how does making it not turn put it under less stress than allowing it to turn with the wind?,(reply>), The problem is the moving parts inside it, it's basically an electric motor which can only turn so fast.,(reply>), The propeller blades pitch is changed to put them parallel to the wind flow. As so you reduce the "push" force. But more importantly the limitation is the rotational speed and centrifugal forces in play. If you let it speed up uncontrolled the blades could just "fly away".