Analysis of airframe/engine interactions for a STOVL aircraft with integrated flight/propulsion control

This paper presents new results from a multivariable analysis technique applied to an advanced STOVL configuration with highly interactive airframe and propulsion subsystems and uncertainty in the interactions between the subsystems. This analysis method is used to assess the effects of the dynamic cross-coupling between the airframe and engine subsystems. The analysis framework addresses two-directional dynamic crosscoupling, and also allows for cross-feeds between the subsystem controllers. The issue of stability and performance robustness is addressed, and the utility of singular value stability robustness criteria is presented. The configuration analyzed includes a thrust vectoringJthrust reversing aft nozzle, powered lift through the use of a ventral nozzle and ejectors, and Reaction Control System jets. Investigation of the open-loop dynamics indicates that significant interactions between the airframe and engine are generated as a consequence of the propulsive augmentation. A critical frequency range where instability would fust occur due to small variations in the coupling dynamics is also indicated by the analysis. A stability sensitivity analysis reveals that the interactions between the engine and the airframe's flight path response are critical with regard to stability and performance robustness.