Robust Aeroservoelastic Design with Structural Variations and Modeling Uncertainties

Abstract

An aeroservoelastic analysis procedure has been integrated with structural optimization and robust-control design tools. The multidisciplinary analysis and design process can address structural constraints, performance, and robust aeroservoelastic stability requirements simultaneously. The design process is expanded to account for structural variations and modeling uncertainties utilizing a reduced-order state-space model of the aeroelastic plant that is advantageous for efficient low-order controller design. Reduced-order modeling introduces unstructured modeling errors. Structural mass variations, such as those associated with a wide range of changeable external stores of a fighter aircraft, are also interpreted as model uncertainties. The models are expressed in a form compatible with standard robust control design procedures such as the μ synthesis and analysis technique incorporated in this study. The robust control system can then be included in an optimization process where more elaborate aeroelastic models are used for tuning selected structural variables and control gains for minimizing specific design objectives under stability, performance, and structural integrity requirements. To provide enhanced physical insight, the μ analysis procedure is supplemented by a technique for computing stability boundaries in multidimensional parametric uncertainty spaces that is based on the classical single-input/single-output gain-margin approach. The integrated design procedure is demonstrated with a realistic model of a fighter aircraft with four wing control surfaces and a wing-tip missile with variable inertial properties.