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.

Various embodiments of an unmanned aerial vehicle are disclosed. In some embodiments, the UAV includes a motor assembly rotatable about rotation axis and a propeller hub assembly removably engageable with the motor assembly. The propeller hub assembly includes a retainer configured and dimensioned for engagement with the motor assembly such that rotation of the motor assembly causes corresponding rotation of the propeller hub assembly. The retainer includes a pair of deflectable arms resiliently repositionable between a first position and a second position, for engagement and disengagement with the motor assembly, respectively. The arms are movable inwardly towards the rotation axis from the first position to the second position upon application of an external force and movable outwardly away from the rotation axis from the second position to the first position upon removal of the external force.

The aircraft can include: an airframe, a tilt mechanism, a payload housing, and can optionally include an impact attenuator, a set of ground support members (e.g., struts), a set of power sources, and a set of control elements. The airframe can include: a set of rotors and a set of support members. By utilizing a larger rotor blade area (and/or larger rotor disc area) and adjusting the blade pitch and RPM, the rotors can augment the lift generated by the aerodynamic profile of the aircraft in the forward flight mode in addition to providing forward thrust. Variants generating lift with the rotors can reduce or eliminate additional control surfaces (e.g., wing flaps, ailerons, ruddervators, elevators, rudder, etc.) on the aircraft since the thrust and motor torque is controllable (thereby indirectly controlling lift) at each rotor, thereby enabling pitch, yaw, and/or roll control during forward flight.

In one embodiment, a hub for a fan of a gas turbine engine is provided. The hub having: a plurality of attachment features located on an outer circumferential surface of the hub, wherein at least some of the plurality attachment features extend radially away from the outer circumferential surface and are axially aligned with each other and at least some of the plurality of attachment features extending radially away from the outer circumferential surface and are off set from each other, and wherein the plurality of attachment features have an opening configured to receive a portion of a pin; and wherein at least some of the plurality of attachment features are located on a forward leading edge of the hub.

A conical hub for a fan of a gas turbine engine is provided. The conical hub having: a plurality of attachment features located on an outer circumferential surface of the conical hub, wherein at least some of the plurality attachment features are axially aligned with each other and at least some of the plurality of attachment features are off set from each other, and wherein each of the plurality of attachment features have an opening configured to receive a portion of a pin; and the outer circumferential surface of the conical hub increases in diameter with respect to an axis of the conical hub in a forward to aft direction of the conical hub.

In one embodiment, a hub for a fan of a gas turbine engine is provided. The hub having: a plurality of attachment features located on an outer circumferential surface of the hub, wherein at least some of the plurality attachment features extend radially away from the outer circumferential surface and are axially aligned with each other and at least some of the plurality of attachment features extending radially away from the outer circumferential surface and are off set from each other, and wherein the plurality of attachment features have an opening configured to receive a portion of a pin; and wherein at least some of the plurality of attachment features are located on a forward leading edge of the hub.

Provided herein is a rotor attachment assembly for an aircraft. A rotor attachment assembly includes a connecting assembly associated with the aircraft and a rotor assembly configured to be connected to the connecting assembly. The rotor assembly includes a plurality of fins configured to fit a respective plurality of cut-outs of the connecting assembly, a hollow section configured to accommodate at least a part of a pin of the connecting assembly so as to center the rotor assembly relative to the connecting assembly, and a spring configured to expand to allow the fins to pass and to close to retain the fins when the rotor assembly is connected to the connecting assembly.

A locking mechanism for unmanned aerial vehicle (UAV) is provided by the present invention, includes: a motor, a base, a blade and a locking component; wherein the base comprises a mounting groove for the blade inserting in; the locking component is configured to fixedly connect the base and a rotor of the motor by passing through the base and the blade; the blade is configured to rotate freely relative to the locking component in a range of angles. The locking component of the present invention is convenient for assembly and disassembly, with a light weight and a small structure.

A locking mechanism for unmanned aerial vehicle (UAV) is provided by the present invention, includes: a motor, a base, a blade and a locking component; wherein the base comprises a mounting groove for the blade inserting in; the locking component is configured to fixedly connect the base and a rotor of the motor by passing through the base and the blade; the blade is configured to rotate freely relative to the locking component in a range of angles. The locking component of the present invention is convenient for assembly and disassembly, with a light weight and a small structure.

An aircraft including at least one unducted turbine engine for the propulsion of the aircraft. The turbine engine comprising: a rotor and a stator comprising a plurality of stator blades extending radially with respect to the longitudinal axis, each stator blade being defined, in a plane transverse to the longitudinal axis, by an angular position; and at least one aerodynamic obstruction positioned close to the turbine engine. The stator of the turbine engine comprises stator blades having a first chord, referred to as conventional blades, and at least one stator blade having a second chord larger than the first chord, referred to as the elongate blade, said at least one elongate blade being positioned in an interference angular range defined opposite the aerodynamic obstacle, so as to increase the straightening of the airflow from the rotor in the interference angular range.