Patent Publication Number: US-8524025-B2

Title: One-piece inner shell for full barrel composite fuselage

Description:
RELATED APPLICATION 
     This application is a continuation of, and claims priority to application Ser. No. 13/347,391, filed Jan. 10, 2012, which is a divisional application of, and claims priority to, application Ser. No. 12/258,138, filed Oct. 24, 2008, now U.S. Pat. No. 8,091,603, which is a divisional application of, and claims priority to, application Ser. No. 11/343,701, filed Jan. 31, 2006, now U.S. Pat. No. 7,459,048, all of which are incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     This application relates generally to a one-piece inner shell for full-barrel composite fuselage manufacture, and, more particularly to a mandrel assembly providing for the manufacture of a unitary seamless section of an aircraft fuselage. 
     BACKGROUND 
     Composite structures are highly prized for their ability to combine high strength and design flexibility with resultant reduced weight structures. As such, in many fields they dominate the manufacturing landscape. Despite their popularity, or perhaps as a result of it, composite lay-up structures have generated a host of new manufacturing challenges. These challenges often stem from attempts to apply the composite design methodologies to complex structures. Large-scale structures such as aircraft fuselage structures provide considerable challenges to composite lay-up manufacturing. 
     Present composite lay-up fuselage methodologies approach fuselage manufacturing through the use of multi-piece sections requiring longitudinal splices between individual sections. This generates an increase in weight and cost of the resultant product. In addition, the tooling is often comprised of multi-sectional tooling that requires seals between tooling sections. These seals may be prone to leakage and may fail to provide the vacuum integrity needed for an autoclave curing procedure. This further complicates and diminishes fuselage lay-up manufacturing. An apparatus and method for laying up a single-piece fuselage section that eliminated the need for seals and had improved vacuum integrity during autoclave procedures would allow for a reduction in weight and cost of both tooling as well as the finalized fuselage section. 
     It would, therefore, be highly desirable to provide a one-piece fuselage mandrel capable of laying up a fuselage section without the need for seals. Similarly, it would be highly desirable to have a methodology for manufacturing a unitary seamless section of an aircraft fuselage. 
     SUMMARY 
     A mandrel is disclosed for use in manufacturing a unitary seamless section of an aircraft fuselage comprising a one-piece inner mandrel shell having an outer shell surface and a thin lay-up mandrel element disposable onto the outer shell surface to form a mandrel with a substantially continuous lay-up surface. When a plurality of resin impregnated skin fibers is layed-up onto the lay-up surface, a unitary pre-cured section of an aircraft fuselage is formed. 
     In a preferred embodiment, the thin lay-up mandrel comprises a plurality of caul plates disposable onto said outer shell surface to form a mandrel with a lay-up surface. The caul plates may be arranged longitudinally parallel to the longitudinal axis of said one-piece inner mandrel shell and comprise a plurality of longitudinal stiffener channels formed into a caul outer surface. A plurality of resin impregnated stiffener fibers are disposable within said plurality of stiffener channels such that top ends of said stiffener fibers form a flush mandrel surface. When a plurality of resin impregnated skin fibers are laid up onto said lay-up surface, a unitary pre-cured section of an aircraft fuselage is formed. In a further embodiment, the caul plates may be abutted end to end around the outer shell surface to form the lay-up surface. 
     Thus, a one-piece fuselage mandrel capable of laying up a fuselage section without the need for seals is provided. Other features will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a unitary seamless section of aircraft fuselage in accordance with a number of embodiments; 
         FIG. 2  is an illustration of a mandrel for use in manufacturing the unitary seamless section of aircraft fuselage illustrated in  FIG. 1 , the mandrel illustrated with only a partial amount of the thin lay-up mandrel element installed; 
         FIG. 3  is an illustration of a mandrel for use in manufacturing the unitary seamless section of aircraft fuselage illustrated in  FIG. 1 , the mandrel illustrated with the entire thin lay-up mandrel element installed; 
         FIG. 4A  is an illustration of the mandrel assembly from  FIG. 3  in operation wherein a plurality of stiffeners are being laid-up; 
         FIG. 4B  is a detailed illustration of a portion of the mandrel assembly illustrated in  FIG. 4A ; 
         FIG. 5  is an illustration of the mandrel assembly from  FIG. 4  in operation wherein a plurality of resin impregnated skin fibers are being laid-up; 
         FIG. 6  is an illustration of the mandrel assembly from  FIG. 5  in operation wherein the mandrel and lay-ups are vacuum bagged and cured; 
         FIG. 7  is an illustration of an alternate embodiment of the mandrel assembly illustrated in the preceding figures, the embodiment including a first and second support ring mounted to the thin lay-up mandrel element; 
         FIG. 8  is an illustration of a plurality of methods of removing the inner mandrel shell from out of the thin lay-up mandrel element illustrated in  FIG. 7 ; 
         FIG. 9  is a detailed illustration of a portion of the thin mandrel shell and thin lay-up mandrel illustrated in  FIG. 8 ; 
         FIG. 10  is an illustration of an alternate feature of the mandrel assembly illustrated in the preceding figures, the embodiment illustrating a complemented tapered inner mandrel shell and tapered thin lay-up mandrel element; and 
         FIG. 11  is a detailed illustration of the tapers described and illustrated in  FIG. 10 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
       FIG. 1  is an illustration of a unitary seamless composite section of aircraft fuselage  10  in accordance with a number of embodiments. It is contemplated that a “section” of an aircraft fuselage is defined as a generally tubular section or barrel of the fuselage, particularly one that is made from a composite. A plurality of such sections  10  may be attachable end to end to form a longer barrel or section of the fuselage. It is intended that the term “unitary” is defined as a one-piece continuous, contiguous, seamless section of fuselage. The unitary seamless section of aircraft fuselage  10  is comprised of a fuselage skin  12  and a plurality of fuselage stiffeners  14  formed on the inner surface of the fuselage skin  12 . 
     The section of fuselage  10  is formed in a novel and unique methodology. In a number of embodiments, the method utilizes a one-piece cylindrical inner mandrel shell  20  ( FIG. 2 ) rotatable about a mandrel axis  22  ( FIG. 4A ), which provides a hard, continuous surface that prevents leaks during the curing process. The one-piece generally cylindrical inner mandrel shell  20  includes an outer shell surface  24  to which a thin lay-up mandrel element  26  can be mounted. Although a variety of thin lay-up mandrel elements  26  are contemplated, one embodiment contemplates the use of a plurality of caul plates  28  abutted end-to-end around the outer shell surface  24  to form a contiguous lay-up surface  30 . The caul plates  28  may be any hard material, for example, metal or graphite materials, and may be temporarily clamped or screwed to the inner mandrel shell  20  to maintain their position. The thin lay-up mandrel element  26  preferably includes a plurality of stiffener channels  32  formed therein. The thin lay-up mandrel element  26  (e.g., the plurality of caul plates  28 ) and solid one-piece cylindrical inner mandrel shell  20  act together to form a mandrel  34  ( FIG. 3 ). 
     By orientating the mandrel  34  horizontally and rotating it in one direction  36  about the mandrel axis  22 , lay-up may be accomplished by way of a work platform  38  positioned adjacent the mandrel  34  as shown in the embodiment of  FIG. 4A . A plurality of resin impregnated stiffener fibers  40  (or “stringers”) are laid up within each of the plurality of stiffener channels  32  as the mandrel rotates. The stiffener channels  32  are provided with a longitudinal groove  33  ( FIG. 4B ) that accepts the top ends  41  of the stiffener fibers  40  to form a flush mandrel surface. A plurality of rubber mandrels  42  may be inserted into each of the stiffener channels  32  after lay-up of the stiffener fibers  40  in order to insure proper stiffener shape prior to curing. After curing, the rubber mandrels  42  are removed. Following the lay-up of stiffener fibers  40 , the disclosure contemplates the lay-up of a plurality of resin impregnated skin fibers  44  on top of the plurality of resin impregnated stiffener fibers  40 . The number of skin fibers  44  used depends on the end-use application. For example, any number of layers from 3 to about 40 may be used. In general, stronger fuselages able to withstand high pressure require more layers. The resultant structure as shown in  FIG. 5  is a pre-cured section of an aircraft fuselage  46  still attached to the mandrel. 
     The pre-cured section of an aircraft fuselage  46  may be manufactured in some of the embodiments without utilizing tooling that requires seals. The solid one-piece cylindrical inner mandrel shell  20  also permits the mandrel  34  to be subjected to vacuum forces without any concern of seal leakage. Accordingly, in a number of embodiments, the pre-cured section  46  may be vacuum bagged  48  while still on the mandrel, with the assembly then being subject to curing  50  ( FIG. 6 ). After curing, the vacuum bagging  48  is removed. The end result of curing is that the unitary seamless section of aircraft fuselage  10  is generated. The unitary section  10  may then be removed from the mandrel  34  to be utilized in the manufacture of an aircraft. 
     A plurality of embodiments to remove the mandrel  34  from the solid unitary section of cured fuselage  10  will be described. In one embodiment, at least one support ring  52  (for example, including a first support ring  54  and a second support ring  56 ) may be utilized ( FIG. 7 ). The support ring  52  ( 54 ,  56 ) may be mounted to the side ends of the thin lay-up mandrel element  26  by a bolt or screw  57  ( FIG. 9 ) or any other attachment means. The support rings  52  may be mounted on the mandrel element either before or after the lay-up and curing steps. The support rings  52  allow for a separating force to be applied to the thin mandrel element  26 , such that the inner mandrel shell  20  can be removed. Once the mandrel shell  20  is removed, the thin mandrel elements  26  are easily separated from the cured product. 
     Referring to  FIG. 8 , the mandrel may be positioned vertically and one of the support rings  56  may be engaged to a lateral support structure  58 . The cylindrical inner mandrel shell  20  can then be supported by a spring or other flexible support  60 . In such an arrangement, gravity may be utilized to allow the relatively unsupported and heavy inner mandrel shell  20  to separate from the thin lay-up mandrel  26 . In a further embodiment shown in  FIGS. 8 and 9 , an air supply  62  may be utilized to force air in between the thin lay-up mandrel  26  and inner mandrel shell  20  in order facilitate their separation. In still another embodiment also shown in  FIGS. 8 and 9 , a vibrational source  64  may alternately load the thin lay-up mandrel element  26  or inner mandrel shell  20  in order to facilitate their separation. 
     As illustrated in  FIGS. 10 and 11 , separation may also be facilitated by the use of a tapered thin lay-up mandrel element  26  and an oppositely tapered one-piece cylindrical inner mandrel shell  20 . The opposite tapers facilitate removal of inner mandrel shell  20 . Tapers of about 0.5 degree are sufficient, but larger tapers may be used. In some of these embodiments, the inner mandrel shell  20  may include a smaller shell outer diameter  66  and a larger shell outer diameter  68 . The thin lay-up mandrel  26  has a tapered inner surface, such that the thickness of the thin lay-up mandrel  26  varies from one end to the other. The thin lay-up mandrel  26  may include a larger plate inner dimension  70  and a smaller plate inner dimension  72 . The larger plate inner dimension  70  complements the smaller shell outer diameter  66  and the smaller plate inner dimension  72  complements the larger shell outer dimension  68  such that a substantially uniform dimension lay-up surface  74  is generated. A detail of the counter tapers  76  is illustrated in  FIG. 11  (shown slightly exaggerated). The counter tapers  76  allow the one-piece cylindrical inner mandrel shell  20  to be removed from the center of the thin lay-up mandrel element(s)  26  after curing by any of the removal methods described above. In this fashion, the manufacturing of a seamless section of an aircraft fuselage  10  is significantly improved. 
     Many modifications and variations may of course be devised given the above description of the principles in this disclosure. It is intended that all such modifications and variations be considered as within the spirit and scope of this disclosure, as defined in the following claims.