Modified blade stiffener and fabrication method therefor

TECHNICAL FIELD

0001The disclosure relates to blade stiffeners for aircraft structures. More particularly, the disclosure relates to a modified blade stiffener having enhanced mechanical properties and a method of fabricating a modified blade stiffener which can be fabricated as a single piece without the use of fasteners.

BACKGROUND

0002In the fabrication of some structures such as aircraft, for example, it may be desirable to use composite panels due to the panels' high strength-to-weight ratio. Stiffening elements may be attached to the composite panels at various locations to reinforce and impart structural strength to the panels. These stiffening elements may include, for example, hat stiffeners; I-beams; blade stiffeners; honeycomb cores; and foam cores.

0003The conventional types of stiffening elements used to stiffen composite panels may have various disadvantages. For example, hat stiffeners may occupy a relatively large area on the panel and may require internal support for cure. I-beams may need to be fabricated from multiple pieces and may require complex tooling during cure to maintain their profile. Furthermore, the tooling may be difficult to remove after cure. Traditional blade stiffeners may not be as structurally efficient as other shapes. Honeycomb and foam core may be heavier and may have a tendency to be crushed during cure and to retain water in service.

0004What is needed is a modified blade stiffener having enhanced mechanical properties and a method of fabricating a modified blade stiffener which can be fabricated as a single piece without the use of fasteners.

SUMMARY

0005The disclosure is generally directed to a modified blade stiffener having additional reinforcement at the top of the blade to increase the mechanical performance. An illustrative embodiment of the modified blade stiffener includes a stiffener-forming material shaped into a pair of coupled blades having first and second ends, a filler cavity provided at the first end of the blades, a blade filler provided in the filler cavity and a pair of blade flanges provided at the second end of the blades.

0006The disclosure is further generally directed to a method of forming a modified blade stiffener. An illustrative embodiment of the method includes providing a blade-forming assembly having a pair of tool dies, a tool gap between the tool dies and a forming cavity in each tool die; providing a layup charge of stiffener-forming material; bridging the tool gap between the tool dies with the layup charge; placing a blade filler on the layup charge at the tool gap; pressing the blade filler through the tool gap between the tool dies until the blade filler reaches and extends into the forming cavities in the tool dies; and pressing the tool dies together to substantially eliminate the tool gap.

0007According to an embodiment of the invention, the blade stiffener comprises: <ul id="ul0001" list-style="none"><li>a stiffener-forming material shaped into a pair of coupled blades having first and second ends;</li><li>a filler cavity provided at said first end of said blades;</li><li>a blade filler provided in said filler cavity;</li><li>a flange filler provided at said second end of said blades; and</li><li>a pair of blade flanges provided at said second end of said blades.</li></ul>

0008Preferably the stiffener-forming material wherein said stiffener-forming material comprises sheets of composite plies.

0009More preferably said stiffener-forming material comprises prepreg material.

0010It is also preferred that said stiffener-forming material comprises resin-infused dry fabric preform.

0011It is also preferred that said blade filler comprises an uncured formed composite.

0012It is also preferred that said blade flanges are oriented in generally perpendicular relationship with respect to said blades, respectively.

0013It is also preferred that said blade stiffener comprises a pair of blade arms extending from said blades at said first end; a pair of straight or curved arm portions extending from said blade arms, respectively; and a blade arm connecting portion connecting said straight or curved arm portions, and wherein said filler cavity is defined by said blade arms; said straight or curved arm portions; and said blade arm connecting portion.

0014It is also preferred that said blade arms are disposed at an obtuse angle with respect to said blades, respectively.

0015According to another embodiment, a blade stiffener for aircraft structure comprises: <ul id="ul0002" list-style="none"><li>a stiffener-forming material shaped into a pair of generally elongated, parallel, coupled blades each having first and second ends;</li><li>a pair of spaced-apart blade arms extending from said first ends of said blades, respectively, and disposed at an obtuse angle with respect to said blades, respectively;</li><li>a pair of generally parallel straight or curved arm portions extending from said blade arms, respectively;</li><li>a generally elongated blade arm connecting portion extending between said straight or curved arm portions;</li><li>a filler cavity defined by said blade arms, said straight or curved arm portions and said blade arm connecting portion;</li><li>a blade filler provided in said filler cavity;</li><li>a pair of blade flanges extending from said second ends of said blades, respectively, at a pair of blade/flange junctions, respectively, and in generally perpendicular relationship with respect to said blades, respectively; and</li><li>a flange filler provided between said blade/flange junctions, respectively, at said second ends of said blades.</li></ul>

0016The invention also relates to a method of forming a blade stiffener for aircraft structure, comprising: <ul id="ul0003" list-style="none"><li>providing a blade-forming assembly having a pair of tool dies, a tool gap between said tool dies and a pair of forming cavities in said tool dies, respectively;</li><li>providing a layup charge of stiffener-forming material;</li><li>bridging said tool gap between said tool dies with said layup charge;</li><li>placing a blade filler on said layup charge at said tool gap;</li><li>forming a pair of blades, a pair of blade flanges and a filler cavity of said blade stiffener by pressing said blade filler through said tool gap between said tool dies until said blade filler reaches and extends into said forming cavities in said tool dies, with said blades and said blade flanges each engaging said pair of tool dies, respectively;</li><li>leaving said blade filler in said filler cavity;</li><li>pressing said tool dies together to substantially eliminate said tool gap; and</li><li>providing a flange filler between said blades.</li></ul>

0017It is to be understood that the features mentioned above and those to be mentioned below can be used not only in the given combination, but also in other combinations or in isolation without leaving the scope of the present invention.

0018Examples of the invention are shown in the drawings and will be further explained in the following description. In the drawings:

BRIEF DESCRIPTION OF THE DRAWINGS

0019<figref idref="f0001">FIG. 1</figref> is a cross-sectional view of a modified blade stiffener attached to a composite panel, with cure tools engaging the modified blade stiffener.

0020<figref idref="f0001 f0002 f0003">FIGS. 2-7</figref> are cross-sectional views which illustrate sequential fabrication of a modified blade stiffener according to a method of fabricating a modified blade stiffener.

0021<figref idref="f0003">FIG. 8</figref> is a cross-sectional view of a modified blade stiffener fabricated according to the method shown in <figref idref="f0001 f0002 f0003">FIGS. 2-7</figref>.

0022<figref idref="f0004">FIG. 9</figref> is a cross-sectional view of a composite panel, with multiple modified blade stiffeners attached to the composite panel.

0023<figref idref="f0004">FIG. 10</figref> is a flow diagram which illustrates an illustrative method of fabricating a modified blade stiffener.

0024<figref idref="f0005">FIG. 11</figref> is a flow diagram of an aircraft production and service methodology.

0025<figref idref="f0005">FIG. 12</figref> is a block diagram of an aircraft.

DETAILED DESCRIPTION

0026Referring initially to <figref idref="f0001">FIGS. 1</figref>, <figref idref="f0003">8</figref> and <figref idref="f0004">9</figref>, an illustrative embodiment of the modified blade stiffener is generally indicated by reference numeral 1. The modified blade stiffener 1 may include a formed sheet of stiffener-forming material 3 which may include a pair of generally elongated, adjacent, parallel blades 4. The stiffener-forming material may be composite plies, prepreg material or resin-infused dry fabric preform, for example and without limitation. A pair of blade flanges 8 may extend outwardly from the respective blades 4 at a pair of respective blade/flange junctions 9. The plane of each blade flange 8 may be disposed in generally perpendicular relationship with respect to the plane of the corresponding blade 4 from which the blade flange 8 extends.

0027A pair of blade arms 5 may extend from the respective blades 4 opposite the blade flanges 8. The plane of each blade arm 5 may be oriented at an obtuse angle or radius of curvature with respect to the plane of the corresponding blade 4 from which the blade arm 5 extends. A pair of straight or curved arm portions 5a may extend from the respective blade arms 5. A blade arm connecting portion 6 may extend between the straight or curved arm portions 5a of the blade arms 5. The blade arms 5, straight or curved arm portions 5a and blade arm connection portion 6 may together define a filler cavity 7 which in fabrication of the modified blade stiffener 1 may contain a blade filler 16 which may be an uncured, partially cured, or fully cured formed composite, for example. The blade filler 16 may be used to form the shape of the blade arms 5, the straight or curved arm portions 5a and the blade arm connecting portion 6 during fabrication of the modified blade stiffener 1, as will be hereinafter described. As shown in <figref idref="f0001">FIG. 1</figref>, a flange filler 14, which may be an uncured formed composite, for example, may be provided between the blades 4 at each blade/flange junction 9.

0028As shown in <figref idref="f0004">FIG. 9</figref> and will be hereinafter described, in typical application the blade flanges 8 of a series of multiple modified blade stiffeners 1 may be attached to a composite panel 2 to stiffen and reinforce the composite panel 2. The composite panel 2 may form a part of an aircraft structure (not shown) or other structure. In <figref idref="f0001">FIG. 1</figref>, a pair of cure tools 12 is shown engaging the respective sides of the modified blade stiffener 1.

0029Referring next to <figref idref="f0001 f0002 f0003">FIGS. 2-7</figref>, sequential steps of an illustrative method of fabricating the modified blade stiffener 1 using a blade-forming assembly 18 is shown. In <figref idref="f0001">FIG. 2</figref>, a pair of tool dies 20 of the blade-forming assembly 18 is initially positioned in spaced-apart relationship with respect to each other. The tool dies 20 may include a pair of respective initially spaced-apart and facing blade shaping surfaces 21 and a pair of blade flange shaping surfaces 22 which may extend in generally perpendicular relationship with respect to the respective blade shaping surfaces 21. Each tool die 20 may also have a tool die base 25. A forming cavity 25a may extend into the blade shaping surface 21 and tool die base 25 of each tool die 20. The forming cavities 25a may have a shape which is generally complementary to that of the blade filler 16. A surface junction 24 may be defined between each blade shaping surface 21 and the corresponding blade flange shaping surface 22. The blade shaping surfaces 21 of the respective tool dies 20 may face each other on opposite sides of a tool gap 23 between the tool dies 20.

0030As further shown in <figref idref="f0001">FIG. 2</figref>, a layup charge of the sheet of stiffener-forming material 3 may be initially placed on the blade flange shaping surfaces 22 of the respective tool dies 20 and extends or bridges over the tool gap 23. A forming bar 26 may include a generally elongated forming bar shaft 27 having a generally V-shaped filler notch 28 in one end thereof. A blade filler 16 may be placed on the segment of the composite plies sheet 3 which spans or bridges the tool gap 23 between the tool dies 20. The filler notch 28 of the forming bar 26 may engage and apply force against the blade filler 16 along the longitudinal axis of the forming bar shaft 27. Accordingly, the blade filler 16 deforms the portion of the composite plies sheet 3 which spans the tool gap 23 as that portion of the composite plies sheet 3 may be pushed into the tool gap 23 and between the blade shaping surfaces 21 of the respective tool dies 20. That portion of the composite plies sheet 3 which may be pushed into the tool gap 23 may eventually form the blade arm connecting portion 6 of the modified blade stiffener 1. The portions of the composite plies sheet 3 which engage the respective blade shaping surfaces 21 at the point in the fabrication process shown in <figref idref="f0001">FIG. 2</figref> may eventually form the respective straight or curved arm portions 5a in the modified blade stiffener 1.

0031As shown in <figref idref="f0001 f0002 f0003">FIGS. 3-6</figref>, the forming bar 26 may continue to push the composite plies sheet 3 through the tool gap 23 between the tool dies 20 to form the blades 4 of the modified blade stiffener 1 until the blade arm connecting portion 6 reaches the base 25 of each tool die 20, as shown in <figref idref="f0003">FIG. 6</figref>. During extension of the composite plies sheet 3 through the tool gap 23, the blade shaping surfaces 21 of the respective tool dies 20 may engage and shape the respective blades 4, whereas the blade flange shaping surfaces 22 of the respective tool dies 20 may engage and shape the respective blade flanges 8. Extension of the composite plies sheet 3 into the tool gap 23 may continue until the entire portion of the composite plies sheet 3 which will become a blade 4 of the modified blade stiffener 1 engages and extends along the blade forming surface 21 of the corresponding tool die 20, as shown in <figref idref="f0003">FIG. 6</figref>. At that point, each blade/flange junction 9 of the modified blade stiffener 1 may be located at the surface junction 24 of each corresponding tool die 20.

0032As shown in <figref idref="f0002">FIGS. 4 and 5</figref>, as the forming bar 26 pushes the composite plies sheet 3 through the tool gap 23 toward the tool die bases 25, the tool dies 20 may be gradually moved toward each other. The forming bar 26 may then be disengaged from the blade filler 16 and removed from the tool gap 23, as shown in <figref idref="f0002">FIG. 5</figref>. Eventually, the blade shaping surfaces 21 of the respective tool dies 20 may press the blades 4 of the modified blade stiffener 1 against each other, as shown in <figref idref="f0003">FIG. 7</figref>. As shown in <figref idref="f0002">FIGS. 5</figref> and <figref idref="f0003">6</figref>, during movement of the tool dies 20 toward each other, the forming cavities 25a of the respective tool die 20 receive the complementary-shaped blade filler 16. Therefore, the composite plies sheet 3 may be pressed between the blade filler 16 and the interior surfaces of the forming cavities 25a, thus forming the composite plies sheet 3 into the blade arms 5 and the straight arm portions 5a of the modified blade stiffener 1. As shown in <figref idref="f0003">FIG. 6</figref>, the blade filler 16 may remain in the filler cavity 7 which may be defined by the blade arms 5, the straight or curved arm portions 5a and the blade arm connecting portion 6. As shown in <figref idref="f0003">FIG. 7</figref>, the flange filler 14 may be provided between the blades 4 at each blade/flange junction 9. The flange filler 14 and the blade filler 16 may be located at the farthest points from the center of the modified blade stiffener 1 to maximize the stiffness and structural efficiency of the modified blade stiffener 1. Finally, the tool dies 20 may be disengaged from the modified blade stiffener 1. It will be appreciated by those skilled in the art that the modified blade stiffener 1 may be fabricated as a single piece with no fasteners or secondary bonding.

0033Referring next to <figref idref="f0001">FIGS. 1</figref> and <figref idref="f0004">9</figref>, in typical application multiple modified blade stiffeners 1 may be bonded or co-cured to the composite panel 2 in a selected pattern, spacing and density to customize local stiffness of the composite panel 2. Accordingly, the blade flanges 8 of each modified blade stiffener 1 may be attached to the surface of the composite panel 2 according to the knowledge of those skilled in the art. As shown in <figref idref="f0001">FIG. 1</figref>, cure tools 12 may be placed in proximity to respective sides of the modified blade stiffener 1 for curing of the composite plies sheet 3.

0034It will be appreciated by those skilled in the art that the shape of the modified blade stiffener 1 allows the use of cure tools 12 (<figref idref="f0001">FIG. 1</figref>) that automatically center on the modified blade stiffener 1 and can be quickly and easily removed after cure without the use of special equipment. Due to its small footprint on the composite panel 2 and the compact nature of the cure tool 12 (<figref idref="f0001">FIG. 1</figref>), the modified blade stiffeners 1 can be placed more closely together on the composite panel 2 than is the case with typical hat-shaped stiffeners to allow specific tailoring of the performance of the overall structure. The compact or low-profile nature of the modified blade stiffener 1 may also allow it to be used in combination with other types of stiffeners such as hat-type stiffeners (not shown) to augment panel stiffness locally where there may be insufficient space to add additional hat-type stiffeners. Furthermore, the modified blade stiffener 1 may not require internal tooling such as the bladders which may be necessary for the fabrication of hat-type stiffeners; therefore, there may be no treatments or tools that must be prepared before use or extracted from the modified blade stiffener 1 after cure. The modified blade stiffeners 1 may be more structurally efficient than standard blade stiffeners and may be located more densely than hat-type stiffeners and may be easier to customize for structural requirements. The blade forming assembly 18 may fabricate finished modified blade stiffeners 1 that can be installed directly on the composite panel 2 without the need for additional assembly steps. In some applications, the bulbous end of the modified blade stiffener 1, defined by the blade arms 5; the straight or curved arm portions 5a; and the blade arm connecting portion 6, may be inserted in a receiving slot (not shown) provided in a frame (not shown) to reduce or eliminate the number of fasteners needed to couple a stringer (not shown) to the frame.

0035Referring next to <figref idref="f0004">FIG. 10</figref>, a flow diagram 1000 which illustrates an illustrative method of fabricating a modified blade stiffener is shown. In block 1002, a blade-forming assembly having tool dies with a tool gap between the tool dies and a forming cavity in each tool die may be provided. In block 1004, a layup charge of a stiffener-forming material may be provided. In block 1006, the tool gap between the tool dies may be bridged with the layup charge. In block 1008, a blade filler may be placed on the layup charge above the tool gap. In block 1010, the blade filler may be pressed through the tool gap between the tool dies until the blade filler reaches and extends into the forming cavities in the tool dies. The blade filler is then removed in block 1011. In block 1012, the tool dies may be pressed together to substantially eliminate the tool gap. In the final block 1013, the tool dies are removed.

0036Referring next to <figref idref="f0005">FIGS. 11 and 12</figref>, embodiments of the disclosure may be used in the context of an aircraft manufacturing and service method 78 as shown in <figref idref="f0005">FIG. 11</figref> and an aircraft 94 as shown in <figref idref="f0005">FIG. 12</figref>. During pre-production, exemplary method 78 may include specification and design 80 of the aircraft 94 and material procurement 82. During production, component and subassembly manufacturing 84 and system integration 86 of the aircraft 94 takes place. Thereafter, the aircraft 94 may go through certification and delivery 88 in order to be placed in service 90. While in service by a customer, the aircraft 94 may be scheduled for routine maintenance and service 92 (which may also include modification, reconfiguration, refurbishment, and so on).

0037Each of the processes of method 78 may be performed or carried out by a system integrator, a third party, and/or an operator (e.g., a customer). For the purposes of this description, a system integrator may include without limitation any number of aircraft manufacturers and major-system subcontractors; a third party may include without limitation any number of vendors, subcontractors, and suppliers; and an operator may be an airline, leasing company, military entity, service organization, and so on.

0038As shown in <figref idref="f0005">FIG. 12</figref>, the aircraft 94 produced by exemplary method 78 may include an airframe 98 with a plurality of systems 96 and an interior 100. Examples of high-level systems 96 include one or more of a propulsion system 102, an electrical system 104, a hydraulic system 106, and an environmental system 108. Any number of other systems may be included. Although an aerospace example is shown, the principles of the invention may be applied to other industries, such as the automotive industry.

0039The apparatus embodied herein may be employed during any one or more of the stages of the production and service method 78. For example, components or subassemblies corresponding to production process 84 may be fabricated or manufactured in a manner similar to components or subassemblies produced while the aircraft 94 is in service. Also, one or more apparatus embodiments may be utilized during the production stages 84 and 86, for example, by substantially expediting assembly of or reducing the cost of an aircraft 94. Similarly, one or more apparatus embodiments may be utilized while the aircraft 94 is in service, for example and without limitation, to maintenance and service 92.

0040Although the embodiments of this disclosure have been described with respect to certain exemplary embodiments, it is to be understood that the specific embodiments are for purposes of illustration and not limitation, as other variations will occur to those of skill in the art.