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Helicopter noise reduction is a topic of research into designing helicopters which can be operated more quietly, reducing the public-relations problems with night-flying or expanding an airport. In addition, it is useful for military applications in which stealth is required: long-range propagation of helicopter noise can alert an enemy to an incoming helicopter in time to re-orient defenses (see acoustic signature). == Sources of helicopter noise == * Rotor noise * Engine noise * Transmission noise The noise from a rotor can be divided into several distinct sources, which will be described as follows: 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「helicopter noise reduction」の詳細全文を読む スポンサード リンク
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