Editing Jet engine (section)

==== Turbofan ====
{{Main article|Turbofan}}
[[File:Turbofan operation lbp.svg|thumb|right|Schematic diagram illustrating the operation of a low-bypass turbofan engine.]]
[[Turbofan]]s differ from turbojets in that they have an additional fan at the front of the engine, which accelerates air in a duct bypassing the core gas turbine engine. Turbofans are the dominant engine type for medium and long-range [[airliner]]s.

Turbofans are usually more efficient than turbojets at subsonic speeds, but at high speeds their large frontal area generates more [[Aerodynamic drag|drag]].<ref>Mattingly, pp. 9–11</ref> Therefore, in supersonic flight, and in military and other aircraft where other considerations have a higher priority than fuel efficiency, fans tend to be smaller or absent.

Because of these distinctions, turbofan engine designs are often categorized as [[Low-bypass turbofan|low-bypass]] or [[High-bypass turbofan|high-bypass]], depending upon the amount of air which bypasses the core of the engine.  Low-bypass turbofans have a [[bypass ratio]] of around 2:1 or less.