Abstract: A strut support system for a ducted fan unmanned aerial vehicle to suppress noise comprising: a ducted fan fuselage that defines an opening; an engine that extends longitudinally through the opening in the fuselage; a drive mechanism rotatably mounted to the engine, wherein a fan is mounted on the drive mechanism within a duct defined by the opening; and a plurality of struts extending between the ducted fan fuselage and the engine each comprising a first leg and a second leg joined together by a curvilinear junction, wherein the first leg is attached to the ducted fan fuselage and the second leg is attached to the engine, wherein the plurality of struts are positioned upstream of the fan, wherein the junction between the first leg of each of the plurality of struts and the ducted fan fuselage is outside the highlight of the ducted fan fuselage's leading edge.

Abstract: A ducted fan air-vehicle having an air duct and a fan is described. The air duct includes an outer rim and an inner rim, and the fan is located within the air duct and rotates in a direction. The fan also includes a hub, a plurality of struts extending from the hub and positioned adjacent the outer rim of the fan, a plurality of stators extending from the hub and positioned adjacent the inner rim of the fan, and a plurality of rotor blades extending from the hub and positioned between the plurality of struts and the plurality of stators. The stators are lean in a plane of fan rotation and swept in a plane normal to fan rotation to create the optimum amount of noise reduction in the ducted fan air-vehicle.

Abstract: A strut support system for a ducted fan unmanned aerial vehicle to suppress noise comprising: a ducted fan fuselage that defines an opening; an engine that extends longitudinally through the opening in the fuselage; a drive mechanism rotatably mounted to the engine, wherein a fan is mounted on the drive mechanism within a duct defined by the opening; and a plurality of struts extending between the ducted fan fuselage and the engine each comprising a first leg and a second leg joined together by a curvilinear junction, wherein the first leg is attached to the ducted fan fuselage and the second leg is attached to the engine, wherein the plurality of struts are positioned upstream of the fan, wherein the junction between the first leg of each of the plurality of struts and the ducted fan fuselage is outside the highlight of the ducted fan fuselage's leading edge.

Abstract: An assembly useful in reducing aircraft engine noise such as turbofan engine noise comprises: (a) a core portion comprising at least one entrance end and at least one exit end for the passage of acoustic energy therethrough; (b) a first member having an exterior face and an interior face, wherein the first member is adjacent to at least a part of the core portion, and the first member has a plurality of openings therein to permit the passage of acoustic energy therethrough; and (c) a second member having an exterior face and an interior face, wherein the interior face of the second member is adjacent to the core portion. The core portion may be a honeycomb acoustic structure, and the first member may be perforated to permit the passage of acoustic energy into and out of the conduit portion.

Abstract: An assembly useful in reducing aircraft engine noise such as turbofan engine noise comprises: (a) a core portion comprising at least one entrance end and at least one exit end for the passage of acoustic energy therethrough; (b) a first member having an exterior face and an interior face, wherein the first member is adjacent to at least a part of the core portion, and the first member has a plurality of openings therein to permit the passage of acoustic energy therethrough; and (c) a second member having an exterior face and an interior face, wherein the interior face of the second member is adjacent to the core portion. The core portion may be a honeycomb acoustic structure, and the first member may be perforated to permit the passage of acoustic energy into and out of the conduit portion.

Abstract: An array of adaptive or fixed Herschel-Quincke tubes aligned in a circumferential or helical array about an inlet of a turbofan engine. The array of tubes effectively divide the acoustic energy generated by the engine. One of the energy components propagates within the tubes while the other propagates within the engine compartment. At some time certain, the acoustic energy in the tubes is reintroduced into the engine compartment to cancel the acoustic energy remaining in the engine as it propagates from the fan towards the inlet and outlet openings.

Abstract: An active vibration absorber including a frame connected to a structure to be controlled and at least two reaction mass elements operatively connected to the frame. Each of the reaction mass elements is independently movable with respect to said frame. The absorber includes a force generating member for controlling relative movement between the reaction mass elements for damping vibration of the structure. The inventive dual reactive mass absorber requires less control force to produce the same vibration attenuation as conventional single reactive mass absorbers.

Abstract: Reduction or cancellation of acoustic noise is achieved by providing an amplified, oppositely phased version of the noise by means of an acousto-fluidic amplifier. The amplified acoustic output noise is delivered through an impedance matching horn in destructively interfering relation with the original noise. Depending on the acoustic noise source and its spatial distribution, the acousto-fluidic amplifier may be a single stage amplifier or multiple stages connected in parallel and/or cascade, with output horns spatially distributed to have the maximum cancellation effect. Sensed noise, prior to fluidic amplification, may be processed in a manner to effect feedback or feedforward control of the amplified acoustic output signals.

Abstract: An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet.

Abstract: An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet.