# Patent

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

## Abstract

A mandrel for manufacturing a unitary seamless section of an aircraft fuselage comprises a thin lay-up mandrel element disposed onto the outer shell surface of an inner mandrel shell, forming a mandrel with a substantially continuous lay-up surface. A unitary pre-cured section of an aircraft fuselage is formed by laying up a plurality of resin impregnated skin fibers onto the mandrel's lay-up surface while the mandrel rotates.

## Background
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.

## Claims

1. A method of manufacturing an aircraft fuselage, the method comprising:
disposing a plurality of tapered caul plates onto an outer shell surface of an inner mandrel shell to form a mandrel with a lay-up surface, the outer shell surface further having an outer taper from a first shell end to a second shell end such that an outer diameter of the inner mandrel shell is larger at the first shell end than at the second shell end, and the plurality of tapered caul plates comprising a plurality of stiffener channels formed into a caul outer surface and comprising a first plate end having a first plate inner dimension and a second plate end having a second plate inner dimension, the first plate inner dimension being larger than the second plate inner dimension, the tapered caul plates complementing the tapered inner mandrel shell to produce a substantially uniform lay-up surface;
laying up a plurality of resin impregnated stiffener fibers within the plurality of stiffener channels to form a plurality of stiffeners; and
laying up a plurality of resin impregnated skin fibers onto the lay-up surface to form a unitary pre-cured section of the aircraft fuselage.

2. The method of claim 1, further comprising:
curing the unitary pre-cured section.

3. The method of claim 1, further comprising:
rotating the mandrel continuously in one direction about a mandrel axis, the mandrel rotating adjacent to at least one work platform;
laying up the plurality of resin impregnated stiffener fibers and the plurality of resin impregnated skin fibers from the work platform.

4. The method of claim 1, further comprising:
inserting a corresponding additional mandrel into each of the plurality of stiffener channels after laying up the plurality of resin impregnated stiffener fibers but before laying up the plurality of resin impregnated skin fibers.

5. The method of claim 1, further comprising:
vacuum bagging the unitary pre-cured section while the unitary pre-cured section remains on the mandrel.

6. The method of claim 1, further comprising:
mounting at least one support ring to the plurality of tapered caul plates;
curing the unitary pre-cured section; and
supporting the plurality of tapered caul plates using the at least one support ring while the inner mandrel shell is removed.

7. The method of claim 1, further comprising:
forcing air in between the plurality of tapered caul plates and the inner mandrel shell to facilitate removal of the inner mandrel shell.

8. The method of claim 1, further comprising:
applying a vibrational load to the plurality of tapered caul plates to facilitate removal of the inner mandrel shell.

9. The method of claim 1
wherein the tapered inner mandrel shell and the plurality of tapered caul plates are complemented to facilitate removal of the tapered inner mandrel shell.

10. A method of manufacturing an aircraft fuselage, the method comprising:
disposing a lay-up mandrel element onto an outer shell surface of an inner mandrel shell to form a mandrel with a lay-up surface;
laying up a plurality of resin impregnated stiffener fibers within a corresponding plurality of stiffener channels formed in the lay-up mandrel element;
inserting a corresponding additional mandrel into each of the corresponding plurality of stiffener channels;
laying up a plurality of resin impregnated skin fibers onto the lay-up surface to form a unitary pre-cured section of the aircraft fuselage;
mounting at least one support ring to the lay-up mandrel element;
curing the unitary pre-cured section; and
supporting the lay-up mandrel element using the at least one support ring while the inner mandrel shell is removed.

11. The method of claim 10, further comprising:
rotating the mandrel continuously in one direction about a mandrel axis.

12. The method of claim 10, wherein inserting is performed after laying up the plurality of resin impregnated stiffener fibers but before laying up the plurality of resin impregnated skin fibers.

13. The method of claim 10, further comprising:
vacuum bagging the unitary pre-cured section while the unitary pre-cured section remains on the mandrel.

14. The method of claim 10, further comprising:
forcing air in between the lay-up mandrel element and the inner mandrel shell to facilitate removal of the inner mandrel shell.

15. The method of claim 10, further comprising:
applying a vibrational load to the lay-up mandrel element to facilitate removal of the inner mandrel shell.

16. The method of claim 10, wherein the lay-up mandrel element comprises an inner element surface having an inner taper from a first element end to a second element end such that an inner diameter of the lay-up mandrel element is smaller at the first element end than at the second element end.

17. The method of claim 10, wherein each of the corresponding additional mandrels are composed of rubber and are removable from the corresponding plurality of stiffener channels.

18. The method of claim 10, wherein top ends of the plurality of resin impregnated stiffener fibers form a flush mandrel surface and are in contact with the plurality of resin impregnated skin fibers.