The handling of a variable cycle engine: The selective bleed turbofan

Abstract

The selective bleed turbofan is a two shaft, three compressor, variable cycle aircraft engine. At subsonic flight speeds it operates as a medium bypass turbofan. It becomes a low bypass turbofan when flying faster and is capable of supersonic cruise in the dry mode. The aim of this paper is to indicate the limits of operation of this power plant and to suggest control schemes that will allow satisfactory handling throughout the flight envelope. The performance benefits of the engine have been described in previous publications. Here its limits of operation are shown for two critical conditions, both at an altitude of 11km. The resulting scheduling requirements of the appropriate engine control variables are indicated. These are the low pressure compressor variable stators, the nozzle areas and the fuel flow. These parameters have to be controlled independently by a sophisticated system. The control strategies simulated indicate satisfactory engine handling over a wide flight envelope.