STATEMENT OF GOVERNMENT RIGHTS 
   The U.S. Government may have rights in this invention pursuant to Contract Number N00010-02-C-3003 with the United States Navy. 


   BACKGROUND OF INVENTION 
   This invention relates to a damper for a stator vane of a gas turbine engine. Specifically, this invention relates to a damper for reducing vibration between a vane assembly and a seal secured to the vane assembly. 
   Gas turbine engines include alternating stages of rotating blades and stationary vanes. Each vane stage comprises a plurality of stator segments. A segment could include a plurality of vanes extending between an outer platform and an inner platform. Stator segments are commonly formed by casting or by brazing. 
   To relieve any build-up of stress caused by temperature gradients in the vanes and platforms during engine operation, the inner platform typically includes relief slits between adjacent vanes. These relief slits also help isolate vanes from vibration modes of adjacent vanes. The stator segment also includes a damper to reduce vibration amplitudes, thereby helping prevent vane cracking, The damper is typically formed into a spring by passing sheet metal through punch-press dies or forming rolls. 
   Conventional damper designs, however, have numerous drawbacks. First, conventional damper shapes can have asymmetric shapes that can apply unequalized damping forces to the mating surfaces on the stator assembly. Unequalized damping forces reduces the effectiveness of the damper. Second, conventional damper shapes require multiple passes through the punch-press dies or forming rolls. Multiple passes through the forming machines increases manufacturing costs. Third, the shape of conventional dampers (i.e. almost tubular) requires more material than is necessary for damping purposes. This additional material increases the weight of the engine. 
   SUMMARY OF INVENTION 
   It is an object of the present invention to provide an improved damper. 
   It is a further object of the present invention to provide a damper that balances damping forces on the mating surfaces of the stator assembly. 
   It is a further object of the present invention to provide a less complex damper. 
   It is a further object of the present invention to provide a damper that can be formed in a single pass through the forming equipment. 
   It is a further object of the present invention to provide a damper that can be formed in a single pass through the forming dies/rolls. 
   It is a further object of the present invention to produce a damper at reduced manufacturing costs. 
   These and other objects of the present invention are achieved in one aspect by a stator assembly, comprising: a stator segment; a seal mounted to said stator segment; and a damper between the stator segment and the seal. The damper has: a medial section; and opposed arms extending from the medial section. The medial section engages one of the stator segment and the seal and the opposed arms engage the other of the stator segment and the seal. 
   These and other objects of the present invention are achieved in another aspect by a damper for reducing vibration between a stator segment and a seal, comprising: a medial section for engaging one of the stator segment and the seal; and opposed arms extending from the medial section for engaging the other of the stator segment and the seal. 
   These and other objects of the present invention are achieved in another aspect by a method of making a damper for reducing vibration between a stator segment and a seal, comprising the steps of: providing a sheet of material having a medial section and opposed arms extending from the medial section; forming a bend at the medial section so that the medial section can engage one of the stator segment and the seal; and forming a bend at each of said arms so that the arms can engage the other of the stator segment and the seal. 


   
     BRIEF DESCRIPTION OF DRAWINGS 
     Other uses and advantages of the present invention will become apparent to those skilled in the art upon reference to the specification and the drawings, in which: 
       FIG. 1  is a perspective view of a conventional stator assembly; 
       FIG. 2  is a cross-sectional view of a section of a gas turbine engine using the stator assembly of  FIG. 1 ; 
       FIG. 3  is a perspective view of a damper from the stator assembly of  FIG. 1 ; 
       FIG. 4  is a cross-sectional view of a section of a gas turbine engine using another conventional stator assembly; 
       FIG. 5  is a perspective view of a damper from the stator assembly of  FIG. 4 ; 
       FIG. 6  is a cross-sectional view of a stator assembly in a gas turbine engine with one alternative embodiment of a damper of the present invention; 
       FIG. 7  is a perspective view of the damper of  FIG. 6 ; 
       FIG. 8  is a cross-sectional view of a stator assembly in a gas turbine engine with another embodiment of a damper of the present invention; and 
       FIG. 9  is a perspective view of the damper of  FIG. 8 . 
   


   DETAILED DESCRIPTION 
     FIGS. 1 and 2  display a conventional stator assembly  30  used in the compressor section of a gas turbine engine. The assembly  30  is a vane segment having a plurality of vanes  31  extending between a radially outer platform  33  and a radially inner platform  35 . The assembly  30  is typically made by a casting or a brazement. A plurality of relief slits  37  in the inner platform  35  help reduce the build-up of stress caused by temperature gradients in the vanes  31  and platforms  33 ,  35  during engine operation. 
   The inner platform  35  includes an upstream flange  39  and a downstream flange  41 . The flanges  39 ,  41  respectively include channels  43 ,  45  that accept an inner air seal  47 . The inner air seal  47  comprises the seal land of a labyrinth seal assembly. Labyrinth seals prevent fluid leakage between a stationary component (e.g. stator assembly  30 ) and a rotating component (e.g. the compressor rotor). 
   The seal land  47  includes an abradable material  49  (such as a metal honeycomb) mounted to a support plate  51 . Seal teeth T extend from the compressor rotor (not shown), face the abradable material and define a clearance therebetween. The clearance determines the effectiveness of the labyrinth seal. 
   The support plate  51  includes opposed feet  53 ,  55  that correspond to the channels  43 ,  45  in the inner platform  35 . When mounted together, the inner platform  35  and the inner air seal  47  define a cavity  57 . An arcuate damper  59  resides in the cavity  57 . An example of this damper  59  is part number 4319363 available from Pratt &amp; Whitney of East Hartford, Conn. 
     FIG. 3  is a detailed view of the damper  59 . The damper  59  includes opposed arms  61 ,  63  extending from a central section  65 . The damper  59  is formed from a sheet (not shown) of metal. At a first step, a forming die (not shown) folds the arms  61 ,  63  away from the central section  65 . At a second subsequent step, another forming die (not shown) bends the damper into an arcuate shape. 
   The damper  59  requires compression for placement within the cavity  57 . After insertion, this compression allows the damper  59  to provide the appropriate amount of loading to the inner platform  35  and the inner air seal  47  for reducing vibration. As seen in  FIG. 2 , the damper  59  contacts the inner platform  35  at two locations  67 ,  69 . Similarly, the damper  59  contacts the inner air seal  47  at two locations  71 ,  73 . 
   One drawback of this stator assembly  30  is the inability of the damper  59  to apply equal loading applied to the inner platform  35  at locations  67 ,  69 . Due to the shape of the flowpath for core flow through the engine, the cavity  57  has a wedge shape. As seen in  FIG. 2 , the cavity  57  enlarges in the downstream direction. This cavity shape requires the damper  59  to have an asymmetric shape. The asymmetric shape of the damper  59  produces unequal forces between the damper  59  and the corresponding mating surfaces of the inner platform  35 . Such unequal loading reduces the effectiveness of the damper  59 . For example, the unequal loading of the damper  59  produces a torsional deformation in the vane when the vane vibrates in the flexing mode (relative to the engine circumferential direction). Similarly, the unequal loading of the damper  59  produces a flexural deformation in the vane when the vane vibrates in a torsional mode. These deformations increase vane stresses. 
   Another drawback is the forming process that produces the damper  59 . When forming an asymmetric shape, the sheet metal tends to deform out of plane. The tooling used to form the damper  59  must compensate for this tendency. This complicates tooling design and increases manufacturing costs. Additional manufacturing costs occasionally occur should the damper  59  require straightening to correct such deformations. 
   Another drawback is the complex design of these dampers. Manufacturing tolerances prevent the manufacture of every damper to match the exact dimensions of every stator platform. To compensate for this possible mismatch and to allow the damper to comply evenly with the surfaces of the stator, the damper must have low stiffness in the circumferential direction. This helps reduce vibrational stresses equally over all vanes of the segment. Asymmetric dampers, however, introduce one additional level of complexity to this problem. Specifically, asymmetric dampers  57  exhibit different bending stiffness (in the circumferential direction) at the fore and aft contact points  67 ,  69 . 
     FIGS. 4 and 5  display another conventional stator assembly  90 . Similar to the aforementioned assembly  30 , the assembly  90  includes a plurality of vanes  91  extending between a radially outer platform (not shown) and a radially inner platform  93 . The inner platform  93  accepts an inner air seal  95 . 
   An arcuate damper  97  resides between the inner platform  93  and the inner air seal  95 . An example of this damper  97  is part number 55H401 available from Pratt &amp; Whitney of East Hartford, Conn. 
     FIG. 5  is a detailed view of the damper  97 . The damper  97  includes opposed arms  99 ,  101  extending from a central section  103 . The damper  97  is formed from a sheet of metal (not shown). At a first step, a forming die (not shown) folds the arms  99 ,  101  over the central section  103 . At a second subsequent step, another forming die (not shown) bends the damper into an arcuate shape. Slots  105  help reduce the bending stiffness of the damper  97 , which permits more even distribution of load into each of the individual vane platforms  35 . 
   The damper  97  requires compression for placement between the inner platform  93  and the inner air seal  95 . After insertion, this compression allows the damper  97  to provide the appropriate amount of loading to the inner platform  93  and inner air seal  95  for reducing vibration. As seen in  FIG. 4 , the damper  97  contacts the inner platform  93  at two locations  107 ,  109 . The damper  97  also contacts the inner air seal  95  at two locations  111 ,  113 . 
   Similar to the damper  57 , the damper  97  has several drawbacks. First, forming the damper  97  requires multiple passes through the tooling equipment. 
   Second, the damper  97  can function only in symmetric cavities. With symmetric cavities, dampers can provide equal damper loading to the contact points  107 ,  109 . In order to use the damper  97 , the designer would have to modify the asymmetric cavity with additional structure to create a symmetric cavity. This, however, introduces unnecessary weight and cost to the engine. 
     FIGS. 6 and 7  display one alternative embodiment of a stator assembly  150  of the present invention. The following description omits features of the stator assembly  150  previous described with respect to assemblies  30 ,  90  that are unnecessary for an understanding of the present invention. The stator assembly  150  of the present invention includes a plurality of vanes  151  extending between a radially outer platform  153  and a radially inner platform  155 . The assembly  150  is typically made by casting. 
   The inner platform  155  accepts an inner air seal  157 . The inner air seal  157  comprises the seal land portion of a labyrinth seal assembly. The other portion of the labyrinth seal comprises seal teeth T on a rotating component (e.g. the compressor rotor). The labyrinth seal prevents fluid leakage between the stator assembly  150  and the rotor. The clearance between the teeth T and the inner air seal  157  determines the effectiveness of the labyrinth seal. 
   When mounted together, the inner platform  155  and the inner air seal  157  define a cavity  159 . Due to the shape of the flowpath for core flow through the engine, the cavity  159  has a wedge shape. As seen in  FIG. 6 , the cavity  159  enlarges in the downstream direction. An arcuate damper  161  resides in the cavity  159 .  FIG. 7  provides a detailed view of the damper  161 . 
   The damper  161  includes opposed arms  163 ,  165  extending from a medial or central section  167 . Differently than with the aforementioned dampers  59 ,  97 , the damper  161  of the present invention can be formed in one pass through forming rolls (not shown) or a punch-press (not shown). The less complex shape of the damper  161  (compared to dampers  59 ,  97 ) allows formation in one pass. In other words, the single pass through the forming rolls/punch press creates bends  169 ,  171 ,  173  and creates the arcuate curve in the damper  161 . The forming rolls/punch press can also create slots  175  when forming the bends  169 ,  171 ,  173  and arcuate curve. Alternatively, the slots  175  could be provided to the sheet metal before passing through the forming rolls/punch press. 
   As with the earlier conventional dampers  59 ,  97 , the damper  161  requires compression for placement within the cavity  159  and to create the required load for vibration damping. Referring back to  FIG. 6 , the damper  161  contacts the inner platform  155  and the inner air seal  157  at three locations. These contact locations correspond to the bends  169 ,  171 ,  173 . Specifically, the damper  161  contacts the platform  155  at two points, the bends  169 ,  173  on the arms  163 ,  165 , and the seal  157  at one point, the bend  171  on the central section  167 . 
   Differently than with the earlier dampers  59 ,  97 , the damper  161  can better compensate for unequal loading applied to the inner platform  155  at bends  169 ,  173 . Should unequal loading exist on the arms  163 ,  165 , the damper  161  will, in response, roll along the mating surface of the inner air seal  157  at bend  171  of the central section  167 . The damper  161  will stop rolling along the bend  171  when the loading applied to the inner platform at bends  169 ,  173  equalizes. 
   As seen in  FIG. 7 , the damper  161  has an asymmetric shape to accommodate the tapered shape of the cavity  159 . The asymmetric design is more amenable to the adjustment of geometric attributes of the damper  161  to produce the desired loads against the platform  155 . This configuration also more readily accommodates variation in the cavity between the platform  155  and the seal  157  created during manufacture or by wear during engine operation. 
     FIGS. 8 and 9  display another alternative embodiment of the present invention, a stator assembly  190 . The stator assembly  190  of the present invention includes a plurality of vanes  191  extending between a radially outer platform  193  and a radially inner platform  195 . The assembly  190  is typically made by casting. 
   The inner platform  195  accepts an inner air seal  197 . The inner air seal  197  faces seal teeth T on a rotating component (e.g. the compressor rotor) to define a labyrinth seal. The clearance between the teeth T and the inner air seal  197  determines the effectiveness of the labyrinth seal. When mounted together, the inner platform  195  and in inner air seal  197  define a cavity  199 . As seen in  FIG. 8 , the cavity  199  has a uniform size. An arcuate damper  201  resides in the cavity  199 .  FIG. 9  provides a detailed view of the damper  201 . 
   The damper  201  has a different shape than damper  161  in order to function properly in cavity  199 . Comparing  FIGS. 6 and 8 , damper  201  is shallower (in the radial direction) than damper  161 . Damper  201  is shallower since the cavity  199  is shallower than cavity  159 . Since the cavity has a uniform size (i.e. no taper in the downstream direction), the damper  201  is symmetric. 
   The damper  201  includes opposed arms  203 ,  205  extending from a central section  207 . The damper  201  is formed from a sheet of metal (not shown) in the same manner as described above with damper  161 . The forming process creates bends  209 ,  211 ,  213  and creates the arcuate curve in the damper  201 . The forming process can also create slots  215  when forming the bends  169 ,  171 ,  173  and arcuate curve. Alternatively, the slots  215  could be provided to the sheet metal before passing through the forming rolls/punch press. The damper  201  also requires compression for placement within the cavity  199  and to create the required load for vibration damping. Referring back to  FIG. 8 , the damper  201  contacts the inner platform  195  and the inner air seal  197  at three locations. These contact locations correspond to the bends  209 ,  211 ,  213 . Specifically, the damper  201  contacts the platform  195  at two points, the bends  209 ,  213  on the arms  203 ,  205 , and the seal  197  at one point, the bend  211  on the central section  207 . 
   Differently than the aforementioned conventional dampers  59 ,  97 , the damper  201  can better compensate for unequal loading applied to the inner platform  195  at bends  209 ,  213 . Should unequal loading exist on the arms  203 ,  205 , the damper  201  will, in response, roll along the mating surface of the inner air seal  197  at bend  211  of the central section  207 . The damper  201  will stop rolling along the bend  211  when the loading applied to the inner platform at bends  209 ,  213  equalizes. 
   As described above, the dampers of the present invention contact the inner platform of the stator at two locations and the seal at one location. The widely, and equally, spaced (about the vane axis) contact points provide sufficient contact force to resist torsion of the vane. If, however, damping vane torsional vibrations is not the prime concern, the dampers could be designed in an opposite arrangement (not shown) so that the damper contacts the inner platform of the stator at one location and the seal at two locations. Such an arrangement is useful, for example, in instances where stress caused by inner air seal vibration may be the prime concern. 
   The present invention has been described in connection with the preferred embodiments of the various figures. It is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.
A damper for a stator assembly, the stator assembly comprising a stator segment and a seal mounted to the stator segment. The damper locates between the stator segment and the seal, and comprises: a medial section; and opposed arms extending from the medial section. The medial section engages one of the stator segment and the seal and the opposed arms engage the other of the stator segment and the seal. A method of making the damper, comprising the steps of: providing a sheet of material having a medial section and opposed arms extending from the medial section; forming a bend at the medial section so that the medial section can engage one of the stator segment and the seal; and forming a bend at each of the arms so that the arms can engage the other of the stator segment and the seal.