Abstract:
An airfoil includes, among other possible things, a main body extending between a leading edge and a trailing edge. Channels are formed into the main body, with a plurality of ribs extending intermediate the channels. A cover skin is attached to the main body. The cover skin is welded to the main body at outer edges. An adhesive is placed between inner surfaces of the cover skin and the main body. The adhesive is deposited inwardly of the outer edges of the cover skin.

Description:
BACKGROUND 
       [0001]    This application relates to a hollow fan blade construction and method of construction wherein a cover is welded to a main blade body, and wherein the cover is also attached to internal components by an adhesive. 
         [0002]    Gas turbine engines are known, and typically include a fan delivering air into a compressor section. The air is compressed in the compressor section, delivered into a combustion section, mixed with fuel and burned. Products of this combustion pass downstream over turbine rotors, driving the turbine rotors to rotate. 
         [0003]    The turbine rotors in turn drive the compressor rotors and the fan. One recent development in gas turbine engines is a so-called “geared” fan. A gear reduction is provided between a turbine spool driving a low pressure compressor and the fan. In this manner, the speed of the fan can be varied relative to the speed of the low pressure compressor. With such an arrangement, larger fan blades can be utilized. 
         [0004]    To reduce the weight associated with the larger fan blades, hollow aluminum fan blades arrangements have been proposed. These hollow blades typically have a number of hollow channels which may or may not include a light weight filler. A cover skin is typically adhesively bonded to the main body to enclose the hollow fan blade. 
       SUMMARY 
       [0005]    In a featured airfoil embodiment, a main body extends between a leading edge and a trailing edge. Channels are formed into the main body, with a plurality of ribs extending intermediate the channels. A cover skin is attached to the main body. The cover skin is welded to the main body at outer edges. An adhesive is positioned between inner surfaces of the cover skin and the main body, and the adhesive is deposited inwardly of outer edges of the cover skin. 
         [0006]    In another embodiment according to the foregoing embodiment, the main body defines a ledge having outer edges formed into the main body at at least one face. The cover skin sits on the ledge with the adhesive being deposited inwardly of the ledge such that the adhesive is not adjacent to the weld. 
         [0007]    In another embodiment according to any of the foregoing embodiments, the adhesive extends outwardly to inner extents of the ledge. 
         [0008]    In another embodiment according to prior embodiments, the adhesive is deposited inwardly of the inner extents of the ledge. 
         [0009]    In another embodiment, a material is positioned in at least one of the channels, with the adhesive being formed over at least portions of the material and portions of the ribs. 
         [0010]    In another embodiment, the cover skin has thicker edges such that when welded to the main body, the thicker edges provide strengthened regions. 
         [0011]    In another embodiment according to prior embodiments, the weld joint is provided by stir welding. 
         [0012]    In another embodiment, the channels extent into the main body to a closed end from an open end such that there is a single cover skin closing off the channels. 
         [0013]    In another embodiment, the airfoil is part of a fan blade having a dovetail with the airfoil extending radially outwardly from the dovetail. 
         [0014]    In another featured embodiment, a method of constructing a fan blade comprises the steps of providing adhesive on a main body extending between a leading edge and a trailing edge. Channels are formed into the main body and a plurality of ribs extend intermediate the channels. A cover skin is placed over the channels. The cover skin is welded to the main body, with the adhesive being provided such that it will be spaced inwardly of the location of a weld joint. 
         [0015]    In another embodiment according to the prior method, the main body defines a ledge having outer edges formed into the main body at at least one face, and the cover skins sits on the ledge. The adhesive is deposited inwardly of the ledge such that the adhesive is not adjacent to the weld. 
         [0016]    In another embodiment according to prior method embodiments, the adhesive extends outwardly to inner extents of the ledge. 
         [0017]    In another embodiment according to prior method embodiments, the adhesive is deposited inwardly of inner extents of the ledge. 
         [0018]    In another embodiment according to the method, the cover skin has thicker edges such that when welded to the main body the thicker edges provide strengthened regions. 
         [0019]    In another embodiment according to the method, the weld joint is formed by stir welding. 
         [0020]    In another featured embodiment, a gas turbine engine includes a fan section delivering air into a compressor section. Air is compressed by the compressor section and delivered into a combustor where it is mixed with fuel and combusted. Products of this combustion pass downstream over a turbine section. The fan section includes a plurality of fan blades, with each of the fan blades having a main body that extends between a leading edge and a trailing edge. Channels are formed into the main body, with a plurality of ribs extending intermediate the channels. The fan blade has a dovetail and an airfoil that extends radially outwardly from the dovetail. A cover skin is attached to the main body and closes off the channels. The cover skin is welded to the main body at outer edges. An adhesive is positioned between inner surfaces of the cover skin and the main body, and the adhesive is deposited inwardly of outer edges of the cover skin. 
         [0021]    In another embodiment, the main body defines a ledge having outer edges formed into the main body at at least one face. The cover skin sits on the ledge with the adhesive being deposited inwardly of the ledge such that the adhesive is not adjacent to the weld. 
         [0022]    In another embodiment according to any of the foregoing embodiments, the adhesive extends outwardly to inner extents of the ledge. 
         [0023]    In another embodiment according to prior embodiments, the adhesive is deposited inwardly of the inner extents of the ledge. 
         [0024]    In another embodiment, a material is positioned in at least one of the channels, with the adhesive being formed over at least portions of the material and portions of the ribs. 
         [0025]    In another embodiment, the cover skin has thicker edges such that when welded to the main body, the thicker edges provide strengthened regions. 
         [0026]    In another embodiment according to prior embodiments, the weld joint is provided by stir welding. 
         [0027]    In another embodiment, the channels extent into the main body to a closed end from an open end such that there is a single cover skin closing off the channels. 
         [0028]    These and other features of the invention would be better understood from the following specifications and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1A  shows a typical gas turbine engine. 
           [0030]      FIG. 1B  shows a fan blade according to this invention. 
           [0031]      FIG. 1C  is a view of a fan blade mounted in a fan rotor. 
           [0032]      FIG. 2  is a cross-sectional view along line  2 - 2  of  FIG. 1B . 
           [0033]      FIG. 3  shows the internal detail of the fan blade. 
           [0034]      FIG. 4  shows an assembled fan blade, with a cover attached. 
           [0035]      FIG. 5  shows an alternative to the  FIG. 4  adhesive arrangement. 
           [0036]      FIG. 6A  shows a first step in assembling the cover to the blade. 
           [0037]      FIG. 6B  shows a subsequent step. 
           [0038]      FIG. 6C  shows the final arrangement. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    A gas turbine engine  210  is shown in  FIG. 1A . As shown, the engine  210  includes a fan  250  (which includes a plurality of fan blades  20 ), a compressor section  254  (which includes both a low pressure compressor  256  and a high pressure compressor  258 ), a combustor  260 , and a turbine section  262  (which includes both a high pressure turbine  264  and a low pressure turbine  266 ). The fan  250  delivers air into compressor section  254 . Air compressed by the compressor section is delivered into combustor  260 . Products of the combustion in the combustor pass downstream over turbine section  262 . The high pressure compressor  258  is driven, via a first spool  268 , by the high pressure turbine  264 . The low pressure compressor  256  is driven, via a second spool  270 , by the low pressure turbine  266 . Also driven by the low pressure turbine  266  are the fan blades  20  of the fan  250 , which fan is coupled to the second spool  270  via a gear  272 . While an engine with two spools is shown, the application extends to three spool engines, and engines having alternative constructions. 
         [0040]    A fan blade  20  is illustrated in  FIG. 1B  having an airfoil  18  extending radially outwardly from a dovetail  24 . A leading edge  21  and a trailing edge  22  define the forward and rear limits of the airfoil  18 . 
         [0041]    As shown in  FIG. 1C , a fan rotor  16  receives the dovetail  24  to mount the fan blade with the airfoil  18  extending radially outwardly. As the rotor is driven to rotate, it carries the fan blade with it. There are higher stresses in fan blade  20  adjacent to the rotor  16  then occur radially outwardly. 
         [0042]      FIG. 2  shows a cross-section of the fan blade  20 , at the airfoil  18 . As shown, the leading edge  21  carries a sheath  37  secured to a main body  28 . A cover skin  32  closes off cavities or channels  30  in the main body  28 . The main body  28  and the skin  32  may all be formed of aluminum or various aluminum alloys. Other materials, such as titanium, titanium alloys or appropriate metals may alternatively be utilized. The sheath  37  is typically formed of a titanium alloy. 
         [0043]    In addition, while the fan blade is shown having one cover, and the channels  30  having a closed inner end  34 , it is also possible that the main body would provide a channel extending across its entire thickness, with covers at each side. 
         [0044]    As shown, a plurality of ribs  26  separate channels  30  in the cross-section illustrated in  FIG. 2 . As shown, filler material  100  may be deposited within the channels  30 . The filler material  100  would typically be of a lighter weight than the main body  28 . As one example, an aluminum foam may be used as material  100 . Other light weight filters, such as honeycomb material, or other materials, may be used. 
         [0045]      FIG. 3  shows the main body  28 . There are a plurality of channels  30  spaced from the front or leading edge  21  to the back or trailing edge  22 . As shown, some of the channels  30  extend generally radially upwardly. Other channels, such as channel  40 , bend toward the leading edge  21 . Channel  41  simply extends generally from the middle of the main body  28  toward the leading edge  21 . Channel  300  receives no material. Any or all of the channels may be left empty. 
         [0046]    As shown in  FIG. 3 , the main body  28  includes a ledge  400  defined by ledge edge  310 ,  312 ,  316  and  318 . Edges  310  and  312  are also shown in  FIG. 2  at the forward and rearward ends. As is clear, from  FIG. 2  the cover  32  sits on ledge  400  when assembled. As shown in  FIG. 3 , an outline  314  of adhesive is positioned laterally inwardly from the edges  310 ,  312 ,  316  and  318 . 
         [0047]    As shown in  FIG. 4 , when the cover skin  32  is assembled on the main body  28 , it sits adjacent ends of ledge  400 . Then, friction stir welding as shown at  320  is provided along the entire periphery of the cover  32  to secure the cover to the main body. 
         [0048]    Since the adhesive is positioned inwardly from edges  310 ,  312 ,  316  and  318 , the adhesive will not move into the area adjacent to the friction stir weld  320 , where it might reduce the weld quality. 
         [0049]      FIG. 5  shows an alternative wherein there is a greater area of adhesive  321 , with the adhesive moving generally outwardly to an outline  323  that fills all of the area inwardly of ledge  400 . If the adhesive has been positioned such that it extends on to the ledge  400 , it can be removed prior to welding of the cover. In addition, a worker in this art should recognize that when placing cover  32  onto the main body  18 , it is possible that adhesive will be squeezed outwardly, and this should be taken into account when designing the coverage area of the adhesive. 
         [0050]    As a further alternative, a braze material could be deposited along the inner edges of the ledge to block adhesive. In addition, the braze material can be selected such that it will melt at temperatures below that of the welding such that the braze material will assist in forming a stronger bond between the cover and the main body. 
         [0051]    While an embodiment is shown having a single cover, and with the channels  30  having closed back ends  34 , this application would also extend to a main body having covers at each of the two sides, with the channels extending through the entire width of the blade. 
         [0052]      FIG. 6A  shows an alternative embodiment the cover skin  432  as initially placed on the main body  28 . As shown at the edge  312 , there is an enlarged portion  322 , which is thicker than the nominal portions of the cover skin  432 . 
         [0053]      FIG. 6B  shows the application of the friction stir weld through a tool  360 . As shown in  FIG. 6C , after this operation, the material from the main body  28  and the enlarged portion  322  have generally intermixed. That is, the thicker area provides a stronger cross-section, or strengthened regions, and will result in less stress at this combined area  350 . 
         [0054]    While a fan blade is specifically disclosed, it should be understood that aspects of this disclosure would extend to any number of other type of airfoils. 
         [0055]    Although embodiments of this invention have been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.