A vibration attenuator for an aircraft has at least one weight mounted in a rotating system of a rotor hub of the aircraft, each weight being rotatable about an axis of rotation of the hub relative to the hub and to each other weight. Drive means are provided for rotating each weight about the axis of rotation at a selected speed for creating oscillatory shear forces that oppose and attenuate rotor-induced vibrations having a selected frequency. A vertically oriented vibration attenuator is configured to oppose and attenuate vertical rotor induced oscillatory forces that would otherwise travel vertical down the rotor mast and into the airframe. A vibration attenuator having weights rotating about separate axes offset from each other.

Methods and apparatus to reduce deflection of an airfoil are disclosed. An example apparatus disclosed herein includes a plate including an aperture, the airfoil disposed in the aperture, and a damper operatively coupled between the plate and a hub of the airfoil, the damper to transform flexural deflection of the airfoil to radial deflection of the plate.

A propeller assembly with at least two propeller blades that are interconnected by associated connection means, the associated connection means defining a common pitch axis for the at least two propeller blades in operation, each one of the at least two propeller blades comprising associated leading and trailing edges that define a respective chord and quarter chord line thereof, wherein the common pitch axis is arranged with a predetermined offset relative to the quarter chord line of each one of the at least two propeller blades, and wherein the associated connection means is adapted to enable, at least in operation in a non-axial inflow field, a passive pitch adjustment of the at least two propeller blades around the common pitch axis.

Systems and methods for protecting an aerodynamic structure, e.g., a wind turbine blade, rotor blade, aerodynamic aerostructure, etc., are provided. Long fiber reinforced composites having a helicoidal architecture with material aligned with a graded hardness and stiffness are used to develop an efficient and highly tailorable leading edge protection (LEP) solution with longer durability than conventional solutions while yielding lighter, and optionally, more environmentally sustainable solutions. At least a portion of the plurality of plies are helicoidally arranged relative to one another to tailor stress wave propagation speed of the aerodynamic blade and to provide load carrying strength for the aerodynamic blade.

A blade of a gas turbine engine may comprise a cavity defined, at least partially, by a first interior surface of the blade and by a second interior surface of the blade. A first rib and a second rib may extend from the first interior surface. A third rib may extend from the second interior surface and may be located between the first rib and the second rib. A bulkhead rib may traverse the cavity and may separate the cavity into a radially inward portion and a radially outward portion. A viscoelastic material may be disposed in the radially inward portion of the cavity.

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.

An aircraft (40). The aircraft comprises a plurality of propellers (46) mounted to wings (44). Each propeller comprises at least one blade (72, 74) coupled to a respective propeller cyclic actuator (78) configured to cyclically alter the pitch of the respective blade (72, 74) as the propeller rotates. The aircraft (40) is configured such that provision of cyclic pitch to the propeller (46) twists at least a portion of the wing (44) about a span of the wing (46) relative to the fuselage (42), to thereby adjust the local angle of incidence of the wing (46).

A propeller system combines innovative strategies to create a new methodology to reduce propeller or rotor noise. The propeller is specifically aimed for ultra-quiet electrically powered aircraft for use in high proximity aviation, but its low-noise advantages will extend to other purposes. The propeller blade includes geometries, along with size and operational limitations that minimize rotational and vortex noise, vibration and span-wise air flow on the blade. To further reduce noise, the propeller provides greater relative thrust on the inboard portions of the blade than do conventional propellers and provides less than conventional relative thrust including negative thrust at the outermost portions of the blade. The propeller blade includes stepped changes in shape at calculated intervals that can reduce resonant blade vibrations and their resultant noise. This ultra-quiet propeller design can also be used for quieting hovercraft, drones, surveillance aircraft, indoor fans, wind tunnels and other applications.

A dual-frequency vibration-reduction apparatus includes a beam having a longitudinal axis and a transverse axis perpendicular to the longitudinal axis. An attachment mechanism mechanically couples a portion of the beam to a structure. One or more masses are attached to the beam such that the apparatus vibrates bi-modally at a primary frequency and a secondary frequency for reducing vibrations of the structure at the primary frequency and the secondary frequency. A first mode may be a bending mode of the apparatus, while a second mode is a torsion mode. The vibration reduction apparatus may be tuned such that the primary frequency substantially matches a blade-pass frequency of a propeller-driven aircraft and the secondary frequency substantially matches a harmonic of the blade-pass frequency. The vibration reduction apparatus includes a mounting mechanism for mounting to any structure requiring low-frequency vibration attenuation.

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.