# US 2021/0276724 A1 · Gas turbine engine with variable speed output > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2021/0276724 A1 - Document ID: US20210276724A1 - Status: Published application - Kind: A1 - Application number: 16/784,591 - Filed: 2020-02-07 - Published: 2021-09-09 - Earliest claimed: 2019-12-20 - Assignees: Pratt & Whitney Canada Corp. - Applicants: Pratt & Whitney Canada Corp. - Inventors: David MENHEERE; Santo CHIAPPETTA; Timothy REDFORD; Daniel VAN DEN ENDE - Web page: https://patentgrep.com/patent/US20210276724A1 ## CPC - F02C 3/113: with variable power transmission between rotors - B64C 29/0041: {the lift during taking-off being created by jet motors} - B64D 27/10: of gas-turbine type (jet aircraft B64D27/16) - F02C 6/206: {the vehicles being airscrew driven} - F02C 9/20: by throttling; by adjusting vanes - F16H 37/0813: {with only one input shaft} - F05D 2220/324: to drive unshrouded, low solidity propeller - F05D 2220/329: in helicopters - F05D 2220/90: in vehicles adapted for vertical or short take off and landing (v/stol vehicles) - F05D 2260/15: Load balancing - F05D 2260/40311: of the epicyclical, planetary or differential type - F05D 2260/96: Preventing, counteracting or reducing vibration or noise - F05D 2270/304: Spool rotational speed - Y02T 50/60: Efficient propulsion technologies, e.g. for aircraft - F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00) - 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 - F16H: GEARING - F05D: INDEXING SCHEME FOR ASPECTS RELATING TO NON-POSITIVE-DISPLACEMENT MACHINES OR ENGINES, GAS-TURBINES OR JET-PROPULSION PLANTS - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract The gas turbine engine for an aircraft includes at least a low pressure spool with a low pressure turbine shaft operatively connected to at least one turbine, the low pressure turbine shaft rotatable about an engine axis, and a low pressure compressor operatively connected to a low pressure compressor shaft that is independently rotatable relative to the low pressure turbine shaft. A differential gearbox has an input operatively connected to the low pressure turbine shaft, a first output and a second output, the first output of the differential gearbox operatively connected to the low pressure compressor shaft and the second output of the differential gearbox operatively connected to an output shaft of the gas turbine engine. The differential gearbox permits the output shaft, the low pressure compressor shaft and the low pressure turbine shaft to rotate at different speeds. ## Claims ### Claim 1 A gas turbine engine for an aircraft, the gas turbine engine comprising: a low pressure spool including a low pressure turbine shaft operatively connected to at least one turbine, the low pressure turbine shaft rotatable about an engine axis; a high pressure spool including at least one high pressure turbine and at least one high pressure compressor operatively connected together by a high pressure shaft and rotatable about the engine axis, the high pressure shaft being independently rotatable relative to the low pressure turbine shaft; a low pressure compressor operatively connected to a low pressure compressor shaft that is independently rotatable relative to the high pressure shaft and the low pressure turbine shaft; and a differential gearbox having an input operatively connected to the low pressure turbine shaft, a first output and a second output, the first output of the differential gearbox operatively connected to the low pressure compressor shaft and the second output of the differential gearbox operatively connected to an output shaft of the gas turbine engine, the differential gearbox permitting the output shaft, the low pressure compressor shaft and the low pressure turbine shaft to rotate at different speeds. ### Claim 2 (depends on 1) The gas turbine engine as defined in claim 1, wherein the low pressure compressor includes a compressor rotor with variable inlet guide vanes. ### Claim 3 (depends on 1) The gas turbine engine as defined in claim 1, wherein the low pressure compressor includes two or more stages each having a compressor rotor, at least one of the two or more stages having a set of the variable inlet guide vanes. ### Claim 4 (depends on 3) The gas turbine engine as defined in claim 3, wherein a number of stages, and therefore compressor rotors, of the low pressure compressor is greater than a number of the sets of variable inlet guides vanes. ### Claim 5 (depends on 3) The gas turbine engine as defined in claim 3, wherein at least two of the two or more stages having said variable inlet guide vanes, the variable inlet guide vanes of each of the at least two stages being independently controllable. ### Claim 6 (depends on 1) The gas turbine engine as defined in claim 1, wherein the aircraft is a vertical takeoff and landing (VTOL) aircraft, and further comprising a control system in operative connection with the gas turbine engine, the control system configured to operate the gas turbine engine in a VTOL engine operating configuration or a cruise engine operating configuration. ### Claim 7 (depends on 6) The gas turbine engine as defined in claim 6, wherein the low pressure compressor includes variable inlet guide vanes, the control system configured to position the variable inlet guide vanes in a substantially open position when the gas turbine engine is operated by the control system in the VTOL engine operating configuration. ### Claim 8 (depends on 7) The gas turbine engine as defined in claim 7, wherein the control system is configured to move the variable inlet guide vanes into a more closed position relative to the substantially open position, when the gas turbine engine is operated by the control system in a cruise engine operating configuration. ### Claim 9 (depends on 7) The gas turbine engine as defined in claim 7, wherein the control system is configured to balance aerodynamic loads on the low pressure compressor by varying positions of the variable inlet guide vanes. ### Claim 10 (depends on 1) The gas turbine engine as defined in claim 1, further comprising a control system in operative connection with the gas turbine engine, the control system configured to use the differential gearbox to vary a ratio between the speeds of the output shaft, the low pressure compressor shaft and the low pressure turbine shaft. ### Claim 11 (depends on 10) The gas turbine engine as defined in claim 10, wherein the control system is configured to switch the gas turbine engine between a VTOL engine operating configuration and a cruise engine operating configuration. ### Claim 12 (depends on 11) The gas turbine engine as defined in claim 11, wherein the differential gearbox is configured to: a) drive the output shaft at a lower speed in the cruise engine operating configuration than in the VTOL engine operating configuration; and b) drive the low pressure compressor shaft at a higher speed in the cruise engine configuration than in the VTOL engine operating configuration. ### Claim 13 (depends on 12) The gas turbine engine as defined in claim 12, wherein the differential gearbox is configured such that, in the cruise engine operating configuration, the output shaft is driven at a reduced speed of between 25% and 100% of a speed in the VTOL engine operating configuration, and the low pressure turbine rotates between 80% and 100% of its nominal design speed for takeoff when operating in the VTOL engine operating configuration. ### Claim 14 (depends on 13) The gas turbine engine as defined in claim 13, wherein, in the cruise engine operating configuration, the low pressure compressor is driven by the differential gearbox at a speed greater than its nominal design speed for takeoff when operating in the VTOL engine operating configuration. ### Claim 15 (depends on 14) The gas turbine engine as defined in claim 14, wherein, in the cruise engine operating configuration, the low pressure compressor is driven by the differential gearbox at between 80% and 150% of its nominal design speed for takeoff when operating in the VTOL engine operating configuration. ### Claim 16 (depends on 1) The gas turbine engine as defined in claim 1, wherein the first output of the differential gearbox operatively connected to the output shaft of the gas turbine engine is connected therewith via a reduction gearbox, the reduction gearbox receiving torque input from the first output of the differential and providing a torque output to the output shaft of the gas turbine engine. ### Claim 17 A method of operating a vertical takeoff and landing (VTOL) aircraft having an aircraft rotor operatively connected to a gas turbine engine that includes a low pressure compressor, a high pressure compressor, a high pressure turbine and a low pressure turbine, the method comprising: during a VTOL flight phase of the aircraft, driving the aircraft rotor at a high-power rotational speed, with the low pressure turbine rotating at a first rotational speed and the low pressure compressor rotating at a second rotational speed; and during a cruise flight phase of the aircraft, driving the aircraft rotor at a low-power rotational speed that is less than the high-power rotational speed by increasing the first rotational speed and decreasing the second rotational speed. ### Claim 18 (depends on 17) The method as defined in claim 17, wherein in the cruise flight phase, maintaining rotational speed of the low power turbine between 80% and 100% of the first rotational speed, and maintaining rotational speed of the low pressure compressor between 80% and 150% of the first rotational speed. ### Claim 19 (depends on 17) The method as defined in claim 17, further comprising using a differential gearbox to drive the aircraft rotor at the low-power rotation speed while maintaining a rotational speed of the low power turbine above 80% of the first rotational speed. ### Claim 20 A gas turbine engine for a vertical takeoff and landing (VTOL) aircraft having an aircraft rotor, the gas turbine engine comprising: a low pressure turbine shaft connected to at least one turbine for driving the low pressure turbine shaft about an engine axis, and a low pressure compressor operatively connected to a low pressure compressor shaft independently rotatable relative to the low pressure the power turbine shaft; and means for operating the gas turbine engine in either a VTOL engine operating configuration or a cruise engine operating configuration, wherein in the VTOL engine operating configuration the low pressure turbine and the low pressure compressor are operated at their respective nominal design speed for takeoff, and in the cruise engine operating configuration, the low pressure turbine is allowed to rotate between 80% and 100% of its nominal design speed for takeoff and the low pressure compressor is driven to rotate at between 80% and 150% of its nominal design speed for takeoff.