Method of reducing noise of aircraft having hybrid power plants

A method of reducing noise generated by an aircraft having a propulsion system including a first hybrid power plant and a second hybrid power plant, the first hybrid power plant including a first electrical motor and a first thermal engine, the second hybrid power plant including a second electrical motor and a second thermal engine, the method comprising:

• driving a first propulsor of the first hybrid power plant using one or more of the first electrical motor and the first thermal engine, and driving a second propulsor of the second hybrid power plant using one or more of the second electrical motor and the second thermal engine;
• receiving a signal from one or more acoustic sensors, the signal indicative of an initial combined noise signature produced by the propulsion system, the combined noise signature resulting from a first noise signature generated by the first hybrid power plant and a second noise signature generated the second hybrid power plant,
• determining, from the signal, that an initial amplitude variation of a periodically fluctuating amplitude of the initial combined noise signature is greater than an amplitude variation threshold indicative that the initial combined noise signature generates beats;
• modulating a thrust produced by the second hybrid power plant, by changing a power output of one of the second thermal engine and the second electrical motor, to produce a modulated combined noise signature having a modulated amplitude variation less than the initial amplitude variation;
• and
• compensating for a difference in thrusts generated by the first hybrid power plant and the second hybrid power plant due to the modulating of the thrust produced by the second hybrid power plant.