A gas turbine engine comprises a core engine, a fan, a bypass duct and a clutch. The fan is driven by the core engine. The bypass duct is configured to receive airflow from the fan. The clutch links the core engine and the fan. The core comprises a reverse-flow, two-spool gas generator in one embodiment. In another embodiment, the fan is driven by a free turbine aerodynamically powered by the core engine. In one embodiment, the clutch includes reverse gearing to reverse rotational output of the fan. In one embodiment, the clutch and reverse gearing are implemented in an epicyclic gear system.