The transient performance of the selective bleed variable cycle engine (VCE) has been optimized during the transition from subsonic to supersonic mode. The selective bleed VCE concept has been developed with a short take-off vertical landing (STOVL) aircraft in mind and the engine is characterized by its twin mode VCE feature. The transition optimization is constrained by the requirement of maintaining thrust and compressor surge margins. The engine variable geometry component schedules and the fuel flow are used as optimization variables. A differential algebraic formulation of an inter-component volume model is used to model the transient behavior of the engine. Sequential quadratic programming (SQP) is applied to the nonlinear transient engine model directly, in order to solve the multivariable control problem. It is predicted that the mode switch can be carried out safely without violating the constraints and that the time required is limited by the actuator time of the hydraulic system.
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