Hybrid gas turbofan powered sub-idle descent mode

Abstract

A method of operating an aircraft hybrid gas turbofan during an idle mode of operation includes reducing a fuel flow to a primary gas turbine engine and boosting a high spool of the primary gas turbine engine using a secondary gas turbine engine via a first power linkage connecting the primary and secondary gas turbine engines, such that a net fuel reduction is achieved. The net fuel reduction accounts for fuel flow to the primary gas turbine engine and fuel flow to the secondary gas turbine engine.

1 . A method of operating an aircraft hybrid gas turbofan during an idle mode of operation of a primary gas turbine engine, the method comprising:
 reducing a fuel flow to the primary gas turbine engine; and   boosting a high spool of the primary gas turbine engine using a secondary gas turbine engine via a first power linkage connecting the primary and secondary gas turbine engines such that a net fuel reduction is achieved,   wherein the net fuel reduction accounts for fuel flow to the primary gas turbine engine and fuel flow to the secondary gas turbine engine.   
     
     
         2 . The method of  claim 1 , wherein the primary gas turbine engine is a propulsion engine and the secondary gas turbine engine is an auxiliary power unit (APU). 
     
     
         3 . The method of  claim 1 , wherein boosting the high spool of the primary gas turbine engine comprises:
 driving a generator with the secondary gas turbine engine;   coupling a motor to the high spool; and   powering the motor via the generator.   
     
     
         4 . The method of  claim 1 , wherein boosting the high spool of the primary gas turbine engine comprises:
 generating compressed air with the secondary gas turbine engine; and   providing the compressed air directly into a turbine of the high spool of the primary gas turbine engine to provide high spool torque.   
     
     
         5 . The method of  claim 1 , wherein boosting the high spool of the primary gas turbine engine comprises:
 driving a generator with the second engine;   coupling a motor to the high spool;   powering the motor via the generator;   generating compressed air in the secondary gas turbine engine; and   providing the compressed air into the turbine of the high spool of the primary gas turbine engine to provide high spool torque.   
     
     
         6 . The method of  claim 1 , wherein the idle mode occurs during descent of the aircraft. 
     
     
         7 . The method of  claim 1 , wherein reducing the fuel flow to the primary gas turbine engine comprises a reduction of fuel flow greater than 10 percent over a conventional idle mode in which power to the high spool of the primary gas turbine engine is not boosted by the secondary gas turbine engine. 
     
     
         8 . The method of  claim 6 , wherein boosting the high spool of the primary gas turbine engine comprises providing supplemental power to the primary gas turbine engine in an amount greater than 100 horsepower. 
     
     
         9 . The method of  claim 1  and further comprising restricting an air flow exiting from a compressor section of the primary gas turbine engine. 
     
     
         10 . A method of operating an aircraft hybrid gas turbofan, the method comprising:
 providing supplemental power to one of a primary gas turbine engine and a secondary gas turbine engine during a mode of operation of the primary gas turbine engine, wherein the primary gas turbine engine is a propulsion engine and the secondary gas turbine engine is an auxiliary power unit (APU);   wherein supplemental power is provided to the primary gas turbine engine by the APU; and   wherein supplemental power is provided to the APU by the primary gas turbine engine; and   reducing a fuel flow to the primary gas turbine engine when supplemental power is provided to the primary gas turbine engine by the APU such that a net fuel reduction is achieved, wherein the net fuel reduction accounts for fuel flow to the primary gas turbine engine and fuel flow to the APU.   
     
     
         11 . The method of  claim 10 , wherein providing supplemental power to the primary gas turbine engine occurs during an idle mode of operation of the aircraft, and wherein providing supplemental power comprises boosting the high spool of a primary gas turbine engine using the secondary gas turbine engine via a first power linkage connecting the primary and secondary gas turbine engines. 
     
     
         12 . The method of  claim 11 , wherein boosting the high spool of the primary gas turbine engine comprises at least one of a first power supplementation method and a second power supplementation method;
 wherein the first power supplementation method comprises:
 driving a generator with the secondary gas turbine engine; 
 coupling a motor to the high spool; and 
 powering the motor via the generator; and 
   wherein the second power supplementation method comprises:
 generating compressed air in the secondary gas turbine engine; and 
 providing the compressed air directly into a turbine of the high spool of the primary gas turbine engine to provide high spool torque. 
   
     
     
         13 . The method of  claim 12 , wherein reducing the fuel flow to the primary gas turbine engine comprises a reduction of fuel flow greater than 10 percent over a conventional idle mode in which power to the high spool of the primary gas turbine engine is not boosted by the secondary gas turbine engine. 
     
     
         14 . The method of  claim 13 , wherein boosting the high spool of the primary gas turbine engine comprises supplementing power to the primary gas turbine engine in an amount greater than 100 horsepower. 
     
     
         15 . The method of  claim 10 , wherein providing supplemental power to the secondary gas turbine engine comprises:
 driving a generator with a high spool of the primary gas turbine engine;   coupling a motor to a spool of the APU; and   powering the motor via the generator.   
     
     
         16 . The method of  claim 15 , wherein the mode of operation is one of a takeoff mode, top of climb mode, or cruise mode. 
     
     
         17 . An aircraft hybrid gas turbofan comprising:
 a primary gas turbine engine having a high spool, wherein the primary gas turbine engine is a propulsion engine;   a secondary gas turbine engine, wherein the secondary gas turbine engine is an auxiliary power unit (APU); and   a means for linking power between the high spool of the primary gas turbine engine and the APU.   
     
     
         18 . The aircraft hybrid gas turbofan of  claim 17 , wherein the means for linking power includes at least one of:
 an electrical coupling comprising:
 a generator driven by the APU; and 
 a motor coupled to the high spool and powered by the generator; and 
   a mechanical coupling comprising a bleed air conduit connecting a compressor section of the APU to a core gas path of a turbine of the high spool.   
     
     
         19 . The aircraft hybrid gas turbofan of  claim 17 , wherein the power linkage includes a combined motor/generator configured to transfer power from a spool of the primary gas turbine engine to the APU. 
     
     
         20 . A method of operating an aircraft hybrid gas turbofan, the method comprising:
 providing supplemental power to a primary gas turbine engine by a secondary gas turbine engine during a mode of operation of the primary gas turbine engine, wherein the primary gas turbine engine is a propulsion engine and the secondary gas turbine engine is an auxiliary power unit (APU); and   reducing a response time of the primary gas turbine engine for spooling up when additional thrust output is needed.