OK here we go.

The sensor is a Linear Variable Resistor (LVR ) or LVDT that is connected to a hydrauiic cylinder rod ( called Pitch Cylinder ). This rod actuates ( via a crank mechanism) the blade pitch angle of a wind mill. And this mechanism is finally in a closed loop with the power generated + the shaft RPM of the wind mill. All this information is finally synthesised into a command signal for the Hydraulic Servo valve so that the power generated by the windmill remains constant ( within a band ) amidst varying wind speeds and direction vectors.

And I am in the process of developing the MCU based simulator to test out the closed loop logic and other paraphernalia on the ground. ( when assembled the whole thing is 60 Meters into the sky - and it is scary doing anything there. I sweat in the palm .. )

So thats it. Maybe the crank mechanism has got something to do with the cosine pattern..

And just for the records : The blades are 25 meters long each ( three of them ) and the generator produces 500KW power - a small fellow in todays standards of 2MW each .

Raghu