed to keep the blades facing the wind?

 

[Nidum]

Large power generating wind turbines have wind direction sensors and powered mechanisms to align the turbine blades .

Smaller and older turbines sometimes just have a tail vane . Basically using the weathercock principle .

The old windmills often had a small auxilliary wind turbine driven mechanism instead of a tailvane . The auxilliary turbine was arranged so that it was inactive when main mill sails were correctly aligned for the wind direction but which powered up and moved the mill head around when the sails were out of alignment .

Many old mills though were just aligned manually .

 

[Baluncore]

As Nidum wrote; A wind-vane on the head, generates an error signal, that controls a servo-motor to drive the windmill head into the wind.

For historical systems, google images; 'windmill fantail'

Tower mills had high fantails at the back, coupled through reduction gears or belts to a pinion running on a fixed azimuth bull gear.

Post mills were walked around when needed with a tail-pole or the rear steps. Some post mills had fantails on the tail-pole or the rear steps that turned a wheel on the ground to keep the mill facing into the wind.

Small wind pumps used on farms offset the horizontal turbine axis sideways from the vertical azimuth axis. The tail is spring loaded from the head so as the wind increases, the turbine blades gradually turn to be side on to the wind. That limits the top speed of the turbine and so prevents destruction in wind storms. When the tail mechanism fails due to lack of regular service, the turbine blades are thrown, until unbalance breaks the shaft, whereupon the damaged turbine wheel heads off across the farm.