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The exoskeletal engine (ESE) is a concept in turbomachinery design. Current gas turbine engines have central rotating shafts and discs and are constructed mostly from heavy metals. They require lubricated bearings and need extensive cooling for hot components. They are also subject to severe imbalance (or vibrations) that could wipe out the whole rotor stage, are prone to high- and low-cycle fatigue, and subject to catastrophic failure due to disc bursts from high tensile loads, consequently requiring heavy containment devices.〔Chamis, Christos C. and Isaiah M. Blankson.("Exo-Skeletal Engine – Novel Engine Concept". NASA, 2006. ) Retrieved: 31 August 2009〕 To address these limitations, the ESE concept turns the conventional configuration inside-out and utilizes a drum-type rotor design for the turbomachinery in which the rotor blades are attached to the inside of a rotating drum instead of radially outwards from a shaft and discs. Multiple drum rotors could be used in a multi-spool design. ==Design== Fundamentally, the ESE drum-rotor configuration typically consists of four concentric open-ended drums or shells: *an outer shell (engine casing) that both supports the bearings for the drum-rotor shell and constrains it, *the drum-rotor shell that rotates within the bearings and carries the compressor- and turbine blades, *a static stator shell that supports the guide vanes, *a hollow static inner shell that provides a flow path through the centre of the engine.〔 In the ESE design, the rotating blades are primarily in radial compression as opposed to radial tension, which means that materials that do not possess high-tensile strength, such as ceramic materials, can be used for their construction. Ceramics behave well in compressive loading situations where brittle fracture is minimized, and would provide greater operating efficiency through higher operating temperatures and lighter engine weight when compared to the metal alloys that typically are used in turbomachinery components. The ESE design and the use of composite materials could also reduce the part count, reduce or eliminate cooling, and result in increased component life.〔Roche, Joseph M., Donald T. Palac, James E. Hunter, David E. Myers, and Christopher A. Snyder. ("Investigation of Exoskeletal Engine Propulsion System Concept". NASA, 2005. ) Retrieved: 31 August 2009〕 The use of ceramics would also be a beneficial feature for hypersonic propulsion systems, where high stagnation temperatures can exceed the limits of traditional turbomachinery materials. The cavity within the inner shell could be exploited in several different ways. In subsonic applications, venting the centre cavity with a free-stream flow could potentially contribute to a large noise reduction; while in supersonic-hypersonic applications it might be used to house a ramjet or scramjet (or other devices such as a pulse-detonation engine) as part of a turbine-based combined-cycle engine. Such an arrangement could reduce the overall length of the propulsion system and thereby reduce weight and drag significantly.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Exoskeletal engine」の詳細全文を読む スポンサード リンク
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