Hypersonic aircraft and their propulsion systems are exposed to severe aerothermal environments which require a system approach to create innovative designs able to respond to the environmental challenges. This paper describes a preliminary study used to scope the technical challenges and identify the necessary development plans for the aircraft propulsion system. Presented here are the interim results of this scoping study for a turboramjet conceptual design conducted by UTC, Pratt & Whitney. This study is the first of four phases in a 6 year program on Hypersonic Transport Ramjet (HYTRAM) system R&D sponsored by NEDO, as an integral part of the Japanese National Project on “Super/Hypersonic Transport Propulsion Systems (HYPR)”.

Various turboramjet configurations were evaluated and two attractive candidates, a co-axial and a split flow configuration, were selected. Performance analyses were conducted for these two by incorporating the subsystem performance data provided by the Japanese companies (IHI on the turbofan and MHI on the inlet and nozzle). Pre–conceptual mechanical design sketches were prepared to provide some elementary definitions of the co–axial and the split flow turboramjet to assist in selecting a baseline configuration. Candidate materials including composites for the major subsystems were selected, using metals for near–term applications and including ceramics for far–term applications. Using the above results from this scoping study, the co–axial configuration was selected as the baseline because of its higher Figure of Merit estimated from its performance, mechanical design characteristics and the technical challenge it presented.

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