Fecha de publicación: 27/09/2018 Fuente: WIPO "swarm" A propeller assembly (200) comprising a propeller hub (201) which can be driven about an axis and at least two propeller blades (203) each mounted to the hub at a point distal from the axis by pivoting means (203, 211, 212) alloying the propeller blades to pivot generally parallel to the said axis between at least two positions relative to the hub, a first, folded position in which the propeller blade is not aligned with the axis and the point and a second, deployed position in which the propeller blade is aligned with the axis and the point, in which the pivoting means (203, 211, 212) is configured to allow the propeller blades to pivot freely relative to the hub when in the first position and, on driving the hub about the axis, to allow the propeller blades to pivot relative to the hub until the or each propeller blade is aligned with the axis and the point, the pivoting means being adapted to hold the or each propeller blade in the second position for as long as the bub is driven. An air vehicle (700) comprising at least one such propeller assembly (701) is also described..