Patent Publication Number: US-2023137264-A1

Title: Architectures for hybrid-electric propulsion

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/706,199 filed Dec. 6, 2019, which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/820,064, filed Mar. 18, 2019. The disclosures of these two prior applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to aircraft engines, and more particularly to hybrid aircraft engines. 
     2. Description of Related Art 
     Aircraft engines vary in efficiency and function over a plurality of parameters, such as thrust requirements, air temperature, air speed, altitude, and the like. Aircraft require the most thrust at take-off, wherein the demand for engine power is the heaviest. However, during the remainder of the mission, the aircraft engines often do not require as much thrust as during take-off. The size and weight of the engines allows them to produce the power needed for take-off, however after take-off the engines are in effect over-sized for the relatively low power required to produce thrust for cruising in level flight. 
     The conventional techniques have been considered satisfactory for their intended purpose. However, there is an ever present need for improved aircraft engines. This disclosure provides a solution for this need. 
     SUMMARY OF THE INVENTION 
     A hybrid propulsion system includes a heat engine configured to drive a heat engine shaft. An electric motor is configured to drive an electric motor shaft. A transmission system includes at least one gearbox. The transmission system is configured to receive rotational input power from each of the heat engine shaft and the electric motor shaft and to convert the rotation input power to output power. 
     The at least one gearbox can include a combining gearbox connecting to the heat engine shaft and to the electric motor shaft to combine rotational input power from the heat engine and electric motor for providing rotational output power to an output shaft. A turbine gearbox can be included, wherein the turbine gearbox is connected between the heat engine shaft and a shaft for driving a turbine and a compressor to drive the turbine and compressor at a different rotational speed from the heat engine. 
     The at least one gearbox can include a combining gearbox connecting to the heat engine shaft, the electric motor shaft, and a shaft for driving a turbine and compressor, to combine rotational input power from the heat engine and electric motor for providing rotational output power to an output shaft and to drive the turbine and compressor. The turbine and compressor can both be on one side of the combining gearbox. It is also contemplated that the turbine and compressor can be connected on opposite sides of the combining gearbox. 
     The heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a reduction gearbox connected to a common output shaft of the electric motor and the heat engine, and a turbine gearbox can be connected between the heat engine shaft and a shaft for driving a turbine and a compressor to drive the turbine and compressor at a different rotational speed from the heat engine and electric motor. 
     The heat engine shaft and electric motor shaft can be concentric with a shaft for rotation of the turbine and compressor, wherein the at least one gearbox includes a reduction gearbox connected to each of the heat engine shaft and the electric motor shaft and to the shaft for rotation of the turbine and compressor. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a combining gearbox connecting to a common output shaft of the electric motor and the heat engine and a shaft for driving a turbine and compressor, to combine rotational input power from the heat engine and electric motor for providing rotational output power to an output shaft and to drive the turbine and compressor. The turbine and compressor can both be on one side of the combining gearbox. It is also contemplated that the turbine and compressor can be connected on opposite sides of the combining gearbox. 
     The at least one gearbox can include a combining gearbox connecting to the heat engine shaft and to the electric motor shaft to combine rotational input power from the heat engine and electric motor for providing rotational output power to an output shaft. A turbine driver motor can be connected to a shaft for driving a turbine and a compressor to drive the turbine and compressor at a different rotational speed ratio from the heat engine and electric motor. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a reduction gearbox connected to a common output shaft of the electric motor and the heat engine. A turbine driver motor can be connected to a shaft for driving a turbine and a compressor to drive the turbine and compressor at a different rotational speed ratio from the heat engine and electric motor. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a reduction gearbox connected to a common output shaft of the electric motor and the heat engine. A turbine gearbox can be connected through a clutch between the heat engine shaft and a shaft for driving a turbine and a compressor to drive the turbine and compressor at a different rotational speed from the heat engine and electric motor when the clutch is engaged. The shaft for driving the turbine and compressor can be connected to a turbine driver motor to drive the turbine and compressor independently from the heat engine and electric motor when the clutch is disengaged. 
     In another aspect, the heat engine shaft and electric motor shaft can be concentric with a shaft for rotation of a turbine and compressor. The at least one gearbox can include a reduction gearbox connected to each of the heat engine shaft and the electric motor shaft. A clutch in the shaft for rotation of the turbine and compressor can connect between the reduction gearbox a turbine driver motor connected to the shaft for rotation of the turbine and a compressor to drive the turbine and compressor with the reduction gearbox when the clutch is engaged, and to drive the turbine and compressor independently from the heat engine and electric motor when the clutch is disengaged. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a reduction gearbox connected to a common output shaft of the electric motor and the heat engine. A clutch can connect between the reduction gearbox and a turbine driver motor connected to a shaft for driving a turbine and a compressor to drive the turbine and compressor with rotational power from the heat engine and electric motor when the clutch is engaged, and to drive the turbine and compressor independently from the heat engine and electric motor when the clutch is disengaged. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a combining gearbox connecting to a common output shaft of the electric motor and the heat engine, and a shaft of a turbine to combine rotational input power from the heat engine, electric motor, and turbine for providing rotational output power to an output shaft. A reduction gearbox can be connected to the output shaft, wherein a compressor is connected to be driven on the output shaft. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a reduction gearbox connected to a common output shaft of the electric motor and the heat engine. A turbine gearbox can be connected between the heat engine shaft and a shaft of a turbine so the turbine can rotate at a different rotational speed from the heat engine and electric motor. A compressor can be connected to the reduction gearbox through a compressor shaft concentric with the common output shaft so the compressor can be driven at a different rotational speed from the common output shaft. 
     In another aspect, the heat engine shaft and the electric motor shaft can be connected for common rotation. The at least one gearbox can include a super position gearbox connecting to a common output shaft of the electric motor and the heat engine, and a shaft for driving a turbine and compressor to combine rotational input power from the heat engine and electric motor for providing rotational output power to an output shaft and to drive the turbine and compressor. The super position gearbox can be configured so speed ratio between the common output shaft and the shaft for driving the turbine and compressor can vary. 
     A turbine can be connected to the heat engine to be driven by exhaust form the heat engine, and a generator can be connected to be driven by the turbine. 
     These and other features of the systems and methods of the subject disclosure will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that those skilled in the art to which the subject disclosure appertains will readily understand how to make and use the devices and methods of the subject disclosure without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein: 
         FIG.  1    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a first gearbox arrangement; 
         FIG.  2    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a second gearbox arrangement; 
         FIG.  3    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a third gearbox arrangement; 
         FIG.  4    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a fourth gearbox arrangement; 
         FIG.  5    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a fifth gearbox arrangement; 
         FIG.  6    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a sixth gearbox arrangement; 
         FIG.  7    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a seventh gearbox arrangement; 
         FIG.  8    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing an eighth gearbox arrangement; 
         FIG.  9    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a ninth gearbox arrangement; 
         FIG.  10    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a tenth gearbox arrangement; 
         FIG.  11    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing an eleventh gearbox arrangement; 
         FIG.  12    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a twelfth gearbox arrangement; 
         FIG.  13    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a thirteenth gearbox arrangement; 
         FIG.  14    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a fourteenth gearbox arrangement; and 
         FIG.  15    is a schematic view of an exemplary embodiment of a hybrid propulsion system constructed in accordance with the present disclosure, showing a fifteenth gearbox arrangement. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of a hybrid propulsion system in accordance with the disclosure is shown in  FIG.  1    and is designated generally by reference character  100 . Other embodiments of hybrid propulsion systems in accordance with the disclosure, or aspects thereof, are provided in  FIGS.  2 - 15   , as will be described. The systems and methods described herein can be used to provide hybrid propulsion, e.g., for improving fuel efficiency in aircraft. 
     The hybrid propulsion system  100  includes a heat engine (or motor)  102  configured to drive a heat engine shaft  104 . An electric motor  106  is configured to drive an electric motor shaft  108 . A transmission system  110  includes at least one gearbox. The transmission system  110  is configured to receive rotational input power from each of the heat engine shaft  104  and the motor shaft  108  and to convert the rotation input power to output power, as indicated by the circular arrow in  FIG.  1   . 
     The at least one gearbox includes a combining gearbox  112  connecting to the heat engine shaft  104  and to the motor shaft  108  to combine rotational input power from the heat engine  102  and electric motor  106  for providing rotational output power to an output shaft  114 , which can drive a reduction gearbox  116  for turning an aircraft propeller, fan, or any other suitable type of air mover for example. A turbine gearbox  118  is included, which is connected between the heat engine shaft  104  and a shaft  120  for driving a turbine  122  and a compressor  124  to drive the turbine  122  and compressor  124  at a different rotational speed from the heat engine  102 . For example, through the turbine gearbox  118 , the heat engine  102  can run at 8000 revolutions per minute (RPM), the heat engines exhaust can be recovered by the turbine  122  to drive the compressor  120  at 35,000 RPM. The turbine gearbox  118  can be a two speed transmission or constant velocity transmission (CVT) which can eliminate the need for a variable inlet guide vane (VIGV) controlling the compressor  124 . It is also contemplated that the turbine  122  and compressor  124  can separately connect to the turbine gear box  118 , e.g., using a concentric shaft for the compressor such as the shaft  1246  shown in  FIG.  14   , so that the turbine  122  and compressor  124  can rotate at different rotational speeds. These types of turbine gearbox can apply to each of the turbine gearboxes described below, even if not specifically repeated. 
     Those skilled in the art will readily appreciate that while described herein in the context of driving the turbine  122  and compressor  124 , that the turbine  122  can actually add power to the shaft  120  and therefore cooperates with the heat engine  102  to drive the combining gearbox  112 , however, in configurations herein where the turbine  122  and compressor  124  spin at a common speed the compressor  124  and turbine  122  are collectively referred to herein as driven. 
     The compressor  120  compresses air and supplies the compressed air to the heat engine  102  through the air line  126 , which includes heat exchanger  128  for cooling the compressed air. After combustion in the heat engine  102 , the combustion products are supplied through a combustion products line  130  to the turbine  122 , which extracts power from the compressed combustion products before exhausting them. The configurations shown in  FIGS.  2 - 15    also include similar air lines  126 , heat exchangers  128 , and combustion products lines  130 , and the details for such are not repeated below for each Figure. Also, unless specified otherwise, the configurations in each of  FIGS.  2 - 15    include an output shaft  114  connecting between a combining gearbox (e.g. combining gearbox  112 ) and reduction gearbox  116 , the details of which will not be repeated below for each Figure. The electric motor  106  can be powered to boost horse power, e.g., for take-off, in parallel with the heat motor  102 , and can be powered down, e.g., for cruising in level flight, where only the heat motor  102  is needed for power. It is also contemplated that the electric motor  106  can be used as a generator to recharge the battery, e.g. source  1138  of  FIG.  13   , when power is available from the heat engine  102  or form wind milling the propeller to drive the reduction gear box  116 . The compressor  124  and turbine  122  improve the thermal efficiency of the heat engine  102 . Similar benefits are derived with the configurations described below with respect to  FIGS.  2 - 15   . The dashed line in  FIG.  1    schematically indicates that the turbine  122  can optionally be moved to connect directly to the combining gearbox  112 , much as described below with respect to  FIG.  13   , which switch in turbine position can also be applied to other arrangements described below wherein the compressor and turbine are shown and described as being on a common shaft. 
     With reference now to  FIG.  2   , a system  200  includes a combining gearbox  212  connecting to the heat engine shaft  204 , the motor shaft  208 , and a shaft  220  for driving the turbine  222  and compressor  224 . The combining gearbox  212  combines rotational input power from the heat engine (or motor)  202  and electric motor  206  for providing rotational output power to an output shaft  114  and to drive the turbine  222  and compressor  224 . While connected on a common shaft  220 , the turbine  222  and compressor  224  can be connected on opposite sides of the combining gearbox  212  as shown in  FIG.  2   . It is also contemplated that the turbine  222  and compressor  224  can both be connected on one side of the combining gearbox  212 , as shown in  FIG.  3   . The portion of the combining gearbox  212  that drives the shaft  220  can be a two speed transmission or constant velocity transmission (CVT) which can eliminate the need for a variable inlet guide vane (VIGV) controlling the compressor  224 . This applies to arrangements described below wherein the turbine and compressor connect directly to a combined gearbox, even if not specifically repeated. 
     With reference now to  FIG.  4   , a system  300  is shown wherein the heat engine shaft  304  and the electric motor shaft  308  are connected for common rotation. A reduction gearbox  316 , e.g. for ultimately outputting power to a propeller, is connected to a common output shaft  305  of the electric motor  306  and the heat engine  302 . A turbine gearbox  332  is connected between the heat engine shaft  304  and a shaft  320  for rotation of the turbine  322  and compressor  324  at a different rotational speed from the heat engine  302  and electric motor  306 . The broken line in  FIG.  4    indicates that the position of the heat engine  302  and electric motor  306  can be reversed on the common shaft  305 . If there is a requirement to guarantee power from one of the heat engine  302  or electric motor  306  in the event of stoppage of the other, each of the heat engine  302  and electric motor can be connected to the reduction gearbox  316  through a concentric shaft, e.g. as indicated by the broken lines between the electric motor  306  and the reduction gear box  316 . The same applies to other configurations herein where the heat engine and electric motor are shown and described as having a common output shaft. 
     With reference now to  FIG.  5   , in the system  400 , the heat engine shaft  404  and electric motor shaft  408  are concentric with a shaft  420  for rotation of the turbine  422  and compressor  424 . The heat engine shaft  404  and electric motor shaft  408  can be a common shaft  405  as shown in  FIG.  5   , or can themselves be concentric with one another as indicated by the broken lines in  FIG.  5   . A reduction gearbox  416  is connected to each of the heat engine shaft  404  and the electric motor shaft  408 , e.g., for driving a propeller with rotational input from the heat engine  402  and electric motor  406 . The reduction gearbox  416  connects to a shaft  420  for rotation of the turbine  422  and compressor  424 . 
     With reference now to  FIG.  6   , a system  500  has a heat engine shaft  504  and the electric motor shaft  508  connected for common rotation. A combining gearbox  512  connects to the common output shaft  505  of the electric motor  506  and the heat engine  502  and a shaft  520  for driving a turbine  522  and compressor  524 , to combine rotational input power from the heat engine  502  and electric motor  506  for providing rotational output power to an output shaft  114  and to drive the turbine  522  and compressor  524 . The turbine  522  and compressor  524  are connected on opposite sides of the combining gearbox  512 . As shown in  FIG.  7   , it is also contemplated that the turbine  522  and compressor  524  can both be on one side of the combining gearbox  512 . The broken lines in  FIGS.  6  and  7    schematically indicate that the positions of the heat motor  502  and electric motor  506  can be switched. 
     Referring now to  FIG.  8   , a system  600  includes a combining gearbox  612  connecting to the heat engine shaft  604  and to the electric motor shaft  608  to combine rotational input power from the heat engine  602  and electric motor  606  for providing rotational output power to an output shaft  114 . A turbine driver motor/generator  634  is connected to a shaft  620  for driving a turbine  622  and a compressor  624  to drive the turbine  622  and compressor  624  at a different rotational speed ratio from the heat engine  602  and electric motor  606 . The compressor  624  can therefore be a variable speed compressor. An electrical system  636  includes a storage  638 , e.g., a battery, battery bank, capacitor, capacitor bank, super capacitor or super capacitor bank, flywheel or flywheel bank, or the like, is connected to a first inverter/rectifier component  640  for supplying power from the storage  638  to drive the electric motor  606  or in an energy recovery mode, to store into the storage  638  energy generated by driving the electric motor  606  in a generator mode. The electrical system  636  includes a second invert/rectifier component  642  for supplying power to drive the turbine driver motor  634 , or to recover energy into the storage  638  from the turbine drive motor  634  if run in a generator mode. The broken line in  FIG.  8    schematically indicates that the position of the motor  634  and compressor can be switched on the shaft  620 .  FIGS.  9 ,  10 ,  11 , and  12    each show similar electrical systems  636  and the description thereof is not repeated below. 
     With reference now to  FIG.  9   , a system  700  has the heat engine shaft  704  and the electric motor shaft  108  are connected for common rotation. A reduction gearbox  716  connected to a common output shaft  714  of the electric motor  706  and the heat engine  702 . A turbine driver motor  734  is connected to a shaft  720  for driving a turbine  722  and a compressor  724  at a different rotational speed from the heat engine  702  and electric motor  706 . The broken arrows in  FIG.  9    schematically indicate that the position of the heat engine  702  and the electric motor  706  can be switched on the common shaft  714 , and that the positions of the motor  734  and compressor  724  can be switched on the shaft  720 . 
     Referring now to  FIG.  10   , in the system  800  the heat engine shaft  804  and the electric motor shaft  808  are connected for common rotation. A reduction gearbox  816  is connected to a common output shaft  814  of the electric motor  806  and the heat engine  802 . A turbine gearbox  818  is connected through a clutch  844  between the heat engine shaft  804  and a shaft  820  for driving a turbine  822  and a compressor  824  at a different rotational speed ratio from the heat engine  802  and electric motor  802  when the clutch  844  is engaged. The shaft  820  for driving the turbine  822  and compressor  824  is connected to a turbine driver motor  834  to drive the turbine  822  and compressor  824  independently from the heat engine  802  and electric motor  806  when the clutch  844  is disengaged. The broken lines in  FIG.  10    schematically indicate that the positions of the clutch  844  and the turbine gearbox  818  can be switched. The clutch  844  can prevent electrical losses at steady state because the clutch engages when system  800  steady state operation, e.g., cruising in level flight, so the shaft  820  is connected to the heat engine  802  to avoid electrical conversion losses. In transients, the clutch  844  can open or disconnect to allow the motor  834  to drive the shaft  820  at a different speed ratio from the heat engine  802  as described above. 
     With respect to  FIG.  11   , a system  900  includes a heat engine shaft  904  and electric motor shaft  908  that are concentric with the shaft  20  for rotation of the turbine  922  and compressor  924  similar to the arrangement in  FIG.  5   . A reduction gearbox  916  is connected to each of the heat engine shaft  904  and the electric motor shaft  908 , e.g., as a common shaft  905  or concentric with one another as described above with respect to  FIG.  5   . A clutch  944  in the shaft  920  connects between the heat engine  902  and a turbine driver motor  934  for rotating the turbine  922  and compressor  924  with the reduction gear box  916  when the clutch  944  is engaged, and to drive the turbine  922  and compressor  924  independently from the heat engine  902  and electric motor  906  when the clutch  944  is disengaged. 
     With reference now to  FIG.  12   , a system  1000  includes a heat engine shaft  1004  and electric motor shaft  1008  are connected for common rotation. A reduction gearbox  1016  is connected to a common output shaft  1014  of the electric motor  1006  and the heat engine  1002 . The upper broken lines in  FIG.  12    schematically indicate that the positions of the heat engine  1002  and the motor  1006  can be switched on the shaft  1014 . A clutch  1044  connects between the reduction gearbox  1016  and a turbine driver motor  1034  connected to a shaft  1020  for driving a turbine  1022  and a compressor  1024  with rotational power from the heat engine  1002  and electric motor  1002  (through the reduction gearbox  1016 ) when the clutch  1044  is engaged, and to drive the turbine  1022  and compressor  1024  independently from the heat engine  1002  and electric motor  1006  when the clutch  1044  is disengaged. The lower broken line in  FIG.  12    schematically indicates that the positions of the motor  1034  and the compressor  1024  can be switched on the shaft  1020 . 
     Referring now to  FIG.  13   , a system  1100  is shown wherein the heat engine shaft  1104  and the electric motor shaft  1108  are connected for common rotation. A combining gearbox  1112  connects to a common output shaft  1105  of the electric motor  1106  and the heat engine  1102 , and to a shaft  1114  of a turbine  1122  to combine rotational input power from the heat engine  1102 , electric motor  1106 , and turbine  1122  for providing rotational output power to an output shaft  1114 . A reduction gearbox  1116  is connected to the output shaft  1114 , wherein a compressor  1124  is connected to be driven on the output shaft  1114 . An electrical system  1136  includes a storage  1138  connected through an inverter/rectifier component  1140  to supply power to the motor  1106 , or to recover power from the motor  1106  in a generator mode to store in the storage  1138 . The other arrangements described above that do not specifically show an electrical system can include a system similar to electrical system  1136 , and  FIG.  14    includes a similar system  1136  even though the details are not repeated. The compressor  1124  can also be connected to the reduction gearbox  1116  on its own shaft concentric with the shaft  1114 , much as described below with respect to  FIG.  14   . The broken lines in  FIG.  13    indicate that optionally the turbine  1122  can be mechanically decoupled from the CGB to drive a generator  1134 , which can be connected through an inverter/rectifier component  1142  to charge the storage  1138 , which can similarly be applied to other arrangements disclosed herein with the turbine decoupled from the compressor. As indicated by broken lines in  FIG.  13   , the compressor and a gear box  1118  can be connected to the heat engine  1102  in lieu of connecting the compressor  1124  on the output shaft  1114 . 
     With reference now to  FIG.  14   , a system  1200  is shown wherein the heat engine shaft  1204  and the electric motor shaft  1208  are connected for common rotation. A reduction gearbox  1216  connected to a common output shaft  1214  of the electric motor  1206  and the heat engine  1202 . A turbine gearbox  1218  is connected between the heat engine shaft  1204  and a shaft  1220  of a turbine  1222  so the turbine can rotate at a different rotational speed from the heat engine  1202  and electric motor  1206 . A compressor  1224  is connected to the reduction gearbox  1216  through a compressor shaft  1246  concentric with the common output shaft  1214  so the compressor can be driven at a different speed from the common output shaft  1214 . 
     Referring now to  FIG.  15   , a system  1300  includes a heat engine shaft  1304  and the electric motor shaft  1308  that are connected for common rotation. A super position gearbox  1316  connects to a common output shaft  1314  of the electric motor  1306  and the heat engine  1302 , and to a shaft  1320  for driving a turbine  1322  and compressor  1324  to combine rotational input power from the heat engine  1302  and electric motor  1306  for providing rotational output power to an output shaft  1314  and to drive the turbine  1322  and compressor  1324 . The super position gearbox  1316  is configured so the speed ratio between the common output shaft  1314  and the shaft  1320  for driving the turbine  1322  and compressor  1324  can vary, e.g., to adjust the speed of the compressor  1324  for altitude or for ground idle. 
     The turbine  1322  can optionally be decoupled from the compressor  1324  to drive a generator as described above with reference to  FIG.  13   . Similarly, the arrangement in  FIG.  3    can be modified so the turbine  222  is decoupled from the compressor  224  to drive a generator. The heat engine, e.g., heat engine  202  in  FIG.  2   , can be split and connected on opposite sides of the respective gear box, e.g., the combined gearbox  212  in  FIG.  2   , as indicated in  FIG.  2    with the broken line box  202 . This split can be applied to other arrangements above besides the one in  FIG.  2   . Disconnect clutches or mechanism, e.g., clutch  844  in  FIG.  10   , can be included, e.g., in each of the shafts  104  and  108  as indicated in  FIG.  1    by the broken lines crossing the shafts  104  and  108 , for disconnecting the heat engine  102  or electric motor  106  as needed. This can also be applied to other embodiments disclosed above besides the arrangement in  FIG.  1   . 
     Even if modules are represented schematically herein vertically on top of each other, those skilled in the art having the benefit of this discourse will readily appreciate that they can be located side by side, one above the other or in any geometrical arrangement and in any order in physical implementations. Similarly, those skilled in the art having had the benefit of this disclosure will readily appreciate that modules represented on one side (right or left) of the respective gearbox herein can also potentially be installed on the other side or even trapped between a respecting reduction gearbox and combining gear box. Module disclosed herein can be installed directly on the respective combining gear box or reduction gear box with a proper speed ratio. Although modules are represented herein with an axial orientation, those skilled in the art having the benefit of this disclosure will readily appreciate that the use of bevel gears (or other mechanical or electrical devices) allows the installation of modules in any suitable orientation. Those skilled in the art having the benefit of this disclosure will readily appreciate that accessories not explicitly represented herein can be included and can potentially be connected mechanically to any module or driven electrically similar to the modules and components disclosed herein. Those skilled in the art having had the benefit of this disclosure will readily appreciate that combining gearboxes and reduction gearboxes disclosed above can be combined into a single respective gearbox. Finally, those skilled in the art having had the benefit of this disclosure considering the number of parts, will readily appreciate that each architecture disclosed herein can be recombined with other architectures disclosed herein to results in dozens of additional configurations, several examples of which are described above, and all of which are within the scope of this disclosure. 
     The methods and systems of the present disclosure, as described above and shown in the drawings, provide for propulsion systems with superior properties including use of hybrid heat engine and electric motor power. While the apparatus and methods of the subject disclosure have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.