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 yoke for providing a centrifugal force retention load path between a proprotor blade and a hub of a soft-in-plane proprotor system operable for use on a tiltrotor aircraft. The yoke includes a continuous loop having a longitudinal axis and first and second longitudinal sections extending between inboard and outboard arcuate sections. A flapping bearing receiving region is disposed at least partially within the inboard arcuate section to an interior of the continuous loop. A centrifugal force bearing receiving region is disposed at least partially within the outboard arcuate section to the interior of the continuous loop. The continuous loop is formed from a composite material having a plurality of double bias material plies and a plurality of unidirectional material plies such that the number of unidirectional material plies is greater than the number of double bias material plies.

Abstract: A soft-in-plane proprotor system for a tiltrotor aircraft having a helicopter mode and an airplane mode. The proprotor system includes a hub, a plurality of proprotor blades and a plurality of loop yokes, each coupling one of the proprotor blades with the hub and each including first and second longitudinal sections extending between inboard and outboard arcuate sections and a bearing assembly disposed between the inboard and outboard arcuate sections of each loop yoke. Each bearing assembly includes a flapping bearing disposed generally within the inboard arcuate section of the respective loop yoke and coupled to the hub, a lead-lag damper coupled to the hub, a centrifugal force bearing disposed generally within the outboard arcuate section of the respective loop yoke and a blade anchor coupled between the lead-lag damper and the centrifugal force bearing. The blade anchor is also coupled to the respective proprotor blade.

Abstract: An aircraft comprises a fuselage, one or more support structures connected to the fuselage, one or more engines or motors disposed within or attached to the one or more support structures or the fuselage, and a distributed propulsion system. The distributed propulsion system comprising two or more propellers symmetrically distributed in an array along the one or more support structures with respect to a center of gravity of the aircraft and operably connected to the one or more engines or motors, wherein each propeller has a rotation direction within a tilted plane of rotation, and a summation of horizontal force vectors created by the tilted plane of rotation of all the propellers is substantially zero when all the propellers are creating a substantially equal thrust magnitude. Movement of the aircraft is controlled by selectively increasing or decreasing a thrust of at least one of the two or more propellers.

Abstract: An aircraft rotor assembly has a central hub and a plurality of rotor blades coupled to the hub for rotation with the hub about an axis, each blade having a Lock number of approximately 5 or greater. A lead-lag pivot for each blade is formed by a flexure coupling the associated blade to the hub. Each pivot is a radial distance from the axis and allows for in-plane lead-lag motion of the associated blade relative to the hub, each pivot allowing for in-plane motion from a neutral position of at least 1 degree in each of the lead and lag directions. Elastic deformation of the flexure produces a biasing force for biasing the associated blade toward the neutral position, and the biasing force is selected to achieve a first in-plane frequency of greater than 1/rev for each blade.

Abstract: A proprotor system operable for use on a tiltrotor aircraft having a helicopter flight mode and an airplane flight mode. The proprotor system includes a rotor hub and a plurality of proprotor blades coupled to the rotor hub such that each proprotor blade has three independent degrees of freedom relative to the rotor hub including blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. Each of a plurality of spherical bearings couples one of the proprotor blades with the rotor hub. In addition, each of a plurality of lead-lag dampers couples one of the proprotor blades with the rotor hub, wherein each lead-lag damper is aligned with the pitch change axis of the respective proprotor blade, thereby providing pitch independent lead-lag damping.

Abstract: One example of a rotor assembly comprises: a rotor hub operable to rotate based on rotation of a mast; a first rotor blade pivotally attached to the rotor hub; a bracing member pivotally attached to the rotor hub at a first end and pivotally attached to the first rotor blade at a second end; and a linkage mechanism coupling the first rotor blade to a second rotor blade. The bracing member is operable to transfer a coning movement of the first rotor blade to a movement of the linkage mechanism and a corresponding coning movement of the second rotor blade.

Abstract: A vibration attenuator for a rotor is rotatable about a mast axis and has a frame configured for rotation about the mast axis relative to the rotor. A first mass is axially translatable in a first direction relative to the frame parallel to a first axis, and a first biasing force urges the first mass toward a first-mass rest position in which the first mass is symmetric about the mast axis. A second mass is axially translatable in a second direction relative to the frame parallel to a second axis, and a second biasing force urges the second mass toward a second-mass rest position in which the second mass is symmetric about the mast axis. A selected first or second mass moves radially outward from the rest position to oppose vibrations in the rotor.

Abstract: A high stiffness hub assembly for a rotor system operable to rotate with a mast of a rotorcraft. The hub assembly includes a yoke and a constant velocity joint assembly. The yoke has a plurality of blade arms each configured to hold a rotor blade. The constant velocity joint assembly provides a torque path from the mast to the yoke that includes a trunnion assembly, a plurality of drive links and a plurality of pillow blocks. The trunnion assembly is coupled to the mast and has a plurality of outwardly extending trunnions. Each drive link has a leading bearing coupled to one of the trunnions and a trailing bearing coupled to one of the pillow blocks. Each pillow block is independently mounted between an upper surface of the yoke and a hub plate.

Abstract: A tiltrotor aircraft has a fuselage and a wing having upper and lower surfaces with a plurality of channels extending therebetween, each with a cycloidal rotor mounted therein. At least two pylon assemblies are rotatably coupled to the wing to selectively operate the tiltrotor aircraft between helicopter and airplane flight modes. Each pylon assembly includes a mast and a proprotor assembly operable to rotate with the mast to generate thrust. At least one engine provides torque and rotational energy to the proprotor assemblies and the propulsion assemblies. Each of the cycloidal rotors has a plurality of blades that travels in a generally circular path and has a plurality of pitch angle configurations such that each cycloidal rotor is operable to generate a variable thrust and a variable thrust vector, thereby providing vertical lift augmentation, roll control, yaw control and/or pitch control in the helicopter flight mode.

Abstract: A high stiffness hub assembly for a rotor system operable to rotate with a mast of a rotorcraft. The hub assembly includes a yoke and a constant velocity joint assembly. The yoke has a plurality of blade arms each configured to hold a rotor blade. The constant velocity joint assembly provides a torque path from the mast to the yoke that includes a trunnion assembly, a plurality of drive links and a plurality of pillow blocks. The trunnion assembly is coupled to the mast and has a plurality of outwardly extending trunnions. Each drive link has a leading bearing coupled to one of the trunnions and a trailing bearing coupled to one of the pillow blocks. Each pillow block is independently mounted between an upper surface of the yoke and a hub plate.

Abstract: Systems and methods of operating a tiltrotor aircraft include providing a control system that includes sensors and/or gauges that provide feedback regarding hub shear forces in rotor systems of the aircraft that produce aeroelastic instability known as whirl flutter. Feedback from the sensors and/or gauges is communicated to a flight control subsystem that includes an algorithm that provides a cascading set of responses to control whirl flutter and a failsafe that adjusts operational characteristics of the aircraft in response to the continuation or excitation of the whirl flutter.

Abstract: A high stiffness hub assembly for a proprotor system operable to rotate with a mast of a tiltrotor aircraft having helicopter and airplane flight modes. The hub assembly includes a yoke and a constant velocity joint assembly. The yoke has four blade arms each adapted to hold a proprotor blade. The constant velocity joint assembly provides a torque path from the mast to the yoke that includes a trunnion assembly, four drive links and four pillow blocks. The trunnion assembly is coupled to the mast and has four outwardly extending trunnions. Each drive link has a leading bearing coupled to one of the trunnions and a trailing bearing coupled to one of the pillow blocks. Each pillow block is independently mounted between an upper surface of the yoke and a hub plate with two connection members that extend through the yoke and the pillow block.

Abstract: A proprotor system operable for use on a tiltrotor aircraft having a helicopter flight mode and an airplane flight mode. The proprotor system includes a rotor hub and a plurality of proprotor blades coupled to the rotor hub such that each proprotor blade has three independent degrees of freedom relative to the rotor hub including blade pitch about a pitch change axis, blade flap about a flapping axis and lead-lag about a lead-lag axis. Each of a plurality of spherical bearings couples one of the proprotor blades with the rotor hub. In addition, each of a plurality of lead-lag dampers couples one of the proprotor blades with the rotor hub, wherein each lead-lag damper is aligned with the pitch change axis of the respective proprotor blade, thereby providing pitch independent lead-lag damping.

Abstract: A wing airframe for a wing of a tiltrotor aircraft includes a wing airframe core assembly and a wing skin assembly disposed on the wing airframe core assembly. The wing skin assembly includes an outer skin and a damping sublayer, the damping sublayer interposed between the outer skin and the wing airframe core assembly. The tiltrotor aircraft includes a pylon assembly subject to aeroelastic movement during forward flight. The wing is subject to deflection in response to the aeroelastic movement of the pylon assembly.

Abstract: A rotor assembly for an aircraft is operable to generate a variable thrust vector. The rotor assembly includes a mast that is rotatable about a mast axis. A ball joint is positioned about and non rotatable with the mast. A tilt control assembly is positioned on and has a tilting degree of freedom relative to the ball joint. The tilt control assembly is non rotatable with the mast. A rotor hub is rotatably coupled to the tilt control assembly. The rotor hub is rotatable with the mast in a rotational plane and tiltable with the tilt control assembly. The rotor hub includes a plurality of grips each coupled to a rotor blade. Actuation of the tilt control assembly changes the rotational plane of the rotor hub relative to the mast axis, thereby generating the variable thrust vector.

Abstract: A high stiffness hub assembly for a proprotor system operable to rotate with a mast of a tiltrotor aircraft having helicopter and airplane flight modes. The hub assembly includes a yoke and a constant velocity joint assembly. The yoke has four blade arms each adapted to hold a proprotor blade. The constant velocity joint assembly provides a torque path from the mast to the yoke that includes a trunnion assembly, four drive links and four pillow blocks. The trunnion assembly is coupled to the mast and has four outwardly extending trunnions. Each drive link has a leading bearing coupled to one of the trunnions and a trailing bearing coupled to one of the pillow blocks. Each pillow block is independently mounted between an upper surface of the yoke and a hub plate with two connection members that extend through the yoke and the pillow block.

Abstract: A tiltrotor aircraft has a fuselage and a wing having upper and lower surfaces with a plurality of channels extending therebetween, each with a cycloidal rotor mounted therein. At least two pylon assemblies are rotatably coupled to the wing to selectively operate the tiltrotor aircraft between helicopter and airplane flight modes. Each pylon assembly includes a mast and a proprotor assembly operable to rotate with the mast to generate thrust. At least one engine provides torque and rotational energy to the proprotor assemblies and the propulsion assemblies. Each of the cycloidal rotors has a plurality of blades that travels in a generally circular path and has a plurality of pitch angle configurations such that each cycloidal rotor is operable to generate a variable thrust and a variable thrust vector, thereby providing vertical lift augmentation, roll control, yaw control and/or pitch control in the helicopter flight mode.

Abstract: A yoke for providing a centrifugal force retention load path between a proprotor blade and a hub of a soft-in-plane proprotor system operable for use on a tiltrotor aircraft. The yoke includes a continuous loop having a longitudinal axis and first and second longitudinal sections extending between inboard and outboard arcuate sections. A flapping bearing receiving region is disposed at least partially within the inboard arcuate section to an interior of the continuous loop. A centrifugal force bearing receiving region is disposed at least partially within the outboard arcuate section to the interior of the continuous loop. The continuous loop is formed from a composite material having a plurality of double bias material plies and a plurality of unidirectional material plies such that the number of unidirectional material plies is greater than the number of double bias material plies.

Abstract: A soft-in-plane proprotor system for a tiltrotor aircraft having a helicopter mode and an airplane mode. The proprotor system includes a hub, a plurality of proprotor blades and a plurality of blade support assemblies coupling the proprotor blades with the hub. Each blade support assembly includes a flapping bearing coupled to the hub and a yoke having first and second longitudinal sections with outboard grip members and an inboard arcuate section connecting the first and second longitudinal sections and coupled to the flapping bearing. A lead-lag damper is coupled between the hub and an inboard station of the respective proprotor blade. A twist shank is coupled between the outboard grip members of the yoke and an outboard station of the respective the proprotor blade. The twist shank defines a virtual lead-lag hinge outboard of the yoke and coincident with the respective pitch change axis.