Criteria for the assessment of the engine efficiency of the multi-purpose aircraft missions

The problem of design parameters selection of the turbine engine is the most important task at the preliminary design stage of the multi-purpose aircraft. A special feature of the multi-purpose aircraft mission is a sudden (even pulse) weight change, especially its decrease as a result of discharge of cargo bombing or rockets due to the ammunition consumption during air combat manoeuvring. In this article the attempt to use economic and mass criteria to assess the impact of the type of air missions on the choice of the design parameters of the engine was done. As the design, parameters there were selected the following measures: compression ratio, the turbine temperature and the bypass ratio. A mathematical model of the engine – aircraft – air task system was built (taking into account the flight conditions, the mission elements – the subsonic and supersonic flight, flight time, thermo-gas-dynamic and mass model of the engine). The model enables to conduct the simulation research of the complex flight missions and their assessment on the basis of the constructed criteria. The model includes a parametric description of physical processes in the turbofan engine, thereby allowing a direct assessment of the impact of the selection of engine parameters on the effectiveness of the mission. The paper presents the results of calculations according to the classical criteria (e.g. kilometre fuel consumption, specific fuel consumption of the engine). New criteria for evaluation were presented; they are the energy efficiency of complex mission of an aircraft and the relative total and specific fuel consumption. The values of circuit parameters that need to be taken as design constraints for the engine to allow the implementation of the aviation missions were determined. The results are shown in an illustrative way on the number of graphs.