1. A method for controlling vibration in a rotorcraft, comprising: measuring a fuselage vibration in the rotorcraft with a sensor, the fuselage vibration originating from a propulsion system of the rotorcraft; determining an actuator command signal with an adaptive reference model algorithm, wherein the determining the actuator command signal with the adaptive reference model algorithm comprises one or more iterations of: continuously identifying a transfer function reference model with a least-squares routine, the transfer function reference model representing a predicted relationship between the sensor and the vibration control actuator; computing a feedback control gain from the transfer function reference model in a closed loop; updating the feedback control gain each time a true transfer function is newly identified; and wherein the continuously identifying the transfer function reference model with the least-squares routine occurs in a background process without interruption of the determining the actuator command signal; and commanding a vibration control actuator with the actuator command signal so as to impart a cancelling vibration in a manner that at least partially cancels the vibrations originating from the propulsion system.