Patent Publication Number: US-2022235815-A1

Title: Eccentric bolt for attaching mission pod to aircraft

Description:
RELATED APPLICATIONS 
     This non-provisional patent application claims priority to U.S. Provisional Patent Application No. 63/141,437 filed on Jan. 25, 2021, which is incorporated by reference as if fully provided herein. 
    
    
     FIELD 
     The disclosure relates to the field of fasteners, and in particular, to an eccentric bolt. 
     BACKGROUND 
     Some aircraft, such as military aircraft, may be equipped with so-called mission pods that detachably secure to an external surface of the aircraft. The pods may house various components or payload that facilitate execution of various operations. For example, a pod may carry electronics for mission-specific communications or surveillance. It is generally beneficial for the pods to be easily swapped on the aircraft for mission adaptability. Additionally, it is beneficial for the pods to attach with different aircraft in a manner that is secure and aligned despite manufacturing tolerance differences among aircraft. 
     SUMMARY 
     Embodiments described herein use an eccentric bolt for attaching a mission pod to an aircraft. The eccentric bolt is inserted through a joint, such as a clevis and lug fitting, that attaches a mission pod with the external surface of the aircraft. Due to manufacturing tolerances of the aircraft, two joints of the aircraft for attaching a pod may be slightly misaligned. The eccentric bolt advantageously enables fine adjustment in one of the joints to correct or compensate for the misalignment between the aircraft and the pod mounting fittings. Moreover, the eccentric bolt facilitates quick, secure attachment of the mission pod to the aircraft in a compact size without drilling. 
     One embodiment is an eccentric bolt to secure a clevis and lug fitting. The eccentric bolt includes a head and a shank. The shank includes multiple shank sections that successively decrease in diameter in an axial direction from the head toward a tail end of the shank. One of the shank sections is an eccentric shank section that is off-center with respect to a center axis of the shank. The eccentric shank section is configured to engage the lug prior to engagement of concentric shank sections with the clevis. While the eccentric shank section is engaged with the lug, the shank is configured to rotate to align the concentric shank sections with the clevis, and to insert through the clevis and lug fitting to compensate for misalignment of the clevis and lug fitting. 
     A further embodiment is a method of attaching a first structure having a clevis to a second structure having a lug. The method includes positioning the lug between forks of the clevis to approximately align respective holes in an axial direction to form a clevis and lug fitting, and inserting an eccentric bolt partially through the clevis and lug fitting until an eccentric shank section of the eccentric bolt engages the lug. The method also includes rotating the eccentric bolt to compensate for horizontal misalignment of the clevis and lug fitting, and adjusting the clevis vertically to compensate for vertical misalignment of the clevis and lug fitting. The method further includes inserting the eccentric bolt further through the clevis and lug fitting to engage the clevis with the eccentric bolt and attach the first structure with the second structure. 
     A further embodiment is a method of attaching a mission pod with an aircraft. The method includes attaching a first end of the mission pod to the aircraft by installing a first straight bolt through a first joint, and attaching a second end of the mission pod to the aircraft by installing a second straight bolt through a second joint. The method also includes attaching the first end of the mission pod to the aircraft by installing an eccentric bolt through a third joint to compensate for misalignment between the first joint and the third joint. 
     Other example embodiments may be described below. The features, functions, and advantages that have been discussed can be achieved independently in various embodiments or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Some embodiments of the present disclosure are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
         FIG. 1A  is a front view of an aircraft. 
         FIG. 1B  is a front perspective view of the mission pod attached to an external body of the aircraft via one or more joints. 
         FIG. 2  is a perspective view of an eccentric bolt in an illustrative embodiment. 
         FIG. 3  is a side cross-sectional view of the eccentric bolt partially inserted through a clevis and lug fitting in an illustrative embodiment. 
         FIG. 4  is a flow chart illustrating a method of attaching a first structure having a clevis to a second structure having a lug in an illustrative embodiment. 
         FIG. 5  is a bottom view of a mission pod attached with an aircraft in an illustrative embodiment. 
         FIG. 6  is a flow chart illustrating a method of attaching a mission pod with an aircraft in an illustrative embodiment. 
         FIG. 7  is a graphical illustration of an example joint misalignment corrected by an eccentric bolt in an illustrative embodiment. 
     
    
    
     DESCRIPTION 
     The figures and the following description illustrate specific exemplary embodiments of the disclosure. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the disclosure and are included within the scope of the disclosure. Furthermore, any examples described herein are intended to aid in understanding the principles of the disclosure, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the disclosure is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
       FIG. 1A  is a front view of an aircraft  100 . The aircraft  100  includes a fuselage  102 , wings  104 , horizontal stabilizers  106 , and a vertical stabilizer  108 . A lower surface  120  of the fuselage  102  includes a mission pod  150  attached to its external surface. The mission pod  150  may house various components or payload that facilitate execution of various operations. For example, the mission pod  150  may carry weapons or electronics (e.g., communications or surveillance equipment) for mission-specific operations. The mission pod  150  is detachable from the aircraft  100  for mission adaptability. Although one attachment site is shown in  FIG. 1 , it will be appreciated that the aircraft  100  may include alternative or multiple attachment locations on aircraft  100  for swapping mission pods  150  on the external body of the aircraft  100 . 
       FIG. 1B  is a front perspective view of the mission pod  150  attached to an external body  122  of the aircraft  100  via one or more joints  160 . In particular, the joints  160  may comprise clevis and lug fittings. The clevis  162  is a component or structure of the mission pod  150  and includes a yoke structure, or forks, with a concentrically aligned pair of holes. The lug  164  is a component or structure of the aircraft  100  and includes a projecting piece with a hole that is configured to situate between the pair of holes of the clevis  162 . Thus, the mission pod  150  may be detachably coupled with the aircraft  100  by installing a bolt  166  through the aligned holes of the clevis  162  and lug  164 . In this example, a front end of the mission pod  150  is attached with two joints  160 , or two clevis and lug fittings, disposed at a left side and right side. 
     Unfortunately, manufacturing tolerances of the aircraft  100  may sometimes result in slight misalignment of left/right lugs  164 . Similarly, slight manufacturing variation of a mission pod  150  may introduce slight misalignment between left/right devises  162 . Accordingly, after coupling one clevis  162  and lug  164  via bolt  166  (e.g., at right side) to establish a joint axis  168 , the other clevis  162  and lug  164  (e.g., at left side) may be undesirably offset with respect to each other and the joint axis  168 . For this reason, joints  160  are sometimes match drilled or fitted with complex link assemblies. However, match drilling is time consuming and necessitates coordinated tooling and drilling that is not compatible with easily swapping mission pods  150 . Match drilling also eliminates interchangeability of mission pods since their attachment becomes limited to the aircraft and specific attachment location to which it has been match drilled. Link assemblies add complexity to installing and removing mission pods  150  and are only able to transmit loads in a single vector along the length of the link. 
       FIG. 2  is a perspective view of an eccentric bolt  200  in an illustrative embodiment. The eccentric bolt  200  is configured to install through a joint to correct misalignment. For example, with reference to  FIG. 1B , the eccentric bolt  200  may be installed through the clevis  162  and lug  164  (e.g., at left side) to correct misalignment therein after coupling clevis  162  and lug  164  via bolt  166  (e.g., at right side). As described in greater detail below, rotation of the eccentric bolt  200  as it is inserted through the joint  160  compensates for misalignment in the joint  160 . Advantageously, the eccentric bolt  200  facilitates quick, secure attachment of the mission pod  150  to the aircraft  100  in a compact size without drilling or complex link assemblies. Additionally, the eccentric bolt  200  is advantageously configured to react loads in multiple directions perpendicular to the axial direction of the eccentric bolt  200 . 
     The eccentric bolt  200  includes a head  202  and a shank  204 . The shank  204  includes multiple shank sections  221 - 224  that successively decrease in diameter in an axial direction from the head  202  toward a tail end of the shank  204 . One of the shank sections  221 - 224  is an eccentric shank section  222  that is eccentric with respect to a center axis  250  of the shank  204 . The eccentric shank section  222  has an axis of rotation  252  that is off center with respect to the center axis  250  of the shank  204 . Therefore, as the eccentric bolt  220  rotates around the center axis  250  an outer circumferential position of the eccentric shank section  222  changes with respect to the center axis  250 . 
     In one embodiment, the shank sections  221 - 224  include: an upper shank section  221  that is concentric and has a first diameter  231 , the eccentric shank section  222  that is eccentric and has as second diameter  232  smaller than the first diameter, a lower shank section that is concentric and has a third diameter  233  smaller than the second diameter, and a bottom shank section  224  that is concentric and has a fourth diameter  234  smaller than the third diameter  233 . Moreover, the eccentric shank section  222  and its second diameter  232  include different distances, d 1  and d 2 , from the center axis  250  of the shank  204  to its outer circumference. In other words, the eccentric shank section  222  includes an offset axis from the center axis  250 . Accordingly, the eccentric shank section  222  occupies a different offset area as the eccentric bolt  200  is rotated about the center axis  250 . Additionally, the shank  204  includes multiple ramps  241 - 243  to taper the diameter between adjacent ones of the shank sections  221 - 224 . The eccentric shank section  222  is thus configured to compensate for misalignment in a joint as described in greater detail below. 
       FIG. 3  is a side cross-sectional view of the eccentric bolt  200  partially inserted through a clevis and lug fitting  300  in an illustrative embodiment. The clevis and lug fitting  300  includes a clevis  302  and a lug  304 . In some embodiments, the clevis  302  is a component or structure of a mission pod (e.g., mission pod  150 ) and includes a yoke structure, or forks  312 , with a concentrically aligned pair of holes  314 - 315 . The pair of holes  314 - 315  extend through a respective pair of bushings  316 - 317  situated in the forks  312 , and the first hole  314  may be larger in diameter than the second hole  315 . The lug  304  may be a component of an aircraft at which an external structure (e.g., mission pod  150 ) is detachably coupled. The lug  304  may include a hole  322  that is configured to situate/align between the pair of holes  314 - 315  of the clevis  302  with a diameter that is a size between the diameters of the pair of holes  314 - 315 . The hole  322  may include a passage extending through a bearing  324 , such as a spherical ball bearing or plane bearing, of the lug  304  to prevent twisting forces acting upon the lug  304 . Generally, as described in greater detail below, the eccentric bolt  200  is configured to engage in a fit through the holes of the clevis and lug fitting  300  to compensate for misalignment. 
     In situations in which the clevis and lug fitting  300  includes slight misalignment due to manufacturing tolerances (e.g., the hole  316  of the lug  304  is misaligned with the pair of holes  314 - 315  of the clevis  302 ), a regular straight bolt may not correctly align/install unless on-site drilling is performed which typically slows and complicates installation. By contrast, the eccentric bolt  200  advantageously enables fine adjustment in the clevis and lug fitting  300  by rotating as the shank sections  221 - 224  engage corresponding areas of the clevis and lug fitting  300 . In particular, the upper shank section  221  is concentric and sized to correspond with a first hole  314  of the clevis  302 , the eccentric shank section  222  is eccentric and sized to correspond with the bearing  324  of the lug  304 , the lower shank section  223  is concentric and sized to correspond with the second hole  315  of the clevis  302 , and the bottom shank section  224  is concentric and may be threaded for securing a nut  330 . 
     As shown in  FIG. 3 , the shank sections  221 - 224  are sized such that the eccentric shank section  222  is configured to engage the bearing  320  of the lug  304  before the upper shank section  221  engages the first hole  314  of the clevis  302  and before the lower shank section  223  engages the second hole  315  of the clevis  302 . This advantageously provides a benefit in that, with the eccentric shank section  222  engaged before the upper shank section  221  and the lower shank section  223 , the eccentric shank section  222  is configured to secure a centerline of the lug  304  to enable vertical adjustment of the clevis  302  with respect to the lug  203 , and to enable rotation of the eccentric bolt  200  until the eccentric bolt  200  fits through the clevis and lug fitting  300  to compensate for the misalignment. 
     Additionally, the eccentric bolt  200  includes multiple ramps  241 - 243  configured to facilitate alignment of the eccentric bolt  200  with respect to the clevis and lug fitting  300  as the eccentric bolt  200  is partially inserted and rotated. One of the ramps  241 - 243  is an eccentric ramp  242  that tapers the diameter between the eccentric shank section  222  and the lower shank section  223 . As the eccentric bolt  200  is partially inserted through the clevis and lug fitting  300 , slight misalignment of holes of the clevis and lug fitting  300  may cause the eccentric shank section  222  to resist sliding through the lug  304 . The eccentric ramp  242  is configured to guide adjustment of the lug  304  with respect to the clevis  302  so that the eccentric shank section  222  slides into the lug  304 . This allows the eccentric bolt  200  to be partially inserted into the lug  304  and rotated to aid further insertion as increased alignment is achieved. The multiple ramps  241 - 243  are thus configured to start/improve the insertion of the eccentric bolt  200  and indicate which way to rotate the eccentric bolt  200  for self-alignment along with the vertical movement of a mission pod (and its clevis  302 ) to achieve alignment. 
     While the eccentric shank section  222  is engaged with the lug  304 , the shank  204  of the eccentric bolt  220  is configured to rotate to align the concentric shank sections  221  and  223  with the clevis  302 , and to insert through the clevis and lug fitting  300  to compensate for misalignment of the clevis and lug fitting  300 . The correctly aligned offset of the eccentric shank section  222  advantageously enables the installed eccentric bolt  200  to react forces in multiple directions (e.g., a vertical z direction and a horizontal x direction) perpendicular to the axial direction (e.g., y direction) of the eccentric bolt  200 . The eccentric bolt  200  thus facilitates quick, secure attachment of an external structure (e.g., mission pod  150 ) to an aircraft in a compact size without drilling. It will be appreciated, however, that the eccentric bolt  200  may be adapted or applied to alternative applications or types of joints. 
       FIG. 4  is a flow chart illustrating a method  400  of attaching a first structure having a clevis to a second structure having a lug in an illustrative embodiment. The steps of method  400  will be described with respect to the eccentric bolt  200  and clevis and lug fitting  300  of  FIGS. 2-3 , although one skilled in the art will understand that the methods described herein may be applied to alternative configurations of joints and bolts. The steps of the methods described herein are not all inclusive and may include other steps not shown. The steps for the flow charts shown herein may also be performed in an alternative order. 
     In step  402 , the lug  304  is positioned between forks  312  of the clevis  302  to approximately align respective holes (e.g., approximately align hole  322  with holes  314 - 315 ) in an axial direction to form a clevis and lug fitting  300 . As earlier described, in some embodiments, the clevis  302  belongs to the first structure or external structure such as a mission pod that is to be assembled or coupled with the lug  304  of a second structure such as an aircraft. 
     In step  404 , the eccentric bolt  200  is partially inserted through the clevis and lug fitting  300  until an eccentric shank section  222  of the eccentric bolt  200  engages the lug  304 . For example, in one embodiment, the eccentric bolt  200  is partially inserted through the clevis and lug fitting  300  until the eccentric ramp  242  engages the lug  304  and resists sliding through the lug  304  due to misalignment of the respective holes of the clevis  302  and the lug  304 . In optional step  406 , the lug  304  is engaged with the eccentric shank section  222  before engaging the clevis  302  with concentric shank sections (e.g., upper shank section  221  and lower shank section  223 ) of the eccentric bolt  200 . 
     In step  408 , the eccentric bolt  200  is rotated to compensate for horizontal misalignment of the clevis and lug fitting  300 . In step  410 , the clevis  302  is adjusted vertically to compensate for vertical misalignment of the clevis and lug fitting  300 . For example, the entire mission pod may be moved vertically as a rigid body including the clevis  302  to adjust vertical misalignment of the pod clevis and aircraft lug. In step  412 , the eccentric bolt  200  is inserted further through the clevis and lug fitting  300  to engage the clevis  302  with the eccentric bolt  200  and attach the first structure with the second structure. This enables optional step  414  of installing a keeper on the eccentric bolt  200  to prevent the eccentric bolt  200  from rotating, and optional step  416  of reacting loads with the eccentric bolt  200  in a vertical direction perpendicular to the axial direction of the eccentric bolt  200 , and also in a horizontal direction perpendicular to the axial direction of the eccentric bolt  200 . That is, a keeper positioned on the head  202  locks the eccentric bolt  200  in the aligned position so that load can be reacted instead of allowing the eccentric bolt  200  to rotate in the joint. Method  400  thus provides a benefit in enabling quick, secure attachment of the first structure to the second structure as compared to prior techniques. 
     In some embodiments, the eccentric bolt  200  may complete installation using an installation nut (e.g., nut  330 ). The bottom shank section  224  may include a threaded portion with increased length to sufficiently protrude through the second hole  315  of the clevis  302 , allowing a nut to engage the bottom shank section  224  and pull the eccentric bolt  200  through the clevis  302  on installation. For example, the eccentric bolt  200  may be rotated while slightly torquing the installation nut (and/or pushing the eccentric bolt  200 ) until the eccentric bolt  200  centers or slides onto/through the clevis  302 . This may continue until the eccentric bolt  200  is fully seated. In further embodiments, the eccentric bolt  200  may be prevented from rotating in the joint by installing a keeper on the head  202 . In yet another embodiment, the eccentric bolt  200  may include a hole drilled through the center axis  250  to be used in conjunction with a tool to remove the eccentric bolt  200  from the clevis  302  during decoupling. 
       FIG. 5  is a bottom view of a mission pod  502  attached with an aircraft  504  in an illustrative embodiment. In particular, the mission pod  502  is attached via installations  511 - 513 . Moreover, the installations  511 - 513  may be secured in order of their numerical element (e.g., installation  511  is secured first, installation  512  is secured second, etc.). For example, the installations  511 - 513  may include bolt installations installed in order. After the first installation  511  and the second installation  512  are secured, a line of rotation  520  is established that may cause a misaligned axis  522  between the first installation  511  and the third installation  513 . Accordingly, steps as further described in  FIG. 6  may be performed to correct the misalignment. After the eccentric bolt  200  is aligned and seated in the third installation  513 , a keeper  530  may be installed on the eccentric bolt  200  to hold the alignment and allow the third installation to react loads in multiple directions perpendicular to an axial direction of the eccentric bolt  200 . The keeper  530  may engage the head  202  of the eccentric bolt  200  prior to nut torque to aid installation of the eccentric bolt  200 . 
       FIG. 6  is a flow chart illustrating a method  600  of attaching a mission pod with an aircraft in an illustrative embodiment. The steps of method  600  will be described with respect to a mission pod and an aircraft, although one skilled in the art will understand that the methods described herein may be applied to one or more alternative structures to be coupled together. The steps of the methods described herein are not all inclusive and may include other steps not shown. The steps for the flow charts shown herein may also be performed in an alternative order. 
     In step  602 , a first end (e.g., back end) of the mission pod  502  is attached to the aircraft  504  by installing a first straight bolt through a first joint (e.g., first installation  511 ). In step  604 , a second end (e.g., forward end) of the mission pod  502  is attached to the aircraft  504  by installing a second straight bolt through a second joint (e.g., second installation  512 ). In step  606 , the first end of the mission pod  502  is attached to the aircraft  504  by installing the eccentric bolt  200  through a third joint (e.g., clevis and lug fitting  300 ) to compensate for misalignment between the first joint and the third joint. Step  606  may include, for example, the steps of method  400  earlier described. Accordingly, method  600  advantageously enables quick, secure attachment of a mission pod to an aircraft in a manner that compensates for the misaligned axis  522 . 
     EXAMPLES 
       FIG. 7  is a graphical illustration of an example joint misalignment corrected by an eccentric bolt  700  in an illustrative embodiment. Suppose, for this example, that the eccentric bolt  700  includes an offset  732  of 0.0300 inches. With reference to  FIG. 2  for example, the eccentric shank section  222  may include an axis of rotation  252  that is offset 0.0300 inches from the center axis  250 . Thus, by using the eccentric bolt  700  in a joint, one structure (e.g., mission pod  150 ) can be adjusted relative to the other structure (e.g., aircraft) by 0.0300 inches relative to a nominal lug location  734 . 
     Specifically, in this example, suppose that left/right lugs of an aircraft are misaligned by 0.0044 inches in an x-direction (e.g., forward/aft direction) and misaligned by 0.0130 inches in a z-direction (e.g., vertical direction). Since the eccentric bolt  700  may be configured, as earlier described, to engage/contact the lug bearing prior to engaging the clevis surfaces, the eccentric bolt  700  is able to rotate (e.g., to take out misalignment in the x-direction) while the pod is adjusted slightly up and down (e.g., to take out misalignment in the z-direction) until alignment is made. 
       FIG. 7  shows that there are two possible alignment positions to compensate for the misalignment and enable the joint to react loads in multiple directions (e.g., x-z directions) perpendicular to the axial direction (e.g., y-direction) of the eccentric bolt  700 . In a first alignment solution  701 , the pod is raised 0.0167 inches (i.e., 0.0297 inches−0.0130 inches=0.0167 inches). In a second alignment solution  702 , the pod is lowered 0.0427 inches (i.e., 0.0297 inches+0.0130 inches=0.0427 inches). In either case, the alignment is achieved by rotating the eccentric bolt  700  a corresponding amount and the overall height change of one corner of the pod (e.g., length of pod may be approximately 20 feet) is not significant. Thus, to compensate for misalignment in this case, the pod may either by raised 0.0167 inches or lowered 0.0426 inches and the tapered ramps of the eccentric bolt  700  aid in starting the eccentric bolt  700  for installing to the joint quickly, securely, and without drilling. 
     Although specific embodiments are described herein, the scope of the disclosure is not limited to those specific embodiments. The scope of the disclosure is defined by the following claims and any equivalents thereof.