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 of 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; and updating the feedback control gain each time a true transfer function is newly identified; wherein the continuously identifying of the transfer function reference model with the least-squares routine occurs in a background process without interruption of the determining of 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; wherein the closed loop includes a gain schedule database, the gain schedule database being available for providing data to the transfer function reference model during times of rapid transfer function changes, and wherein the least squares routine is configured to identify the transfer function reference model during times of slow changes to the true transfer function without needing information from the gain schedule database.