Powerplant and a method of driving a mechanical system via said powerplant

A rotorcraft comprising:

• a engine having an outlet shaft, the engine is configured to be started by rotating the outlet shaft using a starter, wherein the engine has a first torque level associated with an idling speed and a second torque level associated with a maximum torque output of the engine;
• a mechanical system having a drive shaft, a gearbox and a rotor;
• a link member mechanically connecting the outlet shaft of the engine to the drive shaft, the link member comprising a clutch and a declutchable mechanical freewheel, wherein the freewheel has a disconnected mode where the speed of a driving portion of the freewheel is independent of a driven portion of the freewheel and a freewheel mode where the driving portion of the freewheel propels the driven portion when the freewheel is clutched and a speed of rotation of the driving portion is greater than a speed of rotation of the driven portion, wherein the driving portion freewheels in the freewheel mode when the freewheel is clutched and a speed of rotation of the driving portion is less than a speed of rotation of the driven portion to enable autorotation of the rotor, wherein the clutch has an operating torque threshold between the first and second torque levels of the engine;
• and
• a controller configured to (i) operate the rotorcraft in a starting stage to start the engine after declutching said clutch and declutching said declutchable freewheel so as to disconnect said outlet shaft from said drive shaft such that the main rotor is unpowered, (ii) in response to the engine torque being greater than the first torque level and less than the operating torque threshold, operate the rotorcraft in an intermediate stage by clutching said clutch and keeping said declutchable freewheel declutched to connect said outlet shaft to said drive shaft solely via said clutch to rotate the main rotor using the engine and prevent autorotation of the main rotor, and (iii) in response to the engine torque being greater than the operating torque threshold, operate the rotorcraft in a stabilized stage by declutching said clutch and clutching said declutchable freewheel so as to connect said outlet shaft to said drive shaft via said declutchable freewheel to rotate the main rotor using the engine.

A method of controlling a rotorcraft having an engine with an outlet shaft, a mechanical system having a drive shaft, a gearbox and a rotor, and a link member mechanically connecting the outlet shaft of the engine to the drive shaft, the method comprising:

• a first step of declutching a clutch of the link member and declutching a declutchable freewheel of the link member to disconnect the outlet shaft from the drive shaft when the engine speed is less than a minimum idling speed to start the engine with the mechanical system undriven and the rotor unpowered;
• a second step of engaging the clutch and declutching the declutchable freewheel such that the drive shaft is solely driven by the outlet shaft via the clutch when the engine speed is at least the minimum idling speed and the engine torque is less than an optimum torque of the clutch to rotate the rotor;
• and
• a third step of declutching the clutch and clutching the declutchable freewheel such that the drive shaft is solely driven by the outlet shaft via the declutchable freewheel when the engine speed is at least the minimum idling speed and the engine torque is greater than an optimum torque of the clutch to rotate the rotor and enable autorotation of the rotor;
• wherein the first step, second step and third step, in that order, are performed to start the engine and operate the rotorcraft;
• and
• wherein the third step, second step, and first step, in that order, are performed to switch off the engine.