Abstract:
One embodiment of the present invention is a unique aircraft. Another embodiment is a unique aircraft propulsion system. Still another embodiment is a unique system for taxiing an aircraft without starting one or more main aircraft propulsion engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for aircraft taxiing and propulsion systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith.

Description:
FIELD OF THE INVENTION 
     The present invention relates to aircraft, aircraft propulsions systems and systems for taxiing an aircraft without starting main engines. 
     BACKGROUND 
     Aircraft, aircraft propulsions systems and systems that provide for aircraft taxiing without starting one or more main aircraft engines remain an area of interest. Some existing systems have various shortcomings, drawbacks, and disadvantages relative to certain applications. Accordingly, there remains a need for further contributions in this area of technology. 
     SUMMARY 
     One embodiment of the present invention is a unique aircraft. Another embodiment is a unique aircraft propulsion system. Still another embodiment is a unique system for taxiing an aircraft without starting one or more main aircraft propulsion engines. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for aircraft taxiing and propulsion systems. Further embodiments, forms, features, aspects, benefits, and advantages of the present application will become apparent from the description and figures provided herewith. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
         FIG. 1  illustrates some aspects of a non-limiting example of an aircraft in accordance with an embodiment of the present invention. 
         FIG. 2  schematically illustrates some aspects of a non-limiting example of an aircraft propulsion system in accordance with an embodiment of the present invention. 
         FIG. 3  schematically illustrates some aspects of a non-limiting example of a system for taxiing an aircraft in accordance with an embodiment of the present invention. 
         FIG. 4  schematically illustrates some aspects of a non-limiting example of a system for taxiing an aircraft in accordance with another embodiment of the present invention. 
         FIG. 5  schematically illustrates some additional aspects of a non-limiting example of a system for taxiing an aircraft in accordance with the embodiment of  FIG. 4 . 
         FIG. 6  schematically illustrates some aspects of a non-limiting example of the system of  FIGS. 4 and 5  operating in a mode configured for taxiing an aircraft without starting one or more main propulsion engine(s) of the aircraft. 
         FIG. 7  schematically illustrates some aspects of a non-limiting example of the system of  FIGS. 4 and 5  operating in a mode configured for starting an aircraft main propulsion engine. 
     
    
    
     DETAILED DESCRIPTION 
     For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
     Referring to  FIG. 1 , there are illustrated some aspects of a non-limiting example of a vehicle  10  in accordance with an embodiment of the present invention. In one form, vehicle  10  is an aircraft, referred to herein as aircraft  10 . In other embodiments, vehicle  10  may be any type of engine powered vehicle, including one or more types of air-vehicles; land vehicles, including and without limitation, tracked and/or wheeled vehicles; marine vehicles, including and without limitation, surface vessels, submarines and/or semi-submersibles; amphibious vehicles, or any combination of one or more types of air, marine and land vehicles. In various forms, vehicle  10  may be manned and/or autonomous. 
     In one form, aircraft  10  includes a fuselage  12 , wings  14 , an empennage  16  and propulsion systems  18 . In one form, aircraft  10  is a twin engine turbofan aircraft. In other embodiments, aircraft  10  may be any fixed-wing aircraft, including turbofan aircraft, turbojet aircraft and turboprop aircraft. In still other embodiments, aircraft  10  may be a rotary-wing aircraft or a combination rotary-wing/fixed-wing aircraft. In various embodiments, aircraft  10  may have a single main propulsion engine or a plurality of main propulsion engines. In addition, in various embodiments, aircraft  10  may employ any number of wings  14 . Empennage  16  may employ a single or multiple flight control surfaces. 
     Referring to  FIG. 2 , there are illustrated some aspects of a non-limiting example of a propulsion system  18  in accordance with an embodiment of the present invention. Propulsion system  18  includes a gas turbine engine  20  as a main engine, i.e., main propulsion engine, and an auxiliary power unit  22 . Although described herein as with respect to an aircraft propulsion system, in other embodiments, propulsion system  18  may be a propulsion system for providing propulsive thrust to one or more other types of vehicles, e.g., air-vehicles; land vehicles including tracked and/or wheeled vehicles (e.g., battle tanks); marine vehicles, including surface vessels, submarines and/or semi-submersibles; amphibious vehicles; or any combination of one or more types of air, marine and land vehicles. The propulsive thrust provided by propulsion system  18  for an air vehicle in the form of one or more fast moving streams of air generated by one or more propulsors, for example and without limitation, one or more turbofans, propellers, turbines, propfans and/or other rotor systems that generate thrust. The propulsive thrust provided by propulsion system  18  to land-based vehicles may include the tractive effort provided via one or more propulsors in the form of, for example and without limitation, wheels and/or tracks, e.g., using one or more transmissions. The propulsive thrust provided by propulsion system  18  to a marine vehicle may be in the form of one or more fast moving streams of water generated by one or more propulsors in the form of, for example and without limitation, one or more propellers, shrouded and/or not shrouded; hydrojets and/or jet-pumps. 
     In one form, APU  22  is a secondary gas turbine engine. In other embodiments, APU  22  may be one or more other types of thermodynamic machines configured to generate mechanical power from fuel, which may be used to drive other mechanical and/or electro-mechanical machines, e.g., including generators, refrigeration systems, thermal management systems and/or any other type of machine. For example, in some embodiments, APU  22  may be a turbocharged, supercharged and/or normally aspirated piston engine or a hybrid engine. In a particular form, auxiliary power unit  22  is a hybrid auxiliary power unit (hybrid APU  22 ) that includes a secondary gas turbine engine. In other embodiments, APU  22  may not be a hybrid APU. 
     In one form, engine  20  is a primary propulsion engine that provides thrust for flight operations of aircraft  10 . In one form, engine  20  is a two spool engine having a high pressure (HP) spool  24  and a low pressure (LP) spool  26 . In other embodiments, engine  20  may include three or more spools, e.g., may include an intermediate pressure (IP) spool and/or other spools. In one form, engine  20  is a turbofan engine, wherein LP spool  26  is operative to drive a propulsor  28  in the form of a turbofan (fan) system, which may be referred to as a turbofan, a fan or a fan system. In other embodiments, engine  20  may be a turboprop engine, wherein LP spool  26  powers a propulsor  28  in the form of a propeller system (not shown), e.g., via a reduction gearbox (not shown). In still other embodiments, propulsor  28  may take other forms, such as a helicopter rotor or tilt-wing aircraft rotor. In one form, a single propulsion system  18  is coupled to each wing  14  of aircraft  10 . In other embodiments, more than one propulsion system  18  may be coupled to each wing  14 . In still other embodiments, one or more propulsion systems  18  may be coupled to the fuselage or the empennage in addition to or in place of wing-mounted propulsion systems  18 . 
     In one form, engine  20  includes, in addition to fan system  28 , a bypass duct  30 , a compressor system  32 , a diffuser  34 , a combustion system  36 , a high pressure (HP) turbine system  38 , a low pressure (LP) turbine system  40 , a nozzle  42 A, and a nozzle  42 B. In other embodiments, there may be, for example, an intermediate pressure spool having an intermediate pressure turbine system. In various embodiments, engine  20  may also include an electrical machine  44  coupled to LP spool  26 , and an electrical machine  46  coupled to HP spool  24 . In one form, each of electrical machines  44  and  46  are configured to convert mechanical power to electrical power, and to convert electrical power to mechanical power, e.g., as in a motor/generator. In other embodiments, one or both of electrical machines  44  and  46  may be configured to only convert mechanical power into electrical power, e.g., as in a generator. In still other embodiments, one or both of electrical machines  44  and  46  may be configured to only convert electrical power into mechanical power, e.g., as in a motor. In one form, both electrical machine  44  and electrical machine  46  are configured to provide power to aircraft  10  during flight operations. In various embodiments, one or both of electrical machines  44  and  46  may also provide power to aircraft  10  during ground operations. 
     In the depicted embodiment, the engine  20  core flow is discharged through nozzle  42 A, and the bypass flow is discharged through nozzle  42 B. In other embodiments, other nozzle arrangements may be employed, e.g., a common nozzle for core and bypass flow; a nozzle for core flow, but no nozzle for bypass flow; or another nozzle arrangement. Bypass duct  30  and compressor system  32  are in fluid communication with fan system  28 . Nozzle  42 B is in fluid communication with bypass duct  30 . Diffuser  34  is in fluid communication with compressor system  32 . Combustion system  36  is fluidly disposed between compressor system  32  and turbine system  38 . Turbine system  40  is fluidly disposed between turbine system  38  and nozzle  42 B. In one form, combustion system  36  includes a combustion liner (not shown) that contains a continuous combustion process. In other embodiments, combustion system  36  may take other forms, and may be, for example, a wave rotor combustion system, a rotary valve combustion system, a pulse detonation combustion system or a slinger combustion system, and may employ deflagration and/or detonation combustion processes. 
     Fan system  28  includes a fan rotor system  48  driven by LP spool  26 . In various embodiments, fan rotor system  48  includes one or more rotors (not shown) that are powered by turbine system  40 . Fan system  28  may include one or more vanes (not shown). Bypass duct  30  is operative to transmit a bypass flow generated by fan system  28  around the core of engine  20 . Compressor system  32  includes a compressor rotor system  50 . In various embodiments, compressor rotor system  50  includes one or more rotors (not shown) that are powered by turbine system  38 . Turbine system  38  includes a turbine rotor system  52 . In various embodiments, turbine rotor system  52  includes one or more rotors (not shown) operative to drive compressor rotor system  50 . Turbine rotor system  52  is drivingly coupled to compressor rotor system  50  via a shafting system  54 . Turbine system  40  includes a turbine rotor system  56 . In various embodiments, turbine rotor system  56  includes one or more rotors (not shown) operative to drive fan rotor system  48 . Turbine rotor system  56  is drivingly coupled to fan rotor system  48  via a shafting system  58 . In various embodiments, shafting systems  54  and  58  include a plurality of shafts that may rotate at the same or different speeds and directions. In some embodiments, only a single shaft may be employed in one or both of shafting systems  54  and  58 . Turbine system  40  is operative to discharge the engine  20  core flow to nozzle  42 A. 
     During normal operation of gas turbine engine  20 , air is drawn into the inlet of fan system  28  and pressurized by fan rotor system  48 . Some of the air pressurized by fan rotor system  48  is directed into compressor system  32  as core flow, and some of the pressurized air is directed into bypass duct  30  as bypass flow. Compressor system  32  further pressurizes the portion of the air received therein from fan system  28 , which is then discharged into diffuser  34 . Diffuser  34  reduces the velocity of the pressurized air, and directs the diffused core airflow into combustion system  36 . Fuel is mixed with the pressurized air in combustion system  36 , which is then combusted. The hot gases exiting combustion system  36  are directed into turbine systems  38  and  40 , which extract energy in the form of mechanical shaft power to drive compressor system  32  and fan system  28  via respective shafting systems  54  and  58 . 
     Referring to  FIG. 3 , some aspects of a non-limiting example of hybrid APU  22  and some of its connections to engine  20  in accordance with an embodiment of the present invention are schematically depicted. Engine  20  includes a gearbox  59  that is coupled to both HP spool  24  and LP spool  26 . In other embodiments, other gearboxes may be employed. In one form, hybrid APU  22  is coupled to both HP spool  24  and LP spool  26  via gearbox  59 . Hybrid APU  22  is operative to supply rotational power, mechanically, to both HP spool  24  and LP spool  26 , to generate thrust via propulsor  28  for taxiing aircraft  10  without starting engine  20 . In one form, hybrid APU  22  is mechanically coupled to both HP spool  24  and LP spool  26  to directly drive HP spool  24  and LP spool  26  mechanically. In other embodiments, other arrangements, e.g., mechanical arrangements, may be employed to drive both HP spool  24  and LP spool  26 . In other embodiments, hybrid APU  22  may be mechanically coupled to only LP spool  26  to directly drive HP spool  24  and LP spool  26  mechanically, to generate thrust via propulsor  28  for taxiing aircraft  10  without starting engine  20 . 
     In one form, hybrid APU  22  is configured to supply rotational power to both HP spool  24  and LP spool  26  to provide sufficient thrust to taxi aircraft  10  without starting one or more engines  20 . In one form, the primary component of the taxiing thrust is produced by propulsor  28 . The rotational power supplied to HP spool  24  reduces drag on the rotation of LP spool  26 , and may result in a secondary taxiing thrust component being produced by HP spool  24 . LP spool  26  turbines may also provide a secondary taxiing thrust component. 
     In one form, hybrid APU  22  is mounted on engine gearbox  59 . In other embodiments, hybrid APU  22  may be mounted to other structures. Hybrid APU  22  includes an APU compressor  60 , a fuel cell  62 , an APU start-up combustor  63 , an APU turbine  64 , an output reduction gearbox  66  and an electrical machine  68 . APU compressor  60  is coupled to and driven by APU turbine  64 . The discharge of APU compressor  60  is in fluid communication with fuel cell  62  and combustor  63 . Valves (not shown) may be employed to selectively direct the discharge air from APU compressor  60  to one or both of fuel cell  62  and APU start-up combustor  63 . The discharge of fuel cell  62  and combustor  63  is in fluid communication with APU turbine  64 . Valves (not shown) may be employed to selectively direct the discharge air from one or both of fuel cell  62  and combustor  63  into APU turbine  64 . APU Turbine  64  is coupled to compressor  60  and operative to drive compressor  60 . Reduction gearbox  66  is coupled to gearbox  59  for delivering the mechanical power output from hybrid APU  22  to engine  20 . 
     Fuel cell  62  is fluidly disposed between compressor  60  and turbine  64 . Fuel cell  62  is configured to generate electrical power for use by aircraft  10  during ground operations and/or flight operations. Fuel cell  62  is configured to receive a fuel F, and pressurized air from compressor  60  for use as an oxidant, and to generate electrical power using fuel F and the oxidant. Fuel cell  62  is also configured to add heat to the pressurized air received from compressor  60 . The temperature output by fuel cell  62  may vary with the application and/or type of fuel cell. In various embodiments, the output temperature is in the range of 600° C. to 1200° C. In other embodiments, fuel cell  62  may yield other output temperatures outside aforementioned range. Fuel cell  62  discharges the heated pressurized air into turbine  64  for extraction of mechanical power, which is transmitted to reduction gearbox  66 . In some embodiments, a combustor or other heat addition device (not shown) may be positioned downstream of fuel cell  62  to increase the temperature of the gases discharged into turbine  64 . 
     In one form, fuel cell  62  is a solid oxide fuel cell (SOFC). In other embodiments, other fuel cell types may be employed, e.g., such as a molten carbonate fuel cell (MCFC). In one form, fuel cell  62  is electrically coupled to a power conditioner for conditioning the output of fuel cell  62  for subsequent delivery to aircraft  10  components and/or engine  20  components. In other embodiments, fuel cell  62  may be electrically coupled to other components. In one form, a reformer  65  is in fluid communication with fuel cell  62 . Reformer  65  is configured to reform fuel F, e.g., a typical aircraft gas turbine engine fuel, into syngas for use by fuel cell  62 . In other embodiments, fuel cell  62  may not include a reformer, e.g., depending upon the type of fuel cell used in an application and/or the type of fuel F supplied to fuel cell  62 . 
     APU start-up combustor  63  is fluidly disposed between compressor  60  and turbine  64 . APU start-up combustor  63  is configured to receive fuel F and combust fuel in pressurized air received from compressor  60 . In one form, combustor  63  is configured to add heat to the pressurized air received from compressor  60  prior to fuel cell  62  achieving its normal operating temperature. The heated pressurized air is discharged into turbine  64  for extraction of mechanical power. In one form, once fuel cell  62  has achieved its operating temperature, combustor  63  is shut off. In some embodiments, both fuel cell  62  and combustor  63  may both be continuously operated to add heat to pressurized air from compressor  60 . In other embodiments, combustor  63  may be employed alone, e.g., where the electrical output of fuel cell  62  is not required. Still other embodiments may not employ a start-up combustor, such as start-up combustor  63 , e.g., but rather may rely on fuel cell  62  to add heat to air pressurized by compressor  60 . 
     In one form, reduction gearbox  66  is coupled to and driven by turbine  64 . In other embodiments, reduction gearbox  66  may be coupled to compressor  60  and driven by turbine  64  via compressor  60  or a shaft extending from turbine  64 . Reduction gearbox  66  is coupled to engine gearbox  59  for delivering mechanical power to HP spool  24  and/or LP spool  26 . In one form, reduction gearbox  66  is considered a part of hybrid APU  22 . In other embodiments, reduction gearbox  66  may be considered a separate component that is powered by hybrid APU  22 . 
     Electrical machine  68  is operative to convert mechanical power to electrical power. Electrical machine  68  is coupled to hybrid APU  22 . In one form, electrical machine  68  is coupled to compressor  60 . In other embodiments, other mechanical arrangements may be employed. For example, electrical machine  68  may be coupled directly to turbine  64 , or may be coupled to the same or other APU  22  components directly or via a gearbox and/or clutch system. 
     In some embodiments, electrical machine  68  may be also configured to convert electrical power to mechanical power, e.g., as a motor/generator for starting hybrid APU  22 . In some embodiments, a power conditioner  70  is electrically coupled to electrical machine  68  and operative to condition the power output of electrical machine  68 , e.g., for use in supplying electrical power to one or more systems of aircraft  10  during aircraft  10  ground operations and/or flight operations, and/or for supplying electrical power to one or more engine  20  systems or components, such as electrical machines  44  and  46 . In some embodiments, electrical machine  68  is configured to provide electrical power to drive electrical machine  44  and/or electrical machine  46 . For example, in one form, power generated by electrical machine  68  may be employed to start or to aid in the starting of engine  20  by providing electrical power to electrical machines  44  and/or  46 . In the depiction of  FIG. 3 , a line  72  indicates an electrical coupling of electrical machines  44  and  46  to power conditioning unit  70  for supplying power from electrical machine  68  to electrical machines  44  and  46 , and for supplying power from electrical machines  44  and  46  to aircraft  10 , e.g., during aircraft  10  flight and/or ground operations. Although a single line  72  is depicted, it will be understood that the depiction is schematic only, and does limit the type of coupling between electrical machines  44  and  46  and power conditioning unit  70 . In addition, it will be understood that other electrical means may be employed to couple the output of electrical machines  44  and  46  to aircraft  10  and/or to electrical machine  68 . A line  73  similarly schematically indicates an electrical coupling of fuel cell  62  to power conditioning unit  70  for supplying power from fuel cell  62  to electrical machines  44 ,  46  and  68  (e.g., via conditioning unit  70 ), and to aircraft  10  during flight and/or ground operations. It will be understood that other electrical means may be employed to couple the output of fuel cell  62  to electrical machines  44 ,  46  and  68 , and to aircraft  10 . In some embodiments, electrical machine  68  may be electrically coupled to only one of electrical machine  44  and electrical machine  46 . In still other embodiments, electrical machine  68  may not be electrically coupled to either electrical machine  44  or electrical machine  46 . 
     Reduction gearbox  66  is mechanically coupled to LP spool  26  via gearbox  59  and a shafting system  74 , and is operative to drive LP spool  26 . In one form, a clutch  76  is disposed between LP spool  26  and reduction gearbox  66 . Clutch  76  is configured to mechanically engage and disengage hybrid APU  22  from LP spool  26  of the gas turbine engine  20 . Some embodiments may employ an overrunning (sprag) clutch between hybrid APU  22  and LP spool  26 . 
     In one form, reduction gearbox  66  is also mechanically coupled to HP spool  24 , via gearbox  59  and a shafting system  78 , and is operative to drive HP spool  24 . Shafting system  74  and shafting system  78  combine to couple both LP spool  26  and HP spool  24  to reduction gearbox  66 . In other embodiments, other mechanical drive arrangements may be employed to couple hybrid APU  22  to LP spool  26  and HP spool  24 . In still other embodiments, one or more mechanical drive systems may be employed for hybrid APU to drive one or more other engine spools. In addition, some embodiments may not include a shafting system to couple hybrid APU  22  to HP spool  24 . 
     In one form, a transmission  80  is mechanically disposed in shafting system  78  between reduction gearbox  66  and HP spool  24 . In some embodiments, transmission  80  may be considered a part of reduction gearbox  66 . In other embodiments, transmission  80  may be considered separate from reduction gearbox  66 . In yet other embodiments, transmission  80  may be considered a part of engine gearbox  59  and/or installed therein or mounted thereon. In some embodiments, transmission  80  may be mechanically disposed between hybrid APU  22  and LP spool  26 . 
     In one form, transmission  80  is a continuously variable transmission. In other embodiments, other transmission types may be employed. Transmission  80  is configured to vary the speed as between the high pressure spool and the low pressure spool. In one form, transmission  80  is coupled to HP spool  24  and is configured to vary the speed of HP spool  24  relative to LP spool  26 , e.g., in order to optimize or minimize drag while LP spool  26  is being powered by hybrid APU  22 . In other embodiments, transmission  80  is coupled to LP spool  26  and is configured to vary the speed of LP spool  26  relative to HP spool  24 . In one form, transmission  80  is also configured to selectively engage/disengage HP spool  24  with/from hybrid APU  22 . In other embodiments, clutches (not shown) may be used in addition to or in place of transmission  80  to disengage HP spool  24  from hybrid APU  22 , e.g., including overrunning clutches. In embodiments where transmission  80  is mechanically disposed between reduction gearbox  66  and LP spool  26 , transmission  80  may be configured to engage and disengage LP spool  26  with/from hybrid APU  22 . In other embodiments, clutches (not shown) may be used in addition to or in place of transmission  80  to disengage LP spool  26  from hybrid APU  22 . 
     In one form, transmission  80  is controlled by a controller  81 . Controller  81  is in electrical communication with transmission  80  and clutch  76 . Controller  81  is configured to execute program instructions to selectively control transmission  80  to vary the speed ratio between HP spool  24  and LP spool  26  to reduce internal drag in engine  20 , e.g., aerodynamic losses in engine  20 . Controller  81  is also configured to execute program instructions to control clutch  76  to selectively engage and disengage LP spool  26  with hybrid APU  22 . In addition, controller  81  is configured to execute program instructions to selectively direct transmission  80  to engage HP spool  24  and/or LP spool  26  with hybrid APU  22 , and to disengage HP spool  24  and/or LP spool  26  from the hybrid APU. For example, in one form, transmission  80  is coupled to HP spool  24 , and is controlled by controller  81  to vary the speed of HP spool  24 , and to engage and disengage hybrid APU  22  from HP spool  24 . In other embodiments, transmission  80  may be coupled to LP spool  26 , and may be controlled by controller  81  to vary the speed of HP spool  24 , and to engage and disengage hybrid APU  22  from HP spool  24 . In still other embodiments, transmission  80  may be coupled to both HP spool  24  and LP spool  26 , and may be controlled by controller  81  to vary the speed of both HP spool  24  and LP spool  26 , and to engage and disengage hybrid APU  22  from HP spool  24  and LP spool  26 . 
     In one form, controller  81  is microprocessor based and the program instructions are in the form of software stored in a memory and firmware (not shown), such as a full authority digital electronic control (FADEC). However, it is alternatively contemplated that controller  81  and the program instructions may be in the form of any combination of software, firmware and hardware, including state machines, and may reflect the output of discreet devices and/or integrated circuits, which may be co-located at a particular location or distributed across more than one location, including any digital and/or analog devices configured to achieve the same or similar results as a processor-based controller executing software and/or firmware and/or hardware based instructions. 
     In order to begin taxiing aircraft  10 , hybrid APU  22  is started. In one form, hybrid APU  22  is started by supplying power to electrical machine  68  to rotate compressor  60  and turbine  64 . The power may be supplied to electrical machine  68  from a desired source, such as fuel cell  62 , a battery and/or a ground cart. If fuel cell  62  is not at operating temperature, start-up combustor  63  is employed to add heat to the air pressurized by compressor  60  until fuel cell  62  reaches operating temperature. It will be understood that the method for starting hybrid APU  22  may vary, e.g., with the needs of the application and the existing operational environment of the particular application. 
     In one form, hybrid APU  22  is started prior to engaging HP spool  24  and LP spool  26 , e.g., with transmission  80  and clutch  76 , respectively. In other embodiments, one or both of HP spool  24  and LP spool  26  may be engaged with hybrid APU  22  prior to and during start-up of hybrid APU  22 . Once engaged with APU  22 , HP spool  24  and LP spool  26  rotate based on the rotation of hybrid APU  22 . Rotation of LP spool  26  rotates propulsor  28  (fan rotor system  48 ) to produce thrust for taxiing aircraft  10 . Rotation of HP spool  24  results in lower drag on the rotation of LP spool  26 , thereby decreasing the total power output required by hybrid APU  22  to achieve a desired taxiing thrust level. Controller  81  controls transmission  80  to rotate HP spool  24  at a rate determined to result in reduced or minimum aerodynamic losses in engine  20  at the desired LP spool  26  rate of rotation, to reduce the drag on LP spool  26  in engine  20 . 
     During hybrid APU  22  operation, hybrid APU  22  generates an exhaust flow. In one form, hybrid APU  22  exhaust flow is directed to engine  20 , e.g., HP spool  24  in order to warm engine  20  prior to engine start, which may reduce the amount of time it takes to start engine  20 . The hybrid APU  22  exhaust flow to engine  20  is illustrated as line  82  in  FIG. 3 . In various embodiments, valves and ducting (not shown) or other arrangements may be employed to direct the hybrid APU  22  exhaust flow to engine  20 . The hybrid  22  exhaust flow may subsequently be directed away from engine  20 , e.g., after engine  20  is warmed up or started. 
     Once aircraft  10  is ready, hybrid APU  22  may be used to start engine  20 . In various embodiments, engine  20  may be started during or after taxi operations that are powered by hybrid APU  22 . In one form, hybrid APU  22  is configured to start engine  20  by supplying mechanical power to rotate HP spool  24 . In various embodiments, hybrid APU  22  may also rotate LP spool  26  to aid in starting engine  20 . In some embodiments, hybrid APU  22  may be configured to start engine  20  by supplying electrical power to one or both of electrical machines  44  and  46  in addition to or in place of supplying mechanical power to HP spool  24  and/or LP spool  26  via reduction gearbox  66 . In one form, the electrical power to start engine  20  is generated by both fuel cell  62  and electrical machine  68 . In other embodiments, the electrical power may be generated by either fuel cell  63  or electrical machine  68 . In still other embodiments, other electrical power sources may be employed in addition to or in place of one or both of fuel cell  62  and electrical machine  68 . In one form, engine  20  is started following the completion of taxiing operations of aircraft  10 . In other embodiments, engine  20  may be started during taxiing operations. In various embodiments, hybrid APU  22  is disengaged from engine  20  (HP spool  24  and LP spool  26 ) once engine  20  is started 
     Propulsion system  18  is configured to provide sufficient thrust to taxi aircraft  10  without starting engines  20 , which may result in fuel savings and a reduction in emissions during taxi operations, e.g., since hybrid APU  22  is generally more efficient than engine  20  at thrust levels associated with taxiing aircraft  10 . Once aircraft  10  has reached a position where it is desirable to prepare for takeoff, engines  20  may be started, and disengaged from hybrid APUs  22 . 
     By employing hybrid APU  22  to provide rotational power to LP spool  26  and hence propulsor  28 , sufficient thrust may be provided for taxiing aircraft  10  without starting engines  20 . By employing hybrid APU  22  to provide rotational power to HP spool  24  in addition to LP spool  26 , friction is reduced during taxiing, e.g., aerodynamic drag within engine  20 , which may further result in increased efficiency. In addition, because hybrid APU  22  may be used to start engine  20 , the need for a pneumatic starter may be eliminated. 
     During engine  20  operation, engine  20  generates a bleed flow, e.g., from HP spool  24 . The bleed flow is discharged from HP spool  24  through a bleed port  84 . In some embodiments, the bleed flow is directed into APU compressor  60 , indicated in  FIG. 3  by line  86 , which increases the efficiency of hybrid APU  22 , and which may reduce emissions from hybrid APU  22 . The bleed flow may be supplied via valves and ducting (not shown) or by other arrangements. In various embodiments, the bleed flow may be supplied from HP spool  24 , e.g., to the inlet of compressor  60 , during aircraft  10  flight and/or ground operations, including prior to engine  20  start. 
     Referring to  FIGS. 4 and 5 , some aspects of a non-limiting example of propulsion system  18  in accordance with an embodiment of the present invention are schematically depicted. The embodiment of  FIGS. 4 and 5  is similar in many respects to the embodiment of  FIGS. 2 and 3 ; for the sake of brevity, many such similarities are not separately discussed herein. In the embodiment of  FIGS. 4 and 5 , propulsion system  18  includes, in addition to engine  20  as previously described, an APU  122 , an auxiliary electrical machine  124 , an electrical power source  126  and an auxiliary gearbox  128 . 
     In one form, APU  122  is mechanically coupled to LP spool  26 , and is operative to drive LP spool  26 , e.g., via gearbox  128 . In one form, gearbox  128  is a combining gearbox. In other embodiments, other gearbox types may be employed. In one form gearbox  128  is a single gearbox. In other embodiments, combining gearbox  128  may take other forms, including, for example, a plurality of discrete gear drives and/or one or more other mechanical drive types, e.g., harmonic drives, belt drives, chain drives and/or friction drives. Auxiliary electrical machine  124  is also mechanically coupled to LP spool  26 , and is operative to drive LP spool  26 . In particular, APU  122  and auxiliary electrical machine  124  are configured and operative to jointly supply rotational power to LP spool  26  to generate thrust via propulsor  28  for taxiing aircraft  10 . In various embodiments, electrical power source  126  is electrically coupled to auxiliary electrical machine  124  and operative to supply electrical power to auxiliary electrical machine  124  for providing mechanical power to LP spool  26  and/or HP spool  24 . By providing mechanical power via auxiliary electrical machine  124 , the size of APU  122  may be reduced relative to similar systems that provide all of the power to LP spool  26  and/or HP spool  24  using the APU. The reduced size of APU  122  may translate to reduced weight, cost and fuel usage. 
     APU  122  includes an APU compressor  160 , an APU combustor  163 , and an APU turbine  164 . Combustor  163  is fluidly disposed between compressor  160  and turbine  164 . Compressor  160  is coupled to and driven by turbine  164 . In various embodiments, combustor  163  may be a conventional combustor, or may be a start-up combustor as described above with respect to the embodiment of  FIG. 3 . In one form, APU  122  is mounted to gearbox  59 . In other embodiments, APU  122  may be mounted at other locations. 
     In one form, auxiliary electrical machine  124  is configured to convert mechanical power to electrical power, and to convert electrical power to mechanical power, e.g., as in a motor/generator. In other embodiments, auxiliary electrical machine  124  may be configured to only convert electrical power into mechanical power, e.g., as in a motor. 
     In one form, electrical power source  126  is a combination of a battery  130  and a fuel cell  162 . In other embodiments, electrical power source  126  may be a battery only, a fuel cell only, or any combination of one or more power sources capable of supplying electrical power to auxiliary electrical machine  124  in sufficient quantity for auxiliary electrical machine  124  to perform the tasks set forth herein. Battery  130  and fuel cell  162  are both in electrical communication with a power conditioner  170  for conditioning power supplied to aircraft  10  and/or engine  20  components from electrical power source  126 . Power conditioner  170  is configured to receive electrical power from both fuel cell  162  and batter  130 , and is also configured to deliver power to batter  130  to charge battery  130 . 
     In one form, fuel cell  162  is a solid oxide fuel cell (SOFC). In other embodiments, other fuel cell types may be employed, e.g., such as a molten carbonate fuel cell (MCFC). Fuel cell  162  is similar to fuel cell  62 , described above, and hence, descriptive material applied above to fuel cell  62  applies equally to fuel cell  162 . For example, fuel cell  162  may include a reformer  165  similar to the previously mentioned reformer  65  employed by fuel cell  62 . In one form, APU  122  is a hybrid APU configured similarly as hybrid APU  22 , wherein fuel cell is part of the thermodynamic cycle of the APU, and adds heat to the air discharged by APU compressor  160  for mechanical power extraction by the APU turbine. As with hybrid APU  22 , fuel cell  162  is in fluid communication with both compressor  160  and turbine  164  (as indicated by lines  160 A and  164 A, respectively), and functions similarly to fuel cell  62  mentioned previously. In other embodiments, fuel cell  162  may not be coupled APU  122  as part of a hybrid APU, but rather, may serve as a standalone fuel cell system for supplying electrical power to aircraft  10  via power conditioner  170  and/or auxiliary electrical machine  124  via power conditioner  170  and a power converter  180 . 
     Combining gearbox  128  is mechanically coupled to APU  122  and auxiliary electrical machine  124 . Combining gearbox  128  is also coupled to engine  20 , e.g., via gearbox  59 , and configured to transmit mechanical power to HP spool  24  and LP spool  26  via shafting systems  78  and  74 , respectively. In one form, combining gearbox  128  is coupled to engine  20  via a clutch  182 ; auxiliary electrical machine  124  is coupled to combining gearbox  128  via a clutch  184 ; gearbox  59  is coupled to LP spool  26  via a clutch  186 ; and gearbox  59  is coupled to HP spool  24  via a clutch  188  ( FIGS. 6 and 7 ). In other embodiments, combining gearbox  128  may be coupled to engine  20  and spools  24  and  26  by other means in addition to or in place of those illustrated and described. 
     Combining gearbox  128  is configured to transmit mechanical power from auxiliary electrical machine  124  to APU  122  for starting APU  122 . Combining gearbox  128  is also configured to transmit mechanical power from APU  122  to auxiliary electrical machine  124  for generating electrical power, e.g., for use by aircraft  10  via power converter  180  during flight and/or ground operations, for supplying electrical power from auxiliary electrical machine  124  to one or both of electrical machines  44  and  46 , and/or for charging battery  130  via power conditioner  170 . It will be understood that in various embodiments, electrical power generated by electrical machine  124  may be conditioned and/or distributed to aircraft  10 , electrical machines  44  and  46  and battery  130 , via various means in addition to or in place of the means illustrated and described herein. 
     Combining gearbox  128  is also configured to transmit mechanical power from APU  122  and/or auxiliary electrical machine  124  to engine  20  via gearbox  59 , e.g., for taxiing aircraft  10  and/or for starting engine  20 . In one form, mechanical power (shaft power) is transmitted from APU  122  and/or auxiliary electrical machine  124  to gearbox  59  by selectively engaging clutches  182  and  184 . Gearbox  59  is configured to transfer power from APU  122  and/or auxiliary electrical machine  124  to LP spool  26  via clutch  186  for generating thrust via propulsor  28  for taxiing aircraft  10 . Hence, in various embodiments, taxi operations may be performed by supplying mechanical power from APU  122  and/or auxiliary electrical machine  124  to LP shaft  26  via combining gearbox  128 , engine gearbox  59 , and clutches  182 ,  184  and  186 . In other embodiments, other clutch and gearbox arrangements may be employed to obtain the same or similar results. 
     Similarly, gearbox  59  is configured to transfer power from APU  122  and/or auxiliary electrical machine  124  to HP spool  24  for starting gas turbine engine  20 . For example, with reference to  FIG. 6 , in one form, mechanical power is transmitted from APU  122  and/or auxiliary electrical machine  124  to gearbox  59  by selectively engaging clutches  182  and  184 . Gearbox  59  is configured to transfer power from APU  122  and/or auxiliary electrical machine  124  to HP spool  24  via clutch  188  for to mechanically supply power to HP spool  24  to rotate HP spool  24  to a speed sufficient for starting engine  20 . In the depiction of  FIG. 6 , clutches  182 ,  184  and  188  are depicted as being engaged. Hence, in various embodiments engine  20  may be started by supplying mechanical power from APU  122  and/or auxiliary electrical machine  124  to HP spool  24  via combining gearbox  128  and engine gearbox  59 . In other embodiments, other clutch and/or gearbox arrangements and/or other mechanical drive combinations may be employed to obtain the same or similar results. In some embodiments, prior to and/or during engine  20  starting, APU  122  exhaust may be supplied via ducting  190  to engine  20 , e.g., HP spool  24  in order to warm up engine  20 , which in some embodiments may also decrease the amount of time required for engine start. 
     In addition, with reference to  FIG. 7 , engine  20  may be started by supplying electrical power to electrical machine  46  to rotate HP spool  24  to a sufficient speed. In some embodiments, electrical power may also be supplied to LP spool  26  during engine  20  start. In the depiction of  FIG. 7 , clutches  184  and  188  are disengaged, whereas clutch  182  is engaged so that auxiliary electrical machine  124  may be driven by APU  122  to generate electrical power. In various embodiments, the electrical power for starting engine  20  may be supplied from electrical power source  126  (either or both of battery  130  and fuel cell  162 ) and/or auxiliary electrical machine  124  (powered by APU  122  via combining gearbox  128  and clutch  182 ). In other embodiments, other arrangements may be employed to obtain the same or similar results. In some embodiments, prior to and/or during engine  20  starting, APU  122  exhaust may be supplied via ducting  190  to engine  20 , e.g., HP spool  24 , in order to warm up engine  20 , which in some embodiments may also decrease the amount of time required for engine start. It will be understood that in various embodiments, electrical power generated by electrical machine  124  and/or electrical power supplied by battery  130  and/or fuel cell  162  may be conditioned and/or distributed to aircraft  10 , electrical machines  44  and  46  via various means in addition to or in place of the means illustrated and described herein. 
     Embodiments of the present invention include a propulsion system for an aircraft, comprising: a gas turbine engine having a high pressure (HP) spool and a low pressure (LP) spool, wherein the LP spool is operative to drive a propulsor; and a hybrid auxiliary power unit (APU) mechanically coupled to both the HP spool and the LP spool, wherein the hybrid APU includes an APU compressor; an APU turbine; and a fuel cell fluidly disposed between the APU compressor and the APU turbine, wherein the fuel cell is operative to receive as an oxidant air pressurized by the APU compressor; to generate electrical power using a fuel and the oxidant; to heat the air pressurized by the APU compressor; and to discharge the heated pressurized air into the APU turbine, wherein the hybrid APU is operative to supply rotational power to both the HP spool and the LP spool. 
     In a refinement, the hybrid APU further includes a start-up combustor fluidly disposed between the APU compressor and the APU turbine; and wherein the start-up combustor is configured to add heat to the air pressurized by the APU compressor for discharge into the APU turbine. 
     In another refinement, the gas turbine engine includes a gearbox; and wherein the hybrid APU is mounted on the gearbox. 
     In yet another refinement, the propulsion system further comprises a transmission mechanically disposed between the hybrid APU and one of the HP spool and the LP spool, wherein the transmission is operative to vary the speed of the one of the HP spool and the LP spool relative to the other of the HP spool and the LP spool. 
     In still another refinement, the transmission is a continuously variable transmission. 
     In yet still another refinement, the transmission is mechanically disposed between the hybrid APU and the HP spool; and wherein the transmission is operative to vary the speed of the HP spool relative to the LP spool. 
     In a further refinement, the propulsion system further comprises a controller configured to execute program instructions to control the transmission to vary a speed ratio between the HP spool and the LP spool to reduce internal drag in the gas turbine engine. 
     In a yet further refinement, the transmission is operative to selectively engage the one of the HP spool and the LP spool with the hybrid APU and to selectively disengage the one of the HP spool and the LP spool from the hybrid APU. 
     In a still further refinement, the propulsion system further comprises a reformer in fluid communication with the fuel cell, wherein the reformer is operative to reform aircraft fuel into syngas for use in the fuel cell. 
     Embodiments of the present invention include an aircraft, comprising: a fuselage; 
     an empennage coupled to the fuselage; a plurality of wings coupled to the fuselage; and a propulsion system, including: a gas turbine engine having at least a high pressure (HP) spool and a low pressure (LP) spool, wherein the LP spool is operative to drive a propulsor; and wherein the gas turbine engine is coupled to at least one of the fuselage, the empennage and at least one of the plurality of wings; a hybrid auxiliary power unit (APU) mechanically coupled to both the HP spool and the LP spool, wherein the hybrid APU includes an output reduction gearbox, an APU compressor; an APU turbine; and a fuel cell fluidly disposed between the APU compressor and the APU turbine, wherein the fuel cell is operative to receive as an oxidant air pressurized by the APU compressor; to generate electrical power using a fuel and the oxidant; to heat the air pressurized by the APU compressor; and to discharge the heated pressurized air into the APU turbine; and wherein the hybrid APU is operative to supply rotational power to both the high pressure spool and the low pressure spool; and a shafting system mechanically coupling both the HP spool and the LP spool to the output reduction gearbox, wherein the hybrid APU is operative to supply rotational power to both the HP spool and the LP spool via the shafting system and the output reduction gearbox. 
     In a refinement, the hybrid APU is operative to provide power to the LP spool for generating thrust via the propulsor for taxiing the aircraft without having started the gas turbine engine. 
     In another refinement, the aircraft further comprises a clutch operative to selectively engage and to disengage the hybrid APU from the LP spool. 
     In yet another refinement, the fuel cell is configured to generate electrical power for use by the aircraft during ground operations and/or flight operations. 
     In still another refinement, the hybrid APU is configured to start the gas turbine engine by supplying mechanical power to rotate the HP spool. 
     In yet still another refinement, the hybrid APU is configured to start the gas turbine engine by supplying electrical power to rotate the HP spool. 
     In a further refinement, the aircraft further comprises an APU electrical machine mechanically coupled to and powered by the hybrid APU. 
     In a yet further refinement, the APU electrical machine is configured to generate electrical power for use by the aircraft during ground operations and/or flight operations. 
     In a still further refinement, the hybrid APU generates an exhaust; and wherein the exhaust is supplied to the gas turbine engine to warm up the gas turbine engine prior to starting the gas turbine engine. 
     In a yet still further refinement, the propulsor is a turbofan of the gas turbine engine. 
     Embodiments of the present invention include a system, comprising: a gas turbine engine having at least a high pressure (HP) spool and a low pressure (LP) spool, wherein the LP spool is operative to drive a propulsor; and means for supplying mechanical power from a hybrid APU to both the high pressure spool and the low pressure spool, wherein the means for supplying mechanical power is operative to supply rotational power to both the HP spool and the LP spool, wherein the hybrid APU includes an APU compressor; an APU turbine; and a fuel cell fluidly disposed between the APU compressor and the APU turbine, wherein the fuel cell is operative to receive as an oxidant air pressurized by the APU compressor; to generate electrical power using a fuel and the oxidant; to heat the air pressurized by the APU compressor; and to discharge the heated pressurized air into the APU turbine. 
     In a refinement, the system further comprises means for varying a rotational speed of one of the high pressure spool and the low pressure spool relative to the rotational speed of the other of the high pressure spool and the low pressure spool. 
     Embodiments of the present invention include a propulsion system for an aircraft, comprising: a gas turbine engine having at least a high pressure (HP) spool and a low pressure (LP) spool, wherein the LP spool is operative to drive a propulsor; an auxiliary power unit (APU) mechanically coupled to the LP spool and operative to drive the LP spool; an auxiliary electrical machine mechanically coupled to LP spool and operative to drive the LP spool; and an electrical power source electrically coupled to the auxiliary electrical machine, wherein the APU and the auxiliary electrical machine are configured and operative to jointly supply rotational power to the LP spool to generate thrust via the propulsor for taxiing the aircraft. 
     In a refinement, the electrical power source is a battery. 
     In another refinement, the electrical power source is a fuel cell. 
     In yet another refinement, the electrical power source is a combination of a fuel cell and a battery. 
     In still another refinement, the APU is a hybrid APU having an APU compressor; an APU turbine; and a fuel cell fluidly disposed between the APU compressor and the APU turbine, wherein the fuel cell is operative to receive as an oxidant air pressurized by the APU compressor; to generate electrical power using a fuel and the oxidant; to heat the air pressurized by the APU compressor; and to discharge the heated pressurized air into the APU turbine. 
     In yet still another refinement, the propulsion system further comprises an auxiliary combining gearbox mechanically coupled to the APU, the auxiliary electrical machine and the gas turbine engine. 
     In a further refinement, the auxiliary combining gearbox is configured to transmit mechanical power from the auxiliary electrical machine to the APU for starting the APU. 
     In a yet further refinement, the auxiliary combining gearbox is configured to transmit mechanical power from the APU to the auxiliary electrical machine for generating electrical power. 
     In a still further refinement, the auxiliary combining gearbox is configured to transmit mechanical power from the APU to the gas turbine engine. 
     In a yet still further refinement, the auxiliary combining gearbox is configured to transmit mechanical power from the auxiliary electrical machine to the gas turbine engine. 
     In additional refinement, the auxiliary combining gearbox is configured to transmit mechanical power from both the auxiliary electrical machine and the APU to the gas turbine engine. 
     In another additional refinement, the gas turbine engine includes a gearbox; wherein the APU is mounted on the gearbox; and wherein the gearbox is configured to transfer power from the APU to the HP spool for starting the gas turbine engine. 
     In yet another additional refinement, the gearbox is configured to transfer power from the APU and the auxiliary electrical machine to the HP spool for starting the gas turbine engine. 
     In still another additional refinement, the gas turbine engine includes a gearbox; wherein the APU is mounted on the gearbox; and wherein the gearbox is configured to transfer power from the APU and the auxiliary electrical machine to the LP spool to generate thrust via the propulsor for taxiing the aircraft. 
     Embodiments of the present invention include an aircraft, comprising: a fuselage; an empennage coupled to the fuselage; a plurality of wings coupled to the fuselage; and at least one propulsion system, including: a gas turbine engine having at least a high pressure (HP) spool and a low pressure (LP) spool and an engine gearbox, wherein the LP spool is operative to drive a propulsor; and wherein the gas turbine engine is coupled to at least one of the fuselage, the empennage and at least one of the plurality of wings; an auxiliary power unit (APU) mechanically coupled to the LP spool via the gearbox and operative to drive the LP spool; an auxiliary electrical machine mechanically coupled to LP spool via the gearbox and operative to drive the LP spool; an electrical power source electrically coupled to the auxiliary electrical machine, wherein the APU and the auxiliary electrical machine are configured and operative to jointly supply rotational power via the engine gearbox to the LP spool to generate thrust via the propulsor for taxiing the aircraft. 
     In a refinement, the engine gearbox is also configured to mechanically couple the APU to the HP spool for starting the gas turbine engine. 
     In another refinement, the engine gearbox is configured to mechanically couple the auxiliary electrical machine to the HP spool to starting the gas turbine engine. 
     In yet another refinement, the aircraft further comprises an engine electrical machine mounted on the HP spool and electrically coupled to at least one of the electrical power source and the auxiliary electrical machine, wherein the engine electrical machine, and the at least one of the electrical power source and the auxiliary electrical machine are configured to start the gas turbine engine by supplying electrical power to the engine electrical machine, whereby the engine electrical machine imparts rotation to the HP spool sufficient to start the gas turbine engine. 
     In still another refinement, the electrical power source is at least one of a fuel cell and a battery. 
     In a yet still another refinement, the electrical power source is a combination of a fuel cell and a battery. 
     In a further refinement, the APU is a hybrid APU having an APU compressor; an APU turbine; and a fuel cell fluidly disposed between the APU compressor and the APU turbine, wherein the fuel cell is operative to receive as an oxidant air pressurized by the APU compressor; to generate electrical power using a fuel and the oxidant; to heat the air pressurized by the APU compressor; and to discharge the heated pressurized air into the APU turbine. 
     Embodiments of the present invention include a system, comprising: a gas turbine engine having a high pressure (HP) spool and a low pressure (LP) spool, wherein the LP spool is operative to drive a propulsor; and means for supplying mechanical power from at least two sources to the low pressure spool for taxiing an aircraft. 
     In a refinement, the two sources include an auxiliary power unit (APU) and an auxiliary electrical machine, wherein the auxiliary electrical machine is powered by at least one of a fuel cell and a battery. 
     In another refinement, the APU is a hybrid APU employing the fuel cell in the hybrid APU thermodynamic cycle. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.