Reply #3: It's due to "lift" [View All]

[skids]

The design uses drag to get going in low wind speed and shifts to aerodynamic lift thereafter. Lift only works past a particular windspeed (which depends on air density and pressure and various other factors, but is generally sticks around the same order of magnitude.) The trick to this particular design, I believe, is that the shift of blade orientation to do that is achieved simply by the bending of the blades due to centripetal force. Pretty sleek materials engineering there.