Air driven turbine having a blade pitch changing mechanism including overspeed protection

An air driven turbine comprising:

• a) a hub rotatable about an axis of rotation;
• b) a movable blade extending from said hub along a blade pitch axis passing transversely through the hub, said blade being attached to said hub for rotation of the blade about said blade pitch axis through a range of blade pitches of said blade with respect to said axis of rotation, with said range of blade pitches including a failsafe position of said blade;
• and
• c) pitch change actuator means for changing said blade pitch of said blade comprising:
• 1) a linear actuator having an axially extendable shaft disposed for axial movement along said axis of rotation;
• 2) a yoke slidably mounted for axial movement along said shaft;
• 3) coupling means operably coupling said yoke to said blade in such a manner that said axial movement of the yoke causes said blade to rotate about said blade pitch axis, thereby changing the pitch angle of said blade with respect to said rotational axis;
• 4) speed responsive disconnect means operably connecting said yoke to said shaft in such a manner that:
• below a predetermined disconnect speed of said hub, about said axis of rotation, said yoke is constrained to move axially in unison with said shaft;
• and above said predetermined disconnect speed of said hub said disconnect means will decouple said yoke from said shaft such that said yoke may move axially along and with respect to said shaft;
• and
• 5) return spring means for urging said yoke toward an axial position corresponding to said failsafe position of said blade when said disconnect means has decoupled said yoke from said shaft, to thereby drive said blade toward said failsafe position.