This paper focuses on the development of a wind gust load alleviation control system for implementation in very flexible aircraft. The gust load alleviation system is designed using Linear Quadratic Gaussian (LQG) control techniques, and it is based on a nonlinear model of the coupled rigid-body and elastic modes of a very flexible aircraft. The nonlinear model contains the dynamics of the aircraft body reference frame, elastic strains, strain rates and unsteady aerodynamic flow states. The nonlinear model is linearized at a typical operating point corresponding to steady straight level flight conditions. Using model order reduction techniques, a lower order control-oriented model for the longitudinal dynamics of the very flexible aircraft is obtained. Assuming that the gust field is stochastic, the aircraft model is augmented with the disturbance model that matches the experimentally observed von Karman and Dryden power spectral density characteristics. A LQG controller is then designed to reduce the structural deflections, as the aircraft responds to the gust. Additionally, a command tracking control system is presented for longitudinal flight, which tracks a pitch angle command in the presence of a gust disturbance. It is demonstrated that the hard limits on the structural deflections while responding to the pitch angle command can be enforced using reference governor techniques.

This paper considers control of a very flexible aircraft in the presence of gust disturbances. Longitudinal trajectory tracking is performed using a hierarchical control scheme with either a PID or a sliding mode outer loop controller and a dynamic inversion inner loop controller. A Linear Quadratic Gaussian controller based on a reduced order linear model of the system is used to track lateral commands. The closed loop responses are demonstrated in fully nonlinear simulations with gust disturbances. Finally, we demonstrate a coordinated control of the ailerons to reduce wing curvature excursions from trim values.

This paper studies the effect of varying structural stiffness parameters on the gust response of a very flexible aircraft (VFA). Twelve different aircraft models, as well as the baseline model, are subjected to a temporally and spatially distributed gust of varying durations. The open loop response of the models is examined as a function of different natural frequencies and frequency ratios. Linear models are extracted from the nonlinear data using system identification. These linear models are then examined to determine their stability and controllability properties. A Linear Quadratic Gaussian (LQG) controller is used to determine the closed loop response of the models to a pitch step command in the presence of gust. Finally, the models are given a 0° pitch command in order to examine the ability of the LQG controller to maintain level flight while encountering gust.

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