A vibration attenuator for an aircraft having a rotor rotating about a mast axis, the attenuator comprising: first and second coaxial spinners (121,133) configured for rotation about the mast axis and relative to the rotor, each spinner (121,133) having an upper weight (129,141) and a lower weight (131,143), the weights (129,131,141,143) of each spinner (121,133) being spaced radially from the mast axis and positioned 180 degrees from each other about the mast axis, the weights (129,131,141,143) of each spinner (121,133) being spaced from each other a distance parallel to the mast axis, such that each weight (129,131,141,143) rotates about the mast axis in a plane different from each of the other weights (129,131,141,143); wherein the spinners (121,133) are configured to be rotated together relative to the rotor at a selected angular rate; and wherein the spinners (121,133) are selectively rotatable relative to each other between a minimum-moment configuration, in which the upper weight (129,141) of each spinner (121,133) is angularly aligned about the mast axis with the lower weight (131,143) of the other spinner (121,133), and a maximum-moment configuration, in which the upper weights (129,141) are angularly aligned about the mast axis and the lower weights (131,143) are angularly aligned about the mast axis, thereby producing a whirling moment about the mast axis as the spinners (121,133) rotate about the mast axis, the attenuator further comprising: a first motor for causing rotation of the first spinner; and a second motor for causing rotation of the second spinner. first and second coaxial spinners (121,133) configured for rotation about the mast axis and relative to the rotor, each spinner (121,133) having an upper weight (129,141) and a lower weight (131,143), the weights (129,131,141,143) of each spinner (121,133) being spaced radially from the mast axis and positioned 180 degrees from each other about the mast axis, the weights (129,131,141,143) of each spinner (121,133) being spaced from each other a distance parallel to the mast axis, such that each weight (129,131,141,143) rotates about the mast axis in a plane different from each of the other weights (129,131,141,143); wherein the spinners (121,133) are configured to be rotated together relative to the rotor at a selected angular rate; and wherein the spinners (121,133) are selectively rotatable relative to each other between a minimum-moment configuration, in which the upper weight (129,141) of each spinner (121,133) is angularly aligned about the mast axis with the lower weight (131,143) of the other spinner (121,133), and a maximum-moment configuration, in which the upper weights (129,141) are angularly aligned about the mast axis and the lower weights (131,143) are angularly aligned about the mast axis, thereby producing a whirling moment about the mast axis as the spinners (121,133) rotate about the mast axis, the attenuator further comprising: a first motor for causing rotation of the first spinner; and a second motor for causing rotation of the second spinner. a first motor for causing rotation of the first spinner; and a second motor for causing rotation of the second spinner.