Abstract:
A method and an apparatus for carrying out the method for installing an especially dome-shaped pressure bulkhead on a one-piece, substantially conical rear section for an aircraft, wherein said rear section includes a connection area and an end area. The method involves the steps of horizontally accommodating a prefabricated rear section in a horizontal support; inserting the rear section into a pivoting frame; pivoting the rear section into a vertical position using the pivoting frame, wherein the connection area of the rear section points upward; horizontally placing and centering the pressure bulkhead on the connection area, and joining the pressure bulkhead with the rear section in the area of the connection area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of PCT/EP2009/057812 filed Jun. 23, 2009 and claims the benefit of U.S. Provisional Application No. 61/134,141, filed Jul. 7, 2008 and German Patent Application No. 10 2008 040 213.3, filed Jul. 7, 2008, the entire disclosures of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a method for assembling a dome-shaped pressure bulkhead on a one-piece, substantially conical tail section of an aircraft, the tail section having a connection region and an end region. 
     The invention also relates to a device for implementing the method. 
     Nowadays, tail sections of aircraft are usually produced with at least two shells. In order to achieve the required pressure tightness of the aircraft fuselage cell, the tail sections are closed rearwards by a pressure bulkhead which in most cases is dome-shaped. In conventional shell construction, the tail section to be produced is formed by successively adding tail section shells onto the pressure bulkhead which usually stands upright during assembly. Due to the circular addition of the shell segments to the connection region of the pressure bulkhead to produce the tail section, a tolerance compensation can easily be made to compensate for differences in dimensions, which are unavoidable in terms of manufacturing engineering, of the pressure bulkhead or of the connection region of the tail section. 
     To achieve further reductions in weight, composite materials, in particular CFRP materials, are used to an increasing extent in modern aircraft construction to produce the tail section and other fundamental structural components. In order to further increase the weight reduction potential of the core composite materials by reducing the number of connecting welds, the known shell construction method is no longer used in an increasing number of cases. Instead, for example, complete tail sections are produced in one piece from CFRP materials in the winding method or in a TFP laying process. 
     However, due to the one-piece formation of the tail section, a tolerance compensation, as usually occurred hitherto in the shell construction method, is no longer possible during the integration of a pressure bulkhead into a CFRP tail section. Furthermore, the installation of an upright pressure bulkhead becomes complex in terms of manufacturing engineering, as different working heights, inter alia, result as a function of the peripheral position on the fuselage section. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to provide a method which is simple in manufacturing engineering terms and which allows a pressure bulkhead to be integrated into a prefabricated, already cured, one-piece tail section for a pressure-tight aircraft fuselage cell with tolerance compensation. A further object of the invention is to provide a device for implementing the method. 
     This object is firstly achieved by a method which comprises the following steps:
     a) horizontally receiving a prefabricated tail section in a horizontal placement area,   b) introducing the tail section into a swivel frame,   c) swivelling the tail section using the swivel frame into a vertical position, with the connection region of the tail section pointing upwards,   d) horizontally positioning and centring the pressure bulkhead on the connection region, and   e) joining the pressure bulkhead to the tail section in the area of the connection region.   

     In step a), a prefabricated tail section is accommodated in a horizontal placement area (so-called cradle) in a pre-assembly station. This is preferably a tail section which is produced in one piece using a CFRP material and which forms the rear termination of the aircraft fuselage cell. While the tail section is held in the horizontal placement area, additional assembly operations can be carried out on the tail section, for example the attachment of metal fittings to connect the rudder units and/or the horizontal tail plane to the tail section. Holes required for this purpose are made very precisely using a suitable drilling means. The drilling means in the region of the pre-assembly station can be formed, for example using a known articulated robot having at least six degrees of freedom, the drilling tool being attached to the articulated arm thereof. Furthermore, it is conceivable for further working steps to be carried out on the tail section, for example pre-finishing operations with the necessary line systems or the like, because when the dome-shaped pressure bulkhead has been integrated it is difficult to access the interior of the tail section. The prefabricated tail section is brought into the horizontal placement area by a suitable lifting means, for example by an overhead crane. 
     In step b), the tail section prepared thus is introduced by the lifting means into a swivel frame inside a joining station. The swivel frame and thus the tail section are initially still in a horizontal position. Further drilling operations, for example, can be carried out in this horizontal position. To be mentioned in this connection is, for example, the very precise introduction of holes into the rudder unit metal fittings which were attached in step a). The drilling means inside the joining station is preferably configured as a gantry drilling means which is arranged displaceably above the swivel frame or alternatively below the swivel frame. The gantry drilling means is preferably guided on at least two mutually parallel rails and can be positioned with great accuracy. The gantry drilling means makes it possible to position a drilling tool with great accuracy in all three spatial directions. The tail section in the joining station is then brought into a vertical position by the swivel frame so that a connection region or a connection cross section of the tail section to which the pressure bulkhead is connected is directed upwards, while an end portion of the conical tail section usually with significantly smaller cross-sectional dimensions is directed downwards. The swivel frame can also be configured such that a rotation of the tail section about the longitudinal axis is also possible. 
     As a result of the horizontal assembly position of the pressure bulkhead, on the one hand the assembly process is simplified, since the working height is always independent of the respective peripheral position of the joining operations to be carried out on the tail section. Furthermore, an inherent deformation, caused by gravity, of the cross-sectional shape of the tail section is avoided and the pressure bulkhead which is preferably configured to be self-centring can easily be inserted and positioned in a “floating” manner inside the connection region of the tail section. 
     For later attachment of the pressure bulkhead, in step c) a transverse butt strap formed by at least two segments is firstly mounted in the connection region of the tail section, the tail section being in the vertical position. The transverse butt strap is preferably attached by riveting or screwing. Alternatively, any other joining methods can be used, for example welding, compression or adhesive bonding. 
     Only in step d) is the pressure bulkhead positioned and aligned in a substantially horizontal position on the connection region with the circumferential transverse butt strap, resulting in the advantages in terms of manufacturing engineering mentioned at the outset. To accelerate the processing times, at least portions of the pressure bulkhead were provided in a separate pressure bulkhead construction area with a circumferential edge angle for the later mechanical connection of the pressure bulkhead. The edge angle is formed by at least two interconnected edge angle segments corresponding to the annular former. The term “alignment” in this context means the placement or the centring of the pressure bulkhead with respect to the connection region of the tail section. 
     In step e), the pressure bulkhead is connected to the tail section in the connection region, likewise in a horizontal position. In this respect, an annular former which has been prefabricated in an annular former construction area is placed and positioned or aligned on the installed pressure bulkhead. 
     Finally, the connections which are still required between the annular former, the pressure bulkhead (edge angle) and the transverse butt strap are produced inside the connection region of the tail section by riveting, screwing, compression, adhesive bonding or the like, sealants simultaneously being introduced to produce a pressure-tight seal between the pressure bulkhead and the tail section. 
     An advantageous development of the method provides that after the tail section has been received in the horizontal placement area, at least one metal fitting, in particular a rudder unit metal fitting is attached to the tail section. 
     By this measure, the method makes it possible for the tail section to be fitted out with further structural components in addition to the mere integration of the pressure bulkhead. Structural components of this type are, for example, the rudder unit metal fittings, metal fittings for the connection of the tail plane to the tail section and attachment members for an alternative electrical energy supply unit of the aircraft inside the tail section (so-called “auxiliary power unit” or APU). Furthermore, lines for the necessary infrastructure of the aircraft, for example electrical lines, hydraulic lines, water and waste water lines as well as air conditioning and ventilation lines, can at least be pre-assembled. The pre-assembly of these components is advantageously carried out in this step, as it is easy to access the interior of the tail section in particular because the pressure bulkhead has still not been integrated at this stage. 
     A further embodiment of the method provides that the annular former required in the transverse weld region for attaching the pressure bulkhead is pre-assembled in an annular former construction area. 
     This annular former construction area can be disposed externally or alternatively can also be arranged inside the device used for implementing the method. An internal arrangement of the annular former construction area in particular provides a further increase in efficiency when the method is implemented, since a high temporal parallelisation of the production process is achieved at the same time as short transportation distances. The integration of the annular former is preferably concluded at the latest at the time when the fuselage section is transferred from the horizontal pre-assembly position in the horizontal placement area into the swivel frame inside the joining station and is sufficiently prepared for the integration of the pressure bulkhead. 
     The integration of the annular former inside the external or internal annular former construction area preferably also takes place in a horizontal position in a supporting device which allows a precise positioning, gauging and optionally also a tolerance compensation between the annular former segments to be joined together in order to achieve an optimum fitting accuracy relative to the connection region of the tail section, which makes any compensating measures unnecessary (so-called “shim”-free connection). 
     A further development provides that the pressure bulkhead is also pre-assembled in a pressure bulkhead construction area, in other words the edge of the pressure bulkhead is connected over the entire periphery to an edge angle composed of a plurality of edge angle segments. 
     This measure also provides a high temporal parallelisation of the method and thus a short processing time of the tail section up until the complete integration of the pressure bulkhead. During the attachment of the edge angle, the pressure bulkhead is in a horizontal position in a suitable supporting device corresponding to the annular former. 
     The object according to the invention is also achieved by a device comprising the following features:
     a) at least one pre-assembly area with at least one horizontal placement area as well as at least one joining station with at least one swivel frame,   b) at least one drilling means, in particular at least one gantry drilling means, and   c) at least one pressure bulkhead construction area.   

     A supplied tail section is initially mounted in the horizontal seat of the pre-assembly area so that fitting-out operations which may be required can be carried out. An example of this is the introduction of attachment holes for the rudder unit metal fittings or the tail plane metal fittings and the subsequent attachment of the metal fittings by riveting or screwing. For this purpose, the pre-assembly area has, for example, an articulated robot, a suitable drilling means being attached to the articulated arm thereof. Furthermore, a fully automatic riveting means can be provided inside the assembly area. 
     In addition thereto, the device has at least one joining station with a swivel frame in which the integration of the pressure bulkhead is completed. The joining station is also equipped with a high-precision drilling means which can be, for example, a parallel displaceable gantry drilling means. At the same time, the joining station preferably has a fully automatic riveting means. The gantry drilling means can introduce with great precision attachment holes, for example, into the rudder unit metal fittings and tail plane metal fittings which are attached inside the pre-assembly area. 
     Furthermore, the device has at least one pressure bulkhead construction area and at least one external or internal annular former construction area. Inside the pressure bulkhead construction area, an externally supplied pressure bulkhead is initially mounted horizontally in a suitable seat or cradle and then provided with a circumferential edge angle. At the same time, an annular former which is required for the attachment of the pressure bulkhead is integrated in the annular former construction area. The pressure bulkhead construction area can also have means for producing the pressure bulkhead using CFRP materials in the winding method or in the TFP laying process. The pre-assembly area, the pressure bulkhead construction area, the joining station as well as the annular former construction area can be equipped with combined automatic drilling and riveting machines as joining means. 
     The annular former construction area is preferably arranged outside the assembly line or the entire device, but in an alternative embodiment, it can also be provided inside the device (so-called internal annular former construction area). In the annular former construction area, the annular former is joined together with a plurality of annular former segments which are likewise received and mounted in a suitable horizontal seat. 
     During the operating sequence according to the method, the fuselage section is transferred by a suitable lifting means from the pre-assembly area into the swivel frame of the joining station. The lifting means which can be configured, for example, as a conventional overhead crane makes it possible to freely position the tail section spatially, the pre-assembly area, the joining station, the pressure bulkhead construction area and the annular former construction area being located inside the region covered by the lifting means. According to the invention, the swivel frame allows the fuselage section to swivel about a transverse axis into a vertical position to facilitate the assembly of the pressure bulkhead on the connection region of the tail section. Furthermore, the swivel frame can be configured such that it is also possible for the tail section to pivot about its longitudinal axis (i.e. parallel to the longitudinal axis of the aircraft). The device preferably has in each case at least three pre-assembly areas, three joining areas, three annular former construction areas and three pressure bulkhead construction areas in order to achieve a sufficiently short processing time by temporal parallelisation when the pressure bulkhead is integrated. However, the provision of only one lifting means and one gantry drilling means inside the entire assembly device is usually sufficient, whereas each pre-assembly area is preferably equipped at least with one automatic drilling and riveting means. 
     Further advantageous embodiments of the method and device are set out in the further claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a cross-sectional view through a connection region of a tail section with a further fuselage section added on, 
         FIG. 2  is a perspective view of a tail section with a pressure bulkhead, 
         FIG. 3  is a perspective view of a variant of a device, and 
         FIG. 4  is a side view of a joining station with a swivel frame arranged therein for mounting the tail section. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     In the drawings, like constructional components have like reference numerals in each case. 
       FIG. 1  is a sectional view through a connection region of a tail section with a further fuselage section added on. 
     A tail section  1  is provided with a circumferential transverse butt strap  2  which forms a connection region  3  for attaching a further fuselage section  4 . The connection region  3  can, in principle, have any curved shape which is optionally also locally variable, but is preferably at least circular, elliptic and/or oval in portions. A substantially dome-shaped pressure bulkhead  5  is provided with a circumferential edge angle  6 . The actual connection between the fuselage section  4  and the tail section  1  is formed by the transverse butt strap  2 . Positioned on the transverse butt strap  2  are the edge angle  6  of the pressure bulkhead  5  and an annular former  7  which, while cooperating, ensure the mechanical connection of the pressure bulkhead  5  in the connection region  3  of the tail section  1 . All the mentioned components are interconnected at least to some extent by a plurality of attachment elements, in particular rivets  8  or screws. 
       FIG. 2  is a perspective view of the tail section with the pressure bulkhead. To improve clarity, a quadrantal annular former segment has been omitted from  FIG. 2 . 
     The approximately dome-shaped pressure bulkhead  5  is mounted in the connection region  3  of the tail section  1 . The pressure bulkhead  5  is connected mechanically by the circumferential edge angle  6 , while the tail section  1  is coupled with the subsequent fuselage section  4  (not shown in  FIG. 2 ) by means of the transverse butt strap  2 . The connection region  3  of the tail section  1  has an approximately circular cross-sectional shape. A cross-sectional shape of the end region  9  of the tail section  1  is approximately the same as that of the (front) connection region, but in comparison has a significantly smaller cross-sectional area. Thus, a superficial shape of the tail section  1  approximately corresponds to that of a truncated cone or a cone. 
       FIG. 3  illustrates a first variant of a device for implementing the method according to the invention. 
     A device  10  comprises, inter alia, a pre-assembly area  11  with a horizontal placement area  12  for a tail section  13  in a horizontal position, a pressure bulkhead construction area  14  with a preferably combined drilling and riveting means  15  and a joining station  16  with a swivel frame  17  for receiving a further tail section  18  and a gantry drilling means  19 . A coordinate system  20  with an x-axis, a y-axis and a z-axis indicates the spatial position of all the components. 
     The gantry drilling means  19  is guided displaceably on two rails  21 ,  22  parallel to the x-axis of the coordinate system  20 . A preferably combined drilling and riveting means and/or screw tool  23  which is arranged on the gantry drilling means  19  can be freely positioned spatially parallel to all axes of the coordinate system  20 . Thus, the gantry drilling means can simultaneously also insert the rivets or optionally the connection screws in addition to making the holes required for the production of the riveted joint. 
     Rudder unit metal fittings  24 , for example, can be attached to the tail section  13  located in the pre-assembly area  11  by a further, preferably combined and fully automatic drilling and riveting means (not shown in  FIG. 3 ). Furthermore, tail plane metal fittings and/or attachment members for the additional energy supply (“auxiliary power unit”) can also be installed in the tail section  13 . It is also possible for all the electrical and hydraulic lines, including the necessary air conditioning, water and waste water lines for the required infrastructure of the aircraft, to be installed in the tail section  13 . As far as possible, all the pre-finishing operations are preferably carried out on the tail section  13  in the region of the pre-assembly area  11 , because access to the tail section  13  is greatly restricted after the pressure bulkhead has been assembled. During the pre-finishing procedure, the tail section  13  is in the illustrated horizontal position on the horizontal placement area  12  which can be adapted to different tail sections  13  of a large number of types of aircraft. 
     The pressure bulkhead  25  is preferably prepared for assembly in the pressure bulkhead construction area  14  at the same time as and in parallel with the pre-finishing of the tail section  13 . During the pre-assembly of the pressure bulkhead  25 , said pressure bulkhead is supported on a suitable support  26  in a horizontal position, i.e. substantially parallel to the xy-plane of the coordinate system  20 . The pressure bulkhead  25  is for example provided with a circumferential edge angle  27  formed by at least two segments, by means of the preferably likewise combined drilling and riveting means  15 . 
     The device  10  also has a buffer  28  with a further support  29  for feeding into the process of the method and temporarily storing a further, not yet prepared pressure bulkhead. Instead of the buffer  28  or also in addition thereto, for example an annular former construction area (not shown) can be provided in which an annular former which consists of a plurality of annular former segments and is usually provided in the connection region between a tail section  13  and a connection section is joined together with annular former couplings immediately inside the device  10 . This optional annular former construction area is also preferably equipped with a fully automatic, combined drilling and riveting means. A screw means can naturally also be provided instead of the riveting means. 
     The joining station  16  has, inter alia, a rack frame  30  which is provided with two working planes  31 ,  32  which preferably extend parallel to the xy-plane. At least the upper working plane  32  has two flaps  33 ,  34  with an approximately semi-circular cutout in each case to allow the tail section  18  to be introduced from above into the joining station  16 . For this purpose, the flaps  33 ,  34  can be folded upwards in the direction of the two arrows (not designated). An undesignated spacing between the working planes  31 ,  32  parallel to the z-axis of the coordinate system  20  is preferably dimensioned such that an employee can walk upright in this region. As an alternative to the variant of the device  10  shown in  FIG. 3 , the rails  21 ,  22  for guiding the gantry drilling means  19  can also be arranged in the region of the upper working plane  32  instead of being positioned on a base of the device  10 . Different spatial arrangements of the rails  21 ,  22  and of the gantry drilling means  19  or the combined gantry drilling and riveting means  23  are also possible. The flaps  33 ,  34  can be fitted with horizontally displaceable elements in order to ensure that the tail section  18  is embraced without any gaps. 
     The swivel frame  17  can swivel or tilt (transversely to the longitudinal axis of the tail section) the tail section  18  about a rotational axis extending parallel to the y-axis into the vertical position according to the invention for the integration of the pressure bulkhead. In this respect, a connection region  35  of the tail section  18  is directed upwards, while an end region of the tail section  18  is directed downwards. In the vertical assembly position, illustrated in  FIG. 3 , of the tail section  18  which has already been provided with a circumferential transverse butt strap  36 , the installation of the prepared pressure bulkhead  25  is completed. 
     The vertical assembly position of the tail section  18  for the integration of the pressure bulkhead  25  means that the operating sequences are simplified compared to the previous assembly method, since a working height between the connection region  35  and the upper working plane  32  is independent of the respective radial working position on the tail section  18 . Furthermore, gravity-induced changes in the cross-sectional shape of the connection region  35  of the tail section  18  are avoided and the pressure bulkhead  25  provided with the edge angle  27  can be “floated” into the connection region in a simple manner from above, i.e. parallel to the z-axis, by a lifting means (not shown) and aligned. The pressure bulkhead  25  is preferably configured such that when it is lowered by the lifting means, it is centred automatically in the connection region  35  of the tail section  18 , i.e. it is aligned into the final assembly position. 
     For installation, the pressure bulkhead  25  which has been prepared in the pressure bulkhead construction area  14  is transferred by the lifting means, which is preferably an overhead or indoor crane, from the pressure bulkhead construction area  14  to the joining station  16 , is aligned relative the tail section  18  and then lowered parallel to the z-axis. 
     Finally, an annular former is also transferred by the lifting means to the joining station  16  and is aligned in relation to the tail section  18  and lowered. Finally, the combined drilling and riveting tool  23  produces a plurality of holes and riveted joints between the edge angle  27  of the pressure bulkhead  25 , the transverse butt strap  36 , the annular former and the fuselage section to be attached in the connection region  35  to achieve the required connections. Alternatively, immediately after the prepared pressure bulkhead  25  has been aligned, an at least partial connection (fastening) by means of some rivet or screw connections between the transverse butt strap  36  and the edge angle  27  of the pressure bulkhead  25  can be carried out to fix the position. 
     The swivel frame  17  is accommodated such that it can pivot on a bearing bracket  37  inside the rack frame  30  of the joining station  16 . The swivel frame  17  can further be configured such that the tail section  18  is able to rotate about a longitudinal axis  38  of the tail section  18 . As a result of this optional rotation possibility, holes can for example also be made very precisely in tail plane metal fittings which are already on the tail section  18 . 
     After the pressure bulkhead  25  has been integrated into the connection region  35  of the tail section  18 , said tail section can be brought in turn into a horizontal position by the swivel frame  17 . In this position, holes can be drilled very precisely by the combined drilling and riveting means  23 , for example into the rudder unit metal fittings which are attached in the pre-assembly area  11 . Furthermore, additional finishing procedures can also be carried out on the tail section  18  in the joining station  16 . Alternatively, the metal fittings can be drilled before the pressure bulkhead  25  is integrated into the connection region  35  of the tail section  18 . 
     All the components, of the dome or pressure bulkhead assembly device described above, in particular the preferably combined drilling and riveting means  15 , the preferably combined drilling and riveting means  19  in the gantry mode of construction, the tool  23  of the gantry drilling means  19 , the lifting means and the swivel frame  17  in the joining station  16  are controlled by a complex control and regulating means (not shown in the drawings), so that a substantially operator-free, fully automatic, time- and cost-saving operation is possible. Instead of the gantry mode of construction of the drilling means  19 , it is also possible to use standardised articulated robots with at least six degrees of freedom to guide the drilling and riveting tools required inside the pressure bulkhead construction area  14  and the joining station  16 . 
       FIG. 4  illustrates a simplified side view of the joining station with the tail section accommodated in the swivel frame, the gantry drilling means having been omitted to improve the clarity of the drawing. The pressure bulkhead is installed according to the method in the vertical position of the tail section  18  shown in  FIG. 4 . 
     The rack frame  30  of the joining station  16  is formed by a plurality of vertical struts  39  which, with a plurality of horizontal struts  40 , serve as a support for the working planes  31 ,  32  and are latticed together for reinforcement purposes. Inside the rack frame  30 , the swivel frame  17  is mounted on the bearing bracket  37  and on a further concealed bearing bracket such that it can swivel about a rotational axis  41  which extends parallel to the y-axis of the coordinate system  20 . In addition, the swivel frame  17  advantageously also allows a complete rotation of the tail section  18  about the longitudinal axis  38 . In the illustrated position, the pressure bulkhead  25  (also not shown) is connected to the connection region  35  of the tail section  18 . 
     If the tail section  18  is swivelled to the right by approximately 90° about the x-axis, the rudder unit metal fittings  24  are easily accessible from above in an upper position, so that holes can be made with the required accuracy in the rudder unit metal fittings by the gantry drilling means  19  (not shown in  FIG. 4 ). By rotating the tail section  18  about the longitudinal axis  38  by an angle of ±90°, tail plane metal fittings which have already been attached to the sides of the tail section  18  can also optionally be brought into this drilling position and can be drilled very accurately by the gantry drilling means  19 . 
     LIST OF REFERENCE NUMERALS 
     
         
           1  tail section 
           2  transverse butt strap 
           3  connection region (tail section) 
           4  subsequent fuselage section 
           5  pressure bulkhead 
           6  edge angle (pressure bulkhead) 
           7  annular former 
           8  rivet 
           9  end region (tail section) 
           10  device 
           11  pre-assembly area 
           12  horizontal placement area 
           13  tail section 
           14  pressure bulkhead construction area 
           15  drilling and riveting means (pressure bulkhead construction area) 
           16  joining station 
           17  swivel frame 
           18  tail section 
           19  gantry drilling means 
           20  coordinate system 
           21  rail 
           22  rail 
           23  tool (gantry drilling means) 
           24  rudder unit metal fitting 
           25  pressure bulkhead 
           26  support (pressure bulkhead) 
           27  edge angle 
           28  buffer 
           29  support (pressure bulkhead) 
           30  rack frame 
           31  working plane (lower) 
           32  working plane (upper) 
           33  flap 
           34  flap 
           35  connection region (tail section) 
           36  transverse butt strap (tail section) 
           37  bearing bracket (swivel frame) 
           38  longitudinal axis (tail section) 
           39  vertical strut 
           40  horizontal strut 
           41  pivot axis (tail section)