Rotorcraft Smoothing via Linear Time Periodic Methods

Helicopter flight, relying on rotary motion of a complex mechanical system, is predisposed to vibration. While the helicopter has many sources of vibrations the main rotor system generates by far the largest magnitude vibrations, and can render the vehicle inoperable if left unaddressed. Thus, proper maintenance to reduce vibrations is essential to the safe operation of any helicopter. This maintenance, however, is costly and time consuming. Improving the maintenance procedure for balancing the main rotor system has been an area of active interest since the inception of the helicopter. However, the state of the art in rotor balancing still requires several iterations of rotor adjustments, each necessitating a separate test flight and then time consuming maintenance, to reduce the vibrational level to an acceptable amount. This research provides the basis for an improved rotor vibrational reduction methodology that significantly reduces the number of adjustment iterations required to reduce main rotor vibrations. To address these issues, it was the intent of this research to develop an on-line, linear time periodic rotor vibration controller. The Cramer-Rao bound was developed for a linear time periodic system in order to identify the quality of identified system parameters that are used in system models for controller development.