A mechanical protection device including: a transmission shaft having a main axis of rotation and an element that is frangible under a torsional overload; a movable member secured to the transmission shaft to rotate about the main axis and configured to move radially outwards relative to the main axis from a first position to a second position; a spring urging the movable member towards the first position; and a tangential abutment configured to stop rotation of the movable member about the main axis when the movable member is in the second position. The movable member and the spring are calibrated so that from a predetermined trigger angular speed the movable member moves from the first position to the second position under effect of centrifugal force greater than prestress of the spring.