Fan clutch for convertible engine

An aircraft, comprising:

• a fuselage;
• and
• a convertible engine disposed within the fuselage and operable as a turbofan engine in a thrust mode and a turboshaft engine in a shaft power mode, the convertible engine comprising:
• an engine core comprising a low pressure turbine shaft;
• and
• a bypass fan system comprising:
• an inner fan disposed longitudinally along a length of the low pressure turbine shaft;
• an outer fan disposed at least partially concentrically around the inner fan and at least partially longitudinally overlapping the inner fan along the length of the low pressure turbine shaft;
• and
• a fan clutch disposed at least partially concentrically around the inner fan and at least partially longitudinally overlapping the inner fan along the length of the low pressure turbine shaft, the outer fan disposed at least partially concentrically around the fan clutch, and the fan clutch being disposed at least partially longitudinally overlapping the outer fan along the length of the low pressure turbine shaft;
• wherein the fan clutch is configured to selectively rotationally decouple the outer fan from the inner fan.

A method of operating an aircraft, comprising:

• providing an aircraft engine comprising:
• an engine core comprising a low pressure turbine shaft and a bypass fan system comprising an inner fan disposed longitudinally along a length of the low pressure turbine shaft, an outer fan disposed at least partially concentrically around the inner fan and at least partially longitudinally overlapping the inner fan along the length of the low pressure turbine shaft, and a fan clutch disposed at least partially concentrically around the inner fan and at least partially longitudinally overlapping the inner fan along the length of the low pressure turbine shaft, the outer fan disposed at least partially concentrically around the fan clutch, and the fan clutch being disposed at least partially longitudinally overlapping the outer fan along the length of the low pressure turbine shaft;
• operating the aircraft engine to generate bypass airflow in order to induce thrust by selectively coupling at least a portion of the bypass fan to the low pressure turbine shaft;
• selectively rotationally decoupling the outer fan from the inner fan.