Abstract: There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has rotating the first shaft at a flight rotation speed when clutched and rotating the second shaft at a first idle rotation speed when unclutched, the first idle rotation speed above the placarded zone; decreasing a rotation speed of the first shaft from the flight rotation speed to a given rotation speed within the placarded zone; decreasing a rotation speed of the second shaft to the given rotation speed; clutching the second shaft; and decreasing the rotation speeds of the first and second shafts to a second idle rotation speed below the placarded zone.

Abstract: A method of operating a variable guide vane assembly of an aircraft engine, the variable guide vane assembly including guide vanes rotatable about respective spanwise axes and circumferentially distributed about a central axis, the method comprising: obtaining a target exit flow angle defined between a direction of a flow exiting the guide vanes and the central axis; predicting an exit flow angle as a function of at least a geometric angle, the exit flow angle defined between the direction of the flow exiting the guide vanes and the central axis, the geometric angle defined between the guide vanes and the central axis; and when a difference between the exit flow angle and the target exit flow angle is above a threshold, modulating the guide vanes to modify the geometric angle until the difference between the exit flow angle and the target exit flow angle is at or below the threshold.

Abstract: A multi-engine system for an aircraft, has: a first engine having a first output shaft, a first core shaft, and a first electric machine drivingly engaged by the first output shaft or the first core shaft; a second engine having a second output shaft, a second core shaft, and a second electric machine drivingly engaged to the second core shaft; a reduction gearbox drivingly engaged by the first output shaft and by the second output shaft for driving a common load; and a transmission path between the first engine and the second engine, the transmission path being independent from the reduction gearbox and being one or more of: a torque-transfer connection between the second core shaft and the first core shaft or the first output shaft via a coupling gearbox, and an electrical connection between the generator and the electric motor to transmit electrical power to the electric motor.

Abstract: A method of operating a multi-engine system of an aircraft having first and second engines includes accumulating compressed air in a pressure vessel external to the engines, and operating the first and second engines asymmetrically, by controlling the first engine to operate in an active operating condition providing sufficient power and/or rotor speed for demands of the aircraft, and controlling the second engine to operate in a standby operating condition wherein the second engine produces less power output than the first engine. In response to a power demand request, the second engine is accelerated out of the standby operating condition by introducing therein compressed air from the pressure vessel at a location upstream of a combustor of the second engine.

Abstract: An aircraft engine, has: a low-pressure compressor and a high-pressure compressor located downstream of the low-pressure compressor; a gaspath valve upstream of the high-pressure compressor, the gaspath valve movable between an open configuration and a closed configuration; and a bypass flow path having in flow series a bypass inlet, a bypass valve, and a bypass outlet, the bypass inlet fluidly communicating with the gaspath upstream of at least one stage of the low-pressure compressor, the bypass valve having an open configuration in which the bypass valve allows a bypass flow and a closed configuration in which the bypass valve blocks the bypass flow, the bypass outlet fluidly communicating with the bypass inlet via the bypass valve and with the gaspath at a location in the gaspath fluidly downstream of the gaspath valve, downstream of the low-pressure compressor, and upstream of the high-pressure compressor.

Abstract: A method of operating an engine of a multi-engine aircraft includes sequentially operating the engine through a plurality of cycles, each cycle including a breathing-in phase followed by a breathing-out phase. The breathing-in phase includes: i) in response to a speed of a rotor of the engine being at a sub-idle threshold, opening variable guide vanes upstream a compressor and injecting fuel into the combustor to increase rotor speed to a pre-determined upper threshold, and then ii) in response to the rotor speed reaching the pre-determined upper threshold, reducing a supply rate of fuel into the combustor and substantially closing the variable guide vanes. The breathing-out phase includes maintaining the variable guide vanes closed at least until the speed drops from the pre-determined upper threshold to the pre-determined sub-idle threshold.

Abstract: There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has: rotating the first and second shafts at a flight rotation speed above the placarded zone when clutched to a load; decreasing a rotation speed of the first shaft from the flight rotation speed to a first idle rotation speed above the placarded zone; unclutching the first shaft from the load during the decreasing; and subsequently to the decreasing and the unclutching, simultaneously decreasing the rotation speeds of the first shaft and of the second shaft to a second idle rotation speed below the placarded zone, the simultaneously decreasing including clutching the first shaft to the load.

Abstract: There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has: rotating the first and second shafts at a first idle rotation speed below the placarded zone when clutched to a load; increasing a rotation speed of the first shaft from the first idle rotation speed to a flight rotation speed above the placarded zone; unclutching the second shaft from the load during the increasing; and increasing a rotation speed of the second shaft to a second idle rotation speed when the second shaft is unclutched from the load, the second idle rotation speed above the placarded zone and below the flight rotation speed.

Abstract: There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has rotating the first shaft at a flight rotation speed when clutched and rotating the second shaft at a first idle rotation speed when unclutched, the first idle rotation speed above the placarded zone; decreasing a rotation speed of the first shaft from the flight rotation speed to a given rotation speed within the placarded zone; decreasing a rotation speed of the second shaft to the given rotation speed; clutching the second shaft; and decreasing the rotation speeds of the first and second shafts to a second idle rotation speed below the placarded zone.

Abstract: There is described a method of operating a multi-engine system of an helicopter. The multi-engine system has a first turboshaft engine having a first shaft, a second turboshaft engine having a second shaft, a gearbox having a clutch system, and a range of rotation speeds defined as a placarded zone. The method generally has: rotating the first and second shafts at a flight rotation speed above the placarded zone when clutched to a load; decreasing a rotation speed of the first shaft from the flight rotation speed to a first idle rotation speed above the placarded zone; unclutching the first shaft from the load during the decreasing; and subsequently to the decreasing and the unclutching, simultaneously decreasing the rotation speeds of the first shaft and of the second shaft to a second idle rotation speed below the placarded zone, the simultaneously decreasing including clutching the first shaft to the load.

Abstract: A method and a system for providing in-flight reverse thrust for an aircraft are provided. The aircraft comprises an engine having a rotor, a compressor mechanically coupled to the rotor, and a variable geometry mechanism provided upstream of the compressor and configured to modulate an amount of compression work performed by the compressor. The method comprises operating the rotor with the variable geometry mechanism in a first position, receiving a request to increase reverse thrust for the rotor, in response to the request, adjusting the variable geometry mechanism from the first position towards a second position, the variable geometry mechanism having a greater opening angle in the second position than in the first position, and operating the rotor with the variable geometry mechanism in the second position for causing an increase in the amount of compression work performed by the compressor and an increase in reverse thrust for the rotor.

Abstract: A method of operating a multi-engine system of an aircraft having first and second engines includes accumulating compressed air in a pressure vessel external to the engines, and operating the first and second engines asymmetrically, by controlling the first engine to operate in an active operating condition providing sufficient power and/or rotor speed for demands of the aircraft, and controlling the second engine to operate in a standby operating condition wherein the second engine produces less power output than the first engine. In response to a power demand request, the second engine is accelerated out of the standby operating condition by introducing therein compressed air from the pressure vessel at a location upstream of a combustor of the second engine.

Abstract: A multi-engine system for an aircraft, has: a first engine having a first output shaft, a first core shaft, and a first electric machine drivingly engaged by the first output shaft or the first core shaft; a second engine having a second output shaft, a second core shaft, and a second electric machine drivingly engaged to the second core shaft; a reduction gearbox drivingly engaged by the first output shaft and by the second output shaft for driving a common load; and a transmission path between the first engine and the second engine, the transmission path being independent from the reduction gearbox and being one or more of: a torque-transfer connection between the second core shaft and the first core shaft or the first output shaft via a coupling gearbox, and an electrical connection between the generator and the electric motor to transmit electrical power to the electric motor.

Abstract: An aircraft engine, has: a low-pressure compressor and a high-pressure compressor located downstream of the low-pressure compressor; a gaspath valve upstream of the high-pressure compressor, the gaspath valve movable between an open configuration and a closed configuration; and a bypass flow path having in flow series a bypass inlet, a bypass valve, and a bypass outlet, the bypass inlet fluidly communicating with the gaspath upstream of at least one stage of the low-pressure compressor, the bypass valve having an open configuration in which the bypass valve allows a bypass flow and a closed configuration in which the bypass valve blocks the bypass flow, the bypass outlet fluidly communicating with the bypass inlet via the bypass valve and with the gaspath at a location in the gaspath fluidly downstream of the gaspath valve, downstream of the low-pressure compressor, and upstream of the high-pressure compressor.

Abstract: A variable guide vane assembly has: variable guide vanes having airfoils extending from inner ends to outer ends, the variable guide vanes pivotable about respective spanwise axes between one or more open positions and a closed position, in the closed position, trailing edge regions of the airfoils sealingly engage leading edge regions of adjacent ones of the airfoils to block an air flow; an outer wall extending around the central axis, the outer ends of the variable guide vanes pivotably engaged to the outer wall; and an inner wall extending around the central axis, the inner ends of the variable guide vanes pivotably engaged to the inner wall, the inner wall defining inner faces distributed about the central axis, a shape of the inner faces complementary to a shape of the inner ends of the airfoils to form a seal when the variable guide vanes are in the closed position.

Abstract: A method of operating an engine of a multi-engine aircraft includes sequentially operating the engine through a plurality of cycles, each cycle including a breathing-in phase followed by a breathing-out phase. The breathing-in phase includes: i) in response to a speed of a rotor of the engine being at a sub-idle threshold, opening variable guide vanes upstream a compressor and injecting fuel into the combustor to increase rotor speed to a pre-determined upper threshold, and then ii) in response to the rotor speed reaching the pre-determined upper threshold, reducing a supply rate of fuel into the combustor and substantially closing the variable guide vanes. The breathing-out phase includes maintaining the variable guide vanes closed at least until the speed drops from the pre-determined upper threshold to the pre-determined sub-idle threshold.

Abstract: A method and a system for providing in-flight reverse thrust for an aircraft are provided. The aircraft comprises an engine having a rotor, a compressor mechanically coupled to the rotor, and a variable geometry mechanism provided upstream of the compressor and configured to modulate an amount of compression work performed by the compressor. The method comprises operating the rotor with the variable geometry mechanism in a first position, receiving a request to increase reverse thrust for the rotor, in response to the request, adjusting the variable geometry mechanism from the first position towards a second position, the variable geometry mechanism having a greater opening angle in the second position than in the first position, and operating the rotor with the variable geometry mechanism in the second position for causing an increase in the amount of compression work performed by the compressor and an increase in reverse thrust for the rotor.

Abstract: A method of operating a multi-engine aircraft includes operating a first engine of the aircraft to provide motive power; and operating a second engine of the aircraft in a standby mode to provide substantially no motive power, a rotor of the second engine having an idle rotational speed in the standby mode, and in the standby mode, sequentially executing cycles, a given cycle of the cycles including: opening a set of variable guide vanes upstream a compressor section of the second engine, spiking a rate of a fuel flow to a combustor of the second engine, the spiking and the opening timed to increase a rotational speed of the rotor of the second engine to an upper threshold above the idle rotational speed of the rotor, and in response to the rotational speed reaching the upper threshold, at least substantially closing the set of variable guide vanes.

Abstract: The stiffness of a rotor part is varied over its circumference to allow damper rings to effectively work in high speed applications. Circumferentially spaced-apart pockets may be defined in the rotor to create discontinuous strain to increase the force required to lock the damper ring in the groove above the centrifugal force of the ring when the rotor is rotating.

Abstract: An exhaust mixer arrangement for a gas turbine engine comprises an exhaust cone, a lobed exhaust mixer surrounding at least a portion of the exhaust cone and a cover mounted to an outer surface of the exhaust cone. The cover and the outer surface of the exhaust cone define a dead-end cavity for receiving a stiffener ring. A plurality of circumferentially spaced-apart struts interconnect at least a number of lobes of the lobed exhaust mixer to the stiffener ring.