Engine Design Requirements for Supersonic Business Jets

Authors

Timo Schlette - Institute of Aircraft Propulsion Systems, University of Stuttgart
Stephan Staudacher - Institute of Aircraft Propulsion Systems, University of Stuttgart

Abstract

With a double-digit billion US $ market volume, business jets represent a relevant market segment in aviation industry. Their size and range have been increased continuously in incremental steps with cruising speeds barely exceeding those of today's airliners. Consequently, a further increase in range raises customer value by making more specific routes accessible. In contrast, a currently untapped market might be opened by a significant increase in flight speed, which can be served by supersonic business jets. These aircraft are and have been the subject of several research projects and commercial developments aiming for a first flight within this decade. A currently quite advanced design of a supersonic business jet has been examined using an aircraft pre-design model. It is assumed that this aircraft serves a supersonic as well as a subsonic flight mission, which show significant and distinct differences. These result in differing relations of altitude flight and take-off thrust requirements. Engine cycle design is carried out at subsonic maximum climb conditions. Supersonic maximum climb conditions lead to significantly lower non-dimensional values due to a pronounced ram effect of the inlet. Maximum dimensional values of shaft speed and annulus temperatures are observed at supersonic maximum climb conditions. In contrast to subsonic engines, it is those conditions which drive the material choice, dimension the cooling air system and limit the achievable overall pressure ratio of the engine. Various combinations of low- and high-pressure compressor pressure ratios are possible considering these limitations. Combinations are evaluated with regard to the decision point between single-stage and multi-stage fan, the possibility of efficient jet mixing and the selection of inlet and nozzle for the engine.As a result, engine design is closely coupled to the aircraft design and cannot be considered in isolation. Based on the upstream flow conditions, which are influenced by the shock system of the aircraft, an inlet system design with external compression is needed. In the occurring range of nozzle pressure ratios, jet mixing increases efficiency and a variable nozzle is necessary. Since the engine does not require afterburning, the choice is a plug nozzle design. For take-off, the engine is derated to limit jet velocity and hence maintain a necessary jet noise level. Take-off distances of modern business jets can still be achieved.