OPEN ROTOR ENGINE

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In open rotor gas turbines, the fan is placed outside the nacelle and called a propeller. This propeller can be a single rotation type, known as a turboprop, or a pair of contra-rotating propellers, referred to as an open rotor or propfan. Two primary methods exist for driving large, slow tip speed propellers: using a reduction gearbox driven by a high-speed, low stage count, low pressure turbine (Allison P&W 578DX) or directly from a contra-rotating statorless multi-stage low pressure turbine (GE36).