Abstract: A sound absorber comprising a base body and a tongue (24). The base body has a bottom plate, a wall enclosing the bottom plate and an opening enabling the entry of air into the base body. The tongue has a fixed end, a free end and a central portion disposed between the fixed and the free end. The free end of the tongue is spaced from the wall and the bottom plate, and the central portion of the tongue is disposed to extend at least partially straight along a width direction. Furthermore, a sound absorber assembly can include at least two sound absorbers, and an engine, in particular, for an aircraft, comprising such a sound absorber and/or such a sound absorber assembly.

Abstract: A rotorcraft with at least one main rotor 1a and at least one counter-torque rotor, comprising: at least one duct-type portion provided with a shroud that defines at least one transverse duct, the at least one counter-torque rotor comprising a plurality of counter-torque rotor blades and being rotatably arranged within the at least one transverse duct, and a drive shaft fairing that is fixedly supported within the at least one transverse duct and that rotatably supports the at least one counter-torque rotor, the drive shaft fairing comprising a leading edge facing the at least one counter-torque rotor, the leading edge being at least partially equipped with associated acoustical damping means.

Abstract: A sound absorber comprising a base body and a tongue (24). The base body has a bottom plate, a wall enclosing the bottom plate and an opening enabling the entry of air into the base body. The tongue has a fixed end, a free end and a central portion disposed between the fixed and the free end. The free end of the tongue is spaced from the wall and the bottom plate, and the central portion of the tongue is disposed to extend at least partially straight along a width direction. Furthermore, a sound absorber assembly can include at least two sound absorbers, and an engine, in particular, for an aircraft, comprising such a sound absorber and/or such a sound absorber assembly.

Abstract: A method for avoiding a collision of a rotating rotor blade of a rotary-wing aircraft with a blade vortex, and a device for executing the method. An aerodynamic parameter of the rotor blade of a rotary-wing aircraft is controlled, (for example, variation of the angle of incidence of the blade or profile variation of the blade), using a signal processing device that includes at least one open-loop and/or closed-loop control device, in such a way that a collision of the rotor blade with blade vortices becomes avoidable. The frequency content from the signal of the sound-pressure sensors is rapidly and precisely found. The harmonics are progressively adapted. A lesser calculation requirement per step and increase accuracy, as compared with an FFT analysis, is provided.

Abstract: An acoustic absorber (10) comprises a housing or wall (11), defining an interior absorber chamber (12) connected by openings (13) to a duct (20) to reduce the sound in the duct (20). The natural frequency and impedance of the absorber (12) are variable, so that the absorber (12) can be adapted to a sound field in the duct (20) in a manner corresponding to the respective operating conditions. Such adaptation is achieved mechanically, for example, by an elastic membrane (15) for varying the volume of chamber (12), or thermally, for example, by a heating wire (14) or a wire braid (17).

Abstract: A method for avoiding a collision of a rotating rotor blade of a rotary-wing aircraft with a blade vortex, and a device for executing the method. An aerodynamic parameter of the rotor blade of a rotary-wing aircraft is controlled, (for example, variation of the angle of incidence of the blade or profile variation of the blade), using a signal processing device that includes at least one open-loop and/or closed-loop control device, in such a way that a collision of the rotor blade with blade vortices becomes avoidable. The frequency content from the signal of the sound-pressure sensors is rapidly and precisely found. The harmonics are progressively adapted. A lesser calculation requirement per step and increase accuracy, as compared with an FFT analysis, is provided.

Abstract: An acoustic absorber (10) comprises a housing or wall (11), defining an interior absorber chamber (12) connected by openings (13) to a duct (20) to reduce the sound in the duct (20). The natural frequency and impedance of the absorber (12) are variable, so that the absorber (12) can be adapted to a sound field in the duct (20) in a manner corresponding to the respective operating conditions. Such adaptation is achieved mechanically, for example, by an elastic membrane (15) for varying the volume of chamber (12), or thermally, for example, by a heating wire (14) or a wire braid (17).