A design method for morphing wings based on compliant mechanisms

Abstract

The present invention proposes a method for designing a morphing wing based on a compliant mechanism. The morphing wing includes a skin, a four-bar linkage, a main beam, a drive beam, and a compliant mechanism. The main beam and the drive beam are both arranged along the chord direction of the wing, wherein the drive beam and the main beam cooperate through a linear slide along the chord direction of the wing. The drive beam can move along the slide when driven by an external linear drive motor and can drive the main beam to move. The entire wing deformation is achieved by a combination of the four-bar linkage and the compliant mechanism. The middle portion of the wing is deformed by the main beam driving the four-bar linkage, and the leading edge portion is deformed by the drive beam driving the compliant mechanism. The present invention achieves a wing deformation method by optimizing the design to change the leading edge of the driven wing from an arc to a point. By designing a compliant mechanism and combining it with the four-bar linkage, the deformation of the leading edge of the deforming wing from an arc to a point is achieved. The entire deformation process is precisely controllable, and the target airfoil obtained after deformation is accurate and meets the design requirements.

Description

Technical Field

[0001] The invention relates to the technical field of deformable wings, in particular to a deformable wing design method based on a compliant mechanism. Background Art

[0002] Morphing wings are required to be able to achieve smooth and continuous deformation under the action of aerodynamic loads. Therefore, not only is the skin required to have large in-plane deformation capabilities, but it must also have a certain stiffness to be able to transfer aerodynamic loads to the internal skeleton and maintain a smooth and continuous shape to meet aerodynamic shape requirements.

[0003] Currently, aircraft wing deformation primarily relies on hydraulically driven rigid mechanical devices. These devices are complex, heavy, and space-consuming, offsetting the performance gains achieved by wing deformation. Flexible skin designs based on smart materials offer an effective approach to addressing these shortcomings of mechanically driven devices. However, flexible skins have weak out-of-plane stiffness, resulting in poor wing conformal performance under aerodynamic forces. Therefore, the technical maturity required for practical engineering applications remains to be improved.

[0004] In general, a compliant mechanism is a drive device between mechanical drive and flexible skin that realizes smooth deformation of the aircraft wing skin. Unlike traditional rigid mechanisms that achieve wing deformation through kinematic pairs and component connections, compliant mechanisms mainly rely on the elastic deformation of the wing structure to achieve the transmission and conversion of motion, force and energy. Compliant mechanisms have many advantages such as high precision, light weight, low friction, few parts, easy processing and miniaturization. In recent years, more and more researchers and scholars have pointed out that compliant mechanisms are more suitable for application in advanced aircraft design, especially in the field of deformable wings. However, when faced with the complex deformation requirements of large deflection such as the change of the leading edge of the wing from arc to point, the design of compliant mechanisms has many difficulties such as difficulty in precise control and poor deformation. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention proposes a deformable wing design method based on a flexible mechanism. Through optimization design, a wing deformation implementation method of driving the leading edge of the wing from an arc to a point is obtained. By designing a "fishbone-type" steel frame and combining it with a four-bar linkage mechanism, the deformation of the leading edge of the deformable wing from an arc to a point is achieved.

[0006] The technical solution of the present invention is:

[0007] A deformable wing based on a compliant mechanism comprises a skin, a four-bar linkage, a main beam, a driving beam and a compliant mechanism;

[0008] The main beam and the driving beam are arranged along the chord direction of the wing. The driving beam and the main beam are matched through a linear slide groove along the chord direction of the wing. A first collision block is installed on the driving beam, and a second collision block is installed on the main beam. The driving beam can move along the slide groove under the drive of an external linear drive motor. After the first collision block collides with the second collision block, the driving beam can continue to drive the main beam to move.

[0009] The four-bar linkage consists of links BE, BC, and DE. Links BC and DE are connected to the main beam at points C and D. The outer arc of link BE is designed according to the initial airfoil. The U-shaped groove at point A on link BE cooperates with the aircraft body, allowing link BE to have only rotational freedom.

[0010] A compliance mechanism is installed between the driving beam and the leading edge skin, and the ends of the compliance mechanism are hinged to the skin and the driving beam.

[0011] A method for designing a morphing wing comprises the following steps:

[0012] Step 1: According to the formula

[0013]

[0014] Determine the leading edge opening size d; where x is the chord-wise coordinate, y1(x) is the initial airfoil function, L1 is the initial airfoil arc length, L2 is the target airfoil arc length, and y1(x), L1, and L2 are all known quantities;

[0015] Step 2: Use the formula

[0016]

[0017] Calculate the main beam travel u1, where l′ AC , are the AC length, ∠ABC angle, ∠ACB angle, ∠ACD angle, and ∠BCD angle of the initial airfoil; l′ A ' C , are the AC length and ∠ABC angle of the target airfoil state respectively; l AB , l BC They are AB length and BC length respectively;

[0018] Using the formula

[0019] d=2y2(u2)

[0020] Determine the drive beam displacement u2, where d is the opening size determined in step 1, and y2(u2) is the ordinate of the point with abscissa u2 in the target airfoil function;

[0021] Step 3: Optimize the design of the compliant mechanism

[0022] The horizontal coordinate of the end of the compliant mechanism is used as the design variable, and the optimization goal is to achieve accurate deformation of the deformable wing. The maximum stress of the compliant mechanism is less than the allowable stress as a constraint condition. According to the displacement of the main beam and the driving beam in step 2, the deformation is simulated using finite element software. According to the deformation results, the deformed airfoil curve f can be obtained; after solving with the optimization algorithm, the coordinates of the end of the compliant mechanism in the optimal state are obtained, thereby realizing the design of the deformable wing.

[0023] Furthermore, the compliant mechanism adopts a fishbone steel frame, and the fishbone steel frame is connected to the front part of the skin and the driving beam by multiple struts, and the ends of the struts are hinged to the skin and the driving beam.

[0024] Furthermore, in step 3, the optimization model is:

[0025]

[0026] where x i are the coordinates of the ends of the compliant mechanism.

[0027] Beneficial effects

[0028] The present invention proposes a deformable wing design method based on a compliant mechanism. The method uses a "fishbone" steel frame and a four-bar linkage mechanism to achieve the deformation of the leading edge of the deformable wing from an arc to a pointed shape. The entire deformation process is precisely controllable, and the target airfoil obtained after deformation is accurate and meets the design requirements.

[0029] Additional aspects and advantages of the present invention will be set forth in part in the description which follows and, in part, will be obvious from the description which follows, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments with reference to the following drawings, in which:

[0031] Figure 1 Initial airfoil;

[0032] Figure 2 target airfoil;

[0033] Figure 3 side view of the deformed wing;

[0034] Figure 4 Top view of the deformed wing;

[0035] Figure 5 Four-bar linkage;

[0036] Figure 6 "Fishbone" steel frame;

[0037] Figure 7 The deformation process of a morphing wing.

[0038] Among them: 1. Drive beam; 2. Main beam; 3. Four-bar linkage; 4. "Fishbone" steel frame; 5. Leading edge skin; 6. Leading edge opening skin; 7. First collision block; 8. Second collision block. DETAILED DESCRIPTION

[0039] The present invention mainly targets the requirement of large deflection and complex deformation of the leading edge of the wing from arc to sharp, and proposes a design method for a deformable wing based on a compliant mechanism. The "fishbone-type" steel frame is combined with a four-bar linkage mechanism to realize the deformation of the leading edge of the deformable wing from arc to sharp.

[0040] like Figure 3 , Figure 4 , Figure 5 and Figure 6 As shown, the deformable wing based on a compliant mechanism includes a skin, a four-bar linkage, a main beam, a drive beam, and a compliant mechanism. The main beam and drive beam are both arranged along the chord direction of the wing. The drive beam and the main beam are connected by a linear slide along the chord direction of the wing. A collision block 1 is installed on the drive beam, and a collision block 2 is installed on the main beam. The drive beam can move along the slide when driven by an external linear drive motor. After the collision between the collision block 1 and the collision block 2, the drive beam drives the main beam to move. The four-bar linkage includes connecting rods BE, BC, and DE. Connecting rods BC and DE are connected to the main beam at points C and D. The outer arc surface of connecting rod BE is designed according to the initial airfoil. The U-shaped groove at position A of connecting rod BE cooperates with the aircraft body, so that connecting rod BE has only rotational freedom. A fishbone steel frame is installed between the driving beam and the leading edge skin as a compliant mechanism. Specifically in this embodiment, the fishbone steel frame is connected to the front of the skin and the driving beam by four struts, and the ends of the four struts are hinged to the skin and the driving beam.

[0041] Based on the above structure, the coordinates of the ends of the struts in the fishbone steel frame are used as design variables, and the accurate deformation of the morphing wing is taken as the optimization goal. The morphing wing design is realized through the following design method.

[0042] Step 1: Determine the leading edge opening size:

[0043] The chord length of the airfoil is L, the wing width is M, it bears a constant pressure load, and adopts a linear drive mechanism. The initial airfoil is as follows Figure 1 As shown, the target airfoil is Figure 2 As shown in Figure 2, the arc length of the airfoil decreases after wing deformation, so the leading edge of the wing needs to be opened to ensure geometric coordination. Here, the opening size d is determined by comparing the arc length of the target airfoil with the initial airfoil.

[0044]

[0045] Where x is the chord-wise coordinate, y1(x) is the initial airfoil function, L1 is the initial airfoil arc length, L2 is the target airfoil arc length, and d is the opening size. The initial airfoil arc length L1 and the target airfoil arc length L2 are known quantities. First, calculate the corresponding chord-wise coordinate x using the above formula, and then calculate the opening size d.

[0046] Step 2: Design of the Stroke of the Deformed Wing Drive Mechanism

[0047] The deformation of the entire wing is achieved by a combination of a four-bar linkage and a compliant mechanism. The middle part of the wing is deformed by the four-bar linkage driven by the main beam, and the leading edge part is deformed by the driving beam driving the "fishbone-type" steel frame.

[0048] First, determine the main beam travel u1 based on the four-bar linkage motion analysis:

[0049] Using the formula

[0050]

[0051] Calculate the main beam travel u1, the symbols in the formula mean as follows Figure 5 As shown, where l′ AC , are the AC length, ∠ABC angle, ∠ACB angle, ∠ACD angle, and ∠BCD angle in the initial airfoil state. AC , are the AC length and ∠ABC angle under the target airfoil state respectively. AB , l BC The lengths are AB and BC respectively.

[0052] During the wing deformation process, the skin at the leading edge opening is retracted into the wing along with the drive beam. By comparing the leading edge opening size with the target airfoil data, the drive beam displacement is determined to be u2:

[0053] d=2y2(u2)

[0054] Where d is the opening size determined in step 1, and y2(u2) is the ordinate of the point with abscissa u2 in the target airfoil function. Thus, u2 is obtained based on the opening size d and the target airfoil function.

[0055] The present invention adopts a single-motor drive method to meet the requirements of lightweight and easy control. Therefore, a "bump block" mechanism is designed to achieve single-motor drive stroke splitting. The "bump block" mechanism consists of "bump block 1" and "bump block 2". "Bump block 1" is fixed to the drive beam, and "bump block 2" is fixed to the main beam. In the initial airfoil state of the deformed wing, the distance between "bump block 1" and "bump block 2" is l: l = u2 - u1;

[0056] The motor-driven stroke is split by the "bump" mechanism into two components: the main beam displacement u1 and the drive beam displacement u2, respectively achieving wing deformation and skin retraction at the leading edge opening. During movement, the motor first drives the drive beam independently for a distance l. After "bump 1" collides with "bump 2," the motor then drives both the drive beam and the main beam simultaneously.

[0057] Step 3: Optimal design of compliant mechanism

[0058] The compliant mechanism uses a "fishbone" steel frame. The "fishbone" steel frame adopts a symmetrical design, so only one side of the joint coordinates needs to be optimized. Figure 6 As shown in the figure, the fishbone steel frame is driven by the driving beam, "H", "I", "J", and "K" are joints, and the joint coordinates are design variables. With the optimization goal of achieving accurate deformation of the morphing wing, the maximum stress of the fishbone steel frame is less than the allowable stress as a constraint condition, and the joint coordinates x of the steel frame are calculated. H ,x I ,x J ,x K Optimize. Joint J and joint K are connected to the driving beam, the vertical coordinate y J ,y K The coordinates are fixed. Joints H and K are connected to the skin, and the vertical coordinates yH,y I Determined by the initial airfoil function. The skin leading edge opening, drive mechanism, and compliance mechanism designed in steps 1, 2, and 3 are modeled and assembled in finite element software for simulation deformation. The deformed airfoil curve f can be obtained based on the deformation results.

[0059]

[0060] Where f is the deformed airfoil curve, y2 is the target airfoil curve, σ is the stress distribution function after deformation, and [σ] is the allowable stress. An optimization algorithm solves this problem, obtaining the optimal coordinates of the fishbone steel frame joints, thus enabling the design of a deformable wing.

[0061] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0062] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0063] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the technical features being referenced. Therefore, features specified as "first" or "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0064] This embodiment uses the method of the present invention to Figure 1 The initial shape of the wing in the deformation becomes Figure 2 The target shape of the wing in . It is known that the chord length of the wing is 500mm, the wingspan is 100mm, and it is subjected to a constant pressure load of 100Pa during deformation. A linear drive mechanism is used. The entire wing is made of aluminum alloy with an elastic modulus of 70GPa, a Poisson's ratio of 0.3, and an allowable stress of 364MPa. Since the wing is a symmetrical structure up and down, the upper wing surface is selected as the design object according to the principle of symmetry. The initial airfoil and target airfoil data are shown in Table 1. The origin of the coordinate axis is the x-axis, and the y-axis is as follows Figure 1 shown.

[0065] Table 1 Initial airfoil and target airfoil data

[0066]

[0067]

[0068] The main steps of this embodiment are as follows:

[0069] Step 1: Determine the size of the leading edge opening.

[0070] The upper wing surface arc length of the initial wing shape is 516.869 mm. The upper wing surface arc length of the target wing shape is 495.99 mm. Comparison shows that the arc length of the morphing wing decreases by 20.879 mm as it transforms from the initial airfoil to the target airfoil. An opening is added to the wing leading edge to ensure geometric compatibility. The opening size is determined as follows: d = 2 * 11.7 = 23.4 mm.

[0071]

[0072] Step 2: Design the stroke of the deformable wing drive mechanism.

[0073] Determine the main beam stroke u1=18mm as follows.

[0074]

[0075] The displacement of the driving beam is determined to be u2=77 mm according to the following formula.

[0076] d=2y2(u2)

[0077] In the initial airfoil state of the deformed wing, the distance between "bump 1" and "bump 2" is determined to be 59 mm according to the following formula.

[0078] l=u2-u1

[0079] The motor-driven stroke is split by the "bump" mechanism into two components: the main beam displacement u1 and the drive beam displacement u2, respectively achieving wing deformation and skin retraction at the leading edge opening. During movement, the motor first drives the drive beam independently for a distance of l = 59 mm. After "bump 1" collides with "bump 2," both the drive beam and the main beam are driven simultaneously.

[0080] Step 3: Optimal design of the compliant mechanism.

[0081] The compliant mechanism primarily consists of a "fishbone" steel frame. As the main component of the compliant mechanism, the optimized design of this "fishbone" steel frame is the core of this invention. With accurate deformation of the morphing wing as the optimization goal and maximum stress less than the allowable stress as the constraint, the coordinates of the "steel frame" joints are optimized:

[0082]

[0083] With the help of finite element software ABAQUS, the final optimized design is x H =90mm,x I =145mm, x J =125mm, x K =195mm.

[0084] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A design method for a morphing wing based on a compliant mechanism, characterized by: The deformable wing comprises a skin, a four-bar linkage, a main beam, a drive beam and a compliance mechanism; The main beam and the driving beam are arranged along the chord direction of the wing. The driving beam and the main beam are matched through a linear slide groove along the chord direction of the wing. A first collision block is installed on the driving beam, and a second collision block is installed on the main beam. The driving beam can move along the slide groove under the drive of an external linear drive motor. After the first collision block collides with the second collision block, the driving beam can continue to drive the main beam to move. The four-bar linkage consists of links BE, BC, and DE. Links BC and DE are connected to the main beam at points C and D. The outer arc of link BE is designed according to the initial airfoil. The U-shaped groove at point A on link BE cooperates with the aircraft body, allowing link BE to have only rotational freedom. A compliance mechanism is installed between the driving beam and the leading edge skin, and the ends of the compliance mechanism are hinged to the skin and the driving beam; The design method comprises the following steps: Step 1: According to the formula Determine the leading edge opening size d; where x is the chord-wise coordinate, is the initial airfoil function, L1 is the initial airfoil arc length, L2 is the target airfoil arc length, , L1, L2 are both known quantities; Step 2: Use the formula Calculate the main beam displacement u1, where , , , , are the AC length, ∠ABC angle, ∠ACB angle, ∠ACD angle, and ∠BCD angle in the initial airfoil state respectively; , are the AC length and ∠ABC angle under the target airfoil state respectively; , They are AB length and BC length respectively; Using the formula Determine the drive beam displacement u2, where d is the opening size determined in step 1, is the ordinate of the coordinate point with abscissa u2 in the target airfoil function; Step 3: Optimize the design of the compliant mechanism The horizontal coordinate of the end of the compliant mechanism is used as the design variable, and the optimization goal is to achieve accurate deformation of the deformable wing. The maximum stress of the compliant mechanism is less than the allowable stress as a constraint condition. According to the displacement of the main beam and the driving beam in step 2, the deformation is simulated using finite element software. According to the deformation results, the deformed airfoil curve f can be obtained; after solving with the optimization algorithm, the coordinates of the end of the compliant mechanism in the optimal state are obtained, thereby realizing the design of the deformable wing.

2. The method for designing a morphing wing according to claim 1, characterized in that: The compliant mechanism adopts a fishbone steel frame, and the fishbone steel frame is connected to the front part of the skin and the driving beam by a plurality of struts, and the ends of the struts are hinged to the skin and the driving beam.

3. The method for designing a morphing wing according to claim 2, characterized in that: In step 3, the optimization model is: in is the coordinate of the end of the compliant mechanism, f is the airfoil curve after deformation, is the target airfoil curve, is the stress distribution function after deformation, is the allowable stress.

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