Editing Turbofan (section)

===Aft-fan turbofan===
One of the earliest turbofans was a derivative of the [[General Electric J79]] turbojet, known as the [[General Electric CJ805|CJ805-23]], which featured an integrated aft fan/low-pressure (LP) turbine unit located in the turbojet exhaust jetpipe. Hot gas from the turbojet turbine exhaust expanded through the LP turbine, the fan blades being a radial extension of the turbine blades. This arrangement introduces an additional gas leakage path compared to a front-fan configuration and was a problem with this engine with higher-pressure turbine gas leaking into the fan airflow.<ref>{{Cite web|url=http://www.icas.org/ICAS_ARCHIVE/ICAS2002/PAPERS/1.PDF|title=p.01.7|website=Icas.rg|access-date=1 March 2022}}</ref> An aft-fan configuration was later used for the [[General Electric GE36]] UDF (propfan) demonstrator of the early 1980s.

In 1971 a concept was put forward by the NASA Lewis Research Center for a supersonic transport engine which operated as an aft-fan turbofan at take-off and subsonic speeds and a turbojet at higher speeds. This would give the low noise and high thrust characteristics of a turbofan at take-off, together with turbofan high propulsive efficiency at subsonic flight speeds. It would have the high propulsive efficiency of a turbojet at supersonic cruise speeds.<ref>{{Cite book |last=Webber |first=Richard J. |title=VARIABLE GEOMETRY AFT-FAN FORTAKEOFFQUIETINGOR THRUST AUGMENTATION OF A TURBOJET ENGINE |publisher=Lewis Research Centre, NASA |year=1971 |location=Ohio}}</ref>