as particularly illustrated in fig3 a collar 41 is slidably disposed on the propeller shaft 13 for movement longitudinally thereof and a coil compression spring 42 is disposed between this collar 41 and a fixed stop 43 on the propeller shaft the collar 41 is disposed ahead of the propeller 14 with regard to the direction of wind travel and the fixed stop 43 on the propeller shaft 13 is disposed between this slidable collar 41 and the propeller a strut 46 is pivotally mounted at 47 on the slidable collar 41 and is connected by a ball joint 48 to the propeller blade 22 similar strut connections are provided for each of the blades from the collar 41 should the wind force on the blades 22 become excessive there will be a sufficient force applied to the strut 46 to move the collar 41 to the right in fig3 by compressing the coil spring 42 against the fixed stop 43 this will then cause the blades to pivot about the hinge pins 28 of the hub 21 in this respect reference is made to fig4 of the drawings showing a propeller blade 22 having an appropriate airfoil surface as illustrated disposed in normal position for efficient operation at a predetermined wind velocity of say 30 m p h as the wind velocity increases the force on the propeller blade 22 is increased so as to progressively compress the spring 42 of fig3 by sliding the collar 41 linked to the blade by the strut 46 this then allows the blade to pivot about the hinge pin 28 and thus the axis 29 thereof which in fig4 is seen to be disposed as the small angle u03b1 to the axis 15 of the propeller shaft.