US Patent 11104430 Multimode powertrains for multi engine rotorcraft

A powertrain for a rotorcraft includes first and second engines and a transmission system that includes a main rotor gearbox, a first freewheeling unit coupling the first engine to the main rotor gearbox and a second freewheeling unit coupling the second engine to the main rotor gearbox. The first freewheeling unit has a driving configuration and a bypass configuration. In a preflight configuration of the rotorcraft, the first engine provides power to at least one auxiliary component with the first freewheeling unit in the bypass configuration while the second engine provides power to the main rotor. In a flight configuration of the rotorcraft, the first engine provides power to the main rotor with the first freewheeling unit in the driving configuration while the second engine also provides power to the main rotor.