Impacts of Structural Dynamics on Engine Inlet Flow Characteristics

Mixed compression inlets of the type used for supersonic air breathing engines, such as for the SR-71 and the supersonic transport aircraft, perform efficiently at speeds of around Mach 2.0 to 2.5. These inlets are highly susceptible to unstart when operating in a fuel efficient configuration. An unstart margin allows perturbations in mass flow and incoming flow incidence angle, which result from combinations of many contributors, which may include: gust, engine misalignment, control system tolerance, sidewash and upwash due to maneuver, and structural flexibility effects. This paper develops a methodology by which the last two effects may be analyzed to determine their contribution to changes in incoming flow incidence angle.