reheat is relatively low. By definition, both the dry and reheat thrust levels are good. The opposite is true for a low specific thrust engine; i.e., poor reheat SFC, good dry and throttled SFC, good reheat thrust boost and, by definition, low dry and reheated thrust. A high specific thrust engine would favour an aircraft requiring good duration in reheated combat, but it would be penalised on the range available in dry power. On the other hand, a low specific thrust engine, would favour an aircraft with the need for long range in dry power, but compromise the time spent in reheated combat. Thus engine designers often have to make a compromise on engine specific thrust. However, the ideal combat VCE would have the high reheat thrust/good reheat SFC associated with a high specific thrust engine, but would have the low SFC of a low specific thrust engine in dry power and throttled back. Devising such an engine is difficult. General Electric developed a variable cycle Engine, known as the GE37 or General Electric YF120, for the YF-22/YF-23 fighter aircraft competition, in the late 1980s. GE used a double bypass/hybrid fan arrangement, but to date has never disclosed precisely how they exploited the concept. Although the YF120 was a good (possibly better) engine in the fly-off, the USAF erred on the side of caution and selected the more conventional Pratt & Whitney F119 as the powerplant for the production Lockheed Martin F-22 Raptor. References Mechanics Jet engines