Abstract: A strain compensated heterostructure comprising a substrate comprising silicon carbide material; a first epitaxial layer comprising single-crystal aluminum nitride material formed on a top surface of the substrate; a second epitaxial layer formed on the first epitaxial layer opposite the top surface of the substrate, the second epitaxial layer comprising single-crystal scandium aluminum nitride material; and a third epitaxial layer formed on the second epitaxial layer opposite the first epitaxial layer, the third layer comprising single-crystal aluminum nitride material.

Abstract: A multi-engine aircraft includes a first engine drivingly engaged to a common rotatable load and a second engine drivingly engaged to the common rotatable load, the second engine having a bleed air system and a control system in communication with a compressed air switching system. The control system controls operation of the second engine and/or the compressed air switching system. The compressed air switching system includes a switching valve that is displaceable between at least a first position and a second position, the first position interconnecting a lower pressure inlet and a switch outlet, and the second position interconnecting a high pressure inlet and the switch outlet. The switch outlet is in communication with the bleed air system of the second engine. The control system actuates the switching valve to switch between the first and second positions.

Abstract: Cooling a torque probe involves an elongated sleeve extending along a sleeve axis between a first sleeve end and a second sleeve end. The sleeve is mountable about the torque probe to define a flow passage between an inner surface of the sleeve and an outer surface of the torque probe. The flow passage is in fluid communication with a flow passage inlet of the sleeve and with a flow passage outlet of the sleeve spaced apart along the sleeve axis from the flow passage inlet. A cooling airflow is configured to flow into the flow passage via the flow passage inlet, through the flow passage along the outer surface of the torque probe to cool the torque probe, and out of the flow passage via the flow passage outlet.

Abstract: Cooling a torque probe involves an elongated sleeve extending along a sleeve axis between a first sleeve end and a second sleeve end. The sleeve is mountable about the torque probe to define a flow passage between an inner surface of the sleeve and an outer surface of the torque probe. The flow passage is in fluid communication with a flow passage inlet of the sleeve and with a flow passage outlet of the sleeve spaced apart along the sleeve axis from the flow passage inlet. A cooling airflow is configured to flow into the flow passage via the flow passage inlet, through the flow passage along the outer surface of the torque probe to cool the torque probe, and out of the flow passage via the flow passage outlet.

Abstract: A multi-engine aircraft includes a first engine drivingly engaged to a common rotatable load and a second engine drivingly engaged to the common rotatable load, the second engine having a bleed air system and a control system in communication with a compressed air switching system. The control system controls operation of the second engine and/or the compressed air switching system. The compressed air switching system includes a switching valve that is displaceable between at least a first position and a second position, the first position interconnecting a lower pressure inlet and a switch outlet, and the second position interconnecting a high pressure inlet and the switch outlet. The switch outlet is in communication with the bleed air system of the second engine. The control system actuates the switching valve to switch between the first and second positions.

Abstract: Cooling a torque probe involves an elongated sleeve extending along a sleeve axis between a first sleeve end and a second sleeve end. The sleeve is mountable about the torque probe to define a flow passage between an inner surface of the sleeve and an outer surface of the torque probe. The flow passage is in fluid communication with a flow passage inlet of the sleeve and with a flow passage outlet of the sleeve spaced apart along the sleeve axis from the flow passage inlet. A cooling fluid is configured to flow into the flow passage via the flow passage inlet, through the flow passage along the outer surface of the torque probe to cool the torque probe, and out of the flow passage via the flow passage outlet.

Abstract: A method of operating a multi-engine aircraft having two or more gas turbine engines includes operating a first engine in a powered mode to provide motive power to the aircraft, and, in flight, operating a second engine in either a powered mode to provide motive power to the aircraft or in a standby mode to provide substantially no motive power to the aircraft. When operating the second engine in the powered mode, pressurized air is bled from a first bleed location of a compressor of the second engine. When operating the second engine in the standby mode, pressurized air is bled from a second bleed location of the compressor of the second engine and supplying the pressurized air to a bleed air system of the second engine. The second bleed location is downstream of the first bleed location within the compressor of the second engine.

Abstract: A de-aerator for a lubrication system, has: a housing defining an air-oil inlet, an oil outlet, and an air outlet of the de-aerator; a rotor received within the housing and rotatable relative to the housing about a central axis, the rotor having blades distributed about the central axis and extending at least partially radially relative to the central axis, flow passages extending between the blades, the rotor having a hub circumferentially extending around the central axis and around the blades, the hub having a peripheral wall oriented radially inwardly and defining a fore opening leading to the flow passages; and a gap between the housing and the hub of the rotor, a portion of the housing received within the fore opening and axially overlapping the peripheral wall of the hub, the gap having a fore gap inlet between the portion of the housing and the peripheral wall of the hub.

Abstract: The gas turbine engine can have a bearing cavity, an ejector having an air/oil path fluidly connected to the bearing cavity, and a nozzle fluidly coupled with the air/oil path, the nozzle connected to a compressed air source.

Abstract: The heat exchanger system can have a first conduit extending from at least one first conduit inlet through a heat exchanger to at least two first conduit outlets; a second conduit extending from at least one second inlet through the heat exchanger to at least one second outlet, the first and second conduits disposed adjacent to one another in heat exchange engagement within the heat exchanger; and a bypass conduit extending from the first conduit between the at least one first inlet and the heat exchanger to the first conduit between the heat exchanger and at least one of said at least two first outlets.

Abstract: A method of operating a multi-engine aircraft having two or more gas turbine engines includes operating a first engine in a powered mode to provide motive power to the aircraft, and, in flight, operating a second engine in either a powered mode to provide motive power to the aircraft or in a standby mode to provide substantially no motive power to the aircraft. When operating the second engine in the powered mode, pressurized air is bled from a first bleed location of a compressor of the second engine. When operating the second engine in the standby mode, pressurized air is bled from a second bleed location of the compressor of the second engine and supplying the pressurized air to a bleed air system of the second engine. The second bleed location is downstream of the first bleed location within the compressor of the second engine.

Abstract: An oil filtering system comprises: a first inlet, a first outlet, and a first oil filter; a first bypass conduit interconnecting the first inlet to the first outlet; a first valve in the first bypass conduit, the first inlet fluidly connected to the first outlet at least via the first bypass conduit in an opened configuration of the first valve, and via the first oil filter in a closed configuration; a second inlet, a second outlet, and a second oil filter; a second bypass conduit between the first inlet and the second outlet; a second valve disposed in the second bypass conduit, the second outlet fluidly connected to the first inlet via the second bypass conduit in an open configuration of the second valve, and via the second oil filter in the closed configuration thereof.

Abstract: The gas turbine engine can have a bearing cavity, an ejector having an air/oil path fluidly connected to the bearing cavity, and a nozzle fluidly coupled with the air/oil path, the nozzle connected to a compressed air source.

Abstract: Apparatus and methods for controlling a pressure differential across one or more seals of a bearing chamber in a gas turbine engine are disclosed. In some embodiments, the apparatus comprises a scavenge pump in fluid communication with an interior of the bearing chamber for driving oil from the bearing chamber; and a venting valve. The venting valve is configured to cause venting of the interior of the bearing chamber in parallel to the scavenge pump based on the pressure differential across the one or more seals.

Abstract: A controlled gap seal device is adapted to surround a shaft with an annular seal element. A ring is positioned on an outer surface of the seal element, the ring adapted to modify a diametrical dimension of the seal element by thermally expanding/contracting as a function of temperature variations. A housing assembly has an interior enclosing the seal element and the ring, with the seal configured to be generally stationary in the interior. The housing assembly has an air inlet and air outlet in fluid communication with a surrounding environment for directing a flow of gas from the surrounding environment onto the ring to controllably cool and shrink the ring. A method for modifying a diameter of a controlled gap seal relative to the shaft is also provided.

Abstract: An oil filtering system comprises: a first inlet, a first outlet, and a first oil filter; a first bypass conduit interconnecting the first inlet to the first outlet; a first valve in the first bypass conduit, the first inlet fluidly connected to the first outlet at least via the first bypass conduit in an opened configuration of the first valve, and via the first oil filter in a closed configuration; a second inlet, a second outlet, and a second oil filter; a second bypass conduit between the first inlet and the second outlet; a second valve disposed in the second bypass conduit, the second outlet fluidly connected to the first inlet via the second bypass conduit in an open configuration of the second valve, and via the second oil filter in the closed configuration thereof.

Abstract: A heat management system of a gas turbine engine for cooling oil and heating fuel, includes an oil circuit having parallel connected first and second branches. The first branch includes a fuel/oil heat exchanger and a first fixed restrictor in series and the second branch includes an air cooled oil cooler and a second fixed restrictor. The first and second fixed restrictors limit respective oil flows through the first and second branch differently, in response to viscosity changes of the oil caused by temperature changes of the oil during engine operation to modify oil distribution between the first and second branches.

Abstract: Apparatus and methods for controlling a pressure differential across one or more seals of a bearing chamber in a gas turbine engine are disclosed. In some embodiments, the apparatus comprises a scavenge pump in fluid communication with an interior of the bearing chamber for driving oil from the bearing chamber; and a venting valve. The venting valve is configured to cause venting of the interior of the bearing chamber in parallel to the scavenge pump based on the pressure differential across the one or more seals.

Abstract: The heat exchanger system can have a first conduit extending from at least one first conduit inlet through a heat exchanger to at least two first conduit outlets; a second conduit extending from at least one second inlet through the heat exchanger to at least one second outlet, the first and second conduits disposed adjacent to one another in heat exchange engagement within the heat exchanger; and a bypass conduit extending from the first conduit between the at least one first inlet and the heat exchanger to the first conduit between the heat exchanger and at least one of said at least two first outlets.

Abstract: A controlled gap seal device is adapted to surround a shaft with an annular seal element. A ring is positioned on an outer surface of the seal element, the ring adapted to modify a diametrical dimension of the seal element by thermally expanding/contracting as a function of temperature variations. A housing assembly has an interior enclosing the seal element and the ring, with the seal configured to be generally stationary in the interior. The housing assembly has an air inlet and air outlet in fluid communication with a surrounding environment for directing a flow of gas from the surrounding environment onto the ring to controllably cool and shrink the ring. A method for modifying a diameter of a controlled gap seal relative to the shaft is also provided.