Salient White Elephant

April 10, 2009

Precision Wind Turbine Yaw Fin

The upwind variation has two airfoils that are each pitched near the stall angle. When the wind shifts directions, one of the airfoils stall, while the other generates the yaw moment at nearly maximum lift:

Aerial View Precision Wind Turbine Yaw Fin (Upwind Variation)

I suppose the upwind variation will produce stable yawing behavior only if the airfoils have gentle stall characteristics, and only if they can be pitched very near to the stall angle.

Now for the downwind variation. If the wind shifts by (say) 2 degrees, then the angle of attack for one airfoil increases by 2 degrees while the angle of attack for the other airfoil decreases by 2 degrees. The yaw moment thus generated is as if the wind had actually shifted by 4 degrees.

Both of these variations allow for the use of asymmetrical airfoils, which produce more lift than symmetrical airfoils.

Aerial View Precision Wind Turbine Yaw Fin (Downwind Variation)

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