Patent Publication Number: US-2022235662-A1

Title: Trapped rotatable weights to improve rotor balance

Description:
FEDERALLY SPONSORED RESEARCH 
     This invention was made with Government support under W58RGZ-16-C-0047 awarded by the U.S. Army. The Government has certain rights in this invention. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to rotors and, more particularly, to trapped rotatable weights to improve rotor balance. 
     BACKGROUND 
     In recent years, turbine engines have been increasingly utilized in a variety of applications and fields. Turbine engines are intricate machines with extensive availability, reliability, and serviceability requirements. Turbine engines include rotors with fan blades. The rotor and fan blades rotate at high speed and subsequently compress the air flow. The high-pressure compressor then feeds the pressurized air flow to a combustion chamber to generate a high-temperature, high-pressure gas stream. One characteristic of a rotor is balance. The balance of the rotor corresponds to the location of the center of mass of the rotor with respect to the geometric center of the rotor. The closer the center of mass is to the geometric center, the more balanced the rotor is. During implementation, balanced rotors have less vibration than unbalanced rotors, thereby leading to less probability of damage or error, larger lifespan, etc. 
     BRIEF SUMMARY 
     Methods, apparatus, systems, and articles of manufacture corresponding to trapped rotatable weights to improve rotor balance are disclosed. 
     Certain examples provide an example apparatus comprising a lock nut, a rotor assembly, a channel defined by the lock nut and the rotor assembly, the channel wrapped circumferentially around a geometric center of the rotor assembly, and a weight trapped within the channel. 
     Certain examples provide an example turbine engine comprising a shaft and a rotor coupled to the shaft, the rotor including a section defining a channel around a geometric center of the rotor, the channel including a weight trapped within the channel and movable within the channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an example gas turbine engine that can be utilized within an aircraft in which the examples disclosed herein can be implemented. 
         FIG. 2  is an example implementation of the rotor assembly of  FIG. 1  including trapped movable balance weights. 
         FIG. 3  is cross sectional view of the example implementation of the rotor assembly  FIG. 2 . 
     
    
    
     The figures are not to scale. Instead, the thickness of the layers or regions may be enlarged in the drawings. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. As used in this patent, stating that any part (e.g., a layer, film, area, region, or plate) is in any way on (e.g., positioned on, located on, disposed on, or formed on, etc.) another part, indicates that the referenced part is either in contact with the other part, or that the referenced part is above the other part with one or more intermediate part(s) located therebetween. Connection references (e.g., attached, coupled, connected, and joined) are to be construed broadly and may 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. Stating that any part is in “contact” with another part means that there is no intermediate part between the two parts. Although the figures show layers and regions with clean lines and boundaries, some or all of these lines and/or boundaries may be idealized. In reality, the boundaries and/or lines may be unobservable, blended, and/or irregular. 
     Descriptors “first,” “second,” “third,” etc. are used herein when identifying multiple elements or components which may be referred to separately. Unless otherwise specified or understood based on their context of use, such descriptors are not intended to impute any meaning of priority, physical order or arrangement in a list, or ordering in time but are merely used as labels for referring to multiple elements or components separately for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for ease of referencing multiple elements or components. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific examples that may be practiced. These examples are described in sufficient detail to enable one skilled in the art to practice the subject matter, and it is to be understood that other examples may be utilized. The following detailed description is therefore, provided to describe an exemplary implementation and not to be taken limiting on the scope of the subject matter described in this disclosure. Certain features from different aspects of the following description may be combined to form yet new aspects of the subject matter discussed below. 
     When introducing elements of various embodiments of the present disclosure, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
     As used herein, the terms “system,” “unit,” “module,” “engine,” “component,” etc., may include a hardware and/or software system that operates to perform one or more functions. For example, a module, unit, or system may include a computer processor, controller, and/or other logic-based device that performs operations based on instructions stored on a tangible and non-transitory computer readable storage medium, such as a computer memory. Alternatively, a module, unit, or system may include a hard-wires device that performs operations based on hard-wired logic of the device. Various modules, units, engines, and/or systems shown in the attached figures may represent the hardware that operates based on software or hardwired instructions, the software that directs hardware to perform the operations, or a combination thereof. 
     A turbine engine, also called a combustion turbine or a gas turbine, is a type of internal combustion engine. Turbine engines are commonly utilized in aircraft and power-generation applications. As used herein, the terms “asset,” “aircraft turbine engine,” “gas turbine,” “land-based turbine engine,” and “turbine engine” are used interchangeably. A basic operation of the turbine engine includes an intake of fresh atmospheric air flow through the front of the turbine engine with a rotor that includes fans. In some examples, the air flow travels through an intermediate-pressure compressor or a booster compressor located between the fan and a high-pressure compressor. The booster compressor is used to supercharge or boost the pressure of the air flow prior to the air flow entering the high-pressure compressor. The air flow can then travel through the high-pressure compressor that further pressurizes the air flow. The high-pressure compressor includes a group of blades (e.g., fans) attached to a shaft. The blades spin at high speed and subsequently compress the air flow. The high-pressure compressor then feeds the pressurized air flow to a combustion chamber. In some examples, the high-pressure compressor feeds the pressurized air flow at speeds of hundreds of miles per hour. In some instances, the combustion chamber includes one or more rings of fuel injectors that inject a steady stream of fuel into the combustion chamber, where the fuel mixes with the pressurized air flow. 
     In the combustion chamber of the turbine engine, the fuel is ignited with an electric spark provided by an igniter, where the fuel, in some examples, burns at temperatures of more than 2000 degrees Fahrenheit. The resulting combustion produces a high-temperature, high-pressure gas stream (e.g., hot combustion gas) that passes through another group of blades called a turbine. In some examples, a turbine includes an intricate array of alternating rotating rotors and stationary airfoil-section rotors. Alternatively, the turbine can be structured with adjacent rotating rotors or stationary airfoil section rotors, or in any combination of alternating or adjacent airfoil-section blades. As the hot combustion gas passes through the turbine, the hot combustion gas expands, causing rotating blades of the rotating rotors to spin. The rotating blades of the rotating rotors serve at least two purposes. A first purpose of the rotating blades is to drive the booster compressor and/or the high-pressure compressor to draw more pressured air into the combustion chamber. For example, the turbine is attached to the same shaft as the high-pressure compressor in a direct-drive configuration, thus, the spinning of the turbine causes the high-pressure compressor to spin. A second purpose of the rotating blades is to spin a generator operatively coupled to the turbine section to produce electricity. For example, the turbine can generate electricity to be used by an aircraft, a power station, etc. 
     In the example of an aircraft turbine engine, after passing through the turbine, the hot combustion gas exits the aircraft turbine engine through a nozzle at the back of the aircraft turbine engine. As the hot combustion gas exits the nozzle, the aircraft turbine engine and the corresponding aircraft coupled to the aircraft turbine engine are accelerated forward (e.g., thrusted forward). In the example of a land-based turbine engine, after passing through the turbine, the hot combustion gas is dissipated, used to generate steam, etc. 
     When the geometric center of a rotor and the center of mass of the rotor are not at the same point, the rotor is unbalanced. Unbalanced rotors create higher vibrations than balanced rotors (e.g., the more a rotor is unbalanced, the higher the vibrations that occur during rotation). Higher vibrations are undesirable as they lead to an increased likelihood of damage, increased energy consumption, decrease lifespan, and reduced efficiency. The more balanced a rotor is (e.g., the closer the center of mass is to the geometric center of the rotor), the lower the vibrations that occur while the rotor rotates (e.g., spins). During the manufacturing process, a technician performs a balancing test to identify how balanced the rotor is (e.g., where the center of mass is with respect to the geometric center). If the technician determines that the rotor is unbalanced by more than a threshold amount (e.g., the center of mass is more than a threshold distance away from the geometric center), the technician can add weights to different portions of the rotor, thereby adjusting the center of mass. The technician can then retest the balance of the rotor and add and/or subtract weight from the same or a different portion of the rotor until the balance of the rotor satisfies the balance threshold, thereby increasing the balance of the rotor to an acceptable level. The acceptable level and/or the balance threshold can be based on user, industry, manufacturers, and/or protocol standards. 
     Traditionally, the balance weights are installed after an initial rotor balance check but before installation of a rotor into the engine assembly. However, after the rotor is initially assembled, the center of mass can be moved during or after subsequent assembly procedures. Additionally, some traditional balance weights require removal of the rotor from the machine that tests the balance of the rotor to adjust, which is a tedious and time-consuming process. Examples disclosed herein provide a structure that facilitates balance weight adjustments after installation without disassembly of the rotor and/or other parts of a turbine engine by removal of the rotor, a locknut, and/or a tie bolt. 
     Traditional techniques for installing weights that can be adjusted after installation with minimal rotor disassembly include a housing including an open cavity that includes a slot wide enough so that a weight can be placed into the cavity. The slot can be structured so that the weight can only be put into the cavity when the weight is positioned at certain angles. In such traditional techniques, the weight includes a threaded insert through the weight so that a technician can secure the weight to housing with a screw or bolt. However, because the slot is big enough to allow the weight to enter the cavity, the weight can exit the cavity as well (e.g., if the screw or bolt that holds the balance weight in place breaks, fails, or becomes loose). Accordingly, if the screw or bolt fails to hold the weight in place, the weight can be projected out of the rotor and cause damage to the rotor and/or the rest of the turbine engine. Examples disclosed herein achieve rotor balance in a boltless rotor architecture, where a fixed number of weights are trapped (e.g., cannot be removed) in a channel (as referred to as annulus, slot, chamber, groove, cavity, etc.) corresponding to the rotor during installation (e.g., connecting the rotor to other parts via a lock nut and/or tie bolt). The trapped weights can be moved circumferentially within the channel (e.g., around the circumference of the geometric center of the rotor) to adjust the balance of the rotor (e.g., by moving the one or more weights, the center of mass of the rotor is moved). However, once the lock nut is installed, the balance weight cannot be removed from the rotor unless disassembled. Rather, the balance weight can only be rotated around the geometric center of the rotor to adjust the balance of the rotor. In some examples, the part of the rotor into which the weights are fixed in the cavity/channel can include tabs, slots, dimples, etc., to clock and/or lock the balance weight into a preset positions around the circumference of the rotor so that a balance weight can lock into positions corresponding to the tabs, slots, dimples, etc. Examples disclosed herein allow a rotor to be balanced before, during, and/or after installation of a rotor and/or within a balance test machine without disassembly of the rotor by removal of the rotor, a locknut, and/or a tie bolt. 
       FIG. 1  is a schematic illustration of an example gas turbine engine  102 . The example gas turbine engine  102  includes an example core gas turbine engine  106 , an example fan section  108 , an example outer casing  110 , an example annular inlet  112 , an example booster compressor  114 , an example high-pressure, multi-stage, axial-flow compressor  116 , an example combustor  118 , a first example turbine  120 , a first example drive shaft  122 , a second example turbine  124 , a second example drive shaft  126 , an example exhaust nozzle  128 , an example axial-flow fan rotor assembly  130 , an example annular fan casing  132 , example guide vanes  134 , example fan rotor blades  136 , an example downstream section  138 , an example airflow conduit  140 , an example speed reduction device  142 , an example inlet  150 , and example combustion products  158 . 
       FIG. 1  is a cross-sectional view of the engine  102  that can be utilized within an aircraft in accordance with aspects of the disclosed examples. The gas turbine engine  102  is shown having a longitudinal or axial centerline axis  104  extending throughout the gas turbine engine  102  for reference purposes. As used herein, the terms “axial” and “longitudinal” both refer to a direction parallel to the centerline axis  104 , while “radial” refers to a direction perpendicular to the axial direction, and “tangential” or “circumferential” refers to a direction mutually perpendicular to the axial and radial directions. As used herein, the terms “forward” or “front” refer to a location relatively upstream in an air flow passing through or around a component, and the terms “aft” or “rear” refer to a location relatively downstream in an air flow passing through or around a component. The direction of this flow is shown by an arrow  148  in  FIG. 1 . These directional terms are used merely for convenience in description and do not require a particular orientation of the structures described thereby. The example centerline axis  104  represents the geometric center of rotors (e.g., including the example rotor assembly  130 ). 
     The engine  102  of  FIG. 1  includes the core gas turbine engine  106  and the fan section  108  positioned upstream thereof. The core gas turbine engine  106  can generally include the substantially tubular outer casing  110  that defines an annular inlet  112 . In addition, the outer casing  110  can further enclose and support the booster compressor  114  for increasing the pressure of the air that enters the core gas turbine engine  106  to a first pressure level. The high-pressure, multi-stage, axial-flow compressor  116  can then receive the pressurized air from the booster compressor  114  and further increase the pressure of such air to a second pressure level. Alternatively, the high-pressure, multi-stage compressor  116  can be a high-pressure, multi-stage centrifugal compressor or a high-pressure, multi-stage axial-centrifugal compressor. 
     In the illustrated example of  FIG. 1 , the pressurized air exiting the high-pressure compressor  116  can then flow to the combustor  118  within which fuel is injected into the flow of pressurized air, with the resulting mixture being combusted within the combustor  118 . The high-energy combustion products are directed from the combustor  118  along the hot gas path of the engine  102  to the first (high-pressure) turbine  120  for driving the high-pressure compressor  116  via the first (high-pressure) drive shaft  122 , and then to the second (low-pressure) turbine  124  for driving the booster compressor  114  and fan section  108  via the second (low-pressure) drive shaft  126  that is generally coaxial with first drive shaft  122 . After driving each of the turbines  120  and  124 , the combustion products can be expelled from the core gas turbine engine  106  via the exhaust nozzle  128  to provide propulsive jet thrust. 
     In some examples, each of the compressors  114 ,  116  can include a plurality of compressor stages, with each stage including both an annular array of stationary compressor vanes and an annular array of rotating compressor blades (e.g., rotors that are part of the compressor) positioned immediately upstream of the compressor vanes. Similarly, each of the turbines  120 ,  124  can include a plurality of turbine stages, each stage including both an annular array of stationary nozzle vanes and an annular array of rotating turbine blades positioned immediately downstream of the nozzle vanes. 
     Additionally, as shown in  FIG. 1 , the fan section  108  of the engine  102  can generally include the rotatable, axial-flow fan rotor assembly  130  (e.g., also referred to as rotor) that is configured to be surrounded by the annular fan casing  132 . The fan casing  132  can be configured to be supported relative to the core gas turbine engine  106  by the plurality of substantially radially-extending, circumferentially-spaced outlet guide vanes  134 . As such, the fan casing  132  can enclose the fan rotor assembly  130  and its corresponding fan rotor blades  136 . Moreover, the downstream section  138  of the fan casing  132  can extend over an outer portion of the core gas turbine engine  106  to define the secondary, or by-pass, airflow conduit  140  that provides additional propulsive jet thrust. A detailed example of the fan rotor blades  136  is further described below in conjunction with  FIG. 2 . 
     In some examples, the second (low-pressure) drive shaft  126  is directly coupled to the fan rotor assembly  130  to provide a direct-drive configuration. Alternatively, the second drive shaft  126  can be coupled to the fan rotor assembly  130  via the speed reduction device  142  (e.g., a reduction gear or gearbox) to provide an indirect-drive or geared drive configuration. Such a speed reduction device(s) can also be provided between any other suitable shafts and/or spools within the engine  102  as desired or required. 
     During operation of the engine  102 , an initial air flow (indicated by arrow  148 ) can enter the engine  102  through the associated inlet  150  of the fan casing  132 . The air flow  148  then passes through the fan blades  136  and splits into a first compressed air flow (indicated by arrow  152 ) that moves through conduit  140  and a second compressed air flow (indicated by arrow  154 ) which enters the booster compressor  114 . The pressure of the second compressed air flow  154  is then increased and enters the high-pressure compressor  116  (as indicated by arrow  156 ). After mixing with fuel and being combusted within the combustor  118 , the combustion products  158  exit the combustor  118  and flow through the first turbine  120 . Thereafter, the combustion products  158  flow through the second turbine  124  and exit the exhaust nozzle  128  to provide thrust for the engine  102 . 
       FIG. 2  illustrates am implementation of the example rotor assembly  130  coupled to an example shaft  200  (also referred to as drive shaft). In the example of  FIG. 2 , the rotor assembly  130  includes the fan blades  136 , balance weight  202 , dimples  204 , and a channel  206  (e.g., annulus, slot, chamber, groove, cavity, etc.) arranged based on the structure of the drive shaft  200 , the lock nut  201 , and/or the rotor assembly  130 ). Although  FIG. 2  illustrates an example implementation including the balance weights  202  in conjunction with the rotor assembly  130  of  FIG. 1 , the balance weights  202  can be implemented in conjunction with different drive shafts and/or in different rotor types (e.g., the rotational rotors implemented in the compressor(s)  114 ,  116  and/or any other type of rotational rotor). 
     The drive shaft  200  of  FIG. 2  is coupled to the rotor assembly  130  via a tie-bolt. Since the drive shaft  200  is coupled to the rotor assembly  130  with the tie-bolt, when the drive shaft  200  rotates, the rotor assembly  130  (e.g., including the fan blades  136 ) also rotates. As described above, rotation of the fan blade  136  can drive the booster compressor and/or the high-pressure compressor to draw more pressured air into the combustion chamber and/or rotation of the fan blades  136  can spin a generator operatively coupled to the turbine section to produce electricity. The fan blades  136  radially extend outward from the geometric center of the rotor assembly  130 . 
     The balance weights  202  of  FIG. 2  are installed during manufacture of the turbine engine, for example. As explained above, the balance weights can be placed at different locations around the circumference of the rotor in the channel  206 . For example, during installation, the weights  202  are in place so that when the drive shaft  200  is attached to the rotor assembly  130  using a tie bolt, the channel  206  is created (e.g., based on the structure of the locknut  201  or other engageable receptacle and the rotor assembly  130  when installed) and the balance weights  202  are fixed into the channel  206  (e.g., sandwiched between (a) a wall of the lock nut  201  and (b) a wall of the rotor assembly  130 ). Alternatively, the channel  206  may be created when a rotor assembly  130  is attached to an engageable receptacle different than the lock nut  201 , such as a second rotor assembly (e.g., using a bolt, a tie bolt, and/or any other device to attach a first rotor to a second rotor) or other rotating component. In such an example, the alternative engageable receptacle includes a section that has a similar shape to the locknut  201  to create the structure of the channel  206 . The balance weights  202  have one end that is wider than the other end. The lock nut  201  and the rotor assembly  130  have a similar corresponding structure defining the channel  206  (e.g., with an edge at the upper portion of the respective lock nut  201  and the rotor assembly  130  so that the channel  206  has a bottom portion that is wider than the upper portion where a user can access the balance weight  202  to lock or move the balance weight  202 ). Such a structure defines the channel  206  so the balance weight  202  cannot be removed and/or fall out when the drive shaft  200  is connected to the rotor assembly  130  via a tie-bolt, as further illustrated below in conjunction with  FIG. 3 . The balanced weights  202  can be initially set to particular (e.g., equidistant) and/or random positions and adjusted based on the results of a balance test. After being set/secured in the channel  206 , the balance weight  202  can be rotated about the circumference of the channel  206  to allows a user to adjust the balance of the rotor assembly  130  while the rotor is in the balance machine and/or at any other point of manufacturer (e.g., including after the rotor assembly  130  is installed), without removing or disassembling a tie bolt and/or the locknut  201  by adjusting the position of the fixed balance weights  202 . The rotor assembly  130  can have any number of balance weights  202  positioned in the channel  206  based on user and/or manufacturer preferences. 
     The dimples  204  of  FIG. 2  are included in the rotor assembly  130  (e.g., at the base of the channel  206 ) to provide areas around the circumference of the channel  206  where the balance weights  202  can be secured (e.g., by guiding a setscrew of the balanced weight into a preset position, as further described below in conjunction with  FIG. 3 ). The dimples  204  can be spaced (e.g., equidistance, no equidistance, randomly, and/or a combination) around the circumference of the channel  206 . If a balance test identifies that the balance of the rotor is unbalanced (e.g., based on a threshold), a user and/or machine can rotate one or more of the balance weights  202  to different positions based on the location of the dimples  204  and re-secure the balance weights  202  into place for subsequent balance testing. The dimples  204  can alternatively and/or additionally be and/or include tabs, slots, etc., to facilitate clocking (e.g., securing into position) of the balance weights  202 . Although illustrated with a set number of dimples  204  at a set size and shape (e.g., circular), the example rotor assembly  130  can have any number of dimples  204  of any shape and/or size. In some examples, the dimples  204  can be removed and/or not included. The dimples  204  are further described below in conjunction with  FIG. 3 . 
     The channel  206  of  FIG. 2  allows the balance weights  202  to move (e.g., slide) circumferentially around the channel  206 , but prevents the balance weights from being removed from the channel  206  without detaching the lock nut  201  from the rotor assembly  130  (e.g., by detaching the tie-bolt that attaches the drive shaft  200  and/or lock nut  201  to the rotor assembly  130 ). The channel  206  is structured to be circumferentially wrapped around the geometric center of the rotor assembly  130  (e.g., corresponding to axis  104 ). For example, the channel  206  is a cavity whose path is a circle, an oval, a loop, etc. formed around the geometric center of the rotor assembly  130 . The walls of (a) the lock nut  201  and (b) the rotor assembly  130  are structured into a similar structure (e.g., defining the channel  206 ) as the balanced weight  202 . By circumferentially wrapping, the balanced weight  202  can rotate circumferentially around the rotor assembly  130  without being able to fall out of the channel  206 , as further described below in conjunction with  FIG. 3  Thus, the balance weights  202  can be moved to adjust the center of mass for the rotor assembly  130  to more closely align with the geometric center (e.g., the axis  104 ), without risk of breaking or falling off and causing damage. 
       FIG. 3  illustrates an example cross sectional view  300  of a portion of the balance weight  202  secured in the channel  206  between the lock nut  201  and a sidewall  304  of the rotor assembly  130 . The cross sectional view  300  includes part of the rotor assembly  130  of  FIG. 1 , the lock nut  201 , the balance weight  202 , the dimple  204 , and the channel  206  of  FIG. 2 , a tie rod  301  (as referred to as a tie bolt), a lock nut  201 , a sidewall  304 , and a set screw  306 . Although the example cross section view  300  is described in conjunction with the rotor assembly  130  of  FIG. 1 , the balance weights  202  can be implemented in conjunction with different drive shafts or other components and/or with different rotor types (e.g., the rotational rotors implemented in the compressor(s)  114 ,  116  and/or any other type of rotational rotor). 
     The channel  206  shown in the example of  FIG. 3  is defined by the lock nut  201  and the sidewall  304  of the rotor assembly  130 . However, as described above, the lock nut  201  may be replaced with a different engageable receptacle, such as a second rotor assembly or other rotating component including a section that has a similar shape to the lock nut  201  to define the channel  206 . The alternative engageable receptacle may be attached to the first rotor assembly using a bolt, the tie bolt  301 , and/or any other component to attach the second rotor assembly to the first rotor assemble  130 . The lock nut  201  is attached to the tie bolt  301  and the tie bolt  301  is attached to the drive shaft  200  and the rotor assembly  130 . As described above, the illustrated channel  206  incudes a wider base and a narrower top (e.g., the lock nut  201  and the sidewall  304  are structured to when the drive shaft  200  is coupled to the rotor assembly  130  via the tie bolt  301 , the channel  206  has the illustrated shape) corresponding to the structure of the balance weight  202 . The wider base and narrower top prevent the example balance weight  202  from being removed or projected out of the channel  206 , but the balance weight  202  can be moved circumferentially within the channel  206 . To secure the weight to a particular circumferential position around the base (e.g., the geometric center) of the rotor assembly  130 , the balance weight  202  includes the set screw  306 . A user and/or machine can rotate the set screw  306  to protrude the set screw toward the dimple  204  in the sidewall  304  of the rotor assembly  130  as part of the base of the channel  206 . After rotating the set screw  306  by more than a threshold amount, the set screw  306  comes into contact with the dimple  204  to secure the balance weight  202  to a circumferential position within the channel  206  corresponding to the position of the dimple  204 . The dimple  204  can guide the balance weight  202  into the preset position. Additionally, the dimple  204  of the sidewall  304  may be shaped to provide additional surface area for the set screw  306  to come in contact with (e.g., then would be available if the base of the channel was flat or did not have a dimple). The additional surface area provides additional static force that keeps the balance weight  202  into the set position while the rotor assembly  130  rotates. To move and/or change the balance weight  202  (e.g., to adjust the balance of the rotor assembly  130 ), the user and/or machine can rotate the set screw  306  in an opposite direction to move the set screw  306  away from the dimple  204  (e.g., loosen the set screw) to remove the contact with the dimple  204 . After the set screw  306  is loosened, the balance weight  202  can be moved and/or slid around the circumference of the channel  206  to another position. Because the balance weight  202  is installed when the drive shaft  200  is coupled to the rotor assembly  130  using the tie bolt  301 , balance adjustments can be made by circumferentially moving the balance weights  202  to different positions around the geometric center of the rotor via the channel  206  without removing the tie bolt  301 , the lock nut  201 , and/or the rotor assembly  130 . Although the balance weight  202  includes the set screw  306  to clock the balance weight  202  to a position corresponding to the dimple  204 , the balance weight  202  may include any mechanism to clock the weight balance to the position (e.g., a screw, a bolt, a wire, a spring, a device including a screw, a bolt, a wire, a spring, etc.). Although the example view  300  of  FIG. 3  includes the rotor assembly  130 , the lock nut  201 , the channel  206 , and the balance weight  202  structured to a particular size/shape, alternative sizes and/or shapes can be used so long as the balanced weight cannot be removed (e.g., but can be moved circumferentially around the geometric center of the rotor assembly  130 ) from the channel  206  after the lock nut  201  is set in place without removing or disassembling the lock nut  201  and/or a tie bolt  301 . 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc. may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, and (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, and (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” entity, as used herein, refers to one or more of that entity. The terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., a single unit or processor. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
     Further aspects of the invention are provided by the subject matter of the following clauses: 
     Example 1 includes an apparatus comprising an engageable receptacle, a rotor assembly, a channel defined by the engageable receptacle and the rotor assembly, the channel wrapped circumferentially around a geometric center of the rotor assembly, and a weight trapped within the channel. 
     Example 2 includes the apparatus of example 1, wherein the weight moves circumferentially within the channel around the geometric center of the rotor assembly. 
     Example 3 includes the apparatus of example 1, wherein the weight is not removable from the channel without disassembling the engageable receptacle. 
     Example 4 includes the apparatus of example 1, wherein the weight includes a set screw to lock the weight to a position within the channel. 
     Example 5 includes the apparatus of example 4, wherein the rotor assembly includes at least one of a dimple, a tab, or a slot at the position of the channel. 
     Example 6 includes the apparatus of example 1, wherein a position of the weight within the channel affects balance of the rotor assembly. 
     Example 7 includes the apparatus of example 1, wherein the weight can be moved within the channel after the engageable receptacle and the rotor assembly are connected via a tie bolt. 
     Example 8 includes the apparatus of example 1, wherein the weight has first end and a second end narrower than the first end. 
     Example 9 includes the apparatus of example 8, wherein the engageable receptacle and the rotor assembly are structured so that the channel has a third and a fourth end narrower than the third end. 
     Example 10 includes the apparatus of example 9, wherein the third end of the channel corresponds to the first end of the weight and the fourth end of the channel corresponds to the second end of the weight so that the weight cannot be removed from the channel. 
     Example 11 includes the apparatus of example 1, wherein the rotor assembly is a first rotor assembly, the engageable receptacle is at least one of a lock nut or a second rotor assembly. 
     Example 12 includes a turbine engine comprising a shaft, and a rotor coupled to the shaft, the rotor including a section defining a channel around a geometric center of the rotor, the channel including a weight trapped within the channel and movable within the channel. 
     Example 13 includes the turbine engine of example 12, wherein the rotor and the shaft are to rotate. 
     Example 14 includes the turbine engine of example 12, wherein the rotor is coupled to the shaft via at least one of a lock nut or a tie bolt. 
     Example 15 includes the turbine engine of example 14, wherein the lock nut further defines the channel. 
     Example 16 includes the turbine engine of example 14, wherein the weight is removable from the channel by disassembling the lock nut. 
     Example 17 includes the turbine engine of example 12, wherein the weight is circumferentially movable within the channel around the geometric center of the rotor. 
     Example 18 includes the turbine engine of example 12, wherein the weight includes a set screw to lock the weight to a position within the channel. 
     Example 19 includes the turbine engine of example 18, wherein the rotor includes at least one of a dimple, a tab, or a slot at the position of the channel. 
     Example 20 includes the turbine engine of example 12, wherein a position of the weight within the channel affects balance of the rotor. 
     Example 21 includes the turbine engine of example 12, wherein the weight is movable within the channel after the rotor and the shaft are connected. 
     Example 22 includes the turbine engine of example 12, wherein the rotor is a first rotor, further including a second rotor attached to the first rotor, the second rotor further defining the channel. 
     From the foregoing, it will be appreciated that example methods and apparatus have been disclosed that correspond to trapped rotatable weights to improve rotor balance. The disclosed trapped rotatable weights allow for the position of preinstalled weights to be adjusted (e.g., moved) circumferentially around the geometric center of a rotor to adjust the balance of the rotor to meet a balance threshold without disassembly of the rotor, a tie bolt, and/or a locknut during balance testing and/or after installation. Additionally, because the rotatable balance weights are trapped (e.g., fixed, secured, etc.) in a channel, even if a screw nut that secures the balance weight into place fails/breaks, there is no risk of the balance weight being projected out of the channel and causing damage to other components of the engine. 
     Although certain example methods, apparatus and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the claims of this patent. 
     The following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.