A three-dimensional auxetic structure, comprising a plurality of adjoining hollow cells, each hollow cell having cell walls and a transversal cross section of the plurality hollow cells following a two-dimensional auxetic pattern, each cell wall comprising folding lines parallel to a plane containing the auxetic pattern such that peaks and valleys are defined in the cell walls and the cell walls being foldable along the folding lines.

A propeller having a plurality of blades extending radially outward from a hub, the blades forming a loop. Each loop having an intake portion, an exhaust portion and a tip portion extending radially outward from the hub and a gap between the intake root and the exhaust root. The tip portion of each of the blades is 30%-75% of the blade, the tip portion beginning at a first deviation from zero of the roll value and extending to 90 degrees, wherein roll value is zero in a plane parallel to the hub axis, and wherein the blades have a vertical angle between −45 degrees and 45 degrees throughout.

A propeller having a plurality of blades extending radially outward from a hub, the blades forming a loop. Each loop having an intake portion, an exhaust portion and a tip portion extending radially outward from the hub and a gap between the intake root and the exhaust root. The tip portion of each of the blades is 30%-75% of the blade, the tip portion beginning at a first deviation from zero of the roll value and extending to 90 degrees, wherein roll value is zero in a plane parallel to the hub axis, and wherein the blades have a vertical angle between −45 degrees and 45 degrees throughout.

A propeller blade comprises a root, a tip distal from the root, a trailing edge extending from the root to the tip, a trailing edge, e.g. foam, insert, a shell forming an outer surface of the propeller blade and a plurality of stitches of yarn extending through two parts of the shell adjacent the trailing edge, wherein the yarns do not extend through the trailing edge insert.

A foil, such as an aerofoil, having a leading edge and a trailing edge, of which at least a portion of one or both of the leading edge and trailing edge has a serrated profile comprising a plurality of adjoining teeth, each tooth having a tip point that represents a local maximum chord-wise extent of the tooth and, on each side span-wise of the tip point, a root point that represents a local minimum chord-wise extent of the tooth and at which the tooth adjoins a respective adjacent tooth, wherein the tooth edge profile varies with an ogee-like curve between tip point and root point such that the tooth is sharper in the neighbourhood of the tip point and in the neighbourhood of the root point than at locations in between.

A propeller blade for an unmanned aerial vehicle (“UAV”) is disclosed. The UAV includes a plurality of lift propellers and at least one thrust propeller. Each of the plurality of thrust propellers includes a thrust propeller blade coupled to a hub of the thrust propeller. The thrust propeller blade is configured such that a centrifugal force acting on the thrust propeller blade causes a thrust propeller disk area to increase from a first disk area when the UAV is in a first operational state to a second disk area when the UAV is in a second operational state.

A propeller blade for an unmanned aerial vehicle (“UAV”) is disclosed. The UAV includes a plurality of lift propellers and at least one thrust propeller. Each of the plurality of thrust propellers includes a thrust propeller blade coupled to a hub of the thrust propeller. The thrust propeller blade is configured such that a centrifugal force acting on the thrust propeller blade causes a thrust propeller disk area to increase from a first disk area when the UAV is in a first operational state to a second disk area when the UAV is in a second operational state.

An aircraft propulsion system utilizes a rotary engine to drive a centrifugal fan providing a thrust vector that is generally orthogonal to an axis of rotation of the rotary engine and the fan. The aircraft propulsion system may be mounted, for example, in the wing of a fixed-wing aircraft with the rotary engine and the centrifugal fan rotating about an axis of rotation that is generally parallel to a yaw axis of the aircraft.

An aircraft propulsion system utilizes a rotary engine to drive a centrifugal fan providing a thrust vector that is generally orthogonal to an axis of rotation of the rotary engine and the fan. The aircraft propulsion system may be mounted, for example, in the wing of a fixed-wing aircraft with the rotary engine and the centrifugal fan rotating about an axis of rotation that is generally parallel to a yaw axis of the aircraft.

A rotor system is provided in one example embodiment and may include a rotor duct; at least one rotor blade, wherein the at least one rotor blade comprises a tip end; and a multi-material tip extension affixed at the tip end of the at least one rotor blade, wherein the multi-material tip extension comprises an inboard portion fabricated from a first material and an outboard portion fabricated from a second material, wherein the second material is different than the first material.