Aircraft and propeller assemblies may include a propeller adapter with a plurality of propeller blades coupled to the propeller adapter in a common plane. At least one propeller blade of the plurality of propeller blades may be pivotably coupled to the propeller adapter to pivot within the common plane. A spring may be coupled between a portion of the propeller adapter and a portion of the at least one propeller blade pivotably coupled to the propeller adapter. Other aspects, embodiments, and features are also included.

Aircraft and propeller assemblies may include a propeller adapter with a plurality of propeller blades coupled to the propeller adapter in a common plane. At least one propeller blade of the plurality of propeller blades may be pivotably coupled to the propeller adapter to pivot within the common plane. A spring may be coupled between a portion of the propeller adapter and a portion of the at least one propeller blade pivotably coupled to the propeller adapter. Other aspects, embodiments, and features are also included.

An example unmanned aerial vehicle includes a housing; a wireless communication module; a plurality of propulsion systems; and a navigation circuit. At least one of the plurality of propulsion systems includes a motor; and a propeller assembly rotatably connected to the motor. The propeller assembly comprises: a hub structure including a surface facing away from the motor; a first connecting member including a first post and a second post extending in parallel to and spaced apart from the first post, and the first post and the second post are fixed to the surface and are able to move elastically in a second direction perpendicular to the first direction; a first blade detachably coupled to the first connecting member and comprising an opening to which the first post and the second post are coupled; and a cap detachably coupled to the top of the first connecting member.

A negative hinge offset rotor head for a coaxial helicopter, the rotor head having two or more flapping rotor blades having outer and inner tips, the inner tips rotatably attached to a hinge attachment rotated by a driveshaft where the driveshaft is positioned between the rotor blades and the rotor blades' respective hinge attachment.

A negative hinge offset rotor head for a coaxial helicopter, the rotor head having two or more flapping rotor blades having outer and inner tips, the inner tips rotatably attached to a hinge attachment rotated by a driveshaft where the driveshaft is positioned between the rotor blades and the rotor blades' respective hinge attachment.

A tension-torsion strap includes a first spindle and a second spindle, which are spaced apart from each other, such that the first and second spindles are positioned at opposite ends of the tension-torsion strap, a winding formed of a filament wrapped about the first and second spindles a plurality of turns, the winding extending between and connecting the first and second spindles and being positioned within a cavity formed circumferentially about each of the first and second spindles, and a protective layer covering the winding, which is formed according to an arched winding pattern, a portion of the winding extending outside boundaries of the cavity defined by the inner wall and the lateral walls, such that an outer surface of the winding has an arched, or curved, profile.

A tension-torsion strap includes a first spindle and a second spindle, which are spaced apart from each other, such that the first and second spindles are positioned at opposite ends of the tension-torsion strap, a winding formed of a filament wrapped about the first and second spindles a plurality of turns, the winding extending between and connecting the first and second spindles and being positioned within a cavity formed circumferentially about each of the first and second spindles, and a protective layer covering the winding, which is formed according to an arched winding pattern, a portion of the winding extending outside boundaries of the cavity defined by the inner wall and the lateral walls, such that an outer surface of the winding has an arched, or curved, profile.

A fitting for securing a rotor blade in pivotable engagement with a yoke that is coupled to a mast of an aircraft for rotation therewith about a mast axis has a body that extends from an inboard end to an outboard end. The body of the fitting has an opening that extends into the body from the outboard end and that is adapted to receive a root end of the blade. The body further has a first bearing race that is defined along an outer surface of the body and is located between the inboard and outboard ends. The body further has an array of apertures that is located between the inboard end and the first bearing race, each aperture adapted to receive a respective fastener for retaining the blade within the opening.

An extension assembly for a rotor system for rotating a plurality of rotor blades about a rotor axis with a central rotor hub that defines the rotor axis includes a beam assembly and a first bearing assembly. The beam assembly is configured to attach to the central rotor hub and is positioned at least partially within a corresponding one of the plurality of rotor blades. The first bearing assembly is configured to be fastened to the beam assembly and to at least one of a leading edge or a trailing edge of the corresponding one of the plurality of rotor blades.

An extension assembly for a rotor system for rotating a plurality of rotor blades about a rotor axis with a central rotor hub that defines the rotor axis includes a beam assembly and a first bearing assembly. The beam assembly is configured to attach to the central rotor hub and is positioned at least partially within a corresponding one of the plurality of rotor blades. The first bearing assembly is configured to be fastened to the beam assembly and to at least one of a leading edge or a trailing edge of the corresponding one of the plurality of rotor blades.