Power Dense Gas Turbine APUs

Abstract

Future high performance aircraft will require more compact, lighter weight, and self-sufficient secondary power equipment capable of faster starting and delivering high specific powers over wider operating envelopes of inlet temperatures and altitudes. Meeting these requirements may not be entirely compatible with improving thermal efficiency, particularly for the small air-breathing gas turbine since optimum cycle conditions differ for maximum specific power and specific fuel consumption. Further conflict lies in the necessity to provide faster start times with a limited capacity of stored on-board start energy, because compressor and turbine inertias must be minimized although compressor and turbine airflowswallowing capacity must be maximized. This paper discusses the numerous design disciplines which constrain power density for small gas turbine auxiliary power units. Several potentially profitable development avenues are suggested for continuing the improvement of aircraft system performance.