Hybrid aircraft power plant and method of operation

A method of operating a hybrid aircraft power plant having a thermal engine coupled to a propeller via a clutch, a first lubricant pump coupled to the thermal engine, an electric motor coupled to the propeller via a geartrain, a propeller control unit (PCU) coupled to the geartrain, and a second lubricant pump coupled to the electric motor, the method comprising:

• operating the hybrid aircraft power plant in a first mode of operation in which the clutch is in an engaged configuration, including operating the thermal engine to drive the propeller via the clutch and to drive the first lubricant pump and the second lubricant pump to circulate lubricant to the geartrain and to the PCU via a lubricant circuit, the first lubricant pump and the second lubricant pump both contributing to a total lubricant pressure in the lubricant circuit, the total lubricant pressure being too high for the PCU;
• regulating the total lubricant pressure using a pressure regulation valve upstream of the PCU, including recirculating a portion of the lubricant upstream of the PCU, thereby limiting a lubricant pressure at the PCU and protecting the PCU from excessive pressure;
• changing a configuration of the clutch between the engaged configuration and a disengaged configuration, the thermal engine being decoupled from the propeller when the clutch is in the disengaged configuration;
• and
• operating the hybrid aircraft power plant in a second mode of operation in which the clutch is in the disengaged configuration, including operating the electric motor to drive the propeller and to drive the second lubricant pump to circulate the lubricant to the geartrain and to the PCU.