A flexible deformable shell skin for folding wings

Abstract

This invention discloses a flexible shell deformable skin for folding wings, relating to the field of flexible structure design for variator aircraft. The invention involves cutting an airfoil profile into a thin, elastic plate, hollowing out the middle section, and leaving an annular structure with equal upper and lower edges. This annular structure includes a leading edge, trailing edge, upper edge, and lower edge of the airfoil; the upper and lower edges are strip-shaped structures; the upper and lower edges are wavy in the direction perpendicular to the plate surface, forming a wave pattern along the length consisting of several straight segments – crests – straight segments – troughs – straight segments. This flexible shell deformable skin can be used for folding wings, replacing the skin structure near the folding axis. It solves the problem of continuous and smooth surface deformation under large wing skin deformation, possesses load-bearing capacity, strong design flexibility, and is easy to manufacture.

Description

Technical Field

[0001] This invention relates to the field of flexible structure design for variator aircraft, and more specifically to the design and manufacturing method of a flexible shell deformable skin for folding wings. Background Technology

[0002] Variant aircraft can change their shape at any time during flight to adapt to different flight environments, ensuring optimal aerodynamic performance. The shape of a variant aircraft can change in various ways; folding wings are one such transformation. Z-folding reduces wing span, improving maneuverability, while wingtip folding improves directional stability at high speeds, reduces induced drag, and effectively enhances aerodynamic efficiency.

[0003] Folding wings during deformation (such as Figure 1 As shown, the skin closer to the folding center is under compression, while the skin further away is under tension. The skin near the folding axis undergoes significant deformation; therefore, the skin near the folding axis must be flexible. Currently, the flexible skins near the folding axis of folding wings include corrugated structures and "fish-scale" structures. While these have good deformation and load-bearing capacity, they both have issues with surface smoothness, affecting aerodynamic efficiency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a flexible shell deformable skin for folding wings, replacing the skin structure near the folding axis, and meeting the requirements for deformation and load-bearing capacity of the flexible skin during folding, as well as the requirements for smooth and continuous surface.

[0005] This invention is implemented as follows:

[0006] A flexible deformable skin for folding aircraft wings, characterized in that the deformable skin is formed by interconnecting a set of airfoil-section flexible plates; specifically, an airfoil section is cut out of an elastic thin plate, the middle part is hollowed out, leaving an annular structure with equal upper and lower edges, the annular structure including an airfoil leading edge, an airfoil trailing edge, an airfoil upper edge, and an airfoil lower edge; the chord length of the airfoil leading edge is greater than the width of the airfoil upper edge and the width of the airfoil lower edge; the airfoil upper edge and the airfoil lower edge are strip-shaped structures; the wing... The upper edge of the airfoil and the lower edge of the airfoil are made into a wave shape in the direction perpendicular to the plate surface, forming a wave shape of several straight segments-crest segments-straight segments-trough segments-straight segments along the length direction; for the crest segments and trough segments, they are cut in the middle in the width direction of the airfoil to form upper and lower layers. The upper and lower layers of the same segment have opposite wave directions. When the upper layer is a crest, the lower layer is a trough, and when the upper layer is a trough, the lower layer is a crest. The upper and lower layers are naturally connected at the straight segments; the wave shape of the upper edge of the airfoil and the wave shape of the lower edge of the airfoil are symmetrical about the chord plane.

[0007] Furthermore, the wave crests or troughs at the same chordal position on the upper or lower edge of the airfoil are opposite to the wave crests or troughs on the same layer of the flexible plate of the adjacent airfoil section, and the wave plates that are close to each other on the same layer are welded together to form a grid structure.

[0008] Furthermore, the size of the mesh pores in the mesh structure depends on the wavelength and wave height of the wave; foam rubber is used to fill the mesh pores, and a flexible film is used to cover the surface to form a flexible shell deformable skin to transmit aerodynamic loads.

[0009] Furthermore, connecting plates of the same shape as the flexible airfoil section flexible plate are provided at both ends of the flexible shell deformable skin to connect the flexible shell deformable skin to the wing skin near the folding axis. The stiffness of the connecting plate is greater than that of the flexible airfoil section flexible plate to ensure the connection stiffness of the structure.

[0010] Furthermore, the distance d between the flexible plates of the adjacent airfoil profile, the chord length m of the airfoil leading edge, the chord length n of the airfoil trailing edge, and the width h of the airfoil upper and lower edges; in the wave shape of the straight segment-crest segment-straight segment-trough segment-straight segment, the wave direction before and after the straight segment is opposite, the chord length a of the straight segment, the chord length b at both ends of the crest segment (trough segment), and the wave height d / 2 of the crest (trough); the wave shape of the lower edge of the airfoil is symmetrical to the wave shape of the upper edge of the airfoil about the chord plane.

[0011] Furthermore, a coordinate system is established with the leading edge endpoint of the airfoil-shaped flexible plate as the origin, the perpendicular line through the leading edge endpoint in the direction perpendicular to the plate surface as the y-axis, the chord as the x-axis, and the width direction as the z-axis. The bent corrugated plate is projected onto the xy-plane. Let the waveform be a sine wave, and establish the curve equation f(x,y,z)=0 for the midline of the upper and lower edges. In the first corrugated plate, the two endpoints x1=m and x2=m+b. Then, the curve equation of the first corrugated plate projected onto the xy-plane is... From the arc length integral formula Calculate the length of a single wave plate.

[0012] Furthermore, the trailing edge of the flexible airfoil section is cut along the chord plane to form an upper trailing edge and a lower trailing edge, allowing them to slide relative to each other and releasing the shear stress between the upper and lower trailing edges. A groove is dug at the lower trailing edge, with a length of r and a depth of u. A hook-shaped component is installed at the upper trailing edge near the upper edge of the airfoil, with a long side height of q, a short side height of w, a width of r / 2, a depth of k, and a wall thickness of δ. The long side of the hook-shaped component is welded to the upper trailing edge on the inner side of the portion above the chord line, and the short side of the hook-shaped component, i.e., the portion below the chord line, passes through the groove. A rigid rod spans both ends of the groove and connects to the edge of the groove at the lower trailing edge. The hook-shaped component hooks onto the rigid rod to prevent the upper and lower trailing edges from separating.

[0013] The advantages of this invention compared to the prior art are as follows:

[0014] This invention proposes a flexible shell deformable skin for folding wings, which is formed by connecting a set of airfoil-section flexible plates to form a flexible shell. When adjacent airfoil-section flexible plates deform, they rotate relative to each other, forming a smooth deformable surface. It has good deformation capacity and load-bearing capacity, strong design flexibility, and is easy to process.

[0015] The flexible shell deformable skin of the present invention can be used for folding wings to replace the skin structure near the folding axis. Based on the large deformation of the wing skin, it solves the problem of continuous and smooth surface deformation, has high out-of-plane load capacity, strong designability, and is easy to process. Attached Figure Description

[0016] Figure 1 Schematic diagram of spanwise deformation of a folding wing;

[0017] Figure 2 Schematic diagram of flexible shell deformable skin;

[0018] Figure 3 Schematic diagram of the flexible plate and local waveform segment of the airfoil section;

[0019] Figure 4 A schematic diagram of the projection surface of the airfoil flexible shell connecting the grid;

[0020] Figure 5 Schematic diagram of the trailing edge structure of the airfoil.

[0021] Among them, 1-lower corrugated plate, 2-upper corrugated plate, 3-lower rear corrugated plate, 4-upper rear corrugated plate, 5-straight plate, 6-cut slit, 7-crack stop hole, 8-upper rear edge, 9-lower rear edge, 10-hook-shaped piece, 11-rigid rod, 12-groove. Detailed Implementation

[0022] To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the following examples provide a more detailed description of the invention. It should be noted that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0023] The flexible shell deformable skin for folding wings in this invention (e.g.) Figure 2 (As shown) It is composed of a set of interconnected flexible airfoil profile plates. The flexible airfoil profile plates are as follows... Figure 3As shown, an airfoil profile is cut out of an elastic thin plate, with the middle section hollowed out, leaving a ring-shaped structure of equal width at the upper and lower edges. The chord length at the leading edge of the airfoil is longer. The upper and lower edges of the airfoil are strip-shaped structures, which are made into a wave shape in the direction perpendicular to the plate surface, forming a straight segment-crest segment-straight segment-trough segment-straight segment-crest segment…-straight segment along the length direction. For the crest and trough segments, they are cut in the middle in the width direction of the edge strip, forming upper and lower layers. The upper layer is the crest and the lower layer is the trough, and vice versa. The wave shape of the upper edge of the airfoil is symmetrical to the wave shape of the lower edge about the chord plane. When the wing folds and bends upward, the upper side of the skin near the folding axis is under pressure and the lower side is under tension. Due to the Poisson effect, the upper skin of the airfoil elongates and the lower skin shortens. In order to release the internal stress, the trailing edge of the flexible plate of the airfoil profile is cut along the chord plane so that it can slide relative to the lower skin. The crests (or troughs) on the flexible flanges of the airfoil profile are paired with the troughs (or crests) on adjacent flexible flanges of the airfoil profile. These corrugated plates, positioned close together on the same level, are welded together to form a grid structure. The size of the grid pores depends on the wavelength and wave height of the corrugation. To transfer aerodynamic loads, foam rubber is used to fill the grid pores, and the surface is covered with a flexible adhesive film to form a flexible deformable skin. Connecting plates of the same shape as the flexible flanges of the airfoil profile are installed at both ends of the flexible deformable skin, connecting it to the wing skin near the folding axis.

[0024] An airfoil-shaped flexible plate is a thin, elastic plate with an airfoil shape, hollowed out in the middle, leaving a ring-shaped structure with equal width at the top and bottom edges, such as... Figure 3 As shown.

[0025] The annular structure is divided into the airfoil leading edge, trailing edge, upper edge, and lower edge. The chord length of the airfoil leading edge is m, the chord length of the airfoil trailing edge is n, and the width of the upper and lower edges is h. The upper and lower edges are strip-shaped structures. The upper and lower edges are made into a wave shape in the direction perpendicular to the plate surface, forming a straight segment-crest segment-straight segment-trough segment-straight segment-crest segment…-straight segment along the length direction. For the crest and trough segments, they are cut in the middle of the width direction of the edge strip, dividing them into upper and lower layers. The upper and lower layers of the same segment have opposite wave directions. When the upper layer is a crest, the lower layer is a trough, and vice versa. The upper and lower layers are naturally connected at the straight segments. The wave directions before and after the straight segments are opposite. The chord length of the straight segment is a, the chord lengths at both ends of the crest (trough) segment are b, and the crest (trough) height is d / 2. Figure 3 The solid line represents the upper layer (upper wave plate 2, rear upper wave plate 4), and the dashed line represents the lower layer (lower wave plate 1, rear lower wave plate 3); the wave shape of the lower edge of the airfoil is symmetrical to the wave shape of the upper edge of the airfoil about the chord plane.

[0026] A coordinate system is established with the leading edge of the flexible airfoil-section plate as the origin, the perpendicular line through the leading edge in the direction perpendicular to the plate surface as the y-axis, the chord as the x-axis, and the width direction as the z-axis. The bent corrugated plate is then projected onto the xy-plane, as shown below. Figure 4 As shown, let's assume the waveform is a sine wave and establish the curve equation f(x,y,z)=0 for the midline of the upper and lower edges. Taking the first wave plate as an example, with the two endpoints x1=m and x2=m+b, the curve equation of the projection of the first wave plate onto the xy plane is: From the arc length integral formula

[0027] The length of a single wave plate can be calculated.

[0028] When the wing folds and bends upwards, the upper side of the skin near the folding axis is under pressure and the lower side is under tension. Due to the Poisson effect, the upper edge strip of the flexible plate in the airfoil section elongates and the lower edge strip shortens. To release internal stress, the trailing edge of the airfoil is cut along the chord plane, dividing it into an upper trailing edge 8 and a lower trailing edge 9, allowing them to slide relative to each other. A groove 12 is dug at the lower trailing edge, with a length of r and a depth of u. A hook-shaped component 10 is installed at the upper trailing edge near the upper edge of the airfoil. The hook-shaped component has a long side height of q, a short side height of w, a width of r / 2, a depth of k, and a wall thickness of δ. The long side of the hook-shaped component is welded to the upper trailing edge on the inner side of the portion above the chord line, and the short side of the hook-shaped component (the portion below the chord line) passes through the groove. A rigid rod crosses both ends of the groove and connects to the edge of the groove at the lower trailing edge. The hook-shaped component hooks onto the rigid rod 11 to prevent the upper and lower trailing edges from separating. Figure 5 As shown.

[0029] The distance *d* between adjacent flexible airfoil sections is such that the crests (or troughs) at the same chordal position on the upper (or lower) edge of the airfoil are paired with the troughs (or crests) on the same layer of the adjacent flexible airfoil section. The corrugated plates on the same layer are welded together to form a grid structure. In this grid structure, the pore size depends on the wavelength and height of the wave. To transfer aerodynamic loads, foam rubber is used to fill the grid pores, and a flexible adhesive film is applied to the surface, forming a flexible, deformable skin. The skin surface is smooth and even. A schematic diagram of the grid structure's projection is shown below. Figure 4 As shown.

[0030] Connecting plates of the same shape as the flexible airfoil section flexible plate are installed at both ends of the flexible shell deformable skin to connect the flexible shell deformable skin to the wing skin near the folding axis. The stiffness of the connecting plates should be greater than that of the flexible airfoil section flexible plate to ensure the connection stiffness of the structure.

[0031] The following are specific data examples:

[0032] In this embodiment, the NACA0012 airfoil is selected for the design of the flexible airfoil shell. The relative thickness of the airfoil is 12%, the chord length c = 400 mm, the spanwise length of the flexible shell L = 200 mm, the width of both the upper and lower edges of the airfoil is h = 10 mm, the chordwise length of the leading edge is m = 30 mm, the chordwise length of the trailing edge is n = 60 mm, and the thickness is t = 1 mm. The material of the flexible plate of the airfoil profile is 7-series aluminum alloy with an elastic modulus E = 71.7 GPa, Poisson's ratio μ = 0.33, and density ρ = 2.81 g / cm³. 3 .

[0033] When the wing bends, the deformation of the flexible shell deformable skin mainly occurs in the span direction. The size of the deformable mesh pores is related to the chord length *a* of the straight plate, the chord length *b* at both ends of the corrugated plate after bending, and the distance *d* between adjacent flexible plates of the airfoil section. The bending deformation of the flexible shell deformable skin is borne by the deformation of the corrugated plates. Based on the small deformation assumption, the parameters are adjusted to meet the load-bearing capacity and the deformation requirements of the corrugated plates. The distance between adjacent flexible plates of the airfoil section is determined to be d = 10 mm, the thickness of the flexible plate is t = 1 mm, the chord length at both ends of the corrugated plate after bending is b = 26 mm, the chord length of the straight plate 5 is a = 14 mm, and the wave height is 5 mm. Therefore, a single flexible plate of the airfoil section has 9 straight plates and 8 corrugated plates. The two ends of the first corrugated plate are x1 = 30 mm and x2 = 56 mm. The curve equation of the projection of the first corrugated plate onto the xy plane is... From the arc length integral formula The length of a single wave plate can be calculated to be 28.24 mm. Therefore, the initial chord length of the flexible airfoil section is 417.92 mm.

[0034] The NACA0012 airfoil is symmetrical about the chord plane, therefore the flexible plate of the airfoil profile is also an axisymmetric structure. To fabricate a single flexible plate for the airfoil profile, a 1mm thick elastic sheet is selected. The NACA0012 airfoil profile with a chord length of 417.92mm is cut from this sheet. The middle portion of the sheet is hollowed out, leaving equal-width upper and lower edges, which are connected to the leading edge by an arc of length m = 30mm. The width of both the upper and lower edge strips is h = 10mm. The chord length of the straight plate at the trailing edge of the airfoil is f = 64mm. A point x1 = 30mm is taken at the midline of the upper edge width of the airfoil plate. A line 28.24mm to the right is drawn along the midline of the upper edge width. Then, lines 28.24mm to the right are drawn every 14mm along the midline of the upper edge width on the x-axis. The same treatment is applied to the lower and upper edges. A 1.0mm diameter anti-cracking hole 7 is drilled at the endpoints of the scribed lines. The flexible plate is wire-cut using a 0.4 mm diameter molybdenum wire to form a slit 6, thus creating an airfoil-shaped flexible plate. The airfoil-shaped flexible plate is then stamped to form its initial bending shape using a 5 mm crest (trough) and sinusoidal waveform.

[0035] The trailing edge of the flexible airfoil section is cut along the chord line, with a cut length of n = 60 mm. A groove is dug at the lower end of the trailing edge near the lower edge of the airfoil, with a groove length of r = 20 mm and a depth of u = 4 mm. The hook-shaped component has a long side height of q = 8 mm, a short side height of w = 3.7 mm, a length of 10 mm, a width of k = 6.3 mm, and a wall thickness of δ = 1.5 mm. The rigid rod is 25 mm long, 2 mm thick, and 2 mm high. When the wing folds and bends upward, to release internal stress, the trailing edge of the airfoil is cut along the chord plane, allowing the upper and lower edge strips to slide relative to each other. The hook-shaped component is placed in the groove; the inner side of the hook-shaped component on the upper part of the chord line is welded to the upper edge strip, the hook-shaped component passes through the groove, and the rigid rod crosses both ends of the groove and contacts the edge of the groove at the lower end of the trailing edge. Figure 5 As shown.

[0036] Twenty flexible airfoil profile plates are arranged along the span direction, with a distance d = 10 mm between adjacent flexible airfoil profile plates. The wave crests (or troughs) at the same chord position on the upper (or lower) edge of the airfoil are opposite to the wave troughs (or crests) on the same layer of the adjacent flexible airfoil profile plates. The wave plates that are close to each other on the same layer are welded together to form a grid structure.

[0037] In the grid structure, the pore size depends on the wavelength and wave height of the wave. To transfer aerodynamic loads, rubber foam is used to fill the grid pores, and a flexible adhesive film is used to cover the surface, forming a flexible, deformable skin to ensure good airtightness and a smooth skin surface. A schematic diagram of the grid structure's projection is shown below. Figure 4 As shown, connecting plates of the same shape as the flexible airfoil section flexible plate are welded to both ends of the flexible shell deformable skin, connecting the flexible shell deformable skin to the wing skin near the folding axis. The stiffness of the connecting plates must be greater than that of the flexible airfoil section flexible plate to ensure the connection stiffness of the structure.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements can be made without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A flexible deformable shell skin for folding wings, characterized in that, The deformable skin is formed by a set of airfoil-section flexible plates connected to each other; specifically, an airfoil section is cut out on the elastic thin plate, the middle part is hollowed out, leaving an annular structure with an upper edge and a lower edge of equal width. The annular structure includes the airfoil leading edge, the airfoil trailing edge, the airfoil upper edge, and the airfoil lower edge. The chord length of the airfoil's leading edge is greater than the width of the airfoil's upper edge and lower edge; the airfoil's upper and lower edges are strip-shaped structures; the airfoil's upper and lower edges are made into a wave shape in the direction perpendicular to the plate surface, forming several straight segments-crest segments-straight segments-trough segments-straight segments along the length direction; for the crest and trough segments, they are cut in the middle in the width direction of the airfoil to form upper and lower layers, with the upper and lower layers of the same segment having opposite wavy directions, the upper layer being a crest when the lower layer is a trough, and the upper layer being a trough when the lower layer is a crest, and the upper and lower layers naturally connect at the straight segments; The wavy shape at the upper edge of the airfoil is symmetrical to the wavy shape at the lower edge of the airfoil about the chord plane; The crests or troughs at the same chord position on the upper or lower edge of the airfoil are opposite to the troughs or crests on the same layer of the flexible plate of the adjacent airfoil section. The corrugated plates that are close to each other on the same layer are welded together to form a grid structure. Connecting plates of the same shape as the flexible airfoil section flexible plate are set at both ends of the flexible shell deformable skin to connect the flexible shell deformable skin to the wing skin near the folding axis. The stiffness of the connecting plate is greater than that of the flexible airfoil section flexible plate to ensure the connection stiffness of the structure. The trailing edge of the airfoil-shaped flexible plate is cut along the chord plane to divide it into an upper trailing edge and a lower trailing edge, allowing them to slide relative to each other and release internal stress. A groove is dug at the lower end of the trailing edge, with a length of r and a depth of u. A hook-shaped component is installed at the upper end of the trailing edge near the upper edge of the airfoil. The hook-shaped component has a long side height of q, a short side height of w, a width of r / 2, a depth of k, and a wall thickness of δ. The long side of the hook-shaped component is welded to the upper end of the trailing edge on the inner side of the portion above the chord line, and the short side of the hook-shaped component, i.e., the portion below the chord line, passes through the groove. A rigid rod spans both ends of the groove and connects to the edge of the groove at the lower end of the trailing edge. The hook-shaped component hooks onto the rigid rod to prevent the upper end of the trailing edge from separating from the lower end of the trailing edge.

2. The flexible deformable shell skin for folding wings according to claim 1, characterized in that, The distance d between adjacent flexible plates of the airfoil profile, the chord length m of the airfoil leading edge, the chord length n of the airfoil trailing edge, and the width h of the airfoil upper and lower edges; in the wave shape of the straight segment-crest segment-straight segment-trough segment-straight segment, the wave direction before and after the straight segment is opposite, the chord length a of the straight segment, the chord length b at both ends of the crest segment (trough segment), and the wave height d / 2 of the crest (trough); the wave shape of the lower edge of the airfoil is symmetrical to the wave shape of the upper edge of the airfoil about the chord plane.

3. The flexible deformable shell skin for folding wings according to claim 1, characterized in that, Establish a coordinate system with the leading edge endpoint of the flexible airfoil section as the origin, the perpendicular line through the leading edge endpoint in the direction perpendicular to the plate surface as the y-axis, the chord as the x-axis, and the width direction as the z-axis. Project the bent corrugated plate onto the xy-plane. Let the waveform be a sine wave, and establish the curve equation f(x,y,z)=0 for the midline of the upper and lower edges. In the first corrugated plate, the two endpoints x1=m and x2=m+b. Then, the curve equation of the projection of the first corrugated plate onto the xy-plane is: From the arc length integral formula Calculate the length of a single wave plate.

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