Highbypass

High-bypass refers to turbofan engines in which a large portion of the incoming air bypasses the engine core and contributes to thrust mainly through the fan. Bypass ratio, the ratio of air bypassing the core to air passing through the core, is the standard measure. High-bypass engines typically have bypass ratios well above those of early turbojets, and modern civil engines commonly range from about 6 to 12 or more.

In practice, high-bypass turbofans achieve most of their thrust from the large fan, while a smaller core provides the energy to drive the fan and power the aircraft systems. This configuration yields higher propulsive efficiency at subsonic cruise speeds, and quieter operation with lower specific fuel consumption compared with turbojets or low-bypass designs. Trade-offs include a larger, heavier nacelle and airframe footprint, and somewhat reduced performance for very high-thrust, high-speed segments where compactness and weight are critical.

History and use: the move from turbojets to high-bypass turbofans began in the mid-20th century and accelerated as civil aviation demanded greater efficiency and lower noise. Today, high-bypass turbofans are standard on most commercial aircraft, from narrow-body jets to wide-bodies. Engine families commonly described as high-bypass include various designs from manufacturers such as CFM, Pratt & Whitney, GE, and Rolls-Royce, some incorporating geared fan architectures and advanced materials to push bypass ratios and efficiency higher while meeting environmental and noise regulations.