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 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.

The present disclosure is generally related to aircraft having one or more unducted fan propulsors at locations within specific regions relative to an airfoil, such as a wing or horizontal stabilizer. More specifically, the specific regions are located where there is a relatively higher pressure air flow beneath the wings or above a horizontal stabilizer. That higher pressure air flow can be utilized to provide increased thrust from the unducted fan propulsor.

A propulsion system for aircraft having a longitudinal axis and including: a propeller mobile in rotation around the longitudinal axis and including a plurality of blades distributed angularly relative to the longitudinal axis. A blade angle of the blades may be adjusted to modify the blade angle of each blade as a function of the angular position of each blade around the longitudinal axis.

A rotor system for an aircraft that includes one or more rotor blades respectively connected to the rotor via a blade cuff, and a method of manufacturing the rotor system is disclosed. The rotor system includes (i) a blade cuff coupled to a blade, wherein a distal end diameter of the blade cuff is larger in diameter than a middle portion diameter of the blade cuff, and (ii) a blade. The blade is wrapped in a plurality of fibers. At least a subset of the plurality of fibers extend longitudinally down the blade from wrapping the middle portion diameter of the blade cuff and continuing past the distal end diameter of the blade cuff. The blade comprises a plurality of weights disposed in a forward edge section of the blade to balance a front side of the blade and a backside of the blade.

A tail-rotor vibration dampener system for an aircraft is provided. The system includes a fuselage and an open rotor assembly including a powerplant and a set of rotor blades. The system further includes at least one actuator unit connecting the open rotor assembly to the fuselage. The actuator unit includes a hydraulic actuator controlling a position of the open rotor assembly in relation to the fuselage and a dampening device operable to cancel a vibration emanating from the open rotor assembly. The system further includes a computerized vibration dampening controller, including programming to determine a frequency of the vibration emanating from the open rotor assembly and control the dampening device to cancel the vibration emanating from the open rotor assembly based upon the frequency.