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 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.

Methods, apparatus, systems, and articles of manufacture are disclosed for a slot to accommodate a blade of an engine. An example apparatus includes: a socket to receive an end of a blade; and a retaining device to interact with the socket and the blade for retention of the end of the blade in the socket. The example retaining device includes: a spacer to be positioned in the socket with the end of the blade; a wedge positioned inside the spacer; and a spring to tighten to pull the wedge to expand the spacer.

Methods, apparatus, systems, and articles of manufacture are disclosed for a slot to accommodate a blade of an engine. An example blade apparatus includes: a collet including a slot to receive an end of a blade; and a plurality of retainers including a first retainer positioned on a first end of the collet and a second retainer positioned on a second end of the collet to provide axial retention for the blade in the slot.

Methods, apparatus, systems, and articles of manufacture are disclosed for a slot to accommodate a blade of an engine. An example blade apparatus includes: a collet including a slot to receive an end of a blade; and a plurality of retainers including a first retainer positioned on a first end of the collet and a second retainer positioned on a second end of the collet to provide axial retention for the blade in the slot.

Methods, apparatus, systems, and articles of manufacture are disclosed for a slot to accommodate a blade of an engine. An example apparatus includes: a socket to receive an end of a blade; and a retaining device to interact with the socket and the blade for retention of the end of the blade in the socket. The example retaining device includes: a spacer to be positioned in the socket with the end of the blade; a wedge positioned inside the spacer; and a spring to tighten to pull the wedge to expand the spacer.

Methods, apparatus, systems, and articles of manufacture are disclosed to adjust a pitch axis of a blade of an engine. An example blade apparatus includes: a hub to facilitate movement of blades in an engine, the engine having a radial center line; and a trunnion connected to the hub. The example trunnion includes a slot to accommodate a first blade, and at least one of the trunnion or the first blade is positioned with at least one of a tilt or a lean with respect to the radial center line to form a pitch axis offset from the radial center line such that the pitch axis is not parallel to or co-linear with the radial center line. The example hub is to rotate the first blade about the pitch axis.

A pitch control system characterized by a hub with at least two blade housings on the hub that are disposed around the hub axis. The blade housings have corresponding blades that engage with them. The blades spiral along housing longitudinal axes toward and away from the hub axis about a segment of helical path to effect a change in the pitch of each blade. One or more elastic members draw the blades toward the hub axis, either directly or indirectly. There are pitch mechanisms effective to facilitate blades to spiral around housing-longitudinal axes. A blade will spiral away from the hub axis when the centrifugal force exerted on the blade exceeds the opposing elastic force in the housing-longitudinal direction (neglecting other forces). Conversely, blades spiral toward the hub axis when said centrifugal force is less than said elastic force. There is an imaginary plane orthogonal to the hub axis. Housing-longitudinal axes have angles with respect to the imaginary plane of not more than 30 degrees.

A propeller blade arrangement comprising a propeller blade attached to and rotatable with a hub, via a retention bearing, the blade being rotatable about a center line of the blade, the retention bearing configured to tilt the blade such that its center line is tilted with respect to the hub.

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.