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Abstract: The cabin area of civil aircraft with multi-turbofan engines is vulnerable to beat noise during cruise flight. In order to find the method for restraining the beating noise, the beating noise model is established by using the pipe acoustic theory. It is clear that the beating noise mainly comes from the simple tone and harmonics of fan blade passing frequency. Applying the principle of linear superposition of sound wave, the mechanism of beating noise for double-engine/four-engine aircraft is analyzed, and the method for restraining beat noise is to make the physical speed of all engines consistent. During studying the beating noise for four-engine aircraft, the formulas for calculating the interference of simple tone wave with different amplitudes and similar frequencies are derived, which provide a reference for restraining the beating noise of three-engine aircraft and other multiple-engine aircraft. Meanwhile, In order to promote the engineering application of this technology, the method of restraining beating noise by thrust management function of Boeing 787 aircraft is studied. The control law of restraining beating noise is designed. The upper and lower limits of beating noise frequency modulation are analyzed, and the corresponding recommended values are given. When aircraft system provides the N1 synchronization correction to engine electronic controller (EEC), it should compare the target speed for engine control. And EEC control engine should use the target speed which has been added with the N1 synchronization correction.
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