Method for reducing aircraft cabin noise and vibration

The rotation of N-bladed propellers of a multi-engine aircraft is controlled by phase angle synchronizer 30 such that a predetermined phase angle offset φ3 is maintained between the blades of a first propeller 10 and the blades of a second propeller 20, at which offset cabin noise is reduced to a minimum and cabin vibration to a near minimum. The controller 40 determines the optimum phase angle offset φ3 to be that phase angle of the set of N periodic phase angles: φ1+K(360/N), where K ranges in integer steps from 0 to N-1, each characteristic of minimum cabin noise generation, beginning with the minimum first phase angle, φ1, lying between 0 and 360/N degrees, which is closest to the second phase angle, φ2, characteristic of minimum cabin vibration.