Abstract:
A hybrid bearing system for gas turbine engines is disclosed. The hybrid bearing system comprises ball/roller bearings and air bearings. For horizontal applications, compressed air injected into the air bearing provides a lift force such that enables the rotating shaft for the turbine to float freely. The compressed air is also employed to cool the ball/roller bearings. Hence, given the reduced friction on the ball/roller bearings due to the free-floating shaft, as well as the air cooling of the ball/roller bearings, typical lubrication systems are not necessary. For vertical applications, the compressed air provides cooling to the ball/roller bearings which renders the need for conventional lubrication systems unnecessary.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates in general to gas turbine engines. More particularly, the invention is directed to gas turbines employing air bearings. 
         [0003]    2. Description of the Related Art 
         [0004]    Gas turbine engines typically employ ball/roller bearings to provide support for and to limit both the radial and axial excursions of the rotating shaft. Conventional engines may require complex lubrication systems to lubricate and cool the bearings during operation. Such lubrication systems may increase the size and cost of gas turbine engines. 
         [0005]    Accordingly, a need exists to improve bearings for gas turbine engines. 
       SUMMARY OF THE INVENTION 
       [0006]    In the first aspect, a bearing system is disclosed. The bearing system comprises a shaft centered around a generally horizontal centerline, a compressor coupled to the shaft, the compressor supplying compressed air, and an annular sleeve radially surrounding the shaft, the sleeve having a first and a second set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the sleeve and the shaft, the first set of channels formed in the generally upper portion of the sleeve, the second set of channels formed in the generally lower portion of the sleeve, the first and second set of channels receiving compressed air from the compressor. The first and second set of channels are configured to generate a lifting force on the shaft in a generally upward direction. 
         [0007]    In a first preferred embodiment, each of the first set of channels has a first cross sectional area, and each of the second set of channels has a second cross sectional area, where the first cross sectional area is less than the second cross sectional area. Each of the first and second set of channels preferably further comprise a down-stream metering slot, wherein the metering slot is configured to regulate the rate of airflow in the first and second set of channels. The ball bearings are preferably configured for providing support for the shaft. The ball bearings are preferably configured to receive the compressed air for cooling the ball bearings. The system preferably does not employ a lubrication system for the ball bearings. The bearing system preferably further comprises a thrust management cavity receiving the compressed air from the compressor and providing the compressed air to the first and second set of channels in the sleeve, wherein the thrust management cavities are configured to reduce thrust load based on cavity air pressure and shaft-end surface area. 
         [0008]    The bearing system preferably further comprises a second compressor coupled to the opposite end of the rotating shaft, the second compressor supplying a second source of compressed air, and a second annular sleeve radially surrounding the shaft, the second sleeve having a third and a fourth set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the second sleeve and the shaft, the third set of channels formed in the generally upper portion of the second sleeve, the fourth set of channels formed in the generally lower portion of the sleeve, the third and fourth set of channels receiving the second source of compressed air from the second compressor. The airflow through the first and second channels is preferably in a direction opposite to that of the third and fourth channels. 
         [0009]    The bearing system preferably further comprises a second compressor coupled to the opposite end of the rotating shaft, the second compressor supplying a second source of compressed air, and a second annular sleeve radially surrounding the shaft, the second sleeve having a third and a fourth set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the second sleeve and the shaft, the third set of channels formed in the generally upper portion of the second sleeve, the fourth set of channels formed in the generally lower portion of the sleeve, the third and fourth set of channels receiving the second source of compressed air from the second compressor. The airflow through the first and second channels is preferably in the same direction as that of the third and fourth channels. 
         [0010]    In a second aspect, a bearing system is disclosed. The bearing system comprises a shaft centered around a generally vertical centerline, a compressor coupled to the shaft, the compressor supplying compressed air, and an annular sleeve radially surrounding the shaft, the sleeve having channels formed on the inner surface of the sleeve, each channel forming an air passageway between the sleeve and the shaft, the channels receiving compressed air from the compressor. 
         [0011]    In the second preferred embodiment, each of the channels further comprise a down-stream metering slot, wherein the metering slot is configured to regulate the rate of airflow in the channels. The bearing system preferably further comprises one or more ball bearings coupled to the shaft, wherein the ball bearings are configured for providing support for the shaft. The ball bearings are preferably configured to receive the compressed air for cooling the ball bearings. The system preferably does not employ a lubrication system for the ball bearings. The bearing system preferably further comprises a thrust management cavity receiving the compressed air from the compressor and providing the compressed air to the channels in the sleeve, wherein the thrust management cavities are configured to reduce thrust load based on cavity air pressure and shaft-end surface area. The bearing system preferably further comprises a second compressor coupled to the opposite end of the rotating shaft, the second compressor supplying a second source of compressed air, and a second annular sleeve radially surrounding the shaft, the second sleeve having a second set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the second sleeve and the shaft, the second set of channels receiving the second source of compressed air from the second compressor. The airflow through the first set of channels is preferably in the same direction as that of the second channels. 
         [0012]    In a third aspect, a bearing system is disclosed. The bearing system comprises a shaft centered around a generally horizontal centerline, a first hybrid bearing system comprising a compressor coupled to the shaft, the compressor supplying compressed air, an annular sleeve radially surrounding the shaft, the sleeve having a first and a second set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the sleeve and the shaft, the first set of channels formed in the generally upper portion of the sleeve, the second set of channels formed in the generally lower portion of the sleeve, the first and second set of channels receiving compressed air from the compressor, and a first set of one or more ball bearings coupled to the shaft, wherein the ball bearings are configured to provide support for the shaft. The first and second set of channels are configured to generate a lifting force on the shaft in a generally upward direction. The bearing system further comprises a second hybrid system comprising a second compressor coupled to the opposite end of the rotating shaft, the second compressor supplying a second source of compressed air, a second annular sleeve radially surrounding the shaft, the second sleeve having a third and a fourth set of channels formed on the inner surface of the sleeve, each channel forming an air passageway between the second sleeve and the shaft, the third set of channels formed in the generally upper portion of the second sleeve, the fourth set of channels formed in the generally lower portion of the sleeve, the third and fourth set of channels receiving the second source of compressed air from the second compressor, a second set of one or more ball bearings coupled to the shaft, wherein the ball bearings are configured to provide support for the shaft, an engine compressor, and a turbine. 
         [0013]    In a third preferred embodiment, the compressor is optional if the compressed air are supplied by an engine compressor. The airflow through the first and second channels is preferably in a direction opposite to that of the third and fourth channels. The airflow through the first and second channels is preferably in the same direction as that of the third and fourth channels. 
         [0014]    These and other features and advantages of the invention will become more apparent with a description of preferred embodiments in reference to the associated drawings. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  is a schematic diagram of a horizontal turbine engine having an air bearing system in an embodiment. 
           [0016]      FIG. 2  is a schematic diagram of a hybrid bearing system having an air bearing and a ball/roller bearing. 
           [0017]      FIG. 3  is an exploded view of the hybrid bearing system. 
           [0018]      FIG. 4  is a side view of a representation of the air circuit sleeve and the lift cylinder showing the air passageways. 
           [0019]      FIG. 5  is a front view of a representation of the air circuit sleeve and the lift cylinder showing the air passageways. 
           [0020]      FIG. 6  is a schematic diagram of a rotor assembly showing forces of weight, thrust, and lift. 
           [0021]      FIG. 7  is schematic diagram of a horizontal turbine engine having an air bearing system in an embodiment. 
           [0022]      FIG. 8  is a schematic diagram of a vertical turbine engine in an embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0023]    A free-floating shaft for gas turbine engines is disclosed that is capable of producing air pressure differential to reduce thrust and provide lift for weightless rotor rotation during high speed operations. The free-floating shaft also provides air cooling to remove heat generated from ball/roller bearings without using lubricants. The free-floating shaft system is comprised of a rotor shaft, ball/roller bearings, air bearings, compressors, and cavities for thrust load reduction. 
         [0024]    Ball/roller bearings are used extensively in high power density gas turbine engines to provide support for the rotating shaft and limit both radial and axial excursions of the rotor shaft to avoid rubbing. The ball/roller bearings are also designed to take both radial and thrust loads during high speed operation. High speed operation causes heat generation in the bearings and lubrication is normally used to dissipate heat. Adequate lubrication of ball/roller bearings is also required to prevent the rolling element surfaces from touching the inner and outer ring raceways. The use of lubricants in the ball/roller bearings involves a complicated lubrication system, which includes storage, pumping, filtering, circulation, atomization, and cooling. The lubricant sealing or retention in the bearings and housings is also very problematic. 
         [0025]    In order to eliminate the use of lubricant and the associated lubrication system without sacrificing ball/roller bearings performance, the free-floating shaft incorporates a new air bearing to reduce thrust load and provide lift for weightless rotor rotation during high speed ball/roller bearing operations. 
         [0026]    Inlet air for air bearings in the free-floating shaft system are pressurized using compressors and enters cavities located at shaft ends. The use of compressors is optional if pressurized air from engine compressors is available for cavity pressurization. These cavities are designed to reduce thrust load based on the cavity air pressure and shaft-end surface area. The cavity air then flows through the air passageways formed by the rotor shaft and an air-circuit sleeve. Each air passageway has a metering slot at the end of the air-circuit sleeve to regulate airflow rate. Therefore, both the gap and the airflow rate of air passageways can be adjusted to create air pressure differential to lift the rotating shaft. The length of the air-circuit sleeve is determined based on lift surface area needed for weightless rotor rotation, which leads to no metal contact between the rolling element and raceways even without using lubricants and the complicated lubrication system. The air exiting the metering slots is also used to remove heat generated in the ball/roller bearings. 
         [0027]      FIG. 1  is a schematic diagram of a horizontal turbine engine  151  having hybrid bearing systems  101  and  101 ′ in an embodiment. The turbine engine  151  comprises a first hybrid bearing system  101 , a second hybrid bearing system  101 ′, an engine compressor  152 , a combustor  154 , and a turbine  156 . The turbine engine  151  has a rotating shaft centered around a generally horizontal centerline. The rotating shaft comprises a hollow free-floating shaft  160  and an inner rotor shaft  166  in one or more embodiments. The free-floating shaft  160  and the rotor shaft  166  rotate around a center line C L  and connects the first hybrid bearing system  101 , the turbine  156 , the engine compressor  152 , and the second hybrid bearing system  101 ′. 
         [0028]    Referring to  FIGS. 1-3 , the first hybrid bearing system  101  comprises a compressor, such as axial compressor  124  and radial compressor  128 , coupled to the rotor shaft  166  or the floating shaft  160  where the compressors  124  and  128  supply compressed air. In an embodiment, a lift cylinder  120  may be placed around the free floating shaft  160 . The first hybrid bearing  101  also has an annular air-circuit sleeve  110  radially surrounding the lift cylinder  120  and the free-floating shaft  160 . In one or more embodiments, a tie-shaft nut  126  may be secured to rotor shaft  166  and may be used to secure radial compressor  128  to the lift cylinder  120 . The sleeve  110  has a first set of channels  112   a  and a second set of channels  112   b  formed on the inner surface  113  of the sleeve  110 . Each channel  112   a  and  112   b  forms an air passageway  115   a  and  115   b  respectively between the sleeve  110  and the lift cylinder  120  and free-floating shaft  160 . As shown in  FIG. 5  and described below, the first set of channels  112   a  are formed in the generally upper portion  117   a  of the sleeve  110 , and the second set of channels  112   b  are formed in the generally lower portion  117   b  of the sleeve  110 . The first and second set of channels  112   a  and  112   b  receive compressed air from the compressors  124  and  128 . The hybrid system  101  also comprises down-stream metering slots  114 , wherein the metering slot  114  is configured to regulate the rate of airflow in the first and second set of channels  112   a  and  112   b.    
         [0029]    The first hybrid bearing also has a first set of one or more ball bearings  122  coupled to the free floating shaft  160 , wherein the ball bearings  122  are configured to provide support for the free floating shaft  160 . As described below, the first and second set of channels  112   a  and  112   b  are configured to generate a lifting force on the free floating shaft  160  and the rotor shaft  166  in a generally upward direction. 
         [0030]    In one or more embodiments, each of the first set of channels  112   a  has a first cross sectional area  119   a , and each of the second set of channels  112   b  has a second cross sectional area  119   b , where the first cross sectional area  119   a  is less than the second cross sectional area  119   b.    
         [0031]    Likewise, as illustrated in  FIG. 1 , the second hybrid bearing system  101 ′ comprises a compressor, such as axial compressor  124 ′ and radial compressor  128 ′, coupled to the rotor shaft  166  or the floating shaft  160  where the compressors  124 ′ and  128 ′ supply compressed air. In an embodiment, a lift cylinder  120 ′ may be placed around the free floating shaft  160 . The second hybrid bearing  101 ′ also has an annular air-circuit sleeve  110 ′ radially surrounding the lift cylinder  120 ′ and the free-floating shaft  160 . The sleeve  110 ′ has a third set of channels  112 ′a and a fourth set of channels  112 ′b formed on the inner surface  113 ′ of the sleeve  110 ′. Each channel  112 ′a and  112 ′b forms an air passageway  115 ′a and  115 ′b respectively between the sleeve  110 ′ and the lift cylinder  120 ′ and free-floating shaft  160 . As shown in  FIG. 5  and described below, the third set of channels  112 ′a are formed in the generally upper portion  117   a  of the sleeve  110 , and the fourth set of channels  112 ′b are formed in the generally lower portion  117   b  of the sleeve  110 . The third and fourth set of channels  112 ′a and  112 ′b receive compressed air from the compressors  124 ′ and  128 ′. The hybrid system  101 ′ also comprises down-stream metering slots  114 ′, wherein the metering slot  114 ′ is configured to regulate the rate of airflow in the first and second set of channels  112 ′a and  112 ′b. 
         [0032]    The second hybrid bearing  101 ′ also has a second set of one or more ball bearings  122 ′ coupled to the free floating shaft  160 , wherein the ball bearings  122 ′ are configured to provide support for the free floating shaft  160 . As described below, the third and fourth set of channels  112 ′a and  112 ′b are configured to generate a lifting force on the free floating shaft  160  and the rotor shaft  166  in a generally upward direction. 
         [0033]    In one or more embodiments, each of the first set of channels  112 ′a has a first cross sectional area  119 ′a, and each of the second set of channels  112 ′b has a second cross sectional area  119 ′b, where the first cross sectional area  119 ′a is less than the second cross sectional area  119 ′b. 
         [0034]    While embodiments discussed herein describe sleeves with two sets of channels or air passageways, it shall be understood that this is for illustration purposes only and that any number of sets of channels and air passageways are contemplated in one or more embodiments. 
         [0035]    Outside air enters the free-floating shaft  160  at air inlets  162 . As the free-floating shaft  160  is hollow, a cavity  163  is formed between the free-floating shaft  160  and the rotor shaft  166 . Air enters into the cavity  163 , a portion of the air traverses to hybrid bearing system  101  and another portion of air traverses to hybrid system  101 ′. 
         [0036]    For hybrid system  101 , the air enters the axial compressor  124 , is then injected into radial compressor  128  and enters a thrust management cavity  130 . As seen in  FIG. 2 , the thrust management cavity  130  is formed between the housing  132  and the other components of the hybrid system  101  including the tie-shaft nut  126 , the lift cylinder  120 , and the air-circuit sleeve  110 . The thrust management cavity  130  receives the compressed air from the compressors  124  and  128  and provides the compressed air to the first and second set of channels  112   a  and  112   b  in the sleeve  110 , where the thrust management cavity  130  is configured to reduce thrust load based on cavity air pressure and shaft-end surface area. Compressed air then flows though air passageways  115   a  and  115   b , and then flows to ball bearings  122 . The ball bearings  122  are configured to receive the compressed air for cooling the ball bearings  122 . In one or more embodiments, the turbine engine  151  does not employ a lubrication system for the ball bearings  122 . The airflow from the hybrid system  101  exits from air exit  134  which is directed back toward the turbine  156 . The exiting air will either re-enter the turbine engine or discharge into the atmosphere. 
         [0037]    For hybrid system  101 ′, the air enters the axial compressor  124 ′, is then injected into radial compressor  128 ′ and enters a thrust management cavity  130 ′. The thrust management cavity  130 ′ receives the compressed air from the compressors  124 ′ and  128 ′ and provides the compressed air to the third and fourth channels  112 ′a and  112 ′b in the sleeve  110 ′, where the thrust management cavity  130 ′ is configured to reduce thrust load based on cavity air pressure and shaft-end surface area. Compressed air then flows though air passageways  115 ′a and  115 ′b, and then flows to ball bearings  122 ′. The airflow from the hybrid system  101 ′ exits from air exit  134 ′, which is directed toward the turbine  156 . The exiting air will either re-enter the turbine engine or discharge into the atmosphere. As such, the airflow through the first and second channels  112   a  and  112   b  is in a direction opposite that of the third and fourth channels  112 ′a and  112 ′b. 
         [0038]      FIGS. 4 and 5  are schematic representations illustrating the principles of operation. As discussed before, the first hybrid bearing  101  has an annular air-circuit sleeve  110  radially surrounding the lift cylinder  120  and the free-floating shaft  160 , which is represented here as a rotating shaft  121 . The sleeve  110  has a first set of channels  112   a  and a second set of channels  112   b , forming air passageways  115   a  and  115   b  respectively between the sleeve  110  and the rotating shaft  121 . The first set of channels  112   a  are formed in the generally upper portion  117   a  of the sleeve  110 , and the second set of channels  112   b  are formed in the generally lower portion  117   b  of the sleeve  110 . The first and second set of channels  112   a  and  112   b  receive compressed air from the compressors  124  and  128 . The hybrid system  101  also comprises down-stream metering slots  114 , wherein the metering slot  114  is configured to regulate the rate of airflow in the first and second set of channels  112   a  and  112   b.    
         [0039]    As shown in  FIG. 5 , each of the first set of channels  112   a  has a first cross sectional area  119   a , and each of the second set of channels  112   b  has a second cross sectional area  119   b , where the first cross sectional area  119   a  is less than the second cross sectional area  119   b.    
         [0040]    As a result of the differing cross sectional areas  119   a  and  119   b , and metering slots  114  for the air passageways  115   a  and  115   b , air entering the upper, first set of air passageways  115   a , will traverse the air passageway  115   a  at a higher velocity v U  than the velocity v L  of the air traversing through the lower, second set of air passageways  115   b.    
         [0041]    Following aerodynamics principle, an increase in the speed of the air occurs simultaneously with a decrease in pressure. As such, the pressure of the air in the upper, first passageways  115   a , P u , will be less than that of the pressure P L  of the lower, second set of air passageways  115   b . This air pressure differential, combined with the effective, exposed surface area of the rotating shaft  121  determines the lifting force F L  applied to the rotating shaft  121 . The length of the air-circuit sleeve  110  is designed based on lift surface area needed for weightless rotor  121  rotation. As a result, metal contact is removed between the rolling element and raceways of the ball bearings  122  such that the need for lubricants and complicated lubrication systems are eliminated. 
         [0042]      FIG. 6  is a representation of the turbine engine  151  illustrating the forces acting upon the free-floating shaft  160 . The weight of the components affixed to the free-floating shaft F W  comprises the individual weights for the engine compressor  152 , the turbine  156 , the free-floating shaft  160 , the rotor shaft  166 , the axial compressors  124  and  124 ′, the radial compressor  128  and  128 ′, the ball bearings  122  and  122 ′, the lift cylinders  120  and  120 ′, and the tie-shaft nuts  126  and  126 ′. The lifting force of the hybrid bearing system  101  is given by F L , and the lifting force for the hybrid bearing system  101 ′ is given by F L′ . In one or more embodiments, the total lifting forces F L  and F L′  required to overcome the weight F W  may be tailored by the design of the air passageways  115   a  and  115   b , including the cross sectional areas  119   a  and  119   b , the length of the sleeve  110 , and the metering slots  114  an  114 ′. The forward thrust is given by F TF , and the reverse thrust force is given by F TR . The thrust for engine compressors and turbines are varied with turbine engine design.  FIG. 6  depicts the forces at play for a turbine engine having a horizontal free-floating shaft. 
         [0043]      FIG. 7  is a schematic diagram of a turbine engine  251  having hybrid bearing systems  101  and  201  in an embodiment. The turbine engine  251  comprises a first hybrid bearing system  101 , a second hybrid bearing system  201 , an engine compressor  152 , a combustor  154 , and a turbine  156 . The turbine engine  151  has a rotating shaft centered around a generally horizontal centerline C L . The rotating shaft comprises a hollow free-floating shaft  160  and an inner rotor shaft  166  in one or more embodiments. The free-floating shaft  160  and the rotor shaft  166  rotate around a center line C L  and connect the first hybrid bearing system  101 , the turbine  156 , the engine compressor  152 , and the second hybrid bearing system  201 . 
         [0044]    Details of hybrid system  101  are discussed above. For hybrid system  201 , the air enters the axial compressor  224 , is then injected into radial compressor  228  and enters a thrust management cavity  230 . The thrust management cavity  230  receives the compressed air from the compressors  224  and  228  and provides the compressed air to the third and fourth of channels  212   a  and  212   b  in the sleeve  210 , where the thrust management cavity  230  is configured to reduce thrust load based on cavity air pressure and shaft-end surface area. Compressed air then flows though air passageways  215   a  and  215   b , and then flows to ball bearings  222 . The airflow from the hybrid system  201  exits from air exit  234  and is directed away from the turbine  156 . The exiting air will either re-enter the turbine engine or discharge into the atmosphere. As such, the airflow through the first and second channels  112   a  and  112   b  is in the same as that of the third and fourth channels  212   a  and  212   b.    
         [0045]      FIG. 8  is schematic diagram of a vertical turbine engine  351  having hybrid bearing systems  301  and  401  in an embodiment. The turbine engine  351  comprises a first hybrid bearing system  301 , a second hybrid bearing system  401 , an engine compressor  352 , a combustor  354 , and a turbine  356 . The turbine engine  351  has a rotating shaft centered around a generally vertical centerline. The rotating shaft comprises a hollow free-floating shaft  360  and an inner rotor shaft  366  in one or more embodiments. The free-floating shaft and the rotor shaft rotate around a center line C L  and connect the first hybrid bearing system  301 , the turbine  356 , the engine compressor  352 , and the second hybrid bearing system  401 . Hybrid systems  301  and  401  each comprises a bearing system having a compressor coupled to the rotating shaft, the compressor supplying compressed air, and an annular sleeve radially surrounding the rotating shaft, the sleeve having channels formed on the inner surface of the sleeve, each channel forming an air passageway between the sleeve and the rotating shaft, the channels receiving compressed air from the compressor. In one or more embodiments, the channels for each hybrid system are equivalent and do not provide a net force laterally. 
         [0046]    Specifically, for hybrid system  301 , the air enters through air inlet  362  and enters a compressor  324 , and provides the compressed air to the channels  312  in the sleeve  310 . Compressed air then flows though air passageways  315 , and then flows to ball bearings  322 . In one or more embodiments, the channels  312  and slots  314  forming the air passageways  315  are equivalent and do not provide a net force laterally. 
         [0047]    The ball bearings  322  are configured to receive the compressed air for cooling the ball bearings  322 . In one or more embodiments, the turbine engine  351  does not employ a lubrication system for the ball bearings  322 . The airflow from the hybrid system  301  exits through the cavity  363  and is directed to hybrid bearing system  401  at the top. Cavity  363  is formed between the hollow, free-floating shaft  360  and the rotator shaft  366 . 
         [0048]    For hybrid system  401 , the air enters cavity  430  and is directed through a thrust ball bearing  422 , and is injected into compressor  424 . Compressed air then flows though the channels  412  and slots  414  which form passageways  415 , and then to ball bearings  423 . In one or more embodiments, the channels  412  and slots  414  forming the air passageways  415  are equivalent and do not provide a net force laterally. The airflow from the hybrid system  401  exits from air exit  434  and is directed toward the turbine  356 . The exiting air will either re-enter the turbine engine or discharge into the atmosphere. In one or more embodiments, the turbine engine  351  does not employ a lubrication system for the ball bearings  422  and  423 . 
         [0049]    Although the invention has been discussed with reference to specific embodiments, it is apparent and should be understood that the concept can be otherwise embodied to achieve the advantages discussed. The preferred embodiments above have been described primarily as hybrid bearings having both air bearings and ball/roller bearings for gas turbines. In this regard, the foregoing description of the hybrid bearings is presented for purposes of illustration and description. It shall be apparent that various gas turbine engines may also benefit from the hybrid bearings described herein. 
         [0050]    Furthermore, the description is not intended to limit the invention to the form disclosed herein. Accordingly, variants and modifications consistent with the following teachings, skill, and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain modes known for practicing the invention disclosed herewith and to enable others skilled in the art to utilize the invention in equivalent, or alternative embodiments and with various modifications considered necessary by the particular application(s) or use(s) of the present invention.