Abstract: An active noise control system which minimizes noise output by creating a secondary, cancelling noise field using vibrational inputs. The system includes one or more piezoceramic actuators mounted to the inner surface of the shroud of an aircraft engine. The actuators can be either mounted directly to the shroud or to one or more noise cancelling members which are resiliently mounted the shroud. Transducers are also provided for sensing the noise generated by the engine and producing an error signal corresponding to the level of noise sensed. A controller sends a control signal to the actuators in response to the error signal, thereby causing the actuators to vibrate and generate a noise field which minimizes the total noise emanating from the engine. The piezoceramic actuators can be thin sheets of piezoceramic material or can be in the form of a piezoelectric-driven mechanical lever arrangement.

Abstract: The oscillations found to occur in the cavities of an structural frame moving through a fluid are substantially eliminated by the adoption of perturbation elements located at the leading edge of the cavity and reflecting any remaining oscillations out of the cavity at the trailing edge. The perturbation elements may take the form of multiple pins of various shape and geometrical arrangement which prevents the generation and growth of vortices causing acoustic oscillations. The reflection of remaining oscillations out of the cavity may be accomplished by ramping the trailing edge of the cavity.

Abstract: A honeycomb structure includes at least two corrugated strips having major flat surfaces extending angularly between opposed strip edges. The strips are offset relative to each other and joined together to define a series of cells extending between the strip edges along axes which are oriented at an angle other than normal to the strip edges. Each of the major flat surfaces includes a central depressed portion forming a matching sub-flat surface which is parallel to and connected to the major flat surface by sidewalls which may be substantially perpendicular to the major flat surface. Abutting undepressed portions of the major flat surfaces of adjacent strips and abutting sub-flat surfaces of adjacent strips are joined together so that the strips form a series of I-beams disposed one to a cell.

Abstract: An active noise control (ANC) system for a helicopter that is operative to effectively nullify one or more high frequency vibrations emanating from the main transmission gearbox thereof at the gearbox/airframe interface, thereby significantly reducing the interior noise levels of the helicopter, that is design optimized to minimize the number of actuators required, and that is design optimized to minimize contamination forces arising from operation of the system actuators. The ANC system includes modified transmission beams that are mechanically stiffened to function as rigid bodies with respect to the one or more of the high frequency vibrations, a plurality of actuators disposed in combination with the modified transmission beams, a plurality of sensors disposed in combination with the modified transmission beams in a collinear, spaced apart functional correlation with respective actuators, and controllers interconnecting individual actuators with respective functionally correlated sensors.

Abstract: System for reducing vibrations in the cabin of an aircraft driven by two or more propellers each having n blades (n being an integer equal or larger than 2) of which the relative phase angle can be adjusted, said system comprising synchrophase means for adjusting said relative phase angle such that a predetermined relative phase angle is maintained. The system furthermore comprises means supplying information about the vibration level at one or more positions within the cabin or thereto related information and for generating a thereto corresponding level signal, and a control unit which in response to said level signal supplies an error signal to the synchrophase means causing the synchrophase means to adjust the blades of the various propellers such that a new relative phase angle is maintained which differs m.(2.pi./n) radians (m being an integer) from the previous relative phase angle.

Abstract: A gas turbine engine flow mixer includes at least one chute having first and second spaced apart sidewalls joined together at a leading edge, with the sidewalls having first and second trailing edges defining therebetween a chute outlet. The first trailing edge is spaced longitudinally downstream from the second trailing edge for defining a septum in the first sidewall extending downstream from the second trailing edge. The septum includes a plurality of noise attenuating apertures.

Abstract: The Sonic Boom Attenuator is a device designed for use with supersonic aircraft wherein a laser beam is shone down the leading edge of a short, rigid, straight, thin wing, heating thus rarefying the air before it passes over and under the wing. In this manner, the compression (which results from the rarefication) occurs more slowly as the relative wind passes through the beam than it otherwise would by impact with the hard surface of the wing. Because of the simplicity of design there are fewer components than have been proposed by other inventions and fewer mechanical devices to fail. Because of the rarefication, there is an overall reduction in drag to the aircraft and an attenuation of sonic boom in supersonic flight.

Abstract: This invention outlines excitation means to transform the linear momentum of an underwing energized jet into rotational form in a selective manner to provide an asymmetric shear layer to increase compression wave reflection from the forward undersurface of a supersonic wing. The wing compression energy is thereby recovered into useful work as an increase in pressure on the upward reflexed wing backside. The upper surface of the shear layer is comprised of an array of vortices whose rotation is opposite to the wing circulation, providing the required angular momentum reaction. The upper wing surface is flat to avoid generation of waves and an adverse angular momentum reaction above the wing. The vortices below the wing are compressed by the underwing pressure, comprising a pressure shield to enhance the reflection.

Abstract: A system for reducing noise created by multiple rotating machines by synchronizing the machines so as to establish a phase relationship between the machines which minimizes the noise. One or more feedback sensors, such as microphones, are placed so as to sense the noise to be reduced. The noise signals from the microphones are sent to a controller. Tachometer signals of the rotational speed of each machine are also sent to the controller. The controller generates an output signal in response to the inputs from the microphones and the tachometers that is fed to one or more of the rotating machines in order to establish the desired phase relationships.

Abstract: System for reducing vibrations in the cabin of an aircraft driven by two or more propellers each having n blades (n being an integer equal or larger than 2) of which the relative phase angle can be adjusted, said system comprising synchrophase means for adjusting said relative phase angle such that a predetermined relative phase angle is maintained. The system furthermore comprises means supplying information about the vibration level at one or more positions within the cabin or thereto related information and for generating a thereto corresponding level signal, and a control unit which in response to said level signal supplies an error signal to the synchrophase means causing the synchrophase means to adjust the blades of the various propellers such that a new relative phase angle is maintained which differs m.(2.pi./n) radians (m being an integer) from the previous relative phase angle.

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: A noise reduction kit is provided for installation on a bypass turbine engine having a core engine, an outer casing and a thrust reverser. The kit comprises a mixer downstream of the core engine for mixing fan air of the engine with the exhaust gas from the core engine to reduce the peak velocity of the exhaust gas; a structure for supporting and positioning said mixer relative to the engine; a spacer for extending the length of the exhaust gas flow path between said mixer and the thrust reverser to permit sufficient mixing of the fan air with the exhaust gas prior to reaching the thrust reverser; and an acoustic tail pipe assembly configured to define an outlet area for the engine exhaust gas flow path. The outlet area is sized and shaped to reduce pressure loss in the exhaust gas stream in an amount necessary to compensate for the pressure increase in the exhaust gas stream created by the mixer.

Abstract: Noise due to the rotation of the air propeller or fan of an air-cushion vehicle is reduced by: 1) reducing the cross-sectional area of the interior of a duct encompassing the fan on the downstream side relative to the upstream side; 2) using wide-chord fan blades of chords increasing from blade root to tip; 3) using a duct and a nose cone on the hub of the fan both having a sound-absoring structure; and 4) mounting the engine and the duct on a common rigid support base and reducing to a minimum the tip clearance between the tips of the fan blades and the duct inner wall surface.

Abstract: An apparatus for and method of suppressing noise generated by the primary exhaust gas flow from jet engine nozzles or the like without significantly affecting thrust. A secondary jet stream is provided exteriorly of the primary exhaust gas flow for interacting at the boundary between the exhaust gas flow and the ambient air immediately adjacent the exit end of the nozzle to preclude the formation and propagation of noise generating phenomena. The pressure of the secondary jet stream can be varied in accordance with noise levels sensed at the nozzle exit end to provide optimum noise suppression under essentially all conditions of exhaust gas flow.

Abstract: An arrangement for suppressing aerodynamic noise generated by cavity effect interaction between a wing flap shroud and one or more partially deployed trailing edge flaps. Noise suppression vanes are so positioned with respect to the shroud lower trailing edge and the leading edge of the wing flaps at partial deployment that eddies and vortices resulting from airflow separation at the shroud lower surface are diverted sufficiently by the noise suppression vanes to avoid significant noise inducing impingement of the separated flow on the flap leading edge.

Abstract: A woven fabric structure impregnated with a hardened resin has first and second warp fabric sections, the second section comprising a plurality of pleats integrally joined to the first section by warp threads of the second section and interwoven with the weft threads of the first section. The fabric is of an industrial yarn such as aramide fiber, carbon fiber, ceramic fiber, glass fiber or a blend of such fibers.

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: 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 from a multitude of varying depth sound absorption chambers to attenuate sound waves over a broad band of frequencies.

Abstract: A compressor bleed air passageway includes a duct having an upstream section (48) which terminates in a baffle (44) and a downstream duct section (54) having a forward portion (56) which surrounds the baffle (44). Bleed air flow through openings (58) in the baffle wall (52). This reduces velocity of the bleed air stream at the duct discharge port to a value equal to or less than Mach 1.0. The baffle (44) has virtually no effect on a low-velocity, low-pressure air stream. The downstream duct section (54) may be perforated and surrounded by outer wall (64) to form sound-absorbing chambers (66).

Abstract: A protective facility for suppressing jet aircraft noise which has a primarily horseshoe shape for surrounding a jet aircraft. Within the horseshoe and situated to the rear of any plane within the facility is found a metal, mesh lattice which redirects exhaust gasses from the jet aircraft engines upwards. Noise from the engines, in the form of sound waves, passes through the lattice and impinges upon the facility walls; being absorbed by these walls which are covered with a sound absorbing material. At the entrance to the facility are leaves hinged to the top legs of the horseshoe which roll on curved rails. These leaves may thus be swung inwards to substantially completely enclose a plane which has been placed within the horseshoe shaped facility. The leaves are also covered with sound absorbing material to absorb and deaden noises produced at the jet engine intakes. The facility walls, including the gates, are substantially rectangular in cross-section.

Abstract: In propeller of fan driven aircraft, cabin noise levels may be reduced by adjustment of the phase relationship between a reference propeller or fan and some or all of the other propellers or fans. An aircraft cabin (1) contains four microphones and two loudspeakers which form the active elements of a noise control system. The microphone outputs are fed via amplifiers to a digital signal processor (11) having an adaptation algorithm in a memory store. The processor generates an error signal which is used to adjust the synchrophase angle between the reference propeller and a synchrophased propeller, controlled by a synchrophaser. Thus the synchrophase angle is varied dynamically during flight to minimize propeller noise in the cabin over a range of flying conditions.

Abstract: Method of reducing the overflying noise of airplanes having a propeller den by a piston engine. The propeller is arranged on the engine shaft in such a way that positive components of the engine sound pressure fall on negative components of the propeller sound pressure. It is preferable to use an engine/propeller combination in which the number of engine ignitions per revolution of the propeller shaft divided by the number of the propeller blades is an integer, preferably being equal to 1.

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 thermal insulating and/or sound absorbing structure comprising a batting of resilient, elongatable, non-flammable non-linear carbonaceous fibers, said fibers having a reversible deflection ratio of greater than 1.2:1, an aspect ratio greater than 10:1 and an LOI value greater than 40.

Abstract: In one form of the invention, a counterrotating pair of aircraft propellers produces noise in the form of a frequency-modulated carrier wave. The frequency modulation allows a designer to manipulate the energy spectrum of the noise in order to, for example, place much of the acoustic energy into inaudible frequency ranges.

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: In combination with a propeller disposed in an aircraft, aft from the nose portion of the craft, an improvement is provided for reducing noise, as well as mechanical load on the propeller blade, and includes a construction part situated upstream from the propeller and being exposed to the oncoming air flow prior to reaching the propeller, thus being an obstacle that has a particular contour in a plane transversely to an axis of rotation of the propeller, so that at least the rear edge, as seen in peripheral direction of rotation of the propeller, forms an angle that is not zero in relation to a leading edge of the propeller, when the propeller as a whole is in a horizontal disposition.

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: The process makes it possible to determine for sound-absorbing structural elements made of a compact or foamed plastic with cup-shaped protuberances, the thickness and area size of the resonance surfaces that is required for an optimal sound aborption, as a function of the height of the protuberances and the endeavored resonance frequency.The use of this process also makes it possible to adapt the frequency response curve of the sound absorption coefficient of the structural element to the frequency response curve of the sound level of a noise source.

Abstract: A boundary layer control device is installed in the acoustically treated inlet duct of a turbofan engine. The device sucks off the turbulent boundary layer of air flowing over the inner or "air wetted" surface of the inlet during aircraft take-off, cruise and approach. The lip of the inlet can thus be made thinner to reduce drag during cruise without degradation of fan performance during take-off. The acoustic liner of the inlet comprises a microporous honeycomb sandwich structure through which air may be sucked at various locations through headers and conduits connected to an onboard pump.

Abstract: Apparatus is disclosed for attenuating sound radiated from a vibrating surface into a control volume as comprised of a source of a control signal indicative of the amplitude and frequency content of the sound transmitted from the vibrating surface. An actuator(s) or shaker is directly connected to the vibrating surface for further vibrating the vibrating surface to induce a cancelling sound into the control volume for combining with and attenuating the transmitted sound. A sensor(s) is also disposed within the control volume for detecting the resultant sound indicative of the combination of the cancelling and the transmitted sound to provide an error signal indicative thereof.

Abstract: An aerospike is adapted to be attached to the front nose of an aerodynamically asymmetric space vehicle system, such as the external tank and orbiter of the space shuttle. The aerospike basically comprises a tapered elongated portion having a first end which is adapted to be attached to the nose of the space vehicle, and a second free end terminating in a substantially rounded disc-like tip member. Use of the spike reduces aerodynamic heating and drag during ascent of the space vehicle into its orbital position, provides an attachment point for tether operations and for propellant recovery, and permits transportion of an external tank into its orbit.

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: This invention is an improvement of my system for supersonic aircraft which provides the required angular momentum reaction to the continuous generation of new lift circulation by vorticity in lieu of dissipative shock waves. This new system relocates the propulsive jet forward utilizing its excess energy to generate this vorticity in a planar sheet below the wing acting as a pressure shield, which continues downstream beyond the wing trailing edge as a vortex flap simulating an extended wing chord. The present invention provides mechanical vortex generating means to augment this free surface mechanism in cases where the jet velocity is insufficient. This invention also incorporates a wide-body fuselage above this pressure shield, and provides further system improvement in propulsion/wing integration.

Abstract: A sound reducing combined low mid-wing and horizontal stabilizer airplane with near longitudinal center line thrust twin engines having intensified aileron, elevator and rudder control. Small jet engines rigidly attached to the ailerons intensify attitude control for low speed manuevers.

Abstract: Precompression fins extending perpendicular from the wings of a high speed missile are judiciously located relative to an axisymmetric inlet of an airbreathing power plant such that the outwash angle induced by the body and wing of the missile enhances the performance of the inlet.

Abstract: A device for shielding the sound energy radiated from the jet engines of an aircraft formed from two panels being in horizontal and vertical longitudinal view arranged concavely in a clamshell type.

Abstract: This invention is an extension of my system to recover into useful work the energy normally wasted by a supersonic aircraft in its shock wave mechanism. This system utilizes the excess propulsive jet velocity in a sheet below the wing to form a planar vortex flap which acts as a pressure shield. The present improvement extends the pressure generating forward concave wing undersurface of this system into an upward reflexed aft surface so as to benefit from the increased pressure provided by the downstream upwash vortex field. This allows the aft portion of the wing to serve as the energy recovery section by achieving the pressure required for lift on the undersurface of this aft wing portion at a lesser angle with reduced drag. This stream-wise series of functions specifies the wing undersurface as concave, convex, and concave sequentially in the flow direction, thus corresponding to the upper element of a planar supersonic nozzle.

Abstract: A plurality of passageways, each having its longitudinal axis substantially parallel to the flight path of an aircraft, extend through the wings, fuselage, horizontal elevators, and rudder for the purpose of permitting air to pass through these areas. The passageways diverge from front to rear on either side of the longitudinal axis. The front openings leading into the passageways are of such size and so spaced as to exhibit considerable reduction in parasite drag generated at the leading edges of the wings, elevators, and rudder, as well as at the front end of the fuselage.

Abstract: Retractable multiple aperture arrays, mounted behind jet engines that produce jet exhausts that pass chordwise over the wings of an aircraft, are disclosed. In their operative positions, a multiple aperture array lies in the exhaust path of each engine, immediately rearwardly of the engine nacelle. In this position, in a conventional manner, the arrays split the exhausts into separate streams, which entrain ambient air. The entrained ambient air mixes with the separated streams in the region where the streams recombine to suppress engine exhaust noise and move the noise source centers of the engine exhausts to positions above the wings. As a result, the wings act to shield noise from the line-of-sight community located generally beneath the wings. When not in use, the mutliple aperture arrays are each stowed in a compartment formed in the upper surface of the wing, beneath and immediately rearwardly of the engine with which the array is associated.

Abstract: A supersonic wing in turning the airstream downward to generate increased pressure on its underside also increases the air density. The energy of this compression field is normally diverted away from the wing downward towards the ground in the supersonic wave system, coalescing into a strong shock wave which dissipates most of this energy into heat, with a small residual reaching the ground and causing the sonic boom. My copending application No. 342,151, filed Mar. 16, 1973, disclosed the use of an expanding jet under a concave downward wing to transform this compression energy into vorticity. The present continuation-in-part application provides a wing section which concentrates most of the concave downward curvature of the wing underside in a short interaction region to generate the compression near its leading edge, corresponding to the short expansion region of the underexpanded jet.

Abstract: A system for varying the acoustic resistance of an acoustical lining disposed in a duct of an air propulsor comprises a nonlinear sound suppression liner having a porous facing sheet overlying a plurality of cells, header means communicating with each of the cells and air pumping means for forcing a predetermined steady flow of air sequentially through the header means, the cells and the facing sheet to vary the acoustic resistance of the facing sheet to make it optimum for a selected sound level and airflow condition in the duct.

Abstract: A method for the attenuation of the noise emitted by a main exhaust nozzle f a jet engine, wherein an auxiliary exhaust nozzle adapted to emit less noise than the main nozzle is associated with said main nozzle and is located to the side of the main nozzle, in the direction in which it is desired to attenuate the noise of the main nozzle.

Abstract: This invention relates to an improvement in an aircraft having a tail-mounted, shrouded pusher-type propeller and an engine mounted in front of the shroud, the improvement comprising exhaust pipe running from the engine to the shroud.