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

High-speed (supersonic or hypersonic) atmospheric flight vehicles are typic ally characterized by a significant degree of interaction between the highl y elastic airframe and the propulsion system. To achieve adequate stability and performance requirements, robust, integrated multivariable control law s will be required. But to apply robust control analysis or synthesis techn iques such as structured-singular-value techniques (mu) or quantitative fee dback theory, the uncertainty in the plant dynamics must be characterized i n special ways. Furthermore, certain assumptions regarding the uncertaintie s present are frequently made in the application of these techniques. The f ocus of this research is the development of uncertainty models for this cla ss of flight vehicle that are derived from the physics of the system, yet a re compatible with the cited control synthesis techniques. The potential so urces of uncertainty for this class of vehicle are discussed, and three for ms of uncertainty models are developed: real parameter, unstructured, and s tructured. We are especially interested in how the usual sources of uncerta inty manifest themselves in this context. It will be shown that for this cl ass of vehicle care is required in making the usual assumptions regarding t he uncertainty. It is also shown that the flexible degrees of freedom must be considered in the flight-control synthesis for this class of vehicle.