Effects of Improved Propulsion Modelling on the Flight Dynamics of Hypersonic Vehicles

This research effort is focused on developing a control-oriented model of a generic hypersonic vehicle that includes the interactions between several integrated components. The present paper addresses the interactions between the propulsion system and the flight dynamics of the vehicle model for two different propulsion system models. The first model is a low-fidelity propulsion model that assumes the combustion process is Rayleigh flow, and the combustor is coupled with an isentropic diffuser and internal nozzle, thus ignoring the effects of internal shock waves, area variations, and real gas effects. A second, higherfidelity propulsion system model that includes several new phenomena then analyzed. This model includes a pre-combustion shock train within the isolator and its interactions with the combustor, the loss of stagnation pressure due to gas dissociation and recombination, wall heat transfer and skin friction, a fuel-air mixing submodel, and a finite-rate chemistry description of autoignition. When the new propulsion model is added, it is observed that the poles and zeros undergo a shift, with the short-period poles moving closer to the imaginary axis. The unstable transmission zeros associated with the flight path angle are also observed to move towards the imaginary axis, and take a much more pronounced shift as compared to the short-period poles. This is attributed to a reduced lift curve slope and pitch stiffness for the high fidelity propulsion system model that stems from an change in the thrust sensitivity to angle-of-attack.