Abstract: In a gas turbine engine of the type having a high-pressure (HP) spool and a low-pres sure (LP) spool, methods of increasing surge margin and compression efficiency at a given thrust are provided. One method increases compression efficiency and includes transferring mechanical power from the HP spool to the LP spool to reduce a corrected speed of a HP compressor therein and raise a working line of a LP compressor therein. Another method increases surge margin and includes transferring mechanical power from the LP spool to the HP spool to increase a corrected speed of a HP compressor therein and lower a working line of a LP compressor therein.

Abstract: In a gas turbine engine of the type having a high-pressure (HP) spool and a low-pressure (LP) spool, methods of increasing surge margin and compression efficiency at a given thrust are provided. One method increases compression efficiency and comprises transferring mechanical power from the HP spool to the LP spool to reduce a corrected speed of a HP compressor therein and raise a working line of a LP compressor therein. Another method increases surge margin and comprises transferring mechanical power from the LP spool to the HP spool to increase a corrected speed of a HP compressor therein and lower a working line of a LP compressor therein.

Abstract: A gas turbine engine for an aircraft, comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine, the first electric machine having a first maximum output power; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine, the second electric machine having a second maximum output power; and an engine controller configured to identify a condition to the effect that the LP turbine is operating in an unchoked regime, and, in response to an electrical power demand being between zero and the first maximum output power, only extracting electrical power from the first electric machine to meet the electrical power demand.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustion system comprising a fuel metering unit; and an engine controller configured to, in response to a change of a power lever angle setting indicative of a deceleration event, reduce fuel flow to the combustion system by the fuel metering unit, and to operate the first electric machine in a generator mode to reduce the HP spool rotational speed and engine core mass flow.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustor; an electrical energy storage unit; and an engine controller configured to: in response to receipt of a request for an increased electrical power supply by the engine (dPD) within a requested timeframe (dt), evaluating a current HP compressor surge margin (dRH/RH) and a current LP compressor surge margin (dRL/RL) based on the operating points thereof; in response to evaluating that one or more of the HP compressor and the LP compressor has insufficient surge margin to facilitate a change of electrical power supply at a requested rate (dPD/dt), meeting the requested electrical power demand using the electrical energy storage unit whilst increasing fuel flow to the combustor to accelerate the engine.

Abstract: A gas turbine engine for an aircraft, comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine, the first electric machine having a first maximum output power; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine, the second electric machine having a second maximum output power; and an engine controller configured to identify a condition to the effect that the LP turbine is operating in an unchoked regime, and, in response to an electrical power demand being between zero and the first maximum output power, only extracting electrical power from the first electric machine to meet the electrical power demand.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; and an engine controller configured to identify a condition to the effect that the engine is in an approach idle condition, and operate the first electric machine in a motor mode and operate the second electric machine in a generator mode to transfer power electrically from the LP spool to the HP spool to thereby reduce the LP spool rotational speed and increase the HP spool rotational speed.

Abstract: A variable bypass ratio turbofan engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine, the first electric machine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a fan driven by the LP spool and configured to produce a bypass flow for propulsion and a core flow for delivery to the LP compressor, wherein the ratio of the mass flow rates of the bypass flow and the core flow define a bypass ratio; an engine controller configured to, for a fixed thrust setting, control the degree of electrical power generated by one or both of the first electric machine and the second electric machine so as to vary a mass flow rate of the core flow and to thereby vary the bypass ratio of the engine.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine, the first electric machine having a first maximum output power; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine, the second electric machine having a second maximum output power; a combustion system comprising a fuel metering unit; and an engine controller configured to identify a condition to the effect that the engine is in a maximum take-off mode of operation or a maximum climb mode of operation, and, in response to an electrical power demand being between zero and the second maximum output power, only extracting electrical power from the second electric machine to meet the electrical power demand.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustion system comprising a fuel metering unit; and an engine controller configured to, in response to a change of a power lever angle setting indicative of a deceleration event, reduce fuel flow to the combustion system by the fuel metering unit, and to operate the first electric machine in a generator mode to reduce the HP spool rotational speed and engine core mass flow.

Abstract: A gas turbine engine for an aircraft comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; a combustor; an electrical energy storage unit; and an engine controller configured to: in response to receipt of a request for an increased electrical power supply by the engine (dPD) within a requested timeframe (dt), evaluating a current HP compressor surge margin (dRH/RH) and a current LP compressor surge margin (dRL/RL) based on the operating points thereof; in response to evaluating that one or more of the HP compressor and the LP compressor has insufficient surge margin to facilitate a change of electrical power supply at a requested rate (dPD/dt), meeting the requested electrical power demand using the electrical energy storage unit whilst increasing fuel flow to the combustor to accelerate the engine.

Abstract: In a gas turbine engine of the type having a high-pressure (HP) spool and a low-pressure (LP) spool, methods of increasing surge margin and compression efficiency at a given thrust are provided. One method increases compression efficiency and comprises transferring mechanical power from the HP spool to the LP spool to reduce a corrected speed of a HP compressor therein and raise a working line of a LP compressor therein. Another method increases surge margin and comprises transferring mechanical power from the LP spool to the HP spool to increase a corrected speed of a HP compressor therein and lower a working line of a LP compressor therein.

Abstract: A gas turbine engine for an aircraft, comprises a high-pressure (HP) spool comprising an HP compressor and a first electric machine driven by an HP turbine; a low-pressure (LP) spool comprising an LP compressor and a second electric machine driven by an LP turbine; an engine controller configured to identify a condition to the effect that the HP spool has reached or exceeded an HP speed limit whilst the LP spool has not reached an LP speed limit, and to operate the first electric machine in a generator mode of operation to reduce the HP spool speed below the HP speed limit.

Abstract: A compressor or fan is controlled to avoid stall, surge or flutter. The control system includes a look-up table from which is retrieved a margin-adjusted limiting value of a control parameter of the compressor, using inputs representing inlet guide vane angle (IGV), non-dimensional speed of the compressor (N/R?T), vehicle Mach number (Mn) and inlet geometry (IG). A variable stall, surge or flutter safety margin about a nominal limiting value of a control parameter is pre-established to reflect threats to the working, stall, flutter and surge lines, for example as a result of measurement inaccuracies, and from this the margin-adjusted limiting value is derived. An actual value of the control parameter is determined in real time, and the actual value is compared with the margin-adjusted limiting value. An output signal indicating stall, surge or flutter risk is generated if the actual value falls within the stall, surge or flutter safety margin.

Abstract: A compressor or fan is controlled to avoid stall, surge or flutter. The control system includes a look-up table from which is retrieved a margin-adjusted limiting value of a control parameter of the compressor, using inputs representing inlet guide vane angle (IGV), non-dimensional speed of the compressor (N/R?T), vehicle Mach number (Mn) and inlet geometry (IG). A variable stall, surge or flutter safety margin about a nominal limiting value of a control parameter is pre-established to reflect threats to the working, stall, flutter and surge lines, for example as a result of measurement inaccuracies, and from this the margin-adjusted limiting value is derived. An actual value of the control parameter is determined in real time, and the actual value is compared with the margin-adjusted limiting value. An output signal indicating stall, surge or flutter risk is generated if the actual value falls within the stall, surge or flutter safety margin.