Power transfer systems and methods for aircraft engines

An aircraft comprising:

• an aircraft system that operates on bleed air;
• a gas turbine engine having a high-pressure drive shaft and a low-pressure drive shaft;
• and
• a power transfer system including:
• an auxiliary turbine;
• one or more fluid lines coupled between a bleed port on the gas turbine engine, the auxiliary turbine, and the aircraft system;
• and
• a differential having an input shaft, a first output shaft, and a second output shaft, the auxiliary turbine coupled to the input shaft, the second output shaft in gear with the high-pressure drive shaft of the gas turbine engine, such that during a first mode of operation, power is transferred from the auxiliary turbine to the high-pressure drive shaft of the gas turbine engine.

A method comprising:

• disengaging a brake of an auxiliary turbine, the auxiliary turbine coupled to an input shaft of a differential, the differential including:
• the input shaft;
• a first output shaft in gear with a low-pressure drive shaft of a gas turbine engine of an aircraft engine;
• and
• a second output shaft in gear with a high-pressure drive shaft of the gas turbine engine;
• and
• operating one or more valves to direct bleed air from the gas turbine engine through the auxiliary turbine, wherein power extracted by the auxiliary turbine is transferred to the high-pressure drive shaft of the gas turbine engine.