Transition Control and Performance of the Selective Bleed Variable Cycle 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 outline the requirements and response of the engine during the transition phase from one mode of operation to the other. Thus it is follow-on work of Ref. 7. To achieve this several control devices can be employed. These are the fuel flow, the variable compressor stators, the nozzle areas and the valve areas of the bypass ducts. The preliminary analysis described in this paper indicates that all the criteria of performance are satisfied and that the transition can be carried out successfully provided the control variables are co-ordinated properly.