A rotor assembly for an aircraft capable of hovering, said rotor assembly having an axis and comprising: - a supporting member coaxial with said axis; - a drive shaft extending coaxially through said supporting member and fitted to the supporting member in an axially fixed position and so as to rotate about said axis; - a movable member mounted so as to be able to translate along and rotate about said axis; - an oscillating-plate assembly, which is coaxial with said axis, is fitted to said movable member to oscillate with respect to it about transverse axes substantially perpendicular to said axis, and in turn comprises a first annular member angularly fixed to said movable member, and a second annular member which rotates on said first annular member together with said drive shaft; - supporting and actuating means, which cooperate with said first annular member to move said oscillating-plate assembly and said movable member jointly along said axis with respect to said supporting member, and to oscillate said oscillating-plate assembly about said transverse axes with respect to said movable member; and - connecting means for connecting said supporting member and said movable member, to prevent rotation of said movable member about said axis with respect to said supporting member; characterized in that said connecting means comprise: - a retaining arm projecting outwards from one of said supporting member and said movable member, and extending at a distance of other than zero from said axis (a); and - an antirotation bracket, which projects from the other of said supporting member and said movable member, extends at a distance of other than zero from said axis, and defines a through opening engaged in sliding manner by said retaining arm. - a supporting member coaxial with said axis; - a drive shaft extending coaxially through said supporting member and fitted to the supporting member in an axially fixed position and so as to rotate about said axis; - a movable member mounted so as to be able to translate along and rotate about said axis; - an oscillating-plate assembly, which is coaxial with said axis, is fitted to said movable member to oscillate with respect to it about transverse axes substantially perpendicular to said axis, and in turn comprises a first annular member angularly fixed to said movable member, and a second annular member which rotates on said first annular member together with said drive shaft; - supporting and actuating means, which cooperate with said first annular member to move said oscillating-plate assembly and said movable member jointly along said axis with respect to said supporting member, and to oscillate said oscillating-plate assembly about said transverse axes with respect to said movable member; and - connecting means for connecting said supporting member and said movable member, to prevent rotation of said movable member about said axis with respect to said supporting member; - a retaining arm projecting outwards from one of said supporting member and said movable member, and extending at a distance of other than zero from said axis (a); and - an antirotation bracket, which projects from the other of said supporting member and said movable member, extends at a distance of other than zero from said axis, and defines a through opening engaged in sliding manner by said retaining arm.