Commercial gas turbine auxiliary power unit (APU) requirements are in many respects more demanding than those for propulsion engines of a similar power level. The successful modern APU design must provide high reliability and durability in a flight weight package which also satisfies diverse and often conflicting performance requirements. The preliminary design phase represents the first crucial step towards meeting these objectives. This paper examines how the primary APU requirements influence turbomachinery configuration selection, and then flow down through the preliminary design process into individual APU component and sub-system design criteria, using a load compressor APU example.
