Uncertainty modeling for multivariable-control robustness analysis of elastic high-speed vehicles

High-speed (supersonic or hypersonic) atmospheric flight vehicles are typically characterized by a significant degree of interaction between the highly elastic airframe and the propulsion system. To achieve adequate stability and performance requirements, robust, integrated multivariable control laws will be required. But to apply robust control analysis or synthesis techniques such as structured-singular-value techniques (mu) or quantitative feedback theory, the uncertainty in the plant dynamics must be characterized in special ways. Furthermore, certain assumptions regarding the uncertainties present are frequently made in the application of these techniques. The focus of this research is the development of uncertainty models for this class of flight vehicle that are derived from the physics of the system, yet are compatible with the cited control synthesis techniques. The potential sources of uncertainty for this class of vehicle are discussed, and three forms of uncertainty models are developed: real parameter, unstructured, and structured. We are especially interested in how the usual sources of uncertainty manifest themselves in this context. It will be shown that for this class of vehicle care is required in making the usual assumptions regarding the uncertainty. It is also shown that the flexible degrees of freedom must be considered in the flight-control synthesis for this class of vehicle.