Abstract: An example of a hub for a tail rotor includes a body configured to couple to a mast of a rotor system, a trunnion disposed within the body, first and second shafts disposed on opposite sides of the trunnion, first and second end plates secured to the body, and first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

Abstract: A vibration attenuation system for attenuating vibrations in a mast of an aircraft includes a weight attached to the mast but free to orbit about the mast. The weight can be comprised of one or more weight assemblies. Embodiments can include a single weight, or plural weight assemblies wherein each weight assembly can include a mechanical interconnecting mechanism so that each weight assembly receives feedback regarding the position and movement of one or more other weight assemblies. Each weight can be associated with a spring that urges the weight towards a neutral position. Rotation of the mast can cause the weight to orbit about the mast and self-excite such that the weight acts against the urging of the spring towards an attenuating position.

Abstract: An aircraft includes a variable-speed gearbox. The variable-speed gearbox includes a low-speed gear train and a high-speed gear train, each gear train of which is configured to selectively provide torque from an engine of the aircraft to a proprotor. The variable-speed gearbox also includes a hydraulic system configured to provide torque to the proprotor. The hydraulic system includes a hydraulic pump driven by the engine of the tiltrotor aircraft and a variable-displacement motor driven by a hydraulic fluid from the hydraulic pump.

Abstract: A method of increasing a stability speed of a tiltrotor aircraft includes pivoting a rotor assembly having at least three rotor blades from a first position for operating the tiltrotor aircraft in a helicopter mode to a second position for operating the tiltrotor aircraft in an airplane mode, and increasing a stiffness of the rotor assembly when the rotor assembly is in the second position.

Abstract: An example of a hub for a tail rotor includes a body configured to couple to a mast of a rotor system, a trunnion disposed within the body, first and second shafts disposed on opposite sides of the trunnion, first and second end plates secured to the body, and first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

Abstract: An example of a hub for a tail rotor includes a body configured to couple to a mast of a rotor system, a trunnion disposed within the body, first and second shafts disposed on opposite sides of the trunnion, first and second end plates secured to the body, and first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

Abstract: An example of a hub for a tail rotor includes a body configured to couple to a mast of a rotor system, a trunnion disposed within the body, first and second shafts disposed on opposite sides of the trunnion, first and second end plates secured to the body, and first and second end bearings, the first end bearing disposed between the first shaft and the first end plate and the second end bearing disposed between the second shaft and the second end plate.

Abstract: A vibration attenuation system for attenuating vibrations in a mast of an aircraft includes a weight attached to the mast but free to orbit about the mast. The weight can be comprised of one or more weight assemblies. Embodiments can include a single weight, or plural weight assemblies wherein each weight assembly can include a mechanical interconnecting mechanism so that each weight assembly receives feedback regarding the position and movement of one or more other weight assemblies. Each weight can be associated with a spring that urges the weight towards a neutral position. Rotation of the mast can cause the weight to orbit about the mast and self-excite such that the weight acts against the urging of the spring towards an attenuating position.

Abstract: A method of increasing a stability speed of a tiltrotor aircraft includes pivoting a rotor assembly having at least three rotor blades from a first position for operating the tiltrotor aircraft in a helicopter mode to a second position for operating the tiltrotor aircraft in an airplane mode, and increasing a stiffness of the rotor assembly when the rotor assembly is in the second position.

Abstract: An aircraft includes a variable-speed gearbox. The variable-speed gearbox includes a low-speed gear train and a high-speed gear train, each gear train of which is configured to selectively provide torque from an engine of the aircraft to a proprotor. The variable-speed gearbox also includes a hydraulic system configured to provide torque to the proprotor. The hydraulic system includes a hydraulic pump driven by the engine of the tiltrotor aircraft and a variable-displacement motor driven by a hydraulic fluid from the hydraulic pump.

Abstract: A damper has a piston having an axis, an outer surface, and opposing ends. Elastomeric seals are in sealing contact with the outer surface of the piston, the seals being coaxial with the piston and limiting movement of the piston to a path along the axis of the piston. The seals also define fluid chambers adjacent the ends of the piston. A primary passage communicates the fluid chambers, and a selectively switchable valve for controls a flow of fluid from one of the chambers to another of the chambers through the primary passage. When the flow of fluid through the primary passage is permitted, movement of the piston is resisted by a first spring rate due to a shear force required to cause shear deflection of the seals. When the flow of fluid through the primary passage is restricted, movement of the piston is resisted by a second spring rate due to a fluid force required to cause bulging deflection of the seals.

Abstract: A vibration isolator for connecting a first body and a second body. The vibration isolator includes a housing having a first chamber, a second chamber, and a port connecting the first chamber to the second chamber and permitting fluid to flow between the first chamber and the second chamber. The first and second chambers and the port defining a fluid reservoir. The isolator including a gas-to-fluid accumulator in fluid communication with the fluid reservoir through a first one-way valve and a second one-way valve. The first one-way valve allows fluid to pass only from the fluid reservoir to the accumulator and the second one-way valve allows fluid to pass only from the accumulator to the fluid reservoir. At least one of the first and second one-way valves being preloaded to a predetermined force to permit fluid flow through the at least one-way valve only when fluid pressure exceeds the predetermined force.

Abstract: A rotor system vibration absorber for use with a helicopter of other rotocraft is disclosed in which spring forces are provided by a plurality of elongated rods (73) arranged in a selected pattern. The rods are coupled at one end to a fixed base (79) that is coupled to a rotor hub (55), and at the other end to a tuning weight (81).

Abstract: An assembly for providing flexure to a blade of a rotary blade system, the assembly including an upper support plate having an upper curved surface, a lower support plate having a lower curved surface, and a yoke positioned therebetween. At least one of the upper and lower yoke surfaces having a layer of cushioning material positioned thereon and secured thereto. The layer of cushioning material extending along and following the general contour of yoke surface, and the layer of cushioning material directly contacting a support plate. Another embodiment is an assembly for providing flexure to a blade of a rotary blade system, including, an upper support plate having an upper curved surface, a lower support plate having a lower curved surface, and a yoke positioned therebetween and directly contacting the support plates wherein one of the curved surfaces is a non-circular arc that does not form part of the circumference of a circle.