Abstract:
A composite fan case includes a composite fan case body having an outer surface. A bolt attachment is attached to the outer surface of the fan case and has an internal composite boss with at least one threaded metallic insert. The boss is attached to the outer surface of the fan case with a combination of fiber reinforced ply and adhesive. A bolt attachment and a method of attaching components to the outer periphery of the composite fan case are also disclosed.

Description:
BACKGROUND 
     This application relates to creating threaded bolt holes in the outer periphery of a composite fan case for a gas turbine engine to provide mount locations for external components. 
     Gas turbine engines are known, and typically include a fan which delivers air toward a compressor. The air is compressed in the compressor, and passed downstream into a combustion chamber where it is mixed with fuel and burned. Products of this combustion pass downstream, driving turbine rotors to in turn drive a turbine shaft. 
     One recent development in turbine engines is a case for surrounding the fan rotor formed of a composite material, such as carbon epoxy. 
     While these fan cases have many desirable characteristics, one challenge is the components must be attached to the outer periphery of the case, typically through threaded fasteners. However, the material utilized to form the fan case has not been accommodating of bolt holes. 
     SUMMARY 
     A composite fan case includes a composite fan case body having an outer surface. A bolt attachment is attached to the outer surface of the fan case and has a composite boss with at least one threaded metallic insert. The boss is attached to the outer surface of the fan case using a combination of fiber reinforced ply and adhesive. 
     A bolt attachment and a method of attaching components to the outer periphery of the composite fan case are also disclosed. 
     These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  shows a gas turbine engine. 
         FIG. 1B  schematically shows a fan case according to the present invention. 
         FIG. 1C  shows a detail. 
         FIG. 2A  is a cross-sectional view through a connection as incorporated into this invention. 
         FIG. 2B  shows an insert. 
         FIG. 2C  is a view of a bolt attachment. 
         FIG. 3A  shows a first step in assembling the attachment. 
         FIG. 3B  is a cross-sectional view through the  FIG. 3A  structure. 
         FIG. 4  shows a subsequent step. 
         FIG. 5  shows another subsequent step. 
         FIG. 6  is a cross-sectional view through an assembly. 
     
    
    
     DETAILED DESCRIPTION 
     A gas turbine engine  10 , such as a turbofan gas turbine engine, circumferentially disposed about an engine centerline, or axial centerline axis  12  is shown in  FIG. 1A . The engine  10  includes a fan  14 , compressor sections  15  and  16 , a combustion section  18  and a turbine  19 . A fan case  20  surrounds the fan  14 . As is well known in the art, air from fan  14  is compressed in the compressor  15 / 16 , mixed with fuel and burned in the combustion section  18  and expanded in turbine  19 . The turbine  19  includes rotors  122  and  124 , which rotate in response to the expansion. The turbine  19  comprises alternating rows of rotary airfoils or blades  126  and static airfoils or vanes  128 . In fact, this view is quite schematic, and blades  126  and vanes  128  are actually removable. It should be understood that this view is included simply to provide a basic understanding of the sections in a gas turbine engine, and not to limit the invention. This invention extends to all types of turbine engines for all types of applications. 
     A composite fan case  20  is illustrated in  FIG. 1B . The fan case  20  is part of a gas turbine engine, and includes the fan rotor (see  FIG. 1A ) delivering air downstream towards the compressor. 
     Threaded bolt attachments  22  are mounted on the outer surface of the fan case  20 , in a manner to be described below. A component  24  is attached to the attachments  22 , such as through pins  26  mounted at a bracket  28 . The component  24  is shown as a holding bracket for a fluid tube. Any number of other components, and types of mountings may benefit from the present invention. The bracket  28  is threadably attached, such as by bolts  29  (see  FIG. 1C ), to the attachment  22 . 
       FIG. 2A  shows a detail of the attachment  22 , which includes a molded conical “bathtub” or boss which may be formed of a composite material  30 . Of course, the bathtub or boss may be any number of different shapes including rectangular, square, oval, etc. Metallic inserts  32  are embedded within the composite material  30 . A combination of fiberglass plies and adhesive  34  are attached to the outer surface of the composite material  30 . Another combination of adhesive and fiberglass plies is formed on an inner surface of the composite material  30 . This combination will be attached to the outer peripheral surface of the composite fan case  20 , as will be described below. While fiberglass plies are disclosed, it should be understood that other fiber reinforced plies, such as carbon fiber reinforced plies, would come within the scope of this invention. 
     The insert  32  has flat ends  40  and  42 , which will prevent rotation within the composite material  30 . The other ends  46  and  48  are generally conical. An extending cylindrical portion  44  extends upwardly to a hole  50 , which will receive a threaded insert, as will be explained below. Any number of other anti-rotation features can be utilized, such as any number of flat surfaces from one to any higher number. 
       FIG. 2C  shows that there are two of the inserts  32  received within the composite material  30 . The conical portion  46  faces a short circular end  54 , while the composite material  30  has elongated sides  56 . Flat ends  40  and  42  of insert  32  face these sides  56 . Of course, the invention extends to a single insert. 
     As shown in  FIG. 3A , in assembling the attachment  22 , the inserts  32  are initially inserted into openings  60  within pre-molded composite material  30 . They could additionally be molded within the material  30 . An adhesive may be placed on the metallic insert, to secure the metallic insert within the opening  60 . Weight reduction or strengthening opening  62  (see  FIG. 3B ) may be formed within the composite material  30 , as desired. 
       FIG. 4  shows a subsequent step, wherein an adhesive layer, plurality of fiberglass plies, and an outer adhesive  36  are all attached to the composite fan case  20  at a bottom of the composite material  30 . The upper combination includes plurality plies of fiberglass  34 , with an adhesive layer  36  attached to the outer surface of the composite material  30 . 
     Then, as shown in  FIG. 5 , the attachment  22  then has holes  80  drilled through the outer fiberglass and adhesive combination  34  to align with holes  50 , and which then receives inserts  82  which are threaded. 
     A helical insert or key-lock insert may be utilized as the inserts  82 . Examples of brand names would be Helicoil™ or Keensert™. Each of these inserts is threaded into the holes  50 . In fact, the holes  50  can be formed with threads to receive the inserts. The point of the insert is generally to provide a breaking point which will break away from the attachment  22  prior to the attachment  22  breaking away from the fan case  20 . 
     When the combined attachment  22  is placed on fan case  20 , it is then heated and the fiberglass and adhesive cures, forming to the outer surface of the fan case  20 , and is securely fastened. 
       FIG. 6  shows a cross-section, with the threaded insert  82  received within the insert  32 . Openings  62  are formed on each side of the insert  32 . As can be appreciated from  FIG. 6 , the upper combination  34  extends beyond the edges of the boss, such that there is an overlap area  100  where the upper combination and the lower combination are directly in contact. 
     In a sense, the upper ply combination captures the composite material  30  and the insert  32 , and holds it on the fan case. The underlying fiber reinforced ply and adhesive combination  38  holds the combination against the fan case. The areas beyond the material  30  where the upper and lower plies are in contact form a strong bond. 
     To attach the structure to the fan case, the plies, such as seen for example in  FIG. 2A , may be placed on the outer surface of a fan case. A vacuum may be applied, and the material heated, such as to about 250° F. (121° C.). An oven may be utilized to provide this heating. In this manner, the fiber reinforced plies and adhesive cure on the outer surface, and should not break away. 
     In embodiments, the upper adhesive  36  and fiberglass combination  34  includes three plies of fiberglass with a single ply of adhesive in contact with the boss. The lower adhesive and fiberglass combination  36  may include a ply of adhesive  26 , three plies of fiberglass  34 , and then a ply of adhesive  36 . Also, in embodiments, the boss composite material  30  may be injection molded plastic, SMC, or some other filled epoxy. Of course, other materials may be utilized, and other arrangements of the adhesive and fiberglass can also be utilized. 
     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.