A turbine engine module having longitudinal axis X including an unducted propeller for rotating about the longitudinal axis X; —at least one flow straightener wiht a plurality of stator vanes extends substantially along a radial axis Z, each stator vane having a root and a blade rising radially from the root; and—a pitch change system for changing the pitch of the stator vanes. At least two adjacent stator vanes are connected to each other by at least one retaining member coupled to the blades of the stator vanes by at least one pivot shaft and mounted radially from the root of the stator vanes. The pivot shaft extends along a pivot axis B coaxial with the pitch adjustment axis A to enable the stator vanes to pivot about the pivot axis B. An anti-vibration unit dampens vibration of the pivot shaft.

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 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 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 local blade stiffness 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 propeller provided with interchangeable blades, and to a method of mounting such interchangeable blades on the propeller. The propeller comprises a hub, fastening fittings, rotation guide devices for guiding the fastening fittings in rotation relative to the hub, locking parts, and blades. The fastening fittings are configured to be assembled into the hub from the inside of the hub, and the locking parts lock respective ones of the fastening fittings onto the hub. The blades are fastened to respective ones of the fastening fittings outside the hub and can thus easily be replaced with other blades without removing the propeller.

There is provided a method and a system for propeller balancing of an aircraft. The method comprises operating a propeller in-flight, receiving propeller vibration data during operation of the propeller in-flight, computing, after at least one flight of the aircraft, an average vibration magnitude and an average vibration phase angle based on the propeller vibration data, determining a propeller balancing solution based on the average vibration magnitude and the average vibration phase angle, and generating a balancing need indication by outputting the propeller balancing solution.

A data recording and transmission method and system for use in balancing a propeller of an aircraft. The method comprises operating the propeller in-flight, receiving, during operation of the propeller in-flight, vibration data associated with the propeller, retrieving, from a non-volatile memory on-board the aircraft, configuration data associated with the propeller, and transmitting the vibration data and the configuration data to a data processing device configured to determine a balancing solution for the propeller based one the vibration data and the configuration data.

A rotating airfoil including a body and a vibration absorber located within the body. The body has a root end and a tip. The rotating airfoil has a natural frequency, and the vibration absorber has a natural frequency. The natural frequency of the vibration absorber is different than the natural frequency of the rotating airfoil.

A general mounting method for ducted fan propulsors is disclosed. This mounting method uses extremely slender stators that connect the duct ring to the propulsor which is mounted in the middle and drives the rotor, fan or propeller. The slender stators take the form of spokes and as such are so slender that the midspan stresses within the spokes are dominated by axial tension loads rather than the shear loads experienced by conventional stators. The spokes may have an aerodynamic shape and damping methods may be used to retard spoke vibrations and transmission of engine vibrations to the duct and force. The duct itself is also stiffened by the spoke arrangement, thereby reducing low frequency vibration modes.

An unmanned aerial vehicle (UAV) may emit masking sounds during operation of the UAV to mask other sounds generated by the UAV during operation. The UAV may be used to deliver items to a residence or other location associated with a customer. The UAV may emit sounds that mask the conventional sounds generated by the propellers and/or motors to cause the UAV to emit sounds that are pleasing to bystanders or do not annoy the bystanders. The UAV may emit sounds using speakers or other sound generating devices, such as fins, reeds, whistles, or other devices which may cause sound to be emitted from the UAV. Noise canceling algorithms may be used to cancel at least some of the conventional noise generated by operation of the UAV using inverted sounds, while additional sound may be emitted by the UAV, which may not be subject to noise cancelation.