Fiber reinforced shell structure of synthetic material

A fiber reinforced shell structure of synthetic material has an outer skin supported on a skeleton of longitudinal stringers interconnected by ribs. The stringers have a channel cross-section filled with a hard foam. The ribs have an approximately [ or I-shaped cross-section. The ribs are formed by an outer chord and by an inner chord interconnected by a web. If the structure is cylindrical, for example, the ribs extend circumferentially. The rib webs are made of rib web segments which are displaced relative to each other, for example in the circumferential direction in case of a cylindrical structure. The displacement of the web elements corresponds to the on-center spacing between neighboring longitudinal stringers, whereby the fiber reinforced material of the end portions of the rib web segments merge into rib reinforcing or bracing members, where the ribs intersect the stringers. The rib bracing members alternate in opposite directions along a rib and are filled with a hard foam. Such a shell structure can be manufactured with the aid of mold members made substantially of rubber elastic material which greatly facilitates the removal of the mold members from a finished structure, such as an aircraft body.

FIELD OF THE INVENTION 
The invention relates to a fiber reinforced shell structure of synthetic 
material such as an aircraft fuselage, an aircraft wing, or the like. 
DESCRIPTION OF THE PRIOR ART 
Such structural components and ways of manufacturing these components are 
disclosed in U.S. Pat. Nos. 4,524,556 (Sarh et al) and 4,512,837 (Sarh et 
al) corresponding to German Pat. No. 3,003,552. These structural 
components have, for example, a cylindrical shape formed by a skeleton of 
longitudinal stringers interconnected by circumferential ribs with an 
outer skin bonded to the stringers and ribs. The stringers may have a 
channel type cross-sectional configuration while the ribs may have 
approximately an I-cross-section configuration with an outer and inner 
chord interconnected by a web. Each web surface faces toward an end of the 
structural component. Thus, in an aircraft body one rib web surface would 
face toward the nose tip of the fuselage, while the other rib web surface 
would face toward the tail end. 
The skeleton functions as a stiffening grid structure comprising said 
longitudinal stringers and the cross ribs, whereby the entire frame 
structure is assembled from box frames manufactured in a winding 
operation, whereby preimpregnated fiber reinforced synthetic material 
tapes are wound onto form bodies and cured. The form bodies are then 
removed after curing. The desired structure or shape of the structure is 
achieved by assembling a plurality of wound box frames and molding these 
frames in a molding apparatus prior to curing, whereby the form bodies are 
still inside the box frames. These form bodies must be manufactured as 
separate components and are at least partially made of a suitable metal 
that requires a chip removing machining operation. As a result, the 
manufacturing costs which must include the costs for making the form 
bodies are rather high. 
OBJECTS OF THE INVENTION 
In view of the foregoing it is the aim of the invention to achieve the 
following objects singly or in combination: 
to modify the stringer and rib construction in such a way that the 
manufacture will require less expensive machinery; 
to simplify the skeleton structure, that is the stringer and rib structure, 
without reducing the strength of such a structure, while also avoiding 
expensive mold bodies; and 
to construct or assemble the ribs either of two types of rib elements or 
rib segments, whereby one type of rib segments faces toward one end of the 
structural component while the other type of rib segment or element faces 
toward the opposite end of the structural component, or to use the same 
type of rib segments for the rib construction so that it becomes 
immaterial whether a rib segment faces in one or the other direction. 
SUMMARY OF THE INVENTION 
The shell structure according to the invention is characterized in that 
each rib which interconnects the longitudinal stringers comprises a 
plurality of rib segments or elements, whereby one type of rib segments 
faces toward one end of the structural component while another type of rib 
segments faces toward the opposite end of the structural component and 
wherein these rib segments are angularly displaced relative to each other 
in the circumferential direction, the respective displacement 
corresponding to an on-center spacing between neighboring stringers. 
Additionally, rib bracing members are located so that the ends of the rib 
segments can merge into the rib bracing members which are preferably 
located where the stringers join the ribs. 
In a preferred embodiment the fiber reinforced shell structure comprises 
longitudinal stringers and circumferential ribs interconnecting the 
stringers to form a skeleton having a laminated outer skin, wherein the 
ribs include an outer chord and an inner chord interconnected by a web and 
wherein rib bracing members are located on either side of the web for 
connecting the stringers to the ribs. The web comprises a plurality of web 
elements, each web element having a main portion with a flat back and an 
end portion at each end of the main portion, whereby the end portions 
extend away from the flat back. The web elements are arranged in two 
groups so that the end portions of one group point in one direction and 
the end portions of the other group of web elements point in the opposite 
direction. The web elements are so positioned in a back-to-back 
arrangement or relationship that the web elements of one group are 
angularly displaced in the circumferential direction relative to the web 
elements of the other group, whereby the end portions of one group of web 
elements are staggered relative to the end portions of the other group of 
web elements so that the web end portions merge into the rib bracing 
members. 
The advantages achieved according to the invention are primarily seen, 
among others, in that the mold bodies can now be substantially simpler 
without requiring any machining operations. These mold bodies may be made 
substantially of a rubber elastic material which facilitates their removal 
from the finished grid structure. Additionally, the number of laminates 
which heretofore had to be manufactured separately, has been reduced.

DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE 
OF THE INVENTION 
Referring to FIGS. 1 and 2, the present shell structure 1 comprises a 
plurality of longitudinally extending stringers 3, 3a, 3b, 3c, and so on. 
These stringers extend substantially in parallel to one another and are 
spaced from one another by an on-center spacing S. If the shell structure 
is cylindrical, the spacing S extends in the circumferential direction. 
The stringers are interconnected by ribs 4, 4a, and so forth. Each 
stringer 3, 3a, . . . has lateral flanges 5 which are bonded to the outer 
skin 2, for example, as a result of the curing of the fiber reinforced 
synthetic material. The ribs 4, 4a, . . . have radially outer chords 4' 
which are also bonded to the outer skin 2 by the curing of the synthetic 
material. In FIG. 1 the arrow A points toward one end of the shell 
structure, for example, the nose cone of an aircraft fuselage while the 
arrow B points in the opposite direction, for example, toward the tail end 
of the aircraft fuselage. Thus, the surface of a rib web 20 of the rib 4a 
as viewed in the direction of the sectional plane II--II in FIG. 1, faces 
in the direction of the arrow A, for example, toward the nose cone. 
At the intersections between a rib 4 and a stringer 3 there are arranged 
rib bracing members 8 and 9 located on alternately opposite sides of the 
respective rib as best seen in FIGS. 1 and 12. Thus, the rib bracing 
members 8 are located at every other stringer 3 on one side of a rib 4 and 
the bracing members 9 are located at every other stringer 3 on the other 
side of the same rib, but staggered from stringer to stringer, e.g. in the 
circumferential direction of a cylindrical shell relative to the bracing 
members 8. FIG. 12 also shows that each rib comprises two groups of rib 
web segments 20,21. The first group is located on the side having the rib 
bracing members 8. The second group is located on the side having the rib 
bracing members 9. The first group comprises the rib web segments 20 and 
the second group comprises the rib web segments 21. Each rib web segment 
20 and 21 has a flat back or main portion and end portions 10, 11 
extending away from the main portion. The main portions are arranged 
back-to-back but in the staggered relationship e.g. in the circumferential 
direction of a cylindrical shell as seen in FIG. 12. The staggering 
corresponds to the spacing S. 
FIG. 3 shows on an enlarged scale the detail III in FIG. 2, whereby the 
construction of the rib bracing members 8 and 9 appears in greater detail. 
The rib bracing member 8 appears in front of the rib web segment 20 while 
the rib bracing member 9 is shown in dashed lines because it appears 
behind the rib web segments 20, 21. The end portions 10 and 11 of 
neighboring rib web segments 20, 21 merge into the respective rib bracing 
members 8, 9, and thereby form these rib bracing members 8, 9, preferably 
together with a hard foam core 25, please see FIG. 6. As seen in FIG. 3 
the rib bracing members 8 and 9 taper away from the outer skin 2. 
The rib bracing members 8, 9 also merge into the respective stringer 3, 3a 
at an intersection or junction between a rib and a stringer. The channels 
formed by the stringers 3 are filled with a hard foam core 30. The space 
between the end portions 10, 11 of the rib weg sements 20, 21 is filled 
with the above mentioned hard foam core 25 to form the rib bracing members 
8, 9. As shown in FIG. 9, the end portions 10, 11 of the rib web segments 
20 may have a triangular lower portion. 
FIG. 4 shows schematically the layer arrangement of a junction between the 
rib web segment 20 of a rib 4 with its core 25 and a stringer 3 with its 
core 30. The layers are individual preimpregnated layers of fiber 
reinforced material. The layers 12 form the outer skin 2. The layers 13 
form part of a rib chord. The layers 14 form the lateral flanges 5 of the 
channel shaped stringer 3. The layers 15 form the end portion 10 of a rib 
web segment 20. The layers 16 form the end portion 11 of a neighboring rib 
web segment 20. Thus, these layers 15 and 16 together with the core 25 
form the rib bracing member 8, please see FIG. 3. The rib web segment 21 
is layered in the same way. 
FIG. 5 shows the radially inner end of a rib bracing member 8, 9 merging 
with the end portions 10 and 11 of the respective rib web segments 20 and 
with the layers 7 forming the lower chord of the rib web segments 20. 
These layers 7 just as the layers 13, may be continuous tapes. This 
applies also to the layers 12. The layers 13 form the upper chord of the 
rib web segments 20, 21. 
FIG. 6 shows a sectional view along section line VI--VI in FIG. 2, whereby 
the web 19 of a rib 4a is formed by the above described rib web segments 
20 and 21 also shown in their general arrangement in FIG. 12. The rib web 
segments 20 face, for example, toward the nose cone and the rib web 
segments 21 face, for example, toward the tail end of an aircraft fuselage 
as mentioned above with reference to the arrows A and B in FIG. 1. The 
arrangement of the rib web segment end portions 10 and 11 as they merge 
into the rib bracing member 8 is also shown in more detail in FIG. 6, 
whereby the hard foam core 25 is embraced by the end portions 10 and 11 of 
the rib web segment 20 and by the back of a staggered rib web section 21. 
As seen in FIG. 12, the rib bracing members 8 are located to the left of 
rib 4, while rib bracing members 9 are located to the right of rib 4. 
FIG. 7 shows another type of web section element 21 in which the end 
portions 10',11' have a somewhat trapezoidal shape rather than a 
triangular shape as shown in FIG. 9. 
FIG. 8 shows the individual fiber layers 12 and 13 of the outer skin 2 and 
of the radially outer rib chord 13. Preferably, the layers 13 are formed 
by one continuous tape wound around the rib web segments. Layers 26 form 
the rib web segments 20. Layers 27 form the rib web segments 21. Layers 28 
form the radially inner chord, whereby again continuous tapes are 
preferred. 
FIG. 9 shows the section IX--IX in FIG. 1, whereby the embodiment shows the 
rib bracing member 8 left of rib 4. FIG. 10 illustrates the individual 
layers 26, 27 forming the rib web segments 20 and 21, respectively. 
FIG. 11 shows a rib configuration having an I-section made of a left 
]-section 41, a right [-section 42, an upper chord 43, and a lower chord 
44. 
Although the invention has been described with reference to specific 
example embodiments, it will be appreciated that it is intended to cover 
all modifications and equivalents within the scope of the appended claims.