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: A proprotor system for tiltrotor aircraft having a helicopter mode and an airplane mode. The proprotor system includes a hub and a plurality of proprotor blades coupled to the hub such that each proprotor blade is operable to independently flap relative to the hub about a flapping axis and independently change pitch about a pitch change axis. The proprotor blades have a first in-plane frequency less than 1.0/rev.

Abstract: A proprotor system for tiltrotor aircraft having a helicopter mode and an airplane mode. The proprotor system includes a hub and a plurality of proprotor blades coupled to the hub such that each proprotor blade is operable to independently flap relative to the hub and independently change pitch. In the airplane mode, the proprotor blades have a first in-plane frequency greater than 2.0/rev.

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 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.