Abstract: 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 .phi.3 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 .phi.3 to be that phase angle of the set of N periodic phase angles: .phi.1+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, .phi.1, lying between 0 and 360/N degrees, which is closest to the second phase angle, .phi.2, characteristic of minimum cabin vibration.

Abstract: The fuselage (cabin) (15) of a propeller (45) driven aircraft (10) is isolated from vibration associated with the wake (46) of the propeller by vibration isolators (50, 55 and 110) in the wing and tail surfaces of the aircraft.

Abstract: A prop-fan of the type having a high solidity factor (1 or greater) near the root fairing to a lower solidity factor (less than 1) near the tip and operable over a critical Mach No. range is designed for sound suppression by contouring the tip so that its sweep and sweep distribution of the leading and trailing edge bears a judicious relationship with the Mach surface. This feature is obtainable by designing the planform from a prescribed linearized or non-linearized acoustic theory and tailoring in the sweep so that the leading and trailing edges fall behind the Mach surface.

Abstract: A prop-fan of the type having a high solidity factor (1 or greater) near the root fairing to a lower solidity factor (less than 1) near the tip and operable over a critical Mach No. range is designed for sound suppression by contouring the tip so that its sweep and sweep distribution of the leading and trailing edge bears a judicious relationship with the Mach surface. This feature is obtainable by designing the planform from a prescribed linearized or non-linearized acoustic theory and tailoring in the sweep so that the leading and trailing edges fall behind the Mach surface.