Multi-engine system and power transfer between engines thereof

A method of operating a multi-engine system having a first engine and a second engine, the first engine having a first output shaft and a first core shaft, the second engine having a second output shaft and a second core shaft, the first output shaft and the second output shaft drivingly engaged to a common load via a reduction gearbox, the method comprising:

• receiving a power demand;
• determining that the power demand is below a power threshold;
• operating the first engine in a high-power mode;
• and
• operating the second engine in a low-power mode by rotating the second core shaft with a torque-transfer connection between the first output shaft or the first core shaft of the first engine and the second core shaft of the second engine independently of the reduction gearbox, including operating the second engine in the low-power mode with the torque-transfer connection through a coupling gearbox having a first load path and a second load path independent from the first load path, the coupling gearbox being reversible such that the first core shaft and/or the first output shaft is engageable to the second core shaft via the first load path, the second core shaft and/or the second output shaft is engageable to the first core shaft via the second load path, and/or by rotating the second core shaft with an electrical connection between a generator driven by the first engine and an electric motor driving the second core shaft.

A multi-engine system for an aircraft, comprising:

• a first engine having a first output shaft, a first core shaft, and a first electric machine operable as a generator, the first electric machine drivingly engaged by the first output shaft or the first core shaft;
• a second engine having a second output shaft, a second core shaft, and a second electric machine operable as an electric motor, the second electric machine drivingly engaged to the second core shaft;
• a reduction gearbox drivingly engaged by the first output shaft and by the second output shaft for driving a common load;
• and
• means for driving the second core shaft with the first core shaft or with the first output shaft independently of the reduction gearbox, the means including a coupling gearbox having a first load path and a second load path independent from the first load path, the coupling gearbox being reversible such that the first core shaft and/or the first output shaft is engageable to the second core shaft via the first load path, the second core shaft and/or the second output shaft is engageable to the first core shaft via the second load path.