Patent Publication Number: US-2019190336-A1

Title: Method and apparatus for cooling a rotor assembly

Description:
BACKGROUND OF THE INVENTION 
     Contemporary aircraft engines include electric machines, or generator systems, which utilize a running aircraft engine in a generator mode to provide electrical energy to power systems and components on the aircraft. Some aircraft engines can further include starter/generator systems, which act as a motor to start an aircraft engine, and as a generator to provide electrical energy to power systems on the aircraft after the engine is running. Motors and generators can be wet cavity systems, wherein a cavity housing the rotor and stator is exposed to liquid coolant, or dry cavity systems, wherein the cavity is not exposed to liquid coolant. Dry cavity systems can also utilize liquid coolant in one or more contained cooling systems, but they are still considered dry cavity so long as the cavity is not exposed to liquid coolant. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, the present disclosure relates to a rotor assembly for an electric machine including a rotor core having a rotatable shaft and defining at least one rotor post, and a set of windings wound around the post and including a coolant conduit through-opening in the set of windings and extending axially along the post through the set of windings, and wherein the coolant conduit is in a thermally conductive relationship with a portion of the windings. Heat generated in the set of windings when the rotor core rotates is transferred by conduction to a coolant flow in the coolant conduit. 
     In another aspect, the present disclosure relates to a rotor assembly for an electric machine including a rotor core having a rotatable shaft and defining at least one rotor post, the at least one rotor post having a first axial end and a spaced second axial end, a set of rotor windings wound around the post between the first and second axial ends, and a set of radially and laterally-spaced coolant conduit through-openings in the set of windings extending axially between the first and second axial ends, and in a thermally conductive relationship with the set of rotor windings. The set of coolant conduits are internal to the set of windings. 
     In yet another aspect, the present disclosure relates to a method of cooling a rotatable electric machine rotor, including directing a fluid coolant flow to an array of coolant conduits extending axially through a set of rotor windings, wherein the array of coolant conduits are in a thermally conductive relationship with the set of rotor windings, so that the fluid coolant flow removes heat from the set of rotor windings as the rotor rotates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is an isometric view of a gas turbine engine having a generator, in accordance with various aspects described herein. 
         FIG. 2  is an isometric view of an exterior of the generator of  FIG. 1 , in accordance with various aspects described herein. 
         FIG. 3  is a schematic cross-sectional view of the generator of  FIG. 2 , taken along line of  FIG. 2 , in accordance with various aspects described herein. 
         FIG. 4  illustrates a schematic view of a rotor portion illustrating a cross-sectional view of a set of windings of the generator of  FIG. 3 , including a liquid cooling circuit, in accordance with various aspects described herein. 
         FIG. 5  illustrates a schematic cross-sectional view, taken along line V-V of  FIG. 4 , illustrating a set of radial openings of the rotor portion, in accordance with various aspects described herein. 
     
    
    
     DESCRIPTION OF EMBODIMENTS OF THE INVENTION 
     Aspects of the disclosure can be implemented in any environment using an electric motor regardless of whether the electric motor provides a driving force or generates electricity. For purposes of this description, such an electric motor will be generally referred to as an electric machine, electric machine assembly, or similar language, which is meant to clarify that one or more stator/rotor combinations can be included in the machine. While this description is primarily directed toward an electric machine providing power generation, it is also applicable to an electric machine providing a driving force or an electric machine providing both a driving force and power generation. Further, while this description is primarily directed toward an aircraft environment, aspects of the disclosure are applicable in any environment using an electric machine. Thus, a brief summary of a contemplated environment should aid in a more complete understanding. 
     While “a set of” various elements will be described, it will be understood that “a set” can include any number of the respective elements, including only one element. As used herein, the terms “axial” or “axially” refer to a dimension along a longitudinal axis of a generator or along a longitudinal axis of a component disposed within the generator. 
     As used herein, the terms “radial” or “radially” refer to a dimension extending generally between a center longitudinal axis, an outer circumference, or a circular or annular component disposed thereof. Aspects of the disclosure can include components that are not oriented in a “strictly” radial dimension, that is, components having a radial dimension but not oriented perfectly between the center longitudinal axis and an outer circumference. As used herein, the term “laterally” can refer to a dimension generally or relatively perpendicular to a radial dimension. The use of the terms “proximal” or “proximally,” either by themselves or in conjunction with the terms “radial” or “radially,” refers to moving in a direction toward the center longitudinal axis, or a component being relatively closer to the center longitudinal axis as compared to another component. 
     All directional references (e.g., radial, lateral, axial, upper, lower, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise) are only used for identification purposes to aid the reader&#39;s understanding of the disclosure, and do not create limitations, particularly as to the position, orientation, or use thereof. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and can include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily infer that two elements are directly connected and in fixed relation to each other. 
       FIG. 1  illustrates a gas turbine engine  10  having an accessory gear box (AGB)  12  and a generator  14  according to an aspect of the disclosure. The gas turbine engine  10  can be a turbofan engine, such as a General Electric GEnx or CF6 series engine, commonly used in modern commercial and military aviation or it could be a variety of other known gas turbine engines such as a turboprop or turboshaft. The gas turbine engine  10  can also have an afterburner that burns an additional amount of fuel downstream of the low pressure turbine region to increase the velocity of the exhausted gases, and thereby to increase thrust. The AGB  12  can be coupled to a turbine shaft (not shown) of the gas turbine engine  10  by way of a mechanical power take off  16 . The gas turbine engine  10  can be any suitable gas turbine engine used in modern commercial and military aviation or it could be a variety of other known gas turbine engines such as a turboprop or turboshaft. The type and specifics of the gas turbine engine  10  are not germane to the disclosure and will not be described further herein. While a generator  14  is shown and described, aspects of the disclosure can include any electrical machine or generator. 
       FIG. 2  more clearly illustrates the generator  14  and its housing  18 , which can include a clamping interface  20 , used to clamp the generator  14  to the AGB  12 . Multiple electrical connections can be provided on the exterior of the generator  14  to provide for the transfer of electrical power to and from the generator  14 . The electrical connections can be further connected by cables to an electrical power distribution node of an aircraft having the gas turbine engine  10  to power various items on the aircraft, such as lights and seat-back monitors. The generator  14  includes a liquid coolant system for cooling or dissipating heat generated by components of the generator  14  or by components proximate to the generator  14 , one non-limiting example of which can be the gas turbine engine  10 . For example, the generator  14  can include a liquid cooling system using oil as a coolant. 
     The liquid cooling system can include a cooling fluid inlet port  82  and a cooling fluid outlet port  84  for controlling the supply of coolant to the generator  14 . In one non-limiting example, the cooling fluid inlet and output ports  82 ,  84  can be utilized for cooling at least a portion of a stator of the generator  14 . The liquid cooling system can also include a second coolant outlet port  91 , shown at a rotatable shaft portion of the generator  14  (described below). While only a coolant outlet port  91  is shown in the illustrated isometric view, a rotor or rotatable shaft coolant inlet port can be included. While not shown, aspects of the disclosure can further include other liquid cooling system components, such as a liquid coolant reservoir fluidly coupled with the cooling fluid inlet port  82  and cooling fluid outlet port  84 , and a liquid coolant pump to forcibly supply the coolant through the ports  82 ,  84  or generator  14 . Oil is merely one non-limiting example of a liquid coolant that can be used in aspects of the disclosure. 
     The interior of the generator  14  is best seen in  FIG. 3 , which is a sectional view of the generator  14  shown in  FIG. 2 . A rotatable shaft  40  is located within the generator  14  and is the primary structure for supporting a variety of components. The rotatable shaft  40  can have a single diameter or one that can vary along its length. The rotatable shaft  40  is supported by spaced bearings  42  and  44  and configured to rotate about axis of rotation  41 . Several of the elements of the generator  14  have a fixed component and a rotating component, with the rotating component being provided on the rotatable shaft  40 . Examples of these elements can include a main machine  50 , housed within a main machine cavity  51 , an exciter  60 , and a permanent magnet generator (PMG)  70 . The corresponding rotating component comprises a main machine rotor  52 , an exciter rotor  62 , and a PMG rotor  72 , respectively, and the corresponding fixed component comprises a main machine stator  54  or stator core, an exciter stator  64 , and a PMG stator  74 . In this manner, the main machine rotor  52 , exciter rotor  62 , and PMG rotor  72  are disposed on the rotatable shaft  40 . The fixed components can be mounted to any suitable part of the housing  18 . The main machine stator  54 , exciter stator  64 , and PMG stator  74  define an interior through which the rotatable shaft  40  extends. 
     It will be understood that the main machine rotor  52 , exciter rotor  62 , and PMG rotor  72  can each have a set of rotor poles, including, but not limited to two rotor poles having corresponding sets of windings, and that the main machine stator  54 , exciter stator  64 , and PMG stator  74  can each have a set of stator teeth or stator poles, including, but not limited to two stator teeth or stator poles. The set of rotor poles can generate a set of magnetic fields relative to the set of stator poles, such that the generator  14  can operate through the interaction of the magnetic fields and current-carrying conductors to generate force or electrical power. The exciter  60  can provide direct current to the main machine  50  and the main machine  50  and PMG  70  can supply AC electrical power when the rotatable shaft  40  rotates. 
     At least one of the rotor poles can be formed by a core with a post and wire wound about the post to form a winding, with the winding having at least one end turn. The main machine rotor  52 , rotor poles, and rotor windings are further illustrated and described with respect to  FIG. 4 . Aspects of the disclosure shown in  FIG. 3  include at least one set of stator windings  90  arranged longitudinally along the stator housing  18 , that is, in parallel with housing  18  and the rotor axis of rotation  41 . The set of stator windings  90  can also include a set of stator winding end turns  92  extending axially beyond opposing ends of a longitudinal length of a main machine stator  54 . 
     The components of the generator  14  can be any combination of known generators. For example, the main machine  50  can be either a synchronous or asynchronous generator. In addition to the accessories shown in this aspect, there can be other components that need to be operated for particular applications. For example, in addition to the electromechanical accessories shown, there can be other accessories driven from the same rotatable shaft  40  such as the liquid coolant pump, a fluid compressor, or a hydraulic pump. 
     As explained above, the generator  14  can be oil cooled and thus can include a cooling system  80 . The cooling oil can be used to dissipate heat generated by the electrical and mechanical functions of the generator  14 . The cooling system  80  using oil can also provide for lubrication of the generator  14 . In the illustrated aspects, the generator  14  can be a liquid cooled, dry cavity system having the cooling system  80  illustrated as including the cooling fluid inlet port  82  and the cooling fluid outlet port  84  for controlling the supply of the cooling fluid to the cooling system  80 . The cooling system  80  can further include, for example, a cooling fluid reservoir and various cooling passages. In addition or alternatively, the generator  14  can be a liquid cooled, wet cavity system wherein the rotatable shaft  40  can provide one or more flow channels or paths (shown as arrows  85 ) for the main machine rotor  52 , exciter rotor  62 , and PMG rotor  72 , as well as a rotor shaft oil outlet  88 , such as the outlet port  91 , wherein residual, unused, or unspent oil can be discharged from the rotatable shaft  40 . 
       FIG. 4  illustrates a zoomed view of the main machine rotor  52  or rotor assembly, for better understanding of the operation and effect of the cooling system  80 . While  FIG. 4  illustrates a single axially-extending portion of the set of windings  106 , aspects of the disclosure can be included wherein, for instance, the set of windings  106  are wound about a post  150  such that there are multiple (e.g. at least two) axially-extending portions of the set of windings  106 . In this instance, each axially-extending portion of the set of windings  106  can be adapted, as explained herein. 
     As shown, the main machine rotor  52  can include a rotor core  100 , such as a laminated rotor core, rotatably connected to co-rotate with the rotatable shaft  40 . The main machine rotor  52  can further define a first end  102  of the rotor  52  and a second end  104  of the rotor  52 , spaced axially from the first end  102 . The main machine rotor  52  can include at least one rotor pole  152  formed when at least a portion of the rotor core  100  is wound with conductive wiring (i.e. a “winding”) about the post  150 . Collectively, the multiple windings of the conductive wiring forms a set of rotor windings  106 . In the perspective of the illustrated example, the rotor post  150  can underlie the set of rotor windings  106 . 
     Each set of rotor windings  106 , while continuous, can be thought of as having axial segments that run along opposite sides of the pole  152  (e.g. in parallel with the axis of rotation  41 ), with opposing end turn  154  segments on opposite ends  102 ,  104  of the rotor core  100  connecting the axial segments. While only one example of a set of rotor windings  106  are illustrated, aspects of the disclosure can include having multiple sets or rotor windings  106  configured about one or more circumferentially spaced poles  152  of the main machine rotor  52 , such as a portion of a salient pole generator. 
     Each pole  152  of the main machine rotor  52  can further include a cap  108 , at least partially overlaying each pole  152  and set of rotor windings  106 . In one non-limiting example, the rotor core  100  and cap  108  can be formed or comprised by a plurality of laminations, for instance, cobalt laminations. Cobalt laminations are merely one example of a material used to construct the core  100  or cap  108 , and alternate material composition or compositions may be included. 
     The cooling system  80  for the main machine rotor  52  can include a set or series of fluid conduits, passageways, or the like, wherein a coolant fluid can be supplied or otherwise delivered there through for removing heat from the main machine rotor  52 , the set of rotor windings  106 , or a combination thereof. As shown, a portion of the rotor core  100  proximate to the first end  102  can define a first coolant cavity  120  or reservoir fluidly connected with the oil flow channel  85  of the rotor  52  (schematically illustrated). Similarly, another portion of the rotor core  100  proximate to the second end  104  can define a second coolant cavity  122  or reservoir fluidly connected with the oil flow channel  85  of the rotor  52 . In this example, one of the coolant cavities  120 ,  122  (shown as the second coolant cavity  122 ) can receive a fluid coolant flow, while the other of the coolant cavities  122 ,  120  (such as the first coolant cavity  120 ) can supply or return a fluid coolant flow back to the oil flow channel  85  or another coolant reservoir or flow. As shown, the fluid coolant flow is illustrated schematically as arrows  132 . 
     The cooling system  80  of the main machine rotor  52  can also include a first coolant conduit  140  or set of first coolant conduits  140  supported by the set of rotor windings  106  and adapted, configured, disposed, or the like to extend axially along, through, or internal to the rotor post  150  or pole  152 , axis of rotor  41  rotation, or the like. In one non-limiting example, the set of first coolant conduits  140  can be radially spaced through the set of rotor windings  106 , that is, arranged, disposed, located, or the like, at different radii through the set of rotor windings  106 . In this example, “radially spaced” denotes a relative position radially closer to the axis of rotation  41 , relative to the set of rotor windings  106 , between the set of rotor windings  106  and the rotor core  100 , but not necessarily in a “strict” radial direction, as previously described. Stated another way, in the perspective of  FIG. 4 , the set of first coolant conduits  140  run parallel to, and internally through, the set of rotor windings  106 . At least one face of each of the set of first coolant conduits  140  can be in a thermally conductive relationship with a proximate portion or face of the set of rotor windings  106 . 
     The cooling system  80  of the main machine rotor  52  can also include a set of radial openings, such as a through-opening, non-limiting examples of which can include a radially-oriented conduit, a second coolant conduit  142 , or a second set of coolant conduits  142  supported by the set of rotor windings  106  and adapted, configured, disposed, or the like to extend radially through a portion of the set of rotor windings  106  or rotor winding end turns  154  proximate to one of the first or second ends  102 ,  104 . As shown, the second set of coolant conduits  142  includes a conduit proximate to the first end  102  that fluidly connects the first coolant cavity  120  with a set of first ends of the set of first coolant conduits  140 . In this sense, the set of first coolant conduits  140  are fluidly connected with the first coolant cavity  120  by way of the radially-extending, radially-orientated, or radially-arranged set of second coolant conduits  142 . 
     Similarly, the cooling system of the main machine rotor  52  can also include another set of radial openings, such as a through-opening, non-limiting examples of which can include a radially-oriented conduit, a third coolant conduit  144 , or a third set of coolant conduits  144  supported by the set of rotor windings  106  and adapted, configured, disposed, or the like to extend radially through another portion of the set of rotor windings  106  or rotor winding end turns  154  proximate to the other of the first or second ends  102 ,  104 . As shown, the third set of coolant conduits  144  includes a conduit proximate to the second end  104  that fluidly connects the second coolant cavity  122  with a set of second ends of the set of first coolant conduits  140 , wherein the second end of the first coolant conduits  140  is spaced from the first end. In this sense, the set of first coolant conduits  140  are fluidly connected with the second coolant cavity  122  by way of the radially-extending, radially-orientated, or radially-arranged set of third coolant conduits  144 . At least a portion of the set of second coolant conduits  142 , the set of third coolant conduits  144 , or a combination thereof, can be in a thermally conductive relationship with a proximate portion or face of the set of rotor windings  106  or end turns  154 . 
     In one non-limiting example, the set of rotor windings  106  or end turns  154  can be cut, formed, wound, or otherwise configured such that the set of windings  106  themselves define the one or more of the set of first, second, or third coolant conduits  140 ,  142 ,  144 . In another non-limiting example, the set of rotor windings  106  or end turns  154  can include a set of independently-formed conduits or passages (e.g. a housing having sidewalls defining a fluid channel) disposed in, around, or in between the conductive wires of the respective set of rotor windings  106  or end turns  154 . 
     Thus, aspects of the disclosure can include a cooling system  80  defined by, or including a coolant flow path (for example, denoted by the fluid coolant flow  132 ), whereby coolant supplied from a coolant source (such as the oil flow channel  85 ) can be provided to the set of first coolant conduits  140 , and traverse the set of first coolant conduits  140  to remove heat generated in the set of windings  106  during generator operations. The coolant flow path can further be provided from the oil flow channel  85  to one of the first or second coolant cavities  120 ,  122  (shown as the second coolant cavity  122 ), radially through a corresponding one of the set of second or third coolant conduits  142 ,  144  (shown as the third coolant conduit  144 ). The coolant flow path can further be provided from the one of the set of second or third coolant conduits  142 ,  144  through the set of the radially-spaced first coolant conduits  140 , whereby the coolant flow is received by the other of the set of second or third coolant conduits  142 ,  144  (shown as the second coolant conduit  142 ). The coolant flow path can then be provided from the other of the set of second or third coolant conduits  142 ,  144  to the other of the first or second coolant cavities  120 ,  122  (shown as the first coolant cavity  120 ), whereby the coolant flow can be returned to the oil flow channel  85 , or delivered to another cooling system  80  destination. 
     The fluid coolant flow  132  can receive a conductive transfer of heat from the set of rotor windings  106 , the end turns  154 , the proximate portions of the rotor core  100 , the cap  108 , or a combination thereof, and carry away the aforementioned heat, effectively or operably cooling the main machine rotor  52 . In one non-limiting example, the radial spacing of the set of first coolant conduits  140  can be selected, configured, adapted, or the like, to ensure sufficient or adequate conductive heat transfer from the set of rotor windings  106  to the fluid coolant flow  132  during expected generator operations, for instance to ensure an even, balanced, or distributed heating or cooling of the set of rotor windings  106 . For instance, the configuration of the radially-spaced set of first coolant conduits  140  can be adapted to ensure the radially distal portions of the set of windings  106  and the radially proximal (e.g. closer to the axis of rotation  41 ) portions of the set of windings  106  do not experience abnormal heating or heat retention during expected generator operating conditions. 
     As described herein, the fluid coolant flow  132  can be defined in a sequentially-directed flow pathway including the set of third coolant conduits  144 , the set of first coolant conduits  140 , the set of second coolant conduits  142 , or a combination thereof. 
       FIG. 5  illustrates an isometric cross-sectional view of the end turns  154  or set of rotor windings  106  of the main machine rotor  52  proximate to the second end  104 , taken along line V-V of  FIG. 4 , for ease of understanding. While aspects of the disclosure shown in  FIG. 5  will be explained with respect to the set of third coolant conduits  144 , the following aspects can be equally applicable with respect to the second coolant conduits  142 . As shown, the set of third coolant conduits  144  can extend radially from the second coolant cavity  122 , through a portion of the set of windings  106  or end turns  154 , up to the cap  108 . The set of third coolant conduits  144  is fluidly connected with the set of first coolant conduits  140 , as illustrated by the fluid coolant flow  132 . Also as shown, aspects of the disclosure can include radial spacing  152  between adjacent first coolant conduits  140 , as well as lateral spacing  150  between adjacent first coolant conduits  140 . In this sense, aspects of the disclosure can include a radial and laterally-spaced array of coolant conduits. Non-limiting aspects can be included wherein at least one of the radial spacing  152  or lateral spacing  150  can vary, alternate, or be equally spaced between any of the adjacent first coolant conduits  140 . Also as shown, the set of third coolant conduits  144  can include lateral spacing  150  between adjacent third coolant conduits  144  corresponding with lateral spacing  150  of the first coolant conduits  140 . 
     Alternative radial or lateral spacing  152 ,  150  configurations of the set of first or third coolant conduits  140 ,  144  can be included in aspects of the disclosure, for instance, relative to the set of windings  106 . In another non-limiting instance, the set of third coolant conduits  144  does not need to extend radially to the cap  108 . Aspects of the disclosure can be included wherein only a subset of the set of third coolant conduits  144  are fluidly connected with the set of first coolant conduits  140 , or wherein a subset of the first coolant conduits  140  are fluidly connected with the set of third coolant conduits  144 . 
     Further examples of the fluid coolant flow  132  described herein can be reversed, such that, for instance, the fluid coolant flow  132  traverses from the first coolant cavity  120 , radially through the set of second coolant conduits  142 , axially through the set of first coolant conduits  140 , and radially returning through the set of third coolant conduits  144  into the second coolant cavity  122 , and back to the cooling system  80 , based on a desired coolant flow pathway. 
     Thus, as described herein, aspects of the disclosure can include a method of cooling a rotatable electric machine rotor  52 . The method can include receiving a fluid coolant flow  132  to one or more coolant conduits  140 , such as an array of coolant conduits  140 , through the set of rotor windings  106 , wherein the one or more coolant conduits  140  are in a thermally conductive relationship with the set of rotor windings  106 , wherein the fluid coolant flow  132  removes heat from the set of rotor windings  106 . The method can further include receiving the fluid coolant flow  132  at a first axial end  102 ,  104  of the set of rotor windings  106  from a rotatable shaft  40 . In another non-limiting example, the method can further include receiving the fluid coolant flow  132  from the array of coolant conduits  142 ,  144  at a second axial end  102 ,  104  of the set of rotor windings  106 , the second axial end  102 ,  104  spaced from the first axial end  102 ,  104 , and supplying the fluid coolant flow  132  to the rotatable shaft  40   
     Many other possible aspects and configurations in addition to that shown in the above figures are contemplated by the present disclosure. For example, one aspect of the disclosure contemplates coolant conduits that extend along alternative portions or lengths of the set of rotor windings  106 . In another example, the windings or the coolant conduits can further include intervening thermally conductive layers to assist in thermal conduction while, for example, avoiding an electrically conductive relationship between respective components. In yet another example, aspects of the rotor  52  can comprise non-leaking or leak-proof components to ensure proper fluid isolation of the coolant from other aspects of the dry cavity generator. Non-limiting examples of components to ensure proper fluid isolation can include retaining rings and winding supports, such as top and bottom supports. Additionally, the design and placement of the various components such as valves, pumps, or conduits can be rearranged such that a number of different in-line configurations could be realized. 
     The aspects disclosed herein provide method and apparatus for cooling a rotor assembly or a set of rotor windings during electric machine operations (e.g. motor or generator operations). One advantage that may be realized in the above aspects is that the above described aspects have significantly improved thermal conduction to remove heat from the rotor assembly or set of rotor windings. The improved thermal conductivity between the rotor windings and the coolant conduits coupled with the coolant paths or coolant loops provide for heat removal in a much more effective fashion from the windings to the coolant. Another advantage of the above aspects is that a higher level of power generation may be achieved without having to use a wet-cavity configuration, due to the improved heat removal of the set of rotor windings. 
     The increased thermal dissipation of the rotor assembly allows for a higher speed rotation, which may otherwise generate too much heat. The higher speed rotation may result in improved power generation or improved generator efficiency without increasing generator size. Reduced thermal losses in the electric machine allow for greater efficiency and greater power density of the generator. 
     When designing aircraft components, important factors to address are size, weight, and reliability. The above described rotor assemblies have a decreased number of parts, making the complete system inherently more reliable. This results in possibly a lower weight, smaller sized, increased performance, and increased reliability system. The lower number of parts and reduced maintenance will lead to lower product costs and lower operating costs. Reduced weight and size correlate to competitive advantages during flight. 
     To the extent not already described, the different features and structures of the various aspects can be used in combination with each other as desired. That one feature cannot be illustrated in all of the aspects is not meant to be construed that it cannot be, but is done for brevity of description. Thus, the various features of the different aspects can be mixed and matched as desired to form new aspects, whether or not the new aspects are expressly described. Combinations or permutations of features described herein are covered by this disclosure. 
     This written description uses examples to disclose aspects of the disclosure, including the best mode, and also to enable any person skilled in the art to practice aspects of the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.