A ram air turbine (RAT) assembly includes a turbine having at least one turbine blade that rotates about a turbine driveshaft, a lower gear box coupled to the driveshaft, a generator/pump housing and a strut connected between the lower gear box and the generator/pump housing. The assembly also includes a damping element connected to one of the strut and the lower gear box. The damping element includes an actuator including an extendable member and a mass element connected to the extendable member and that can be moved by the extendable member from a retracted position to an extended position, wherein the mass element is closer to the actuator when in the retracted position than when in the extended position.

Rotor blades may be modified with field-installable profiles, or wedges towards the rear trailing end. The wedges may incorporate one or more porous sections to enhance fluid flow through the wedge, and thus reduce trailing edge noise and rotor vibrations when the rotors are in use. The use of porous materials on the trailing end of the blade and/or wedge reduces the intensity of high-frequency noise. A portion of the wedge may retain impermeable characteristics and be paired with a more porous section to minimize the boundary layer, and thus reduce noise. The wedges may be installed in the field, and easy removed, replaced, and/or applied manually to the rotor blade trailing edge. As the vehicle is used, the placement and choice of location and number of wedges applied to one or more rotor blades may be modified each time the vehicle rotor blade come to rest.

A ram air turbine (RAT) assembly includes a turbine having at least one turbine blade that rotates about a turbine driveshaft, a lower gear box coupled to the driveshaft, a generator/pump housing and a strut connected between the lower gear box and the generator/pump housing. The assembly also includes a damping element connected to one of the strut and the lower gear box. The damping element includes an actuator including an extendable member and a mass element connected to the extendable member and that can be moved by the extendable member from a retracted position to an extended position, wherein the mass element is closer to the actuator when in the retracted position than when in the extended position.

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 vibration attenuator for a rotor of an aircraft has a track housing adapted for rotation relative to the rotor and configured for rotation at a second angular velocity greater than a first angular velocity of the rotor. A track is located within the track housing and has a reaction surface, a pair of weights being configured for movement within the track and in contact with the reaction surface. A stop assembly has a pair of stops spaced 180 degrees apart, the stops separating the weights from each other, and each weight being allowed to travel within the track between the stops. A motor rotates the track housing relative to the rotor. The weights are free to travel relative to each other between a minimum-force configuration, in which the weights are positioned 180 degrees apart, and a maximum-force configuration, in which both weights are adjacent one of the stops.

Aerial vehicles may be operated with discrete sets of propellers, which may be selected for a specific purpose or on a specific basis. The discrete sets of propellers may be operated separately or in tandem with one another, and at varying power levels. For example, a set of propellers may be selected to optimize the thrust, lift, maneuverability or efficiency of an aerial vehicle based on a position or other operational characteristic of the aerial vehicle, or an environmental condition encountered by the aerial vehicle. At least one of the propellers may be statically or dynamically imbalanced, such that the propeller emits a predetermined sound during operation. A balanced propeller may be specifically modified to cause the aerial vehicle to emit the predetermined sound by changing one or more parameters of the balanced propeller and causing the balanced propeller to be statically or dynamically imbalanced.

A pitch control system characterized by a hub with at least two blade housings on the hub that are disposed around the hub axis. The blade housings have corresponding blades that engage with them. The blades spiral along housing longitudinal axes toward and away from the hub axis about a segment of helical path to effect a change in the pitch of each blade. One or more elastic members draw the blades toward the hub axis, either directly or indirectly. There are pitch mechanisms effective to facilitate blades to spiral around housing-longitudinal axes. A blade will spiral away from the hub axis when the centrifugal force exerted on the blade exceeds the opposing elastic force in the housing-longitudinal direction (neglecting other forces). Conversely, blades spiral toward the hub axis when said centrifugal force is less than said elastic force. There is an imaginary plane orthogonal to the hub axis. Housing-longitudinal axes have angles with respect to the imaginary plane of not more than 30 degrees.

In some examples, an aircraft comprises an airframe, a rotor system coupled to the airframe, and a vibration attenuation system. The rotor system is operable to exert a vibratory force on the airframe. The vibration attenuation system comprises two or more batteries and elastic devices. The two or more batteries are operable to supply power to the rotor system. The elastic devices coupled to the two or more batteries and the airframe. The elastic devices are configured to attenuate the vibratory force based on facilitating oscillation of the two or more batteries. In other examples, a method comprises coupling elastic devices to two or more batteries and an airframe of an aircraft. The elastic devices receiving a vibratory force via the airframe and attenuate the vibratory force based on facilitating oscillation of the two or more batteries.

The present invention includes a balancing system that includes a weight box, mounted substantially within the rotor-blade spar, flush with a rotor-blade spar outer surface, operably accessible from a rotor-blade tip, and retained within the rotor-blade spar by a weight-box retention pin, one or more weight-box contact surfaces bonded to a rotor-blade-spar inner surface, or a weight-box lip providing a bearing contact with an edge of a spar rotor-blade spar cutout; and a weight package attached to the weight box, the weight package including a weight-box cover, two or more weight guide-rods attached to the weight-box cover, wherein one of the two or more weight guide-rods is positioned forward of a pitch change axis or center of twist and wherein one of the two weight guide-rods is positioned aft of the pitch change axis or center of twist, and one or more balance weights mounted on the weight guide-rods.

The present invention includes a rotor-blade span-balancing system, including a span-balance pocket in a surface of a rotor blade; a cover operably configured to cover the span-balance pocket, wherein the cover is operably configured to be substantially flush with the surface of the rotor blade surface when covering the span-balance pocket, and wherein the cover includes a cover boss for reacting centrifugal force of the cover into the rotor blade; and one or more span-balance weights attached to the cover to span-balance the rotor blade.