In an embodiment, a propeller assembly includes a blade and a joint. The blade is adapted to rotate about a longitudinal axis of the blade to vary a pitch of the blade, wherein the blade includes a plurality of bearings provided on a proximal end of the blade. The joint is adapted to couple the blade to a central shaft of the assembly via the plurality of bearings, where the joint is adapted to telescope and twist along the central shaft of the assembly such that in a first position, the blade is at a first angle. In a second position, the blade is at a second angle greater than the first angle.

A bistable pitch propeller includes a ball, a spring, and a clutch module where the clutch module has a range of rotational movement between a locked end position and a released end position. The clutch module includes a detent, where the ball sits inside and outside of the detent when the clutch module is in the locked end position and released end position, respectively. In response to an input torque and a spring force from the spring, the clutch module rotates toward the released end position and the locked end position, respectively. The bistable pitch propeller also includes an aircraft blade where the aircraft blade is at the first pitch angle and the second pitch angle when the clutch module is in the locked end position and the released end position, respectively.

A hinged propeller comprising a hub and one or more blades is disclosed. In various embodiments, a blade is connected to the hub via a hinge, wherein at least a substantial part of the blade has a longitudinal axis that is substantially parallel to a line extending radially from a center of the hub, and wherein the hinge has an axis of hinge rotation that is oriented at a non-zero acute angle to a line that is perpendicular, in a plane of rotation of the hub, to said longitudinal axis.

A hinged propeller comprising a hub and one or more blades is disclosed. In various embodiments, a blade is connected to the hub via a hinge, wherein at least a substantial part of the blade has a longitudinal axis that is substantially parallel to a line extending radially from a center of the hub, and wherein the hinge has an axis of hinge rotation that is oriented at a non-zero acute angle to a line that is perpendicular, in a plane of rotation of the hub, to said longitudinal axis.

A passively varying pitch propeller includes a hub and a first and a second blade assembly. Each blade assembly respectively has a blade having an airfoil shape yielding a positive zero-lift pitching moment for the blade assembly, a pitching axis located such that a disturbance in pitch angle creates a restoring pitching moment, yielding static pitch stability, and a mass distribution resulting in a zero pitching moment contribution due to product of inertia in a plane normal to blade pitch rotation.

A rotor system for electrically powered rotorcraft is described, providing the benefits of autorotation for safety, and fast thrust response, regardless of rotor inertia. The rotor system includes a rotor hub and two or more rotor blades, and an electric motor driving the rotor hub. The rotor hub includes a mechanism which adapts the collective incidence of the rotor blades in response to the torque applied by the electric motor. When there is little or no motor torque, the rotor hub holds the blades at a shallow incidence, which supports autorotative descent. During autorotative descent, the motor controller coupled to the electric motor utilizes electrical braking to moderate the rotor RPM and thrust. When the electric motor provides power to the rotor for normal flight, the collective blade incidence adjusts in response to the motor torque, providing a fast response in rotor thrust, thus avoiding the lag in rotor thrust that would occur through RPM control.

A fluid interaction apparatus includes a wing having a first configuration with a first profile drag coefficient and a second configuration with a second profile drag coefficient that is less than the first profile drag coefficient. The fluid interaction apparatus further includes a body having a longitudinal axis, wherein the body is coupled to the wing. The fluid interaction apparatus further includes an actuator configured to change the wing from the first configuration when moving in a first direction relative to the body to the second configuration when moving in a second direction relative to the body, the second direction having a substantial component parallel to the longitudinal axis of the body.

A bistable pitch propeller includes a ball, a spring, and a clutch module where the clutch module has a range of rotational movement between a locked end position and a released end position. The clutch module includes a detent, where the ball sits inside and outside of the detent when the clutch module is in the locked end position and released end position, respectively. In response to an input torque and a spring force from the spring, the clutch module rotates toward the released end position and the locked end position, respectively. The bistable pitch propeller also includes an aircraft blade where the aircraft blade is at the first pitch angle and the second pitch angle when the clutch module is in the locked end position and the released end position, respectively.

A propeller includes a blade free to rotate about a longitudinal axis of the blade. The propeller also includes a mechanical stop positioned to engage mechanically a first portion of the blade and/or a first structure coupled mechanically to the blade when the blade is in a first position. The propeller also includes a magnetic stop positioned to engage magnetically a second portion of the blade and/or a second structure coupled mechanically to the blade when the blade is in a second position. The blade rotates to the first position against the mechanical stop when the propeller is rotated at a first rotational speed and the blade rotates to the second position against the magnetic stop when the propeller is rotated at a second rotational speed in a same direction as when the blade is in the first position.

A propeller includes a blade free to rotate. A first stop is positioned to mechanically engage one or both of a first portion of the blade and a first structure coupled to the blade when the blade is in a first position at a first end of the rotational range of motion. A second stop is positioned to mechanically engage one or both of a second portion of the blade and a second structure coupled to the blade when the blade is in a second position at a second end of the defined rotational range. The blade rotates to the first position against the first stop when the propeller is rotated in a first direction and to the second position against the second stop when the propeller is rotated in a second direction.