Abstract: A method of determining a sound nuisance level outside an aircraft, wherein an aircraft is fitted with a plurality of external microphones, then during a flight of the aircraft, sound levels are measured using on-board microphones and at least two components are measured of the speed of the aircraft relative to air, and thereafter the kurtosis of samples of the sound level measurements is calculated and a model is determined of variations in a sound nuisance level as function of the air speed components, with the sound nuisance level being determined as a function of the kurtosis.

Abstract: The present invention relates to a method of minimizing the noise emitted by a ducted rail rotor anti-torque device at a frequency FE and perceived at a frequency FP, in which method the diameter D, the number of blades b, and the tangential speed U of the rotor are determined so that the perceived frequency FP is less than or equal to the bottom limit frequency FL of a predetermined one-third frequency octave centered on a frequency FC.

Abstract: An aircraft has a streamlined structure (10) pierced by an air flow duct (20) having an axis of symmetry (AX) contained in a plane of symmetry (P) perpendicular to a longitudinal axis (AL) of the aircraft, the aircraft possessing a shrouded rotor (1) having a plurality of blades (2) arranged in the air flow duct (20). The aircraft is also fitted with blower elements (40) suitable for propelling compressed air towards a first injection zone (44) opening out in a first front inject (22?) of a first lip (22) of the periphery (21) of the duct (20) and towards a second injection zone (45) opening out in a second front portion (24?) of a second lip (22) of the periphery (21) of the duct (20).

Abstract: The present invention relates to a method of minimizing the noise emitted by a ducted rail rotor anti-torque device at a frequency FE and perceived at a frequency FP, in which method the diameter D, the number of blades b, and the tangential speed U of the rotor are determined so that the perceived frequency FP is less than or equal to the bottom limit frequency FL of a predetermined one-third frequency octave centered on a frequency FC.

Abstract: An absorbent structure for reducing the propagation of soundwaves emitted by noisy devices such as rotors or motors, the structure includes a rigid partition (1), at least one porous wall (4), and separator elements (2) for placing the porous wall (4) at a determined distance from the rigid partition (1), defining cavities (3) of a height h1 between the porous wall (4) and the rigid partition (1), the height h1 being determined to obtain maximum absorption of a given frequency of the emitted soundwaves, wherein includes additional absorption elements for obtaining maximum absorption of at least one additional frequency of the emitted soundwave.

Abstract: An absorbent structure for reducing the propagation of soundwaves emitted by noisy devices such as rotors or motors, the structure includes a rigid partition (1), at least one porous wall (4), and separator elements (2) for placing the porous wall (4) at a determined distance from the rigid partition (1), defining cavities (3) of a height h1 between the porous wall (4) and the rigid partition (1), the height h1 being determined to obtain maximum absorption of a given frequency of the emitted soundwaves, wherein includes additional absorption elements for obtaining maximum absorption of at least one additional frequency of the emitted soundwave.

Abstract: An aircraft has a streamlined structure (10) pierced by an air flow duct (20) having an axis of symmetry (AX) contained in a plane of symmetry (P) perpendicular to a longitudinal axis (AL) of the aircraft, the aircraft possessing a shrouded rotor (1) having a plurality of blades (2) arranged in the air flow duct (20). The aircraft is also fitted with blower elements (40) suitable for propelling compressed air towards a first injection zone (44) opening out in a first front inject (22?) of a first lip (22) of the periphery (21) of the duct (20) and towards a second injection zone (45) opening out in a second front portion (24?) of a second lip (22) of the periphery (21) of the duct (20).

Abstract: The method includes a preliminary period in which a reference rotorcraft is used that corresponds to a rotorcraft of a particular type, with a series of noise measurements being performed on said rotorcraft (1) in flight using noise sensors (C) disposed on said reference rotorcraft, and with operating domains being determined for the reference rotorcraft in which noise is less than a maximum noise level. Thereafter, the operating point without wind and operating domains with wind are subsequently determined for a rotorcraft of the particular type on the basis of operating domains for the reference rotorcraft.

Abstract: The method includes a preliminary period in which a reference rotorcraft is used that corresponds to a rotorcraft of a particular type, with a series of noise measurements being performed on said rotorcraft (1) in flight using noise sensors (C) disposed on said reference rotorcraft, and with operating domains being determined for the reference rotorcraft in which noise is less than a maximum noise level. Thereafter, the operating point without wind and operating domains with wind are subsequently determined for a rotorcraft of the particular type on the basis of operating domains for the reference rotorcraft.

Abstract: A method of determining a sound nuisance level outside an aircraft, in which method: an aircraft is fitted with a plurality of external microphones (11, 110); then during a flight of the aircraft, sound levels are measured using on-board microphones and at least two components are measured of the speed of the aircraft relative to air; and thereafter the kurtosis of samples of the sound level measurements is calculated and a model (15, 150) is determined of variations in a sound nuisance level as function of the air speed components, with the sound nuisance level being determined as a function of the kurtosis.