What are adaptive cycle engines and how do they improve performance?

Adaptive cycle engines vary their bypass ratio and operating mode for different mission segments. Key technologies: Variable bypass ducts (divert fan flow between bypass and core), Third stream for additional bypass flow, and Variable area fan nozzle. Benefits: High BPR for efficient cruise, Low BPR for supersonic dash, Improved specific thrust without afterburner, 25%+ fuel savings and 30%+ range increase. GE XA100 and P&W XA101 are developing for NGAD/F-35. Challenges: Complex actuated variable geometry, Control system integration, Weight management, and Reliability of moving components. The three-stream design adds complexity but enables unprecedented mission flexibility for next-generation fighters.