A rotorcraft rotor, equipped with a rotary wing comprising a plurality of blades, the blades being individually articulated on a hub of the rotor by means of respective mounting members, the rotor comprising an abutment mechanism comprising abutment members (5, 6) which are mounted on the hub and which cooperate with contact members (7, 8) borne by the hub, comprising lower abutment members and upper abutment members between which the individual flapping path of a blade which is associated therewith is limited, -) the upper abutment members being mounted mobilely on the hub between an engagement position in which the upper abutment members cooperate with corresponding contact members, forming an obstacle to the upward flapping path of the blades, and a disengagement position in which the upper abutment members are retracted, leaving the upward flapping path of the blades free, -) the abutment mechanism comprising means (9,12) for manoeuvring the upper abutment members between the engagement position and the disengagement position, the means for manoeuvring comprising a first manoeuvring means and a second manoeuvring means which develop opposing forces which cause the upper abutment members to pass towards the disengagement position and towards the engagement position, respectively, -) the first manoeuvring means making use of a centrifugal force which generates a centrifugal force which causes the upper abutment members to pass towards the disengagement position as from a predetermined centrifugal force threshold, -) the second manoeuvring means comprising return means which generate a spontaneous return force for returning the upper abutment members towards the engagement position counter to the centrifugal force generated by the first manoeuvring means, the return means causing the upper abutment members to pass towards the engagement position as from a predetermined return force threshold corresponding to a predetermined weakening of the centrifugal force generated by the first manoeuvring means, characterised in that the abutment mechanism comprises at least one bistable engagement latch which is selectively engaged on the upper abutment members between an active state of the engagement latch, in which the engagement latch is engaged on the upper abutment members which it keeps blocked in the engagement position, and an inactive state of the engagement latch in which said engagement is broken, allowing independent mobility of the upper abutment members with respect to the engagement latch. -) the upper abutment members being mounted mobilely on the hub between an engagement position in which the upper abutment members cooperate with corresponding contact members, forming an obstacle to the upward flapping path of the blades, and a disengagement position in which the upper abutment members are retracted, leaving the upward flapping path of the blades free, -) the abutment mechanism comprising means (9,12) for manoeuvring the upper abutment members between the engagement position and the disengagement position, the means for manoeuvring comprising a first manoeuvring means and a second manoeuvring means which develop opposing forces which cause the upper abutment members to pass towards the disengagement position and towards the engagement position, respectively, -) the first manoeuvring means making use of a centrifugal force which generates a centrifugal force which causes the upper abutment members to pass towards the disengagement position as from a predetermined centrifugal force threshold, -) the second manoeuvring means comprising return means which generate a spontaneous return force for returning the upper abutment members towards the engagement position counter to the centrifugal force generated by the first manoeuvring means, the return means causing the upper abutment members to pass towards the engagement position as from a predetermined return force threshold corresponding to a predetermined weakening of the centrifugal force generated by the first manoeuvring means,