Phugoid Damping Control

A novel phugoid damping control design methodology is developed, based on the use of wind axes and a point-mass aircraft model. The state variables are air speed, flight-path angle, and heading angle; the control variables are thrust setting, angle of attack, bank angle, and sideslip angle; and the command signals are air speed, flight-path angle, and heading angle or heading rate. All of the variables and parameters are nondimensionalized. A multivariable set point controller is developed that consists of the following: First, it consists of a trim calculation-based nonlinear feedforward control computer; thus, given a commanded new trim state (air speed, flight-path angle, and yaw rate), the required trim thrust setting and trim angle of attack, bank angle, and sideslip angle inputs are determined. Second, the controller consists of a small signal linear feedback regulator. The equations of motion linearized about the trim condition of wings level and constant altitude flight, which simplify the dynamics to allow separation between the lateral and longitudinal control channels, are used, and a small-signal linear multivaribale regulator is designed. The linear compensator also entails integral action. Thus, the controller consists of a strongly nonlinear feedforward module and a linear small-signal compensator. The novel proposed multivariable and nonlinear set point controller encompasses full three-axes autopilot functions. Moreover, this controller is used as a tracking controller, also known as a phugoid damping controller, provided that the bandwidth of the command signal is substantially less than the bandwidth of the closed-loop flight control system. The phugoid damping controller's performance is examined in extensive simulations, and its wide operational envelope is demonstrated.