Abstract: In order to create a process for producing muffler inserts as well as novel muffler inserts, which are most optimally adaptable in size and shape to the interior space of the muffler housing to be filled, by simple means, and which also can be produced economically and have improved effect, a process is proposed for producing muffler inserts which operate entirely or partially according to the absorption principle, whereby a predetermined amount of a loose bundle of individual elements of a suitable sound-absorbing material is formed, the loose bundle is shaped roughly in an assembly shaping unit corresponding to the intended shape of the muffler insert, and whereby the loose bundle is fixed into a shaped composite in the shape corresponding to the assembly shaping unit, in such a way that the fixed shape can be handled without individual elements loosening until assembly for the specified uses of the muffler insert; however during the specific use as a muffler insert the fixing is at least partially released

Abstract: A silencing member has a plurality of elongate members each having a plurality of elongate glass fibers, with the plurality of elongate members being cross-layered to define a fabric.

Abstract: Silencer for gas discharge device employing easily replaceable cartridge utilizing juxtapositioned layers of wire mesh and porous resilient material which dissipate the energy stored in an exhaust system and deflect under pressure of the exhaust gases to provide a self cleaning function and a cylindrical liner mounted within the cartridge comprising the same or larger wire mesh and wire diameter size than used in the cartridge for capturing the large particles of the exhaust gases before they pass through the layers of wire mesh forming the cartridge.

Abstract: An apparatus for reducing distortion of air flow entering the inlet of a fan. The device includes a perforated body member that has a first end that is attachable to the inlet end of the fan and a second end. The apertures in the body member are arranged in a plurality of circumferential rows. Preferably, the apertures in each successive row from the first end to the second end increase in diameter with the apertures in the row adjacent the first end being smaller in diameter than the apertures in the row adjacent the second end. The body member can be frusto-conical, cylindrical or ellipsoidal in shape. In addition, the body member can be equipped with an apparatus for reducing airflow noise.

Abstract: Apparatus and method for determining the location of the source of seismic energy around a well are provided. Multiple seismic receivers, each receiver having orthogonal seismic sensors, are axially spaced on a tool which is capable of sending real-time seismic signals to the surface. A method for calculating the location with respect to the receivers is also provided.

Abstract: A stator assembly for reducing noise in the outermost portion of the working medium flow path is disclosed. Various construction details are developed which relate to the reduction in noise within the outer twenty percent (20%) of the working medium flow path. In one particular embodiment, an annular channel extends rearwardly from a location between the blades and the vanes for capturing a significant portion of the wake turbulent flow from the tip region of the rotor blades. The annular channel is bounded by a pair of circumferentially extending walls, at least one of which has acoustic treatment to absorb tonal and broadband noise.

Abstract: A stator assembly for reducing noise in the outer most portion of the working medium flow path is disclosed. Various construction details are developed which relate to the reduction to noise within the outer twenty percent (20%) of the working medium flow path. In one particular embodiment, the number of radially extending surfaces in the outermost portion of the working medium flow path is reduced.

Abstract: An improved silencer panel construction for use in the exhaust gas stream of power generation equipment is described. The silencer panel has an outer periphery of U-shaped channel. Perforated webbing is attached within the outer periphery to strengthen the outer periphery and reduce thermal gradients building up within the web during operation. Acoustical insulation is provided within the silencer panel and held in place by screening as well as perforated cladding. A plurality of silencer panels are spaced apart within the silencer chamber to attenuate the noise produced by the exhaust gas stream.

Abstract: To reduce a noise and to cool a nozzle in a supersonic jet propelling engine, a sound absorbing member made of a porous plate (4) and a honeycomb structure (2) or a porous plate (4) and a torus core (3) is provided between a nozzle plate (5) and a liner (1), a cooling air (7) is caused to flow along an inner surface of the nozzle plate (5) and to impinge against the liner (1) through holes (10) of the porous plate (4). Furthermore, a number of holes (11) which are slanted on a rear side are formed in the liner (1) so that the cooling air (9) are injected through the holes (11).

Abstract: A sound muffling device for use in lawnmowers includes a hollow body containing an aperture plate, a plurality of serpentine configured pipes, a plurality of fans, a double net having a bundle of wires, and a microporous plate, an adaptor having a sound inlet disposed on the exterior of the front end of the hollow body, and a sound outlet of the exterior of a rear end of the hollow body.

Abstract: A flexible coupling for connecting an engine manifold to an exhaust pipe to relieve torque. Concentrically spaced flexible tubes, which have insulation filling the annular space between them, are connected to inlet and outlet tubes having interior ends located between the ends of the flexible tubes. The inlet and outlet tubes have enlarged upstream ends and smaller downstream ends. By overlapping the ends of the inlet and outlet tubes, the tubes are able to have relative angular movement when the flexible tubes bend due to engine torque. One or more separate tubes which also have enlarged and smaller upstream and downstream ends may be provided to overlap with the inlet and outlet tubes to allow bending of longer couplings.

Abstract: An acoustic liner comprising a sound permeable inside plate forming a first closed annulus, and a sound impermeable outside plate forming a second closed annulus located outside of and extending around the first closed annulus. The inside and outside plates are spaced apart and thus form an annular chamber therebetween; and a core member is secured in this annular chamber, between the inside and outside plates. The core member forms or has the shape of a sine wave form annularly extending around the inside plate, and the core member and the inside plate form a multitude of varying depth sound absorption chambers to attenuate sound waves over a broad band of frequencies.

Abstract: The present invention relates to a novel installation of a sound attenuating laminate. More particularly, the invention relates to the installation of a simpler, lighter, and more effective noise attenuating laminate which is made up of seven layers of material. The laminate includes a duct liner, a moisture barrier, a first protecting layer, a screen, acoustic attenuating material, a second protecting layer, and a solid backing sheet. The laminate is readily incorporated into various sections of a jet engine compartment in order to attenuate the sound produced by the jet engine. Hollow rivets are used to conduct acoustical energy to the intermediary layers of the laminate. This novel means for conducting the acoustical energy to the intermediary layers of the laminate also allows for an improved anti-icing system, for more efficient jet engine operation, and for more efficient dissipation of acoustic energy.

Abstract: A circumferentially extending structure 30 for containing particles having an axial component of velocity and a radial component of velocity is disclosed. The structure includes an inner casing, such as the first casing 48, and an outer casing, such as the second casing 50. The outer casing is flexible. The outer casing is formed of a plurality of layers of fabric and by applying a load to the fabric such as a plurality of bars 80, 82 and turnbuckles 74. A method of forming the structure is disclosed. The method includes the step of wrapping a fabric having a first length about the inner casing and the step of stretching the fabric to a second length to affect the operative response of the fabric to the impact of a particle.

Abstract: The present invention relates to a novel sound attenuating laminate. More particularly, the invention relates to a simpler, lighter, and more effective noise attenuating laminate which is made up of seven layers of material. The laminate includes a duct liner, a moisture barrier, a first protecting layer, a screen, acoustic attenuating material, a second protecting layer, and a solid backing sheet. The laminate is readily incorporated into various sections of a jet engine compartment in order to attenuate the sound produced by the jet engine. Hollow rivets are used to conduct acoustical energy to the intermediary layers of the noise attenuating laminate.

Abstract: A noise suppression system for use with a jet aircraft engine having a plug support cylinder affixed to the engine, a tubular ejector shroud affixed to the engine and encompassing the plug support, the shroud having a reduced internal diameter adjacent the aft end and a plurality of spaced apart blow-in openings formed circumferentially about the shroud forward end providing passageways for the entrance of ambient air from the exterior to the interior of the shroud. A blow-in door is secured to the shroud for opening and closing each of the blow-in openings. A translating plug is supported on the plug support cylinder and is positionable between a forward position and an aft position and forms an annular exhaust nozzle between the exterior of the plug and the interior of the aft end of the shroud. A daisy mixing nozzle is positioned within the shroud aft of the blow-in doors, the nozzle being configured of a plurality of lobes providing undulating interior and exterior surfaces.

Abstract: A tube of a muffler for an internal combustion engine includes at least two generally rectangular sheets which are joined together at one end by crimping and wound in a tubular configuration to constitute two consecutive layers. In the tubular configuration, the other end of each of the two sheets overlaps the sheet itself and welded to the latter straddling a coupling portion where the two sheets are joined. While one of the sheets which constitutes an inner layer of the tube is made of a material which is resistive to corrosion due to chemical reactions with combustion gas and others flowing through the tube, the other which constitutes an outer wall of the same is made of a material which withstands adverse ambient conditions such as briny air and high humidity.

Abstract: The present invention relates to a novel sound attenuating system. More particularly, the invention relates to a simpler, lighter, and more effective noise attenuating laminate which is made up of five specific layers of material. The laminate includes a duct liner, a moisture barrier, a fire barrier, acoustic attenuating material, and a solid backing sheet. The laminate is readily inserted into various sections of a jet engine compartment in order to attenuate the sound produced by the jet engine. Hollow rivets are used to conduct acoustical energy to the noise attenuating laminate. This novel means for conducting the acoustical energy to the laminate of the jet engine compartment allows for an improved anti-icing system, for more efficient jet engine operation, and for more efficient dissipation of acoustic energy.

Abstract: A system is provided for existing three-engine jet aircraft to reduce the noise levels at take-off and landing in order to meet governmental noise regulations. The system is particularly suitable for 727-200 aircraft having three JT8D engines. A hush kit is formed of the modified components for installation in existing airplanes.

Abstract: An aircraft cowl, and in particular a translating cowl, used as a component of a thrust reverser, formed of at least one one-piece bondment cured in a single operation. Preferably, a one-piece inner bondment and a one-piece outer bondment fastened together at a joining region. The bondments have constant density cores and tapered closures. Acoustically absorbing materials are part of the lay up for one of the bondments and are integrally cured therein.

Abstract: A quiet nacelle system for jet aircraft engines includes a nose cowl and nose dome having a sound-attenuating liner, a concentric ring between the nose cowl and nose dome, and fan duct components having a sound-attenuating liner. The system is particularly suitable for JT3D-3B and JT3D-7 engines for use with DC-8 aircraft. The components may be combined as a hush kit for retrofit in existing nacelle systems.

Abstract: A noise reduction nacelle for a jet engine having an inlet duct, a center body and at least one exit duct and which includes a composite sandwich panel positioned in the inlet duct, the center body and the at least one exit duct. The panel includes an inner face sheet, a honey comb core and an outer face sheet wherein the inner face sheet and the outer face sheet are connected to the inner and outer surfaces, of the core. A plurality of perforations are provided in the inner face sheet of a predetermined density and wherein each of the perforations is of a predetermined diameter. A method of forming the composite sandwich panel is also provided.

Abstract: Disclosed is an exhaust silencer for high-power gas turbines having an outer case made from steel plate formed into a Greek fret pattern, and proved with inner soundproofing panels of which are covered with standardized, insulating-soundproofing compound bricks. Each compound brick is preferably of square shape and include a front brick and a rear brick. The front brick is made from an annealed stainless steel plate, beveled at its corners, perforated in its central area only, and bent along each of its edges to form a bracket shape in cross section, inside which bracket-edged perforated steel plate is inserted a pad of insulating material of standardized dimensions, to act as an insulator-soundproofer made from very-high-quality materials subject for high temperature use.

Abstract: An engine noise suppression kit for use on the inside surfaces of the cowlings or doors of conventional jet aircraft nacelles surrounding the jet aircraft engines. Each nacelle cowling or door comprises a skin mounted on a framework made up of longitudinal stringers and transversely extending ribs or formers. The formers divide the inside surface of the nacelle cowlings or doors into bays surrounding the jet engine located within the nacelle. The kit comprises a plurality of sound attenuating modules adapted to be affixed to an adjacent pair of cowling or door formers and to span the bay defined thereby such that at least those bays surrounding the combuster chamber/turbine area of the jet engine are covered by said modules. Each module constitutes a sealed metallic basket comprising a pair of perforated metallic panels spaced from each other by a surrounding metallic framework. The facing surfaces of said metallic panels being covered by silicon rubber-coated glass cloth.

Abstract: A compact turbine engine exhaust gas noise suppressor has a housing having a first chamber, a second chamber having an outlet and communicating with the first chamber through a transfer passage, and a third chamber communicating with the first chamber through a perforated dividing wall and having a resonant sound attenuator positioned therein. A sound absorbing member is positioned in the second chamber to create therein a serpentine flow path extending between the transfer passage and the outlet. The exhaust gas noise is attenuated by flowing the exhaust gas into the first chamber through a duct into which ambient cooling air is educted, and then forcing the exhaust gas outwardly through the serpentine flow path.

Abstract: An air inflow control device (10) simulates flight-like air inflow conditions into the intake (36) of a turbofan engine (18) during static ground tests. The device (10) has a truncated spherical portion (12) with a circular opening that is closed by a bellmouth (14). The bellmouth (14) provides an inwardly projecting conical surface having a central high-lite and throat portion (28, 35) that permits air to flow from inside the sphere (12) into the engine (18).

Abstract: Acoustic attenuation apparatus (2) is provided for a duct (4) guiding an acoustic wave propagating (6) therethrough. A silencer (8) is provided for passively attenuating the acoustic wave in the duct, and a cancelling speaker (32) is provided within the silencer. The combination provides hybrid active/passive combined attenuation. Various rectangular and circular structures are disclosed, together with multi-path and multi-speaker arrangements.

Abstract: In acoustic panels employing a layer of perforate metal adhesively bonded to a layer of porous fibrous metal of a different type with the perforations of the perforated layer and the pores of the porous fibrous layers open to communication therethrough and the layers being isolated therebetween. The isolation between the layers is maintained by applying a coating of liquid epoxy resin material to selected locations, curing the epoxy coating, cutting or drilling the layers as required, and recoating the cut or drilled areas with a second coating of liquid epoxy resin.

Abstract: A circumferentially extending apparatus 46 for containing particles having an axial component and a radial component of velocity is disclosed. The apparatus is comprised of a support structure 48 and a flexible casing 50 formed of a fabric 78. The external surface of the support structure has a first diameter and a second diameter not equal to the first diameter at a location spaced axially from the location of the first diameter. The fabric is preloaded to increase the length of the fabric and is wrapped under tension about the surface of the support structure such that the installed length of the fabric is greater than the free length of the fabric. A method for forming the circumferentially extending structure is disclosed which includes the steps of forming a support structure and wrapping a preloaded fabric about the support structure to cause an elongation of the fabric and tension in the fabric in the installed condition, which varies depending on the diameter of the support structure.

Abstract: A circumferentially extending structure 30 for containing particles having an axial component and a radial component of velocity is disclosed. The apparatus is comprised of a hollow annular beam 48 and a fabric 46 wrapped under tension about the annular beam such that the installed length of the fabric is greater than the free length of the fabric. In one particular embodiment the fabric is coated with a layer 116 of epoxy resin such that the resin penetrates only the top layer of the fabric to form a shield. The shield layer protects the containment fabric from injury.

Abstract: A circumferentially extending structure 30 for containing particles having an axial component of velocity and a radial component of velocity is disclosed. The structure includes an inner casing 48 and an outer casing 50. The outer casing is formed of a plurality of layers of flexible fabric and includes layers having differing masses per unit length in the fabric. The layers of fabric extend about the inner casing. A means for applying a load to the fabric engages the fabric to place the fabric in tension. One such means is a plurality of bars 80, 82 and turnbuckles 74. In one embodiment, the fabric has a greater mass per unit length in the leading edge region and a greater tension is applied to the leading edge region than other regions of the fabric. A method of forming the structures is disclosed.

Abstract: A sound absorbing structure 38, 52 for a gas turbine engine 10 is disclosed. The sound absorbing structure 52 includes a wall element 54 and a casing 34 of the engine or nacelle 12. The casing is spaced from the wall element leaving a cavity 62 therebetween which is compartmentalized by partitions 64, 66. In one embodiment the partitions are attached to either the wall element or the casing element. In another embodiment the partitions are all attached to the wall element and spaced from the casing element or are all attached to the casing element and spaced from the wall element. In another embodiment the partitions are alternately spaced from the casing element and the wall element such that every other partition 64a is spaced from the wall and the remaining partitions 64b are spaced from the casing.

Abstract: A sandwich type acoustical absorbing panel for use adjacent to high speed gas flow areas in and around the engines of high speed aircraft. The panel in one embodiment comprises an imperforate facing sheet including having upright side and end walls, the inner volume of the panel and upright side and end walls are divided by means of partitions into a plurality of individual cavities or cells, each of the plurality of individual cavities or cells are filled with a bulk absorber material having many small torturous air passages, such as, open celled foam, fiberglass, felts or the like, the bulk absorber filling each cavity or cell is encapsulated in a membrane of thin limp material for preventing bulk absorber contamination and a perforated sheet overlay for attaching to the side, end walls and partitions for containing the bulk absorber within the cavities or cells.

Abstract: A duct lining exposing a substantially smooth, liquid impermeable outer surface to fluid flowing therealong.

Abstract: An acoustic lining for a flow duct has a first perforate skin fixed to an underlying sound-absorbing layer. The first perforate skin is overlain by a second perforate skin which forms the wall of the flow duct. One of the skins is relatively moveable in a sliding sense with respect to the other skin so as to vary the acoustic impedance of the duct wall as the perforations in the respective skins slide into and out of registration with each other. This enables the acoustic impedance of the duct wall to be varied to suit the flow and noise conditions prevailing in the duct and so obtain optimum noise attenuation in the duct, which may be the intake duct of a turbofan aeroengine.

Abstract: A noise suppressor for small rocket motors including a plurality of perfoed metal cylinders disposed in concentric relation and secured to a support plate. A noise suppression material is disposed in the chamber of each adjacent cylinder. Noise suppression material is also disposed in the center cylinder and is expelled by the rocket motor thrust. A collar on the support plate secures the motor to the suppressor.

Abstract: A sandwich type acoustical absorbing panel for use adjacent high speed gas flow areas in and around the engines of high speed aircraft. The panel comprises a pan type base having an imperforate base member and upstanding sides and end walls, an acoustic absorbing medium is disposed within the pan type base, a rigid perforated plate is secured to the distal surfaces of the upstanding sides and end walls for enclosing the acoustic absorbing medium and a sheet of fine woven mesh is secured to the outer surface of the rigid perforated plate. The outer positioned fine woven mesh enhances acoustic properties of the panel and substantially prevents entry of water, dust, chemicals and similar foreign matter from penetrating into the panel structure and reduces the aerodynamic drag loss normally encountered by high speed gas flows across perforated material, such as, that normally used for the outer surface of acoustic panels.

Abstract: A double degree acoustic attenuation sandwich panel having a plurality of stacked components adhered together to form a unitary sandwich structure. The structure comprising an impervious facing of thin sheet material, a first honeycomb core with end wise directed cells, a first perforate facing of thin sheet material, a first thin layer of porous fibrous material, a second perforated facing of thin sheet material, a second honeycomb core with end wise directed cells, a third perforate facing of thin sheet material, the second perforated facing sheet having substantially larger perforations than the first and third sheets, and a second layer of porous fibrous material. The resulting sandwich panel has a pre-determined flow through resistance between the outer surface of the first and second layers of porous fibrous material and the cells of the first and second honeycomb cores.

Abstract: A combined sound damper and oil trap for compressed air apparatus comprising an oil trap having a hose or tube (5) which is directly connected to the compressed air apparatus and which at the outer end thereof encloses a scraper sleeve (7), whereby a radial space is formed between the scraper sleeve (7) and the hose or tube. The hose or tube is connected to an oil collector housing (1) whereas the scraper sleeve (7) is connected to a pressure chamber (2) which in turn directly communicates with a filter housing (3) containing a sound damper. The said sound damper comprises both a diffusor plate (11) provided between the pressure chamber and the filter housing (3) and a filter (12) which is mounted at the outlet end of the filter housing. The diffusor plate (11) provides a damping of low frequency noise and a substantially even distribution of the outlet air over the entire diffusor plate, and the filter (12) provides both a separation of oil mist from the outlet air and a damping of high frequency noise.

Abstract: Apparatus for attentuating noise emitted from an inlet port to a centrifugal fan comprises a panel member which is mounted in spaced confronting relationship to the inlet port and includes a rigid backing member, a facing mounted in spaced disposition from the rigid backing member, partitions dividing the space between the rigid backing member and the facing into a plurality of cavities, and acoustic infill in the cavities. The facing has a plurality of perforation zones, and is formed in each perforation zone with small perforations whereby the facing is rendered acoustically permeable over a limited area only. One wall of each cavity includes a perforation zone of the facing, whereby the cavities constitute Helmholtz absorption cavities. The facing is adapted to face the inlet port and transmit noise for attenuation in the cavities.

Abstract: Disclosed is a turbulence control structure for use during static noise testing of jet aircraft engines. A flow transparent substantially spherical geodesic dome defined by a modified 9-frequency icosahedral frame encloses the intake of a jet engine on a test stand. The surface of the dome is covered by flat flow panels constructed of aluminum honeycomb adhesively bonded to stainless steel perforated sheet. The combination of perforated sheet and honeycomb attenuate streamwise and transverse components of inflow distortions in the intake air entering the engine. As a result, clear inflow is achieved, engine speed is stabilized, and engine intake noise approximating that of in-flight operation are achieved.

Abstract: A method of making a panel for installation in the high velocity air flow region of an engine nacelle and other applications requiring sound absorbing material and increased air frame strength. The panel utilizes a single layer of either a metallic or nonmetallic cellular core with a solid or perforated septum disposed internally therein. The septum may have a planar or nonplanar configuration within the individual cells of the core thereby providing means for reducing the noise level of various sound frequencies created by a jet engine or any other sound producing devices for that matter. The planar or nonplanar septum provides structural stabilization and/or vibration dampening to a bonded sandwich assembly. The panel may also be used in strengthening air frame construction and other applications besides sound attenuating panels.

Abstract: In a mixed flow gas turbine engine of the type which includes an outer nacelle spaced apart from a core engine to define an annular bypass duct therebetween, there is provided a convoluted lobed mixer having a plurality of cold chutes in flow communication with the bypass duct and hot chutes in flow communication with the core engine. In order to suppress engine turbomachinery and exhaust noise, the mixer is alternatively provided with various combinations of acoustically treated lobes, spool pieces, radial splitters, and/or circumferential splitters. These acoustic treatments act in conjunction with an acoustically treated nozzle assembly and an acoustically treated plug assembly to provide an effective low aerodynamic pressure loss noise suppression system.

Abstract: Combination bulk absorber-honeycomb acoustic panels particularly adapted for use in the inlet and fan air duct of a fan jet engine are disclosed. Each panel comprises a broadband noise-suppressing bulk absorber layer mounted between a back sheet and a perforated septum; and, a narrow band noise-suppressing honeycomb layer mounted between the septum and a perforated face sheet. The panels are mounted in an engine such that the perforated face sheet interfaces with airflow in the inlet or the fan air duct, as the case may be, whereby the face sheet, honeycomb layer and septum protect the bulk absorber from deterioration by isolating the high speed inlet and fan air duct airflows from the bulk absorber layer.

Abstract: A method of and a device for attenuating the noise radiated by a free-expion gas jet throughout the audible-frequency range as well as in the ultrasonic and infrasonic frequency ranges. Concomitantly with the complete and shock-free expansion of the gas into the atmosphere, the acoustic field of the jet is organized by the substantial diminution of the low-frequency tones by causing them to pass from the annular section of the jet to the narrow annular section of the nozzle slot. This is followed by sound-wave diffraction on emergence from the slot in the presence of a baffle, and by a wave reflection towards the sound-absorption lining of the device housing. The final noise results from an intensive ejection of ambient air by the primary gas which, leaving the nozzle slot, entrains the air by means of turbulence, the air entering through the annular channels of the case, reaching the outer orifices of the nozzle, and dividing into two flows, namely inside and outside the nozzle.

Abstract: A centrifugal fan is treated acoustically by the provision of tuned noise absorption cavities preferably including absorbent infill between an acoustically permeable scroll and casing of the fan. Alternatively, or in addition an acoustically absorbent panel structure is provided in spaced confronting relationship with the inlet port of the fan. The panel structure has an acoustically permeable facing spaced from a rigid backing and the space may be divided into noise absorption cavities and specifically Helmholtz type absorption cavities, the absorption bands of which are broadened by including acoustic infill. It is most advantageous to provide a multiplicity of Helmholtz absorption cavities tuned to respective different center frequencies of their acoustic absorption bands.

Abstract: A ring of tubes extends inwardly from a noise suppressor housing wall sufficiently far to impinge upon the periphery of the high velocity core of a supersonic jet exhaust to disrupt the core and reduce the sound power generated. A large volume of outside cooling air is induced by jet pump action into the suppressor; and a portion of this cooling air is ducted through the tubes and into the exhaust stream to maintain the temperature of the tubes below an acceptable level to prevent their premature destruction.

Abstract: A gas turbine engine exhaust duct of combination circular and rectangular configuration, and accompanying muffler which provides cooling and silencing of exhaust flow from the gas turbine engine. The arrangement utilizes minimum space without sacrifice of performance.

Abstract: When fan-blade tips in a turbofan aero engine reach a velocity of greater than about mach 1.1, the regular shock-wave pattern near the blade tips degenerates into an irregular pattern as it moves upstream, thus causing "buzz-saw" noise. An anit-buzz acoustic liner of the spaced-cell type forms part of the fan duct wall near the blade tips and combats the degeneration by reinforcing the regular shock-wave pattern at the expense of the irregular one. This is achieved by making the depth of the cells equal to half the wavelength of the blade passing frequency at the supersonic condition of interest.

Abstract: Production of a downwardly and forwardly directed reverse thrust discharged from a reverse-thrust duct is controlled .Iadd.during landing .Iaddend.by a door in the rearward-discharge duct having its rearward portion pivotally mounted for swinging of its forward portion between a position lodged in a recess in the side of the rearward-discharge duct and a position in which the forward edge of the door is spaced from the recess and the door is inclined to deflect jet exhaust from the rearward-discharge duct into the reverse-thrust duct branching from the rearward-discharge duct. The discharge end of the reverse-thrust duct can be closed by a second door and actuating .[.means.]. .Iadd.mechanism .Iaddend.interconnecting the two doors can move them simultaneously through proportionate degrees of movement.