1966-02-01

Aerodynamic Installation of High-Bypass-Ratio Fan Engines 660732

The nacelle design for high bypass ratio turbofan engines installed on high subsonic aircraft is treated in this paper. The high bypass ratio turbofan, with its greater airflow per pound of thrust, presents different problems from those of existing turbojets and low bypass ratio turbofans. For example, there is some bypass ratio, depending upon aircraft payload range and engine geometry, above which the “ short duct” has advantage. The determination of this bypass ratio for a typical case is presented. For a bypass ratio 8 turbofan, the short duct nacelle has 3–4% better airplane direct operating costs than the long duct. With the short duct established as the preferred geometry for high bypass ratio turbofans, the problems of the air inlet, inlet cowl, fan nozzle, fan afterbody, and gas generator afterbody are discussed. Also, the thrust reverser, which affects the nacelle geometry, has been considered. It has been shown that when the bypass ratio is greater than about 4, the gas generator reverser does not reduce landing distances enough to justify its weight and complication.

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