A foldable composite material flapping wing structure for micro flapping-wing aircraft and its preparation method

Abstract

This invention discloses a composite material foldable flapping wing structure based on a micro flapping-wing aircraft. Inspired by the foldable and unfoldable hindwing structure of insects, this invention provides a method for manufacturing an integrated strip spring-carbon rod-flapping wing. The composite material used in the strip spring-carbon rod structure is a carbon fiber reinforced epoxy resin-based composite material, which is obtained by molding unidirectional epoxy resin carbon fiber prepreg strips and curing them at high temperature. Its position is designed at the leading edge of the flapping wing, and its geometric parameters are calculated based on the type of prepreg used and mechanical requirements. This allows the flapping wing to maintain the unfolded shape required to provide specific lift during flapping, and also to act as a buffer when colliding with external objects. When the micro flapping-wing aircraft is not in operation, the flapping wing can be folded up to reduce space occupation and enhance the portability and practicality of the micro flapping-wing aircraft.

Description

Technical Field

[0001] This invention provides a foldable composite material flapping wing structure and its preparation method for a micro flapping wing aircraft, belonging to the field of aircraft design and manufacturing. Background Technology

[0002] Bionic micro flapping-wing aircraft, as a type of micro-aircraft, possess advantages such as light weight, small size, good stealth, and low cost, and have broad application prospects in both military and civilian scenarios. For example, in some military scenarios, aircraft are required to navigate confined spaces and have a certain degree of resistance to external obstacles. Currently, traditional bionic micro flapping-wing aircraft can provide sufficient lift through wing flapping, enabling hovering and climbing maneuvers in relatively open spaces. However, these aircraft cannot fly within spaces smaller than their unfolded dimensions, and when the wings collide with other objects during flapping, their flight attitude and trajectory often change drastically, leading to loss of balance and uncontrollability. This problem stems from the fact that the carbon fiber composite rods on traditional flapping wings are inflexible for support, and the designed wingspan is difficult to miniaturize in order to provide sufficient lift for aircraft of this size, hindering portability. Existing foldable wings are often complex in structure and heavy, requiring only manual folding and cannot be applied to the actual flight of flapping-wing aircraft. In 2020, Konkuk University in South Korea designed a foldable wing. The wing's leading edge is replaced with a 0.2mm diameter super-elastic nickel-titanium alloy wire, which can fold longitudinally and laterally. When subjected to external impacts during flight, it can bend to cushion the impact and store energy through deformation for rapid unfolding, achieving a breakthrough in the practical application of foldable wings in flight. Its disadvantages are that repeated bending at this point can easily lead to fatigue fracture, resulting in a shorter lifespan, and the addition of many parts and complex manufacturing processes.

[0003] In nature, insects' hindwings not only provide ample lift during flapping but also fold up when landing, thanks to the wing veins that resemble a spring-like structure. Inspired by the foldable and deployable hindwing structure of insects, this invention provides a foldable and deployable composite material flapping wing structure and its manufacturing method for micro flapping-wing aircraft. The foldable and deployable composite material flapping wing structure includes a spring-like structure positioned at the middle of the leading edge of the flapping wing. Thanks to the mechanical properties of the spring, it can be designed to provide the required stiffness, allowing the flapping wing to maintain the required deployed shape to provide specific lift during normal flapping. Only when colliding with an external object and the impact load exceeds the peak bending moment of the spring will the spring bend and fold to achieve a buffering and energy-absorbing effect. In the non-operating state of the micro flapping-wing aircraft, the flapping wing is completely folded up by the spring, reducing storage space and enhancing the portability and practicality of the micro flapping-wing aircraft. In the preparation method of the foldable composite flapping wing structure, prepreg is used as raw material and molding method is adopted to realize the one-piece molding of the foldable composite flapping wing structure. It has the advantages of good integrity, simple processing technology and long service life, and provides a new idea for the development of foldable wings for micro flapping wing aircraft. Summary of the Invention

[0004] The purpose of this invention is to provide a foldable composite material flapping wing structure and its preparation method for micro flapping wing aircraft, so as to improve the service life of existing foldable wings and improve the processing technology.

[0005] The technical solution adopted in this invention is as follows:

[0006] This invention discloses a foldable composite material flapping wing structure for a micro flapping-wing aircraft. The structure includes an integral strip spring hinge used in conjunction with the flapping wing membrane, allowing for both deployed and folded states. The foldable composite material flapping wing structure is formed by two single-sided integral strip springs bonded to opposite sides of the leading edge of the flapping wing membrane. Along the wingspan, from the inside out, the corresponding construction order is: a slender rod region, an opposing strip spring region, and a slender rod region. The slender rod region has a rectangular cross-section, with the bonding surface in the front view, bonded to the leading edge of the flapping wing membrane. The opposing strip spring region has a cross-section of two symmetrical arc segments, corresponding to the opening area of ​​the flapping wing membrane, and is not bonded to the membrane, ensuring the foldable performance of the foldable composite material flapping wing structure. A curved transition area is provided at the junction of the opposing strip spring region and the two slender rod regions to ensure the integrity of the foldable composite material flapping wing structure. The shape and size design of the foldable composite material flapping wing structure requires mechanical calculation and analysis in conjunction with the type of composite material selected. It is necessary to design the width and thickness of one side of the slender rod area, design the thickness, radius, and cross-sectional parameters such as the central angle of the cross-sectional arc corresponding to the opposing strip spring area, and design a variable thickness scheme at the junction of the areas.

[0007] The advantages of the foldable composite material flapping wing structure for a micro flapping-wing aircraft of the present invention are:

[0008] This invention discloses a foldable composite material flapping wing structure for a micro flapping-wing aircraft. The structure features a composite material flapping wing structure located at the leading edge of the flapping wing membrane, which has folding and unfolding functions. The middle section of this structure is a counter-facing strip spring. Through shape and size design, it can provide the stiffness required for the flapping wing of the micro flapping-wing aircraft to maintain its unfolded configuration under normal flapping, avoiding repeated bending and improving service life. When the outer section of the flapping wing encounters an obstacle during flapping, the impact load is greater than the peak moment of the strip spring bending. The counter-facing strip spring area can absorb energy and buffer external impacts through bending.

[0009] The present invention discloses a foldable composite material flapping wing structure for a micro flapping wing aircraft. The design features an integral foldable composite material flapping wing structure with smooth connections between different areas. It requires no auxiliary components, has a simple structure and few parts, and achieves lightweight and integrated foldable wings.

[0010] This invention discloses a method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft, the preparation steps of which are as follows:

[0011] Step 1: Obtain the dimensions of the foldable composite flapping wing structure based on mechanical calculations and analysis. Cut the prepreg according to the designed layup scheme to obtain a single layer of prepreg, and lay the prepreg according to the designed layup scheme.

[0012] Step 2: Use molding to prepare two identical single-sided integral strip springs.

[0013] Step 3: According to the size and other requirements of the micro aircraft, cut the flapping wing membrane to the corresponding size. Leave a notch at an appropriate position on the leading edge of the flapping wing membrane for the area of ​​the opposing strip spring, and leave adhesive tape for the area of ​​the slender rod.

[0014] Step 4: Adhesive surfaces of two identical single-sided integral strip springs are bonded to both sides of the adhesive tape of the flapping wing membrane using adhesive to form a foldable composite material flapping wing structure.

[0015] In step one, the prepreg material is used as the reinforcing material of the composite material, which is carbon fiber, glass fiber, Kevlar fiber, boron fiber, plant fiber or the above fiber fabrics. The matrix of the composite material is epoxy resin, polyester resin, styrene, styrene-butadiene, trans polyisoprene, cyanate ester, polyurethane, polynorbornene, polyimide, bismaleimide, polyamide, polyphenylene sulfide, polyaryletherketone, or polyvinyl alcohol.

[0016] The flapping wing membrane mentioned in step three is a polyimide film, polyethylene terephthalate film, polyimide film, polyester fiber film, polytetrafluoroethylene film, polyetheretherketone film, polyphenylene sulfide film, or polybenzimidazole film.

[0017] The adhesive mentioned in step four includes, but is not limited to, one of epoxy resin adhesive, epoxy phenolic adhesive, polyimide adhesive, phenolic resin adhesive and silicone resin adhesive. The specific type of adhesive selected is determined according to the polymer material in the selected component material. That is, the curing conditions of the adhesive, especially the curing temperature, must match the polymer material in the component material.

[0018] The advantages of the method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft according to the present invention are:

[0019] 1. The present invention provides a simple and feasible method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft, achieving integrated molding. By utilizing the layup and bonding of prepreg, a laminated structure with varying thickness is designed at the junction of the slender rod region and the opposing strip spring region, ensuring a natural and smooth transition and excellent overall integrity.

[0020] 2. The foldable wing fabricated according to the method for preparing a foldable composite material flapping wing structure for a micro flapping wing aircraft of the present invention has strong design flexibility. The leading edge of traditional handmade wings often uses composite carbon fiber rods of fixed diameter, which limits the design space. However, when fabricating a foldable wing according to this method, the thickness of the slender rod region and the opposing strip spring region can be designed separately by utilizing the changes in composite material layup, which has strong design flexibility. Attached Figure Description

[0021] Figure 1 This is a schematic diagram illustrating the application of a deployable composite material flapping wing structure for a micro flapping-wing aircraft during deployment.

[0022] Figure 2 This is a schematic diagram illustrating the application of a foldable composite material flapping wing structure for a micro flapping-wing aircraft during folding.

[0023] Figure 3 This is a front view of the unfolded composite material flapping wing structure.

[0024] Figure 4 This is a schematic cross-sectional view of the opposing strip spring region of the foldable composite material flapping wing structure.

[0025] Figure 5 This is a schematic diagram showing the dimensions of the cut flapping wing membrane.

[0026] Figure 6 This is a schematic diagram showing the bonding position between the adhesive surface of the strip spring and the flapping wing membrane.

[0027] Figure 7 This is a flowchart illustrating the fabrication method of a foldable composite material flapping wing structure for micro flapping-wing aircraft.

[0028] Figure 1 Chinese: 1. flapping wing membrane.

[0029] Figure 3 In the middle: 2. Slender rod region, 3. Opposing strip spring region, 4. Slender rod region.

[0030] Figure 5 5. Adhesive tape. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] The present invention discloses a foldable composite material flapping wing structure for a micro flapping-wing aircraft. It is an integral strip spring hinge used in conjunction with the flapping wing membrane 1, enabling deployment (e.g., Figure 1 (as shown) and folding (as shown) Figure 2(As shown) Two states. The foldable composite flapping wing structure is formed by bonding two single-sided integral strip springs to the front and back sides of the flapping wing membrane at the leading edge. Along the wingspan from the inside to the outside, the corresponding order of its construction is as follows: slender rod region 2, opposing strip spring region 3, slender rod region 4 (as shown) Figure 3 (As shown). The slender rod regions 2 and 4 have rectangular cross-sectional shapes, and the surface corresponding to the front view is the adhesive surface, which is bonded to the leading edge of the flapping wing membrane; the opposing strip spring region 3 has a cross-sectional shape of two symmetrical arcs (as shown). Figure 4 As shown in the diagram, this area corresponds to the opening area of ​​the flapping wing membrane and is not bonded to it, ensuring the foldable performance of the foldable composite flapping wing structure. The connection between the opposing strip spring area 3 and the two slender rod areas 2 and 4 has a curved transition area, ensuring the integrity of the foldable composite flapping wing structure. The shape and size design of the foldable composite flapping wing structure requires actual mechanical calculations based on the selected composite material type. This includes designing the width and thickness of one side of the slender rod areas 2 and 4, designing the thickness, radius, and central angle of the cross-sectional arc of the opposing strip spring area 3, and designing a variable thickness scheme at the area connection. For the foldable composite flapping wing structure of this invention used in micro flapping wing aircraft, the length of the slender rod area 2 or 4 at the end connected to the biomimetic micro flapping wing aircraft can be flexibly designed according to actual needs, reserving the length for connection with the biomimetic micro flapping wing aircraft.

[0033] This invention discloses a foldable composite material flapping wing structure for a micro flapping-wing aircraft. Based on the flapping motion of the micro flapping-wing aircraft's wings, the structure ensures that its stiffness meets requirements under normal flapping conditions, and that it can buffer external impacts by bending when the outer wing section encounters obstacles. When designing this foldable composite material flapping wing structure for a micro flapping-wing aircraft, key considerations include the selected composite material properties, the dimensions of the slender rod regions 2 and 4, and the geometry and dimensions of the opposing strip spring region 3. Based on the flapping wing dimensions of the micro flapping-wing aircraft, the recommended range for the width and thickness of the slender rod region of the designed foldable composite material flapping wing structure is (0.5-2.0) mm; the width and thickness of the single-sided opposing strip spring region should be on the same order of magnitude as the corresponding dimensions of the slender rod region, and the recommended range for the central angle of the cross-section of this region is (30-150)°.

[0034] The process of the fabrication method of the foldable composite material flapping wing structure for micro flapping wing aircraft of the present invention is as follows: Figure 5As shown, the layup angle and number of layers for the slender rod regions 2 and 4 and the strip spring region need to be designed first. The prepreg is then laid up and cut to obtain two identical composite material sheets. Two identical single-sided integral strip springs are prepared using compression molding as the curing method. According to the size requirements of the micro-aircraft, flapping wing membranes of corresponding sizes are cut, and a notch is left at an appropriate position on the leading edge of the flapping wing membrane for the opposing strip spring region 3 (e.g., ...). Figure 5 As shown), adhesive tape 5 is left for the slender rod areas 2 and 4. Finally, the adhesive surfaces of the two identical single-sided integral strip springs are bonded to both sides of the adhesive tape 5 of the flapping wing membrane 1 with adhesive, forming a foldable composite material flapping wing structure combined with the flapping wing membrane 1 (as shown). Figure 6 (As shown).

[0035] See Figure 7 This invention discloses a method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft, the specific preparation steps of which are as follows:

[0036] Step 1: Based on mechanical calculations, obtain the dimensions of the foldable composite flapping wing structure, lay up and cut the prepreg to obtain two identical prepreg sheets.

[0037] Step 2: Use molding to prepare two identical single-sided integral strip springs.

[0038] Step 3: According to the size requirements of the micro aircraft, cut the flapping wing membrane to the corresponding size. Leave a notch at an appropriate position on the leading edge of the flapping wing membrane for the opposing strip spring area 3, and leave adhesive tape 5 for the slender rod areas 2 and 4.

[0039] Step 4: Adhesive surfaces of two identical single-sided integral strip springs are bonded to both sides of adhesive tape 5 of flapping wing membrane 1 using adhesive to form a foldable composite material flapping wing structure combined with flapping wing membrane.

[0040] In step one, the prepreg material is used as the reinforcing material of the composite material, which is carbon fiber, glass fiber, Kevlar fiber, boron fiber, plant fiber or the above fiber fabrics. The matrix of the composite material is epoxy resin, polyester resin, styrene, styrene-butadiene, trans polyisoprene, cyanate ester, polyurethane, polynorbornene, polyimide, bismaleimide, polyamide, polyphenylene sulfide, polyaryletherketone, or polyvinyl alcohol.

[0041] The flapping wing membrane mentioned in step three is a polyimide film, polyethylene terephthalate film, polyimide film, polyester fiber film, polytetrafluoroethylene film, polyetheretherketone film, polyphenylene sulfide film, or polybenzimidazole film.

[0042] The adhesive mentioned in step four includes, but is not limited to, one of epoxy resin adhesive, epoxy phenolic adhesive, polyimide adhesive, phenolic resin adhesive and silicone resin adhesive. The specific type of adhesive selected is determined according to the polymer material in the selected component material. That is, the curing conditions of the adhesive, especially the curing temperature, must match the polymer material in the component material.

Claims

1. A foldable composite material flapping wing structure for a micro flapping-wing aircraft, characterized in that: The deployable composite material flapping wing structure includes an integral strip spring hinge, used in conjunction with the flapping wing membrane, and has two states: deployed and folded. The deployable composite material flapping wing structure is formed by two single-sided integral strip springs bonded to opposite sides of the leading edge of the flapping wing membrane. Along the wingspan from the inside out, the corresponding construction order is: slender rod region, opposing strip spring region, and slender rod region. The slender rod region has a rectangular cross-section, with the bonding surface corresponding to the front view, bonded to the leading edge of the flapping wing membrane. The opposing strip spring region has a cross-section of two symmetrical circular segments. The arc-shaped area corresponds to the opening of the flapping wing membrane and is not bonded to it, ensuring the foldable and deployable performance of the composite material flapping wing structure. The connection between the opposing strip spring area and the two slender rod areas has a curved transition area, ensuring the integrity of the foldable and deployable composite material flapping wing structure. This provides the necessary stiffness for the flapping wings of the micro flapping wing aircraft to maintain their deployed configuration under normal flapping, avoiding repeated bending and improving service life. When the outer section of the flapping wing encounters an obstacle during flapping, the impact load is greater than the peak moment of the strip spring bending. The opposing strip spring area can absorb energy and buffer external impacts through bending.

2. A method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft according to claim 1, characterized in that: The preparation steps are as follows: Step 1: Obtain the dimensions of the foldable composite flapping wing structure based on mechanical calculations and analysis. Cut the prepreg according to the designed layup scheme to obtain a single layer of prepreg and lay it up according to the designed layup scheme. Step 2: Prepare two identical single-sided integral strip springs using a molding method; Step 3: According to the size and other requirements of the micro aircraft, cut the flapping wing membrane to the corresponding size, leave a notch at an appropriate position on the leading edge of the flapping wing membrane for the area of ​​the opposing strip spring, and leave adhesive tape for the area of ​​the slender rod. Step 4: Adhesive surfaces of two identical single-sided integral strip springs are bonded to both sides of the adhesive tape of the flapping wing membrane using adhesive to form a foldable composite material flapping wing structure.

3. The method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft as described in claim 2, characterized in that, The prepreg mentioned in step one, the reinforcing material of the composite material is carbon fiber, glass fiber, Kevlar fiber, boron fiber, plant fiber or the above fiber fabric, and the matrix of the composite material is epoxy resin, polyester resin, styrene, styrene-butadiene, trans polyisoprene, cyanate ester, polyurethane, polynorbornene, polyimide, bismaleimide, polyamide, polyphenylene sulfide, polyaryletherketone, polyvinyl alcohol.

4. The method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft as described in claim 2, characterized in that, The flapping wing membrane mentioned in step three is a polyimide film, polyethylene terephthalate film, polyimide film, polyester fiber film, polytetrafluoroethylene film, polyetheretherketone film, polyphenylene sulfide film, or polybenzimidazole film.

5. The method for preparing a foldable composite material flapping wing structure for a micro flapping-wing aircraft as described in claim 2, characterized in that, The adhesive mentioned in step four includes one of epoxy resin adhesive, epoxy phenolic adhesive, polyimide adhesive, phenolic resin adhesive and silicone resin adhesive. The selection of adhesive needs to be determined according to the polymer in the component, that is, the curing temperature of the adhesive must match the polymer material in the component material.

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