Abstract: A turboprop propulsion unit for an aircraft comprises a propeller 22 which is driven by a core engine by means of a propeller turbine 26 which drives the propeller 22 through a shaft 28 and a propeller gearbox 24. Restarting of the engine in flight is achieved by windmilling of the propeller 22, which drives a propeller gearbox lubricant pump 30. A diverter valve 40 causes lubricant delivered by the propeller gearbox lubricant pump 30 to be supplied to a turbomachinery lubricant pump 18 along a restart conduit 44, so as to drive the turbomachinery lubricant pump 18 as a motor. Torque generated by the turbomachinery lubricant pump 18 is transferred through an accessory gearbox 12 to a spool 4, 6, 8 of the core engine 2 and to a fuel pump 16. Control of the pitch of blades 36 of the propeller 22 enables the windmilling propeller 22 to achieve a desired speed of the spool 4, 6, 8 and output of the fuel pump 16 sufficient to restart the engine 2, even at low air speeds.

Abstract: A turboprop propulsion unit for an aircraft comprises a propeller 22 which is driven by a core engine by means of a propeller turbine 26 which drives the propeller 22 through a shaft 28 and a propeller gearbox 24. Restarting of the engine in flight is achieved by windmilling of the propeller 22, which drives a propeller gearbox lubricant pump 30. A diverter valve 40 causes lubricant delivered by the propeller gearbox lubricant pump 30 to be supplied to a turbomachinery lubricant pump 18 along a restart conduit 44, so as to drive the turbomachinery lubricant pump 18 as a motor. Torque generated by the turbomachinery lubricant pump 18 is transferred through an accessory gearbox 12 to a spool 4, 6, 8 of the core engine 2 and to a fuel pump 16. Control of the pitch of blades 36 of the propeller 22 enables the windmilling propeller 22 to achieve a desired speed of the spool 4, 6, 8 and output of the fuel pump 16 sufficient to restart the engine 2, even at low air speeds.

Abstract: In a fluid system for a gas turbine engine, oil is supplied from an oil tank (10) by a constant displacement pump (12) to lubricate engine components (18). The oil is supplied to the components (18) via a heat exchanger (16) in which oil and fuel are placed in direct heat exchange relationship. The flow of oil to the components (18) is controlled by recirculating a proportion of the oil flow through a bypass (20). The bypass (20) regulates the flow of oil to the components (18) so that the amount of heat transferred to the fuel in the heat exchanger (16) is controlled. At low engine powers a greater proportion of the oil flows through the bypass (20) to reduce the oil flow to the components (18). This reduces the heat transferred to the fuel in the heat exchanger (16) and so prevents overheating of the fuel.

Abstract: In a fluid system for a gas turbine engine, oil is supplied from an oil tank (10) by a constant displacement pump (12) to lubricate engine components (18). The oil is supplied to the components (18) via a heat exchanger (16) in which oil and fuel are placed in direct heat exchange relationship. The flow of oil to the components (18) is controlled by recirculating a proportion of the oil flow through a bypass (20). The bypass (20) regulates the flow of oil to the components (18) so that the amount of heat transferred to the fuel in the heat exchanger (16) is controlled. At low engine powers a greater proportion of the oil flows through the bypass (20) to reduce the oil flow to the components (18). This reduces the heat transferred to the fuel in the heat exchanger (16) and so prevents overheating of the fuel.

Abstract: In a fluid system for a gas turbine engine, oil is supplied from an oil tank (10) by a constant displacement pump (12) to lubricate engine components (18). The oil is supplied to the components (18) via a heat exchanger (16) in which oil and fuel are placed in direct heat exchange relationship. The flow of oil to the components (18) is controlled by recirculating a proportion of the oil flow through a bypass (20). The bypass (20) regulates the flow of oil to the components (18) so that the amount of heat transferred to the fuel in the heat exchanger (16) is controlled. At low engine powers a greater proportion of the oil flows through the bypass (20) to reduce the oil flow to the components (18). This reduces the heat transferred to the fuel in the heat exchanger (16) and so prevents overheating of the fuel.

Abstract: In a fluid system for a gas turbine engine, oil is supplied from an oil tank (10) by a constant displacement pump (12) to lubricate engine components (18). The oil is supplied to the components (18) via a heat exchanger (16) in which oil and fuel are placed in direct heat exchange relationship. The flow of oil to the components (18) is controlled by recirculating a proportion of the oil flow through a bypass (20). The bypass (20) regulates the flow of oil to the components (18) so that the amount of heat transferred to the fuel in the heat exchanger (16) is controlled. At low engine powers a greater proportion of the oil flows through the bypass (20) to reduce the oil flow to the components (18). This reduces the heat transferred to the fuel in the heat exchanger (16) and so prevents overheating of the fuel.