Patent Publication Number: US-6905311-B2

Title: Fan blade assembly

Description:
FIELD OF THE INVENTION 
   The present invention relates to a fan blade assembly for a turbofan gas turbine engine, and relates in particular to the manner in which the fan blades are mounted in the fan rotor to prevent movement of the fan blades during windmilling of the fan blade assembly. 
   BACKGROUND OF THE INVENTION 
   The fan assembly of a turbofan gas turbine engine comprises a fan rotor having a plurality of generally axially extending slots in its periphery, which receive the root portions of the fan blades. The slots and fan blade root portions are of corresponding generally dovetail cross-section shape so as to ensure radial retention of the fan blades. 
   Our European patents EP0597586B1 and EP0690203B1 disclose a fan blade assembly of a turbofan gas turbine engine in which the fan blade root portions and the axially extending slots are provided with generally radially extending slots. The radially extending slots in each fan blade root portion are aligned with the radially extending slots in the corresponding axially extending slot in the periphery of the fan rotor. A U-shaped key is located in each of the sets of aligned radially extending slots to lock the fan blade root portions in position. Each key is provided with a spring to bias the key into the aligned radially extending slots and each key is moved against the spring and out of the radially aligned slots to allow the fan blade root portion to be moved axially for assembly or disassembly of the fan blades on the fan rotor. Locking means are provided in the axially extending slots between the fan blade root portions and the bottoms of the axially extending slots to lock the keys in position in the aligned radially extending slots. Additionally rubber pads are provided between the locking means and the bottoms of the axially extending slots to provide a tight, vibration free fit for the locking means and to prevent movement of the fan blades in the axial and tangential directions of the fan blade assembly during windmilling of the fan blade assembly. 
   In a variation of this arrangement springs are provided between the locking means and the bottoms of the fan blade root portions to provide a tight, vibration free fit for the locking means and to prevent movement of the fan blades during windmilling of the fan blade assembly. 
   The fan blade root portions and the springs between the locking means and the fan blade root portions are provided with wear resistant coatings to reduce wear or fretting. 
   These arrangements have proved satisfactory for turbofan gas turbine engines for fan blade assemblies with current sizes of fan blades. 
   There is a requirement for turbofan gas turbine engines with fan blade assemblies with larger, longer, and heavier fan blades. 
   However, the use of the existing arrangements is unsatisfactory because the forces required to prevent movement of the fan blades during windmilling of the fan blade assembly are too high to allow assembly and disassembly of the fan blades into the fan blade assembly and/or if the fan blades are assembled into the fan blade assembly the wear resistant coatings on the springs and fan blade root portions are rubbed off. 
   SUMMARY OF THE INVENTION 
   Accordingly the present invention seeks to provide a novel fan blade assembly, which reduces, preferably overcomes, the above-mentioned problems. 
   Accordingly the present invention provides a fan blade assembly comprising a fan rotor and a plurality of circumferentially spaced radially extending fan blades, the fan rotor having a plurality of circumferentially spaced axially extending slots in the periphery of the fan rotor, each of the fan blades having a root portion which locates in one of the plurality of axially extending slots in the periphery of the fan rotor, each axially extending slot having a respective one of a plurality of slider members, each slider member being locatable between the fan blade root portion and the bottom of the axially extending slot, each axially extending slot having a respective one of a plurality of biasing means, each biasing means being locatable between the fan blade root portion and the slider member, each axially extending slot having a respective one of a plurality of wedges, each wedge being locatable between the slider member and the biasing means, each wedge being movable axially between a first position in which the wedge moves the biasing means radially outwardly into engagement with the fan blade root portion to at least reduce vibration of the fan blade and a second position in which the wedge allows the biasing means to move radially inwardly to allow assembly or disassembly of the fan blade. 
   Preferably each wedge and respective slider member have guide means to guide the axial movement of the wedge. 
   Preferably the guide means comprises at least one slot in the slider member and at least one projection on the wedge. 
   Preferably the guide means comprises two parallel slots in the slider member and two projections on the wedge. 
   Preferably each wedge comprises a first surface at a first end of the wedge, a second surface at the second end of the wedge, the second surface is arranged parallel to the first surface and a third inclined surface connects the first flat surface and the second surface. 
   Preferably each slider member comprises an axially extending groove and each biasing means locates in the axially extending groove in the respective slider member. 
   Preferably each biasing means comprises a spring. 
   Preferably each spring comprises a leaf spring. 
   Preferably a first end of each slider member comprises a radial projection, which abuts against the fan rotor. 
   Preferably the first end of each wedge comprises a radial projection, which abuts against the first end of the respective slider member. 
   Preferably the first end of each wedge has means to allow the wedge to be removed from the fan blade assembly. 
   Preferably the first end of each slider member has means to allow the slider member to be removed from the fan blade assembly. 
   Preferably each of the fan blade root portions and its respective axially extending slot being provided with generally radially extending slots, each radially extending slot in the axially extending slot in the fan rotor being aligned with a corresponding radially extending slot in the fan blade root portion, key means being provided to locate in the aligned radially extending slots, biasing means being positioned to bias the key means into a first position in which it locates in the aligned radially extending slots to prevent relative axial movement between the fan blade root portions and the fan rotor from a second position in which the key means does not prevent such relative axial movement, whereby retention of the key means in second position permits axial assembly and disassembly of the each of the fan blade root portions and its corresponding axially extending slot in the periphery of the fan rotor, the slider member being provided to selectively lock each of the keys in the first position in the aligned radially extending slots. 
   Preferably the key means is of generally U-shaped configuration, the arms of the U-shaped key means locating in the aligned radially extending slots. 
   Preferably one of the biasing means is attached to each of the fan blade root portions to maintain the associated key means in position on the fan blade upon removal of the fan blade from the fan rotor. 
   Preferably the biasing means comprises a leaf spring. 
   Preferably the biasing means is formed from spring steel or rubber. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more fully described by way of example with reference to the accompanying drawings in which: 
       FIG. 1  shows a turbofan gas turbine engine having a fan assembly according to the present invention. 
       FIG. 2  is an enlarged cross-sectional view through the fan assembly according to the present invention shown in FIG.  1 . 
       FIG. 3  is an enlarged exploded view of the spring, wedge and slider member of the fan assembly according shown in FIG.  2 . 
       FIG. 4  is a further enlarged cross-sectional view of the spring, wedge and slider member of the fan assembly shown in  FIG. 2  showing the wedge in a first position. 
       FIG. 5  is a further enlarged cross-sectional view of the spring, wedge and slider member of the fan assembly shown in  FIG. 2  showing the wedge in a second position. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   A turbofan gas turbine engine  10 , as shown in  FIG. 1 , comprises an intake  12 , a fan section  14 , a compressor section  16 , a combustion section  18 , a turbine section  20  and an exhaust  22 . The fan section  14  comprises a fan blade assembly  24  and a fan casing  26  surrounding the fan blade assembly  24 . The fan blade assembly  24  comprises a fan rotor  28  and a plurality of circumferentially spaced radially outwardly extending fan blades  30  secured to the fan rotor  28 . The fan casing  26  defines a fan duct  32  and the fan casing  26  is secured to a core engine casing  34  by a plurality of circumferentially spaced radially extending fan outlet guide vanes  36 . 
   The fan blade assembly  24  is shown more clearly in figures  2 ,  3 ,  4  and  5 . The fan rotor  28  comprises a plurality of circumferentially spaced axially extending slots  40  in the periphery  38  of the fan rotor  28 . Each of the fan blades  30  comprises a root portion  42  and an aerofoil portion  44  and the aerofoil portion  44  has a leading edge  46  and a trailing edge  48 . 
   The root portion  42  of each fan blade  30  locates in one of the plurality of axially extending slots  40  in the periphery  38  of the fan rotor  28 . Each axially extending slot  40  has a respective one of a plurality of slider members  50  and each slider member  50  is locatable radially between the fan blade  30  root portion  42  and the bottom  41  of the respective axially extending slot  40 . Each axially extending slot  40  has a respective one of a plurality of biasing means  52  and each biasing means  52  is locatable radially between the fan blade  30  root portion  42  and the slider member  50 . Each axially extending slot  40  has a respective one of a plurality of wedges  54  and each wedge  54  is locatable radially between the respective slider member  50  and the respective biasing means  52 . Each wedge  54  is movable axially between a first position, as shown in  FIG. 4 , in which the wedge  54  moves the biasing means  52  radially outwardly into engagement with the fan blade  30  root portion  42  to at least reduce vibration of the fan blade  30  and a second position, as shown in  FIG. 5 , in which the wedge  54  allows the biasing means  52  to move racially inwardly to allow assembly or disassembly of the fan blade  30  into the slot  40  of the fan rotor  28 . 
   Each wedge  54 , as shown more clearly in  FIG. 3 , has a first end  62  and a second end  64  and each wedge  54  comprises a first flat surface  66  at a first end  62  of the wedge  54 , a second flat surface  68  at a second end  64  of the wedge  54  and a third inclined surface  70 . The second flat surface  68  is arranged parallel to the first flat surface  66  and the third inclined surface  70  connects the first flat surface  66  and the second flat surface  68 . The first end  62  of each wedge  54  has means to allow the wedge  54  to be removed from the fan blade assembly  24 . The means to allow the wedge  54  to be removed comprises an axially extending threaded aperture  86  in the first end  62  of the wedge  54 . The first end  62  of each wedge  54  comprises a radial projection  84 , which in use abuts against the first end  82  of the respective slider member  50 . 
   Each slider member  50 , as shown more clearly in  FIG. 3 , has a first end  72  and a second end  74  and each slider member  50  comprises an axially extending groove  76 , which extends from the first end  72  to the second end  74 . Each biasing means  52  locates in the axially extending groove  76  in the respective slider member  50 . The first end  72  of each slider member  50  comprises a radial projection, which in use abuts against the fan rotor  28 . The first end  72  of each slider member  50  has means to allow the slider member  50  to be removed from the fan blade assembly  24 . The means to allow the slider member  50  to be removed comprises an axially extending threaded aperture  88  in the first end  72  of the slider member  50 . 
   Each wedge  54  and respective slider member  50  have guide means to guide the axial movement of the wedge  54 . The guide means comprises at least one slot  58  in the slider member  50  and at least one projection  60  on the wedge  54 . In this particular arrangement the guide means comprises two parallel slots  58  in the slider member  50  and two parallel projections  60  on the wedge  54 . 
   Each biasing means  52 , as shown more clearly in  FIG. 3 , has a first end  78  and a second end  80 . Each biasing means  52  comprises a spring, preferably each spring comprises a leaf spring. 
   Each of the fan blade  30  root portions  42  and its respective axially extending slot  40  is provided with generally radially extending slots  90  and  92  respectively. Each radially extending slot  92  in the axially extending slot  40  in the fan rotor  28  is aligned with a corresponding radially extending slot  90  in the fan blade  30  root portion  42 . Key means  94  are provided to locate in the aligned radially extending slots  90  and  92 . Biasing means  96  are positioned to bias the key means  94  into a first position in which it locates in the aligned radially extending slots  90  and  92  to prevent relative axial movement between the fan blade  30  root portions  42  and the fan rotor  28  from a second position in which the key means  94  does not prevent such relative axial movement. Retention of the key means  94  in second position permits axial assembly and disassembly of the each of the fan blade  30  root portions  42  and its corresponding axially extending slot  40  in the periphery  38  of the fan rotor  28 . The slider members  50  are provided to selectively lock each of the keys means  94  in the first position in the aligned radially extending slots  90  and  92 . 
   The key means  94  is of generally U-shaped configuration and the arms of the U-shaped key means  94  locate in the aligned radially extending slots  92  and  94 . One of the biasing means  96  is attached to each of the fan blade  30  root portions  42  to maintain the associated key means  94  in position on the fan blade  30  upon removal of the fan blade  30  from the fan rotor  28 . The biasing means  94  comprises a metal leaf spring or a rubber band. 
   In order to install a fan blade  30  into the fan blade assembly  24 , the U-shaped key means  94  is pressed radially inwardly in the radially extending slots  90  against the biasing means  96  to a second position. The fan blade  30  root portion  42  is then slid/pushed axially along the axially extending slot  40  in the periphery  38  of the fan rotor  28  until the radially extending slots  90  and  92  on the fan blade  30  root portion  42  and fan rotor  28  slot  40  are aligned. The U-shaped key means  94  is then biased radially outwardly to a first position into the radially extending slots  92  in the axially extending slot  40  in the fan rotor  28  by the biasing means  96  to locate the fan blade  30  axially in position. 
   The biasing means  52  is positioned in the slot  76  in the slider member  50  and the second end  64  of the wedge  54  is positioned in the slot  76  in the slider member  50  radially between the first end  72  of the slider member  50  and the first end  78  of the biasing means  52  such that the radial projections  60  on the wedge  54  are inserted into the axially extending slots  58  in the slider member  50 . Additionally the first end  78  of the biasing means  52  is located on the second flat surface  68  of the wedge  54 , as shown in FIG.  5 . 
   The slider member  50 , biasing means  52  and wedge  54  are slid/pushed together axially along the axially extending slot  40  in the fan rotor  28  radially between the fan blade  30  root portion  42  and the bottom  31  of the axially extending slot  40  until the radial projection  82  on the slider member  50  abuts the upstream surface of the rotor member  28  as shown on FIG.  5 . The second end  74  of the slider member  50  locates radially between the fan blade  30  root portion  42  and the U-shaped key means  94  and the bottom  31  of the axially extending slot  40  of the fan rotor  28  to lock the U-shaped key means  94  in the first position. Additionally the biasing means  52  engages the fan blade  30  root portion  42  and the biasing means  52  becomes partially compressed. 
   The wedge  54  is slid/pushed axially along the axially extending slot  76  in the slider member  50  until the radial projection  84  on the first end  62  of the wedge  54  abuts the first end  72  of the slider member  50 . This axial movement of the wedge  54  causes the first end  78  of the biasing means  52  to move from the second flat surface  68  along the inclined surface  70  of the wedge  54  and on to the first flat surface  66  of the wedge  54  as shown in FIG.  4 . This causes the first end  78  of the biasing means  52  to move radially outwardly from a second position, the second flat surface  68 , in which the biasing means  52  is in engagement with the fan blade  30  root portion  42  but is only partially compressed, into a first position, the first flat surface  66 , in which the biasing means  52  is in engagement with the fan blade  30  root portion  42  and is fully compressed to at least reduce vibration of the fan blade  30  during windmilling, or slow speed operation of the turbofan gas turbine engine  10 . 
   In order to remove a fan blade  30  from the fan blade assembly  24 , the wedge  54  is pulled axially along the axially extending slot  76  in the slider member  50  until the radial projections  64  on the second end  62  of the wedge  54  abut the end of the slots  58  in the slider member  50 . The wedge  54  is pulled along the axially extending slot  76  using a threaded tool, which is inserted into the threaded aperture  86  in the first end  62  of the wedge  54 . This axial movement of the wedge  54  causes the first end  78  of the biasing means  52  to move from the first flat surface  66  along the inclined surface  70  of the wedge  54  and on to the second flat surface  68  of the wedge  54 . This causes the first end  78  of the biasing means  52  to move radially inwardly from the first position, the first flat surface  66 , in which the biasing means  52  is fully compressed and is in engagement with the fan blade  30  root portion  42  to the second position, the second flat surface  68 , in which the biasing means  52  is only partially compressed and is in engagement with the fan blade  30  root portion  42 . 
   The slider member  50 , biasing means  52  and wedge  54  are pulled together axially along the axially extending slot  40  in the fan rotor  28  radially between the fan blade  30  root portion  42  and the bottom  31  of the axially extending slot  40  until they are completely removed from the axially extending slot  40  in the fan rotor  28 . The slider member  50  is pulled along the axially extending slot  40  using a threaded tool, which is inserted into the threaded aperture  88  in the first end  72  of the slider member  50 . 
   The U-shaped key means  94  is pressed radially inwardly in the radially extending slots  90  and  92  against the biasing means  96  to a second position. The fan blade  30  root portion  42  is then slid/pushed/pulled axially along the axially extending slot  40  in the periphery  38  of the fan rotor  28  until the fan blade  30  root portion  42  is completely removed from the axially extending slot  40  in the fan rotor  28 . 
   The first and second flat surfaces  66  and  68  of the wedge  54  are substantially parallel. The first and second flat surfaces  66  and  68  are arranged substantially perpendicular to the radial direction so that in use there is no tendency for the biasing means  52  to push the wedge  54  out of the axially extending slot  76  in the slider member  50 . The third surface  70  of the wedge  54  is designed so that the biasing means  52  gradually moves up the third surface  70  without jamming. 
   The projections  60  on the second end  64  of the wedge  54  and the slots  58  in the slider member  50  are provided to ensure that the direction of movement of the wedge  54  is in line with the biasing means  52 . 
   Thus the slider member  50 , biasing means  52  and wedge  54  chock the fan blade  30  root portion  42  in the axially extending slot  40  of the fan rotor  28 . 
   The fan rotor  28  and the fan blades  30  are preferably formed from a suitable titanium alloy, for example 6 wt % vanadium, 4 wt % aluminium and the balance titanium plus incidental impurities. 
   Similarly slider member  50 , the biasing means  52  and the wedge  54  are preferably formed from a suitable titanium alloy, for example 6 wt % vanadium, 4 wt % aluminium and the balance titanium plus incidental impurities. 
   The surfaces of the fan blade root portion, the axially extending slot in the fan rotor, the biasing means and the slider member may be provided with wear resistant coatings to minimise wear of these components during operation of the turbofan gas turbine engine. 
   The advantage of the present invention is that the biasing means prevents rocking movement of the fan blades in the fan rotor slots in the axial and tangential directions of the fan blade assembly during low speed operation, windmilling, and enables the biasing means to be installed and removed from the fan blade assembly. Additionally if there are wear resistant coatings on the surfaces of the biasing means, slider member, fan blade root portion or axially extending slot of the fan rotor the present invention enables the biasing means to be installed and removed from the fan blade assembly without rubbing off the wear resistant coatings.