# US 2023/0056974 A1 · Stowable Lift Rotors for VTOL Aircraft > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2023/0056974 A1 - Document ID: US20230056974A1 - Status: Published application - Kind: A1 - Application number: 17/407,108 - Filed: 2021-08-19 - Published: 2023-02-23 - Earliest claimed: 2021-08-19 - Assignees: Textron Innovations Inc. - Applicants: Textron Innovations Inc. - Inventors: Christopher Edward Foskey; Robert Roe - Web page: https://patentgrep.com/patent/US20230056974A1 ## CPC - B64C 27/30: with provision for reducing drag of inoperative rotor - B64C 27/001: {Vibration damping devices} - B64C 29/0033: {the propellers being tiltable relative to the fuselage} - B64C 39/04: having multiple fuselages or tail booms - B64D 35/02: specially adapted for specific power plants - B64C 2027/002: {mounted between the rotor drive and the fuselage} - B64C: AEROPLANES; HELICOPTERS - B64D: EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT ## Abstract A stowable lift rotor is coupled to an airframe of a VTOL aircraft. The VTOL aircraft is convertible between a VTOL flight mode and a forward flight mode. The stowable lift rotor includes a lift arm. The proximal end of the lift arm is coupled to the airframe of the VTOL aircraft. The stowable lift rotor also includes a rotor assembly including rotor blades coupled to the distal end of the lift arm. The lift arm is movable between various positions including an extended position in the VTOL flight mode, a stowed position in the forward flight mode and intermediate positions therebetween such that the distance between the rotor assembly and the airframe is greater in the extended position than in the stowed position. ## Claims ### Claim 1 A stowable lift rotor coupled to an airframe of a VTOL aircraft, the VTOL aircraft convertible between a VTOL flight mode and a forward flight mode, comprising: a lift arm having proximal and distal ends, the proximal end coupled to the airframe of the VTOL aircraft; and a rotor assembly including a plurality of rotor blades coupled to the distal end of the lift arm; wherein, the lift arm is movable between a plurality of positions including an extended position in the VTOL flight mode, a stowed position in the forward flight mode and intermediate positions therebetween such that a distance between the rotor assembly and the airframe is greater in the extended position than in the stowed position. ### Claim 2 (depends on 1) The stowable lift rotor as recited in claim 1 wherein the airframe forms a recess to receive the lift arm in the stowed position. ### Claim 3 (depends on 1) The stowable lift rotor as recited in claim 1 wherein the lift arm moves between the stowed and extended positions in response to a magnitude of lift generated by the rotor assembly. ### Claim 4 (depends on 1) The stowable lift rotor as recited in claim 1 wherein the proximal end of the lift arm comprises a forward end rotatably coupled to the airframe of the VTOL aircraft and the distal end of the lift arm comprises an aft end rotatably coupled to the rotor assembly. ### Claim 5 (depends on 4) The stowable lift rotor as recited in claim 4 further comprising a motor coupled to the airframe of the VTOL aircraft adjacent to the proximal end of the lift arm; wherein, the lift arm comprises a driveshaft transmitting rotational energy from the motor at the proximal end of the lift arm to the rotor assembly at the distal end of the lift arm. ### Claim 6 (depends on 5) The stowable lift rotor as recited in claim 5 further comprising a first plurality of bevel gears transmitting rotational energy from the motor to a proximal end of the driveshaft and a second plurality of bevel gears transmitting rotational energy from a distal end of the driveshaft to the rotor assembly. ### Claim 7 (depends on 5) The stowable lift rotor as recited in claim 5 wherein the rotor assembly comprises a rotor hub housing and the lift arm comprises a linkage having proximal and distal ends, the proximal end of the linkage rotatably coupled to the airframe of the VTOL aircraft and the distal end of the linkage rotatably coupled to the rotor hub housing. ### Claim 8 (depends on 4) The stowable lift rotor as recited in claim 4 further comprising an actuator assembly configured to move the lift arm between the extended position and the stowed position. ### Claim 9 (depends on 8) The stowable lift rotor as recited in claim 8 wherein the actuator assembly comprises a ball screw actuator assembly and a strut, a first end of the strut coupled to the ball screw actuator assembly and a second end of the strut coupled to the lift arm. ### Claim 10 (depends on 1) The stowable lift rotor as recited in claim 1 wherein the lift arm comprises a telescoping shaft assembly including a lower shaft slidably coupled to an upper shaft, the lower shaft coupled to the airframe of the VTOL aircraft and the upper shaft coupled to the rotor assembly. ### Claim 11 (depends on 10) The stowable lift rotor as recited in claim 10 wherein the lower shaft comprises one of a male spline or a female spline and the upper shaft comprises the other of the male spline or the female spline to form a slidable spline joint therebetween. ### Claim 12 (depends on 10) The stowable lift rotor as recited in claim 10 further comprising a motor coupled to the airframe of the VTOL aircraft adjacent to the proximal end of the telescoping shaft assembly, the motor configured to rotate the telescoping shaft assembly such that the telescoping shaft assembly transmits rotational energy from the motor to the rotor assembly. ### Claim 13 (depends on 10) The stowable lift rotor as recited in claim 10 further comprising a motor coupled to the upper shaft of the telescoping shaft assembly, the motor configured to rotate the rotor assembly. ### Claim 14 (depends on 10) The stowable lift rotor as recited in claim 10 wherein the telescoping shaft assembly comprises a spring configured to exert a spring force biasing the upper shaft toward the lower shaft, the spring moving the telescoping shaft assembly into the stowed position in response to the spring force exceeding a lift force generated by the rotor assembly, the rotor assembly moving the telescoping shaft assembly into the extended position in response to the lift force generated by the rotor assembly exceeding the spring force. ### Claim 15 (depends on 10) The stowable lift rotor as recited in claim 10 wherein the telescoping shaft assembly comprises a damper configured to reduce vibration transmission between the rotor assembly and the airframe. ### Claim 16 (depends on 1) The stowable lift rotor as recited in claim 1 wherein the plurality of rotor blades comprise first and second rotor blades; and wherein, the rotor assembly is lockable in the stowed position such that the first and second rotor blades are parallel to a longitudinal axis of the VTOL aircraft, thereby reducing drag by minimizing a frontal profile area of the rotor assembly exposed to freestream airflow in the forward flight mode. ### Claim 17 A VTOL aircraft convertible between a VTOL flight mode and a forward flight mode comprising: a fuselage; a tailboom coupled to the fuselage; and a stowable lift rotor coupled to the tailboom, the stowable lift rotor comprising: a lift arm having proximal and distal ends, the proximal end coupled to the tailboom; and a rotor assembly including a plurality of rotor blades coupled to the distal end of the lift arm; wherein, the lift arm is movable between a plurality of positions including an extended position in the VTOL flight mode, a stowed position in the forward flight mode and intermediate positions therebetween such that a distance between the rotor assembly and the tailboom is greater in the extended position than in the stowed position. ### Claim 18 (depends on 17) The VTOL aircraft as recited in claim 17 further comprising a wing coupled to the fuselage; wherein, the tailboom comprises left and right tailbooms coupled to the fuselage via the wing; and wherein, the stowable lift rotor comprises left and right stowable lift rotors, the left stowable lift rotor coupled to the left tailboom and the right stowable lift rotor coupled to the right tailboom. ### Claim 19 (depends on 17) The VTOL aircraft as recited in claim 17 wherein the stowable lift rotor comprises a four-bar linkage extending through the lift arm. ### Claim 20 (depends on 17) The VTOL aircraft as recited in claim 17 wherein the plurality of rotor blades are rotatable in a first rotational plane in the extended position; wherein, the plurality of rotor blades lie in a second plane in the stowed position; and wherein, the first rotational plane is substantially parallel to the second plane.