An aircraft, damper assembly for an aircraft and method for reducing a vibration in a rotating shaft. The damper assembly includes a damper element, a first plate and a second plate. The damper element has a damper opening shaped to surround the shaft. The first plate has a first opening shaped to surround the shaft and a recess receptive to the damper element, the damper element being rotatable within the recess. The second plate has a second opening shaped to surround the shaft and secured to the first plate to close the recess and secure the damper element between the first plate and second plate. The damper element rotates within the closed recess.

A vibration damper for an additively manufactured structure includes a structure at least partially formed with an additive manufacturing technique. Also included is a damping element embedded within the structure at an internal location of the structure. A method of damping vibration of an additively manufactured component is provided. The method includes additively manufacturing a structure. The method also includes embedding at least one damping element within the structure at an internal location of the structure.

A vibration attenuator has a first spinner configured for rotation about a first axis and a first mass coupled to the first spinner for rotation therewith, the first mass being movable radially relative to the first axis between an inner position and an outer position. An actuator is coupled to the first mass for selectively controlling a radial location of the first mass relative to the axis, and a first motor is configured for driving the first spinner in rotation about the first axis.

A rotor system is provided including a rotor hub configured to rotate about an axis and a plurality of rotor blade assemblies mounted to the rotor hub and configured to rotate within a plane about the axis. A vibration reducing system is operably coupled to the rotor hub. The vibration reducing system is arranged at a position offset from a center of rotation of the rotor hub.

A system to prevent or limit resonance in a rotocraft. The system comprises an airframe, a rotor system having a natural frequency and including a rotor and a mast attached to the airframe, and a non-linear spring positioned between the rotor system and the airframe. The rotor system and the airframe are operable to move relative to each other as the rotor system begins to oscillate. The non-linear spring is configured to be deformed when the rotor system and the airframe move relative to each other such that the deformation of the non-linear spring causes the natural frequency of the rotor system to change. Also disclosed is a related method for preventing or limiting resonance in a rotorcraft.

Some examples of rotating shaft damping with electro-rheological fluid can be implemented as a method. At least a portion of a circumferential surface area of a portion of a rotorcraft rotating shaft is surrounded with multiple hollow members. Each hollow member includes an electro-rheological fluid having a viscosity that changes based on an electric field applied to the electro-rheological fluid. A vibration of the rotorcraft rotating shaft is controlled by changing the viscosity of the electro-rheological fluid in response to the electric field applied to the electro-rheological fluid.

A resonator having a support and a seismic mass. Movement means include a first electromagnetic assembly comprising a first electric coil that is not electrically powered. An actuator is connected to a processor unit, the processor unit electrically powering the actuator with adjustable electrical power. A resilient member is interposed between said seismic mass and said support.

In an embodiment, a rotorcraft includes an airframe; a main rotor transmission; one or more brackets mounting the main rotor transmission to the airframe, longitudinal axes of the one or more brackets being substantially parallel with a longitudinal axis of the rotorcraft; and one or more restraints mounting the main rotor transmission to the airframe, the one or more restraints being mounted at an angle non-orthogonal to the longitudinal axis of the rotorcraft and a lateral axis of the rotorcraft.

A force generator includes a hub, which is rotatable about an axis thereof, an elongate member coupled to the hub such that the elongate member is rotatable with the hub and extends radially outwardly away from the hub and the axis along a radial dimension defined with respect to the axis and a mass, which is movably disposed along the elongate member and is adjustable to multiple radial mass positions relative to the hub.

A main rotor trim tab retention system includes, a blade housing having flanges separated by a cavity defined between the flanges, and a trim tab assembly. The trim tab assembly includes, a trim tab having an aerodynamic surface, at least one arm extending from the trim tab positionable within the cavity while the trim tab extends outward from the cavity, and a spherical bearing connecting the trim tab and the at least one arm, the spherical bearing having a first axis which is substantially perpendicular to the aerodynamic surface of the trim tab. The at least one arm is pivotable about the spherical bearing about a second axis substantially perpendicular to the first axis to rotate the trim tab relative to the blade housing.