A propulsion assembly includes a fan and a fan case system disposed about the fan. The fan case system includes at least one perforated portion including a plurality of holes. The propulsion assembly further includes at least one acoustic panel mounted to the exterior surface of the fan case system coincident with the at least one perforated portion. The at least one acoustic panel includes a core including a plurality of cells extending between a first side of the core and a second side of the core. The at least one acoustic panel further includes a back skin attached to the second side of the core. The first side of the core is in contact with the exterior surface of the fan case system to form a plurality of resonant cavities defined by the plurality of holes, the plurality of cells, and the back skin.

A ducted fan of an aircraft includes a rotor-side fan and a stator-side duct that surrounds the rotor-side fan radially at the outside and defines a flow channel for air flowing via the fan. The stator-side duct has an inner wall that faces toward the rotor-side fan and which is perforated at least in certain sections. The stator-side duct has an outer wall that faces away from the fan. Between the inner wall and the outer wall of the stator-side duct, there are formed cavities which, forming sound-deadening resonators, are coupled via the perforated inner wall to the flow channel for the air flowing via the rotor-side fan. The cavities are filled, in a region which faces away from the inner wall and thus faces toward the outer wall, with activated carbon.

An acoustic panel includes a first skin, a second skin and a cellular core vertically between and connected to the first skin and the second skin. The cellular core includes a plurality of cavities, a plurality of sidewalls and a plurality of septums. Each of the plurality of cavities extends vertically through the cellular core between the first skin and the second skin. Each of the plurality of cavities extends laterally within the cellular core between a respective laterally adjacent pair of the plurality of sidewalls. Each of the plurality of septums vertically divides a respective one of the plurality of cavities into a set of fluidly coupled sub-cavities. A set of the plurality of septums is formed by a ply of folded material. Each of the set of the plurality of septums have a four-sided polygonal shape when viewed in a plane that is parallel to the first skin.

A method for manufacturing a sound-absorbing panel with a sandwich structure for reducing noise impact of an aeronautic engine includes providing a first skin of a thermoplastic polymeric material, making a plurality of micro-holes through the first skin by mechanical punching of the first skin, securing the first skin to a central layer by arranging a structural adhesive layer between the first skin and the central layer and/or by a thermal weld between the first skin and the central layer, and securing the central layer to a second skin by arranging a structural adhesive layer between the central layer and the second skin and/or by a thermal weld between the central layer and the second skin.

An exemplary ducted fan includes a duct having a central longitudinal axis, a rotor hub and stator hub extending along the central longitudinal axis, rotor blades extending from the rotor hub, each of the rotor blades operable to rotate about its own pitch-change axis, the pitch-change axes lying in a rotor plane that is generally perpendicular to the central longitudinal axis, each of the rotor blades having a rotor trailing edge and a rotor chord length, stators extending from the stator hub to an interior surface of the duct, each of the stators having a stator leading edge and a stator thickness, and a first separation between the rotor plane and the stator leading edge of not less than approximately 1.5 times the stator thickness.

Systems and devices of the various embodiments may provide a low-drag, variable-depth acoustic liner having shared inlet volumes. Various embodiments may include a low-drag, variable-depth acoustic liner providing aircraft noise reduction. Acoustic liners according to the various embodiments may be used in engine nacelles and/or on external surfaces of an aircraft to reduce acoustic radiation. Acoustic liners according to various embodiments may provide increased broadband acoustic performance with less drag than conventional liners. Various embodiments may provide an acoustic liner with a reduced open area of the facesheet, and therefore reduced drag of the liner, when compared with conventional acoustic liners.

A ring assembly has a housing made of woven composite material carrying on its radially inner face an acoustic panel with a cellular structure covered with a composite material. The housing includes at least one radial recess in which is engaged at least one radially outwardly projecting part of the radially outer face of the acoustic panel.

A production method for an acoustic panel comprising a step of producing a composite structure, a step of providing inserts, wherein each insert comprises a nozzle formed as a hollow cylinder with a through-bore and a cap comprising a base formed as a cylinder and a cover formed as a cone, and wherein the base is accommodated in the bore, a step of positioning the inserts in the composite structure by penetration of the cover into the composite structure so that the bore opens at one side and the other of the composite structure, a step of polymerizing during which the composite structure with the inserts is polymerized, a step of removing the caps, a first step of fixing a honeycomb structure to the polymerized composite structure, and a second step of fixing a rear skin to the honeycomb structure.

An assembly forming an acoustic insulator having a first sheet, a pierced second sheet, and a plurality of first and second structures. Each first structure comprises a first and a second strip, wherein each is shaped to form half of the wall of a cage and wherein, for two successive halves, each strip comprises a facet of a joining wall. Each second structure is made up of a first and a second strip, wherein each is shaped to form half of the wall of a cone, wherein. For each strip, at least one of the wall halves of each cone is pierced. For two successive halves, each strip comprises one facet of the connecting wall. Each cone is located in a cell and each connecting wall is located between the two facets of a joining wall, and, between two adjacent first structures, a second structure is likewise fitted.

A resistive skin shell for an acoustic panel or inner wall of an aircraft air intake, comprising an alternation, in a transverse direction, of perforated metal bands and of composite solid bands extending in a longitudinal direction. The perforated metal bands and the composite solid bands form a smooth outer face configured to be in contact with an aerodynamic stream, and a crenelated inner face. The composite solid bands have a thickness greater than the perforated metal bands. Since the perforations are provided in metal bands, which are intrinsically resistant to wear and erosion, the future proofing of the acoustic performance of the resistive skin is guaranteed. Since the composite solid bands, which are thicker, can ensure the mechanical strength of the skin, the thickness of the perforated metal bands can be reduced, allowing perforations with dimensions that are also reduced, having a lower impact on drag.