Abstract: A wind turbine generator blade includes a movable front portion, extending from the faster-moving blade tip in a span-wise direction along the blade, and mounted on a pivot axis permitting the front portion to be displaced to a "high drag" position in which it has a high negative angle of incidence which will in turn give rise to a high negative angle of attack to the relative airflow and hence an increased drag tending to slow down an overspeeding blade, but will also give rise to an increased lift which assists in slowing down the overspeeding blade. It has been found that a truncated aerofoil section such as that used for the front blade portion has a relatively high stalling angle, allowing its use in conditions such that the angle of attack may approach 30.degree. without stalling of the front blade portion, but in the presence of a considerably increased total drag on the blade.