| A methodology for designing helicopter active rotor control algorithms has been developed. A rotor may be regarded as an actuator whose outputs are the three components of thrust and whose inputs are collective, longitudinal cyclic, and lateral cyclic blade pitch. Active control can make the output response faster and more precise, eliminate cross-coupling, attenuate unwanted responses to gusts, and suppress vibration.;Feedback control logic is used to improve the rotor command response, by eliminating cross-coupling and attenuating rotor gust response. The helicopter and rotor have numerous structural modes that are at a low enough frequency that they might interact with the controller. The design of feedback control for gust attenuation is challenging since the multivariable controller must provide substantial disturbance attenuation while not destabilizing any structural modes. Feedback control was designed using linear, quadratic synthesis techniques using integral of flapping error weighting in the performance index. The rotor response to a sudden gust was attenuated by a factor of eight within two revolutions.;The dynamics of a rotor are periodically time-varying in forward flight. The helicopter active rotor control logic was designed based on both periodic and time-invariant models of the rotor dynamics, in order to determine which model is most appropriate. The periodic model is more accurate, but the time-invariant model produces simpler control logic. For gust alleviation, the simpler control logic based on the time-invariant model performed well, and therefore, there is little motivation for using the more complicated periodic models. However, modem helicopters also require vibration suppression. Helicopter rotor vibration is essentially a phenomenon of the periodically time-varying nature of the rotor dynamics (and can be represented by a linear periodic time-varying model). A periodic controller was designed that simultaneously provides gust alleviation and vibration suppression, based on the periodic model.;The active control concept investigated here consists of sensors that measure the angles of rotation of the rotor flapping hinges of a fully articulated rotor, a computer that implements the control logic, and servo actuators that move the swashplate to control blade pitch. This dissertation describes a methodology for designing the control logic. |
