# US 11,305,871 B2 · Passive rotor alignment in a free-wheeling state > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,305,871 B2 - Document ID: US11305871B2 - Status: Granted - Kind: B2 - Application number: 16/515,340 - Filed: 2019-07-18 - Published: 2021-01-21 - Granted: 2022-04-19 - Earliest claimed: 2019-07-18 - Assignees: Aurora Flight Sciences Corporation - Applicants: Aurora Flight Sciences Corporation - Inventors: Andrew Mark Heafitz; Robert William Parks - Web page: https://patentgrep.com/patent/US11305871B2 ## CPC - B64C 27/30: with provision for reducing drag of inoperative rotor - B64C 11/28: Collapsible or foldable blades - B64C 27/22: Compound rotorcraft, i.e. aircraft using in flight the features of both aeroplane and rotorcraft - B64C 27/463: {Blade tips} - B64C 27/473: Constructional features - B64C 29/0025: {the propellers being fixed relative to the fuselage} - B64C: AEROPLANES; HELICOPTERS ## Abstract Rotor assemblies for aircraft are described where one or more blades of the rotor assembly includes a blade alignment device that passively orients a blade in response to an airflow around the blade alignment device when the rotor assembly is free-wheeling. One embodiment comprises a method of operating a rotor assembly for aircraft. The method comprises operating the rotor assembly in a free-wheeling state, where the rotor assembly includes a rotary hub that rotates about an axis and a plurality of blades extending radially from the rotary hub. At least one of the plurality of blades includes a blade alignment device. The method further comprises aligning the at least one of the plurality of blades in response to airflow around the blade alignment device when the rotor assembly is in the free-wheeling state. ## Claims ### Claim 1 A method of operating a rotor assembly for aircraft, the method comprising: operating the rotor assembly in a free-wheeling state when the aircraft is in forward flight, the rotor assembly comprising a rotary hub configured to rotate about an axis, and a plurality of blades extending radially from the rotary hub, wherein at least one of the plurality of blades includes a blade alignment device; and aligning the at least one of the plurality of blades that includes the blade alignment device with airflow generated when the aircraft is in forward flight in response to the airflow around the blade alignment device when the rotor assembly is in the free-wheeling state, wherein the blade alignment device comprises a spanwise fin pivotably coupled to an airfoil surface of the at least one of the plurality of blades along a longitudinal direction, wherein the spanwise fin pivots along an edge substantially parallel with the longitudinal direction to project away from the airfoil surface in a deployed position when the rotor assembly is in the free-wheeling state, and pivots along the edge to lay flat with respect to the airfoil surface in a stowed position when the rotor assembly is driven in rotation. ### Claim 2 (depends on 1) The method of claim 1, wherein: the spanwise fin is held within a surface relief of the airfoil surface when in the stowed position, and pivots out of the surface relief to the deployed position. ### Claim 3 (depends on 2) The method of claim 2, wherein: the spanwise fin is held within the surface relief of the airfoil surface by a retaining device. ### Claim 4 (depends on 1) The method of claim 1, wherein: the spanwise fin passively transitions to the stowed position when a rate of rotation of the rotor assembly is greater than a first rotational rate, the spanwise fin passively transitions to the deployed position when the rate of rotation of the rotor assembly is less than a second rotational rate, and the first rotational rate is greater than the second rotational rate. ### Claim 5 (depends on 1) The method of claim 1, wherein: the spanwise fin passively transitions to the stowed position when a chordwise airflow for the at least one of the plurality of blades is greater than a first airflow rate, the spanwise fin passively transitions to the deployed position when the chordwise airflow is less than a second airflow rate, and the first airflow rate is greater than the second airflow rate. ### Claim 6 (depends on 1) The method of claim 1, wherein: the spanwise fin is disposed near a tip of the at least one of the plurality of blades. ### Claim 7 A rotor assembly for aircraft, the rotor assembly comprising: a rotary hub configured to rotate about an axis; and a plurality of blades extending radially from the rotary hub, wherein at least one of the plurality of blades includes a blade alignment device, wherein the rotor assembly is configured to operate in a free-wheeling state when the aircraft is in forward flight, wherein the blade alignment device is configured to align the at least one of the plurality of blades with airflow generated when the aircraft is in forward flight in response to airflow around the blade alignment device when the rotor assembly is in the free-wheeling state, wherein the blade alignment device comprises a spanwise fin pivotably coupled to an airfoil surface of the at least one of the plurality of blades along a longitudinal direction, wherein the spanwise fin pivots along an edge substantially parallel with the longitudinal direction to project away from the airfoil surface in a deployed position when the rotor assembly is in the free-wheeling state, and pivots along the edge to lay flat with respect to the airfoil surface in a stowed position when the rotor assembly is driven in rotation. ### Claim 8 (depends on 7) The rotor assembly of claim 7, wherein: the spanwise fin is held within a surface relief of the airfoil surface when in the stowed position, and pivots out of the surface relief to the deployed position. ### Claim 9 (depends on 8) The rotor assembly of claim 8, wherein: the spanwise fin is held within the surface relief of the airfoil surface by a retaining device. ### Claim 10 (depends on 9) The rotor assembly of claim 9, wherein: the spanwise fin is configured to project from the airfoil surface utilizing a spring. ### Claim 11 (depends on 7) The rotor assembly of claim 7, wherein: the spanwise fin is configured to passively transition to the stowed position when a rate of rotation of the rotor assembly is greater than a first rotational rate, and to passively transition to the deployed position when the rate of rotation is less than a second rotational rate; and the first rotational rate is greater than the second rotational rate. ### Claim 12 (depends on 7) The rotor assembly of claim 7, wherein: the spanwise fin is configured to passively transition to the stowed position when a chordwise airflow for the at least one of the plurality of blades is greater than a first airflow rate, and to passively transition to the deployed position when the chordwise airflow is less than a second airflow rate; and the first airflow rate is greater than the second airflow rate. ### Claim 13 (depends on 7) The rotor assembly of claim 7, wherein: the spanwise fin is disposed near a tip of the at least one of the plurality of blades. ### Claim 14 (depends on 7) The rotor assembly of claim 7, wherein: the airfoil surface comprises a lower surface of the at least one of the plurality of blades. ### Claim 15 An aircraft, comprising: at least one rotor assembly configured to provide lift for the aircraft, the at least one rotor assembly comprising: a rotary hub configured to rotate about an axis; and a plurality of blades extending radially from the rotary hub, wherein the at least one rotor assembly is configured to operate in a free-wheeling state when the aircraft is in forward flight, wherein at least one of the plurality of blades includes a blade alignment device, the blade alignment device configured to align the at least one of the plurality of blades with airflow generated when the aircraft is in forward flight in response to airflow around the blade alignment device when the rotor assembly is in the free-wheeling state, wherein the blade alignment device comprises a spanwise fin pivotably coupled to an airfoil surface of the at least one of the plurality of blades along a longitudinal direction, wherein the spanwise fin pivots along an edge substantially parallel with the longitudinal direction to project away from the airfoil surface in a deployed position when the rotor assembly is in the free-wheeling state, and pivots along the edge to lay flat with respect to the airfoil surface in a stowed position when the rotor assembly is driven in rotation. ### Claim 16 (depends on 15) The aircraft of claim 15, wherein: the spanwise fin is held within a surface relief of the airfoil surface when in the stowed position, and pivots out of the surface relief to the deployed position. ### Claim 17 (depends on 16) The aircraft of claim 16, wherein: the spanwise fin is held within the surface relief of the airfoil surface by a retaining device. ### Claim 18 (depends on 15) The aircraft of claim 15, wherein: the spanwise fin is configured to passively transition to the stowed position when a rate of rotation of the at least one rotor assembly is greater than a first rotational rate, and to passively transition to the deployed position when the rate of rotation is less than a second rotational rate, and the first rotational rate is greater than the second rotational rate. ### Claim 19 (depends on 15) The aircraft of claim 15, wherein: the spanwise fin is configured to passively transition to the stowed position when a chordwise airflow for the at least one of the plurality of blades is greater than a first airflow rate, and to passively transition to the deployed position when the chordwise airflow is less than a second airflow rate, and the first airflow rate is greater than the second airflow rate. ### Claim 20 (depends on 15) The aircraft of claim 15, wherein: the spanwise fin is disposed near a tip of the at least one of the plurality of blades. ### Claim 21 (depends on 15) The aircraft of claim 15, further comprising: wings extending from opposite sides of a fuselage; and a propeller that provides thrust for forward flight.