Motorized aircraft and other mechanical constructs subject to a force vibrate at resonant frequencies, causing parts degradation, unpleasant sensations for occupants, unwanted noise, and other undesirable effects. Tuned vibration absorbers that mitigate these effects typically counteract vibrations at specific frequencies traveling in specific directions at specific locations within a given structure and are not adjustable. The present disclosure details a disk-shaped tuned vibration absorber that may be tuned on-the-spot within a structural mount such that the frequency at which the disk resonates may be varied and such that the working direction of the disk may be varied. The direction of vibration absorption of the disk may be altered by reconfiguring the disk within its mount, and the resonance of the disk may be altered by rotating an inner component of the disk. The inner component comprises a mass and an elastomer of circumferentially varying stiffness.

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.

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.

A rotary wing aircraft has a body (2), a rotor (3) positioned so as to extend outward from within the body (2) and to rotate about its axis, at least one blade (4) extending outward from the rotor (2) and providing lift and/or thrust force to the body (2) by its movement, at least one outer blade (401) positioned in the blade (4) and providing lift and/or thrust force to the body (2), and at least one mechanism (5) enabling the outer blade (401) to switch from a retracted first position in which the it is almost entirely located in the blade (4) to a second position in which it extends outward from the blade (4) by moving linearly under the influence of the centrifugal force generated during the movement of the rotor (2).

There is described herein a propeller balancing system and method that selects at least a portion of received propeller vibration data by comparing received aircraft data collected concurrently with the propeller vibration data with at least one customizable flight criterion, and identifying the portion of the vibration data acquired at a time when the aircraft data meets the at least one customizable flight criterion. The selected portion of the propeller vibration data is analyzed to assess a vibration level of the propeller and a balancing need is signaled when the vibration level reaches a threshold.

There is described herein a propeller balancing system and method that determines a stable cruise condition of an aircraft during flight, and considers vibration data for propeller balancing collected while the aircraft is in the stable cruise condition. Parameters used to determine stable cruise condition may be unique for each flight and/or aircraft, and balancing solutions may be determined based on these unique parameters.

Sounds are generated by an aerial vehicle during operation. For example, the motors and propellers of an aerial vehicle generate sounds during operation. Disclosed are systems, methods, and apparatus for actively adjusting the position of one or more propeller blade treatments of a propeller blade of an aerial vehicle during operation of the aerial vehicle. For example, the propeller blade may have one or more propeller blade treatments that may be adjusted between two or more positions. Based on the position of the propeller blade treatments, the airflow over the propeller is altered, thereby altering the sound generated by the propeller when rotating. By altering the propeller blade treatments on multiple propeller blades of the aerial vehicle, the different sounds generated by the different propeller blades may effectively cancel, reduce, and/or otherwise alter the total sound generated by the aerial vehicle.

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 method of and system for damping vibrations in a hybrid-electric propulsion system configured to drive a propulsor is provided. The hybrid-electric propulsion system includes a thermal engine, an electric motor, and an inverter. The method includes: a) controlling the thermal engine and the electric motor to operate at a target propulsion parameter, wherein the inverter is used in the controlling of the electric motor; b) determining a presence of a vibrational response within the hybrid-electric propulsion system; c) producing a vibration compensation signal configured to damp the vibrational response within the hybrid-electric propulsion system; and d) controlling the electric motor to damp the vibrational response using the vibrational compensation signal.

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.