An ultra-elliptical cross-section closed-cell sandwich spar for small solar-powered drones

Abstract

The application provides a super-elliptical cross-section closed chamber sandwich wing beam for a small solar unmanned aerial vehicle, and relates to the technical field of aircraft design. The device comprises an internal carbon fiber flange sandwich beam and a beam skin covering the outside of the internal carbon fiber flange sandwich beam; the internal carbon fiber flange sandwich beam comprises a light core layer, an upper carbon fiber flange and a lower carbon fiber flange, and the upper carbon fiber flange and the lower carbon fiber flange are arranged on the upper side and the lower side of the light core layer respectively; the beam skin continuously covers the outer contour of the internal carbon fiber flange sandwich beam and forms an annular closed chamber structure extending along the axial direction of the wing beam. The super-elliptical cross-section closed chamber sandwich wing beam for a small solar unmanned aerial vehicle has high bending stiffness and bearing efficiency, high torsional capacity, low stress concentration and cross-section warping, and enhances the overall structural stability and anti-instability capacity, and also meets the process requirements of low manufacturing cost, stable forming quality and simple assembly.

Description

Technical Field

[0001] This invention relates to the field of aircraft design technology, and in particular to a superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles. Background Technology

[0002] Currently, solar-powered long-endurance UAVs typically employ high aspect ratio wings and lightweight structural designs to reduce cruise power consumption, with their main load-bearing wing structure relying primarily on composite material spars. There are two main types of spars commonly used in engineering: one is a circular cross-section carbon fiber thin-walled tubular spar, which has a simple shape, is easy to form, and its closed-cell structure provides good torsional resistance; the other is a carbon fiber flange sandwich beam, composed of upper and lower unidirectional carbon fiber flanges and a lightweight core in the middle. This design fully utilizes the airfoil thickness to place high-modulus materials away from the neutral axis, thereby achieving higher bending load-bearing efficiency.

[0003] However, both of these existing structures have significant technical bottlenecks. While circular tube beams have good torsional resistance, their circular cross-sections are difficult to match with airfoil thickness, and the areas available for arranging carbon fiber flanges on the upper and lower sides are narrow, resulting in low bending efficiency. Furthermore, thin-walled tubes are prone to cross-sectional flattening deformation under bending loads, reducing load-bearing capacity and increasing the risk of local instability. While sandwich beams have high bending efficiency, they typically do not form a complete closed cell and have limited torsional resistance. They often require the use of the wing leading-edge skin to form a D-shaped box-shaped closed cell to meet torsional stiffness requirements, which additionally increases structural weight and manufacturing complexity. At the same time, traditional rectangular or near-rectangular cross-sections have abrupt curvature changes at corners, which can easily lead to stress concentration and cross-sectional warping. Additionally, debonding, local buckling, or compressive instability can easily occur near the compression flange.

[0004] Therefore, under the strict weight constraints of small solar-powered UAVs, how to simultaneously achieve high bending stiffness, high torsional stiffness, and good instability resistance in the wing spars structure, while also considering low manufacturing complexity and the risk of processing defects, has become an urgent problem to be solved. To this end, it is necessary to develop a new type of composite material wing spars structure to meet the low-cost, high-quality manufacturing requirements of small solar-powered UAVs. Summary of the Invention

[0005] The purpose of this invention is to provide a super-elliptical cross-section closed-cell sandwich wing sparb for small solar-powered drones, overcoming the shortcomings of existing circular carbon fiber tube beams, such as low bending load-bearing efficiency and easy cross-sectional flattening instability, as well as the insufficient torsional resistance, stress concentration at corners, and easy buckling and debonding of flanges of traditional rectangular sandwich beams. This invention enables the wing sparb to simultaneously possess high bending stiffness and load-bearing efficiency, high torsional resistance, low stress concentration and cross-sectional warping, enhancing the overall structural stability and instability resistance, while also taking into account the process requirements of low manufacturing cost, stable molding quality, and simple assembly. Ultimately, this invention provides a lightweight, high-efficiency, high-reliability, and easily engineering-implemented solution for small solar-powered drones.

[0006] To achieve the above objectives, the present invention provides a superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles, comprising an inner carbon fiber flange sandwich beam and a beam skin covering the outer side of the inner carbon fiber flange sandwich beam. The internal carbon fiber flange sandwich beam includes a lightweight sandwich layer, an upper carbon fiber flange, and a lower carbon fiber flange, with the upper and lower carbon fiber flanges respectively located on the upper and lower sides of the lightweight sandwich layer. The beam skin continuously covers the outer contour of the inner carbon fiber flange sandwich beam, forming an annular closed-cell structure extending along the axial direction of the wing beam.

[0007] Preferably, the outer contour composed of the internal carbon fiber flange sandwich beam and the beam skin satisfies the superelliptical cross-sectional shape: ; Where a is the half-width of the hyperelliptical cross section, b is the half-height of the hyperelliptical cross section, n is the hyperelliptic index, and n>2.

[0008] Preferably, the value range of the hyperelliptic index n is 3≤n≤5.

[0009] Preferably, the half-height b of the hyperelliptical cross section is less than half of the maximum thickness of the airfoil.

[0010] Preferably, the lightweight sandwich layer is a PMI foam sandwich and extends continuously along the axial direction of the wing beam to support the upper carbon fiber flange and the lower carbon fiber flange and maintain the cross-sectional height between them.

[0011] Preferably, both the upper carbon fiber flange and the lower carbon fiber flange are unidirectional carbon fiber laminates, and the fiber directions of the upper carbon fiber flange and the lower carbon fiber flange are arranged along the axial direction of the wing beam.

[0012] Preferably, the beam skin includes at least one +45° carbon fiber layup and at least one -45° carbon fiber layup.

[0013] Preferably, the beam skin is attached to and covers the upper and lower carbon fiber flanges of the internal carbon fiber flange sandwich beam, as well as the lateral transition area of ​​the lightweight sandwich layer.

[0014] Preferably, the internal carbon fiber flange sandwich beam serves as the forming support core and assembly positioning reference for the beam skin.

[0015] Therefore, the present invention employs the above-mentioned superelliptical cross-section closed-cell sandwich wing spars for small solar-powered drones, and the beneficial technical effects are as follows: (1) The present invention adopts an internal bending structure composed of an upper carbon fiber flange, a lower carbon fiber flange and a lightweight core, so that the high modulus carbon fiber material is arranged in the upper and lower approximately flat areas of the super elliptical cross section, which can make full use of the airfoil thickness, thereby improving the bending stiffness and bending load efficiency of the wing beam.

[0016] (2) The present invention forms an annular closed cell structure extending along the wing sparsity through ±45° carbon fiber layup, which enables the wing sparsity to have independent torsional load-bearing capacity, reduces the dependence on rigid wing skin or D-shaped box closed cell structure, thereby helping to reduce structural weight and manufacturing complexity.

[0017] (3) The present invention uses a super elliptical cross section as the outer contour of the wing beam. While maintaining a large width in the upper and lower regions to arrange unidirectional carbon fiber flanges, it eliminates the right angle and small rounded corner transition area of ​​the traditional rectangular sandwich beam, effectively reducing the adverse effects of local stress concentration and cross section warping.

[0018] (4) In this invention, the PMI foam core provides radial support for the ±45° carbon fiber closed cell layup, which can effectively reduce the possibility of cross-sectional flattening deformation and local buckling of the thin-walled closed cell structure under bending load, and reduce the risk of local instability.

[0019] (5) In this invention, the ±45° carbon fiber closed cell layup is bonded to the internal carbon fiber flange sandwich beam, which can form an auxiliary constraint on the upper carbon fiber flange and the lower carbon fiber flange, reducing the risk of debonding and buckling instability of the pressure flange.

[0020] (6) The present invention designs a step-by-step molding and overall curing assembly method. The internal carbon fiber flange sandwich beam also serves as a positioning part and a support core mold during the molding process, avoiding the complex demolding process of closed-cell section carbon fiber beams. It has the advantages of low cost, stable molding quality and high structural strength. Attached Figure Description

[0021] Figure 1 This is an overall schematic diagram of an embodiment of a superelliptical cross-section closed-cell sandwich wing spars for a small solar-powered unmanned aerial vehicle according to the present invention; Figure 2 This is a layered sectional view of an embodiment of a superelliptical cross-section closed-cell sandwich wing spars for a small solar-powered unmanned aerial vehicle according to the present invention; Figure 3 This is an axial cross-sectional view of an embodiment of a superelliptical cross-section closed-cell sandwich wing spars for a small solar-powered unmanned aerial vehicle according to the present invention. Figure 4 This is an exploded view of an embodiment of a superelliptical cross-section closed-cell sandwich wing spars for a small solar-powered unmanned aerial vehicle according to the present invention.

[0022] Figure Labels 1. Internal carbon fiber flange sandwich beam; 101. Upper carbon fiber flange; 102. Lower carbon fiber flange; 103. Lightweight sandwich layer; 2. Beam skin; 201. Left half shell; 202. Right half shell. Detailed Implementation

[0023] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0025] Example 1 like Figures 1-4 As shown, a superelliptical cross-section closed-cell sandwich wing spars for small solar-powered drones includes an inner carbon fiber flange sandwich beam 1 and a beam skin 2 covering the outside of the inner carbon fiber flange sandwich beam 1.

[0026] The internal carbon fiber flange sandwich beam 1 includes a lightweight sandwich layer 103, an upper carbon fiber flange 101 and a lower carbon fiber flange 102, with the upper carbon fiber flange 101 and the lower carbon fiber flange 102 respectively disposed on the upper and lower sides of the lightweight sandwich layer 103.

[0027] The lightweight sandwich layer 103 is a PMI foam sandwich layer that extends continuously along the axial direction of the wing beam. It supports the upper carbon fiber flange 101 and the lower carbon fiber flange 102 and maintains the cross-sectional height between them. Both the upper carbon fiber flange 101 and the lower carbon fiber flange 102 are unidirectional carbon fiber laminates, and the fiber directions of the upper carbon fiber flange 101 and the lower carbon fiber flange 102 are arranged along the axial direction of the wing beam.

[0028] The beam skin 2 continuously covers the outer contour of the inner carbon fiber flange sandwich beam 1, forming an annular closed-cell structure extending along the axial direction of the wing beam.

[0029] The beam skin 2 includes at least one +45° carbon fiber layup and at least one -45° carbon fiber layup, and the beam skin 2 adheres to and covers the lateral transition area of ​​the upper carbon fiber flange 101, the lower carbon fiber flange 102, and the lightweight core layer 103 of the internal carbon fiber flange sandwich beam 1. The internal carbon fiber flange sandwich beam 1 serves as the molding support core and assembly positioning reference for the beam skin 2.

[0030] The outer contour, composed of the internal carbon fiber flange sandwich beam 1 and the beam skin 2, satisfies the superelliptical cross-sectional shape: ; Where a is the half-width of the hyperelliptical cross section, b is the half-height of the hyperelliptical cross section, n is the hyperelliptic index, and n>2.

[0031] In this embodiment, the value of n should comprehensively consider the width of the carbon fiber flange arrangement, local stress concentration, and manufacturing difficulty. When n is close to 2, the hyperelliptical cross-section is close to an ellipse, and the area available for arranging unidirectional carbon fiber laminates on the upper carbon fiber flange 101 and the lower carbon fiber flange 102 is narrow, which is not conducive to improving bending load-bearing efficiency. When the value of n is too large, the hyperelliptical cross-section gradually approaches a rectangle, the local curvature change increases, and it may lead to higher stress concentration. Therefore, the value range of the hyperelliptic index n is 3≤n≤5, preferably n=4. This value can achieve a good balance between bending load-bearing efficiency, torsional closed chamber area, local stress level, and processing feasibility. In addition, the half-height b of the hyperelliptical cross-section is less than half of the maximum thickness of the airfoil, so as to make full use of the airfoil thickness to improve bending stiffness.

[0032] The present invention also provides a method for forming a superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles, comprising the following steps: Step S1: Prepare the PMI foam sandwich core of the required shape, and lay unidirectional carbon fiber laminates on the upper and lower sides of the PMI foam sandwich core to form the initial carbon fiber flange sandwich beam.

[0033] Step S2: The outer contour of the initial carbon fiber flange sandwich beam is machined into a superelliptical cross section to obtain the inner carbon fiber flange sandwich beam 1.

[0034] When machining the outer contour of the initial sandwich beam into a superelliptical cross section, a cutting and grinding process is adopted. During the machining process, it is ensured that the upper carbon fiber flange 101 and the lower carbon fiber flange 102 have sufficient continuous laying width, and sharp corners, notches or local thickness changes are avoided at the flange edges.

[0035] Step S3: The left half shell 201 and the right half shell 202 with superelliptical cross sections are made by using a half mold. A ±45° carbon fiber layup is laid in each half mold so that the left half shell 201 and the right half shell 202 form a semi-closed cell structure respectively.

[0036] Step S4: Using the internal carbon fiber flange sandwich beam 1 obtained in step S2 as the assembly positioning reference, place it between the left half shell 201 and the right half shell 202 for mold closing to obtain the wing beam semi-finished product.

[0037] During the molding process, the overall structure is vacuum bagged or molded, so that the left half shell 201 and the right half shell 202 are closed in the circumferential direction of the wing beam to form a continuous ±45° carbon fiber closed cell layup, namely the beam skin 2, and achieves gapless bonding with the outer contour of the internal carbon fiber flange sandwich beam 1.

[0038] Step S5: Inspect the mold line of the outer closed-cell ply of the semi-finished wing beam to obtain the super-elliptical cross-section closed-cell sandwich wing beam.

[0039] If there are discontinuous areas at the parting line, carbon fiber filaments are added to repair them to ensure the continuity of the outer closed cell.

[0040] Therefore, the present invention adopts the above-mentioned ultra-elliptical cross-section closed-cell sandwich wing beam for small solar-powered drones, which overcomes the defects of existing circular carbon fiber tube beams, such as low bending load-bearing efficiency and easy cross-section flattening instability, as well as the defects of traditional rectangular sandwich beams, such as insufficient torsional resistance, stress concentration at corners, and easy buckling and debonding of flanges. The wing beam has high bending stiffness and load-bearing efficiency, high torsional resistance, low stress concentration and cross-section warping, which enhances the overall structural stability and instability resistance. It also takes into account the process requirements of low manufacturing cost, stable molding quality and simple assembly. Finally, it provides a lightweight, high-efficiency, high-reliability and easy-to-engineer solution for small solar-powered drones.

[0041] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles, characterized in that, Includes an internal carbon fiber flanged sandwich beam and a beam skin covering the outside of the internal carbon fiber flanged sandwich beam; The internal carbon fiber flange sandwich beam includes a lightweight sandwich layer, an upper carbon fiber flange, and a lower carbon fiber flange, with the upper carbon fiber flange and the lower carbon fiber flange respectively disposed on the upper and lower sides of the lightweight sandwich layer. The beam skin continuously covers the outer contour of the inner carbon fiber flange sandwich beam, forming an annular closed-cell structure extending along the axial direction of the wing beam.

2. The superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, The outer contour formed by the internal carbon fiber flange sandwich beam and the beam skin satisfies a superelliptical cross-sectional shape: ； Where a is the half-width of the hyperelliptical cross section, b is the half-height of the hyperelliptical cross section, n is the hyperelliptic index, and n>2.

3. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 2, characterized in that, The range of values ​​for the hyperelliptic exponent n is 3 ≤ n ≤ 5.

4. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 2, characterized in that, The half-height b of the hyperelliptical cross section is less than half of the maximum thickness of the airfoil.

5. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, The lightweight sandwich layer is a PMI foam sandwich and extends continuously along the axial direction of the wing beam to support the upper carbon fiber flange and the lower carbon fiber flange and maintain the cross-sectional height between them.

6. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, Both the upper carbon fiber flange and the lower carbon fiber flange are unidirectional carbon fiber laminates, and the fiber directions of the upper carbon fiber flange and the lower carbon fiber flange are arranged along the axial direction of the wing beam.

7. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, The beam skin comprises at least one +45° carbon fiber layup and at least one -45° carbon fiber layup.

8. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, The beam skin is attached to and covers the upper and lower carbon fiber flanges of the internal carbon fiber flange sandwich beam, as well as the lateral transition area of ​​the lightweight sandwich layer.

9. A superelliptical cross-section closed-cell sandwich wing spars for small solar-powered unmanned aerial vehicles according to claim 1, characterized in that, The internal carbon fiber flange sandwich beam serves as the forming support core and assembly positioning reference for the beam skin.

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