Polyethylene film airship inflatable tail and method of manufacture

Abstract

This application discloses an inflatable tail fin for an airship made of polyethylene film, characterized by comprising: a spherical membrane made of polyethylene film; reinforcing ribs for securing the spherical membrane; and longitudinally extending partitions welded into the cavity of the spherical membrane, wherein the longitudinal direction refers to the direction from the root of the tail fin to the tip of the tail fin; and multiple partitions arranged laterally within the cavity of the spherical membrane. This application also discloses a method for manufacturing an inflatable tail fin for an airship made of polyethylene film. This solves the problem that polyethylene film cannot withstand high pressure.

Description

Technical Field

[0001] This application relates to the field of near-space airship design, and in particular to the design of airship tail structure. Background Technology

[0002] Aerostats rely on an internal gas lighter than air to fly, and include airships, tethered balloons, and free balloons. One current development direction for airships is the stratospheric high-altitude airship. Stratospheric airships have received considerable attention in near-space flight platforms. Unlike free balloons, they can perform powered flight, gaining a degree of trajectory control, making them of significant application value and broad development prospects. Currently, stratospheric airships are mostly made of fabric skin materials, gaining rigidity after withstanding the internal and external pressure differences at their service ceiling. However, traditional fabric airship membranes have a high density, relying solely on the membrane's own resistance to pressure differences, similar to the early development of overpressure balloons.

[0003] The excessive weight of the capsule increases the cost of various processes, including manufacturing, folding and transportation, pressure holding and unfolding, and distribution.

[0004] Polyethylene film airships integrate overpressure balloon technology into their design, using polyethylene film as the airship's body material and employing warp and circumferential reinforcing ribs to withstand stress. Furthermore, the airship's shape is modified into a teardrop-shaped streamline to reduce drag, overcoming the problems caused by the airship's own weight during manufacturing, pressurization, and deployment of fabric airships. This results in increased flight altitude and payload capacity. Polyethylene film airships can serve as an effective supplement to traditional fabric airships and overpressure balloons, offering significant application value in long-endurance flights and area-based loitering.

[0005] The tail fin plays a crucial role in the stability and control of an airship. A simple hull lacks attitude stability.

[0006] Because the main gasbag of a polyethylene film airship is made of an extremely thin polyethylene film structure, a rigid tail fin structure cannot be installed; only a flexible inflatable tail fin structure can be attached. Furthermore, the tail fin must also be made of polyethylene film. This makes the design of a polyethylene tail fin structure with overpressure resistance a major technical challenge for polyethylene film airships. Summary of the Invention

[0007] This application proposes an inflatable tail fin for a polyethylene film airship and a manufacturing method thereof, which solves the problem that polyethylene film cannot withstand high pressure.

[0008] On one hand, this application provides an inflatable tail fin for a polyethylene film airship, comprising: a spherical membrane made of polyethylene film; reinforcing ribs for holding the spherical membrane in place; and longitudinally extending partitions welded into the cavity of the spherical membrane, wherein the longitudinal direction refers to the direction from the root of the tail fin to the tip of the tail fin; and multiple partitions arranged laterally within the cavity of the spherical membrane.

[0009] In one embodiment of this application, the tail fin is constructed by longitudinally stacking columns restrained by multiple circumferential reinforcing ribs, with longitudinal reinforcing ribs connecting adjacent columns at multiple designated points.

[0010] In one embodiment of this application, the bottom of the tail fin leaves space for the expansion of the main airbag bulge, so that the bottom of the tail fin conforms to the radial bulge of the main airbag.

[0011] In one embodiment of this application, the tail fin is provided with multiple longitudinal reinforcing ribs, which are used to be fixed to the main airbag reinforcing ribs at the root of the tail fin.

[0012] In one embodiment of this application, the partition is rectangular, isosceles trapezoidal, or isosceles triangle in shape.

[0013] In one embodiment of this application, the tail fin membrane has longitudinal wrinkles.

[0014] In one embodiment of this application, the spherical membrane deforms when subjected to the pressure difference between the inside and outside, and the maximum force on the partition is at the middle position of the bottom of the tail fin.

[0015] On the other hand, this application also proposes a method for manufacturing an inflatable tail fin of an ethylene film airship to manufacture the inflatable tail fin of an ethylene film airship as described in any embodiment of this application. The method includes the following steps: making a spherical membrane from a polyethylene film; reinforcing the spherical membrane with reinforcing ribs to withstand the pressure difference between the inside and outside; and welding a longitudinally extending partition layer into the cavity of the spherical membrane.

[0016] Furthermore, the layout of the partitions and stiffeners is analyzed using the mass point discretization method of three-dimensional triangular membrane elements, satisfying at least one of the following conditions:

[0017] Maximum pressure difference between the inside and outside of the tail fin;

[0018] Weld the partition layer in a location where the longitudinal stress is relatively small;

[0019] When the tail fin maintains a flat shape, the longitudinal force is less than the lateral force.

[0020] Furthermore, in one embodiment of this application, longitudinal reinforcing ribs are connected at designated points between adjacent cylindrical air bubbles of the tail fin to maintain the geometry of the tail fin, and / or, the tail fin is mounted on the radial bulge at the tail of the main airbag, and the mounting method is that the tail fin reinforcing ribs and the main airbag reinforcing ribs are fixed at the bottom.

[0021] Furthermore, in one embodiment of this application, stiffness and pressure tests are performed on the tail fin.

[0022] The above-described technical solutions adopted in the embodiments of this application can achieve the following beneficial effects:

[0023] This invention differs from previous inflatable tail fin designs. It uses reinforcing ribs to hold the polyethylene film in place to bear the internal and external pressure differences, and employs rope connections at the common contact surfaces of the airfoils to maintain the tail fin's geometric shape. This cable-membrane tail fin configuration allows for easy attachment to the meridional and circumferential reinforcing ribs of the polyethylene airship. Furthermore, the assembly of multiple airfoils increases the tail fin's inherent rigidity, offering several beneficial effects. Attached Figure Description

[0024] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0025] Figure 1 A schematic diagram of a polyethylene film airship and its tail structure for the application scenario of this application.

[0026] Figure 2 This is a flowchart illustrating an embodiment of the method of this application;

[0027] Figure 3 This is the initial calculated shape of the tail fin;

[0028] Figure 4.a It is a change in the shape of the tail fin;

[0029] Figure 4.b This is the shape of the tail section assembled on the airship; a view of the tail section.

[0030] Figure 4.c This is a side view of the shape of the tail fin assembled on the airship;

[0031] Figure 5 This refers to the stress condition of the longitudinal partition;

[0032] Figure 6 These are the radial and circumferential stresses on the bottom bulge;

[0033] Figure 7.a It is the shape of a large bubble planar membrane on the upper part of the tail fin;

[0034] Figure 7.b It is the shape of a large bubble in the middle of the tail fin;

[0035] Figure 7.c It is the shape of a large bubble planar membrane at the lower part of the tail fin;

[0036] Figure 8 Final mold shape;

[0037] Figure 9 The fitted diaphragm plane cutting shape;

[0038] Figure 10 The completed polyethylene inflatable tail fin structure. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0040] To address the shortcomings of existing technologies, this patent solves the problem of installing an inflatable tail fin at the tail of a polyethylene film airship, thereby achieving airship stability and good maneuverability.

[0041] The technical solutions provided by the various embodiments of this application are described in detail below with reference to the accompanying drawings.

[0042] Figure 1 This is a schematic diagram of a polyethylene film airship and tail fin structure applicable to the scenario described in this application. This application proposes an inflatable tail fin for a polyethylene film airship, comprising: a spherical membrane made of polyethylene film; reinforcing ribs for securing the spherical membrane; and longitudinally extending partitions welded into the cavity of the spherical membrane, wherein the longitudinal direction refers to the direction from the root of the tail fin to the tip of the tail fin; multiple partitions are arranged laterally within the cavity of the spherical membrane. To ensure structural cleanliness, the membrane used is still a 38μm polyethylene film. The method for maintaining the tail fin's shape remains the same: using ropes (3mm reinforcing ribs) to secure the spherical membrane to withstand the internal and external pressure difference, and welding partitions at locations with lower longitudinal stress. The initial tail fin shape is as follows: Figure 3 As shown.

[0043] In one embodiment of this application, the tail fin structure comprises longitudinally stacked cylinders restrained by multiple rings of circumferential reinforcing ribs, with longitudinal reinforcing ribs connecting adjacent cylinders at multiple designated points. The basic design concept of the tail fin is to use stacked cylinders restrained by rings of circumferential reinforcing ribs, with longitudinal reinforcing ribs connecting adjacent cylinders at designated points. That is, traditional tail fins use layered linear restraint, while polyethylene cable membrane tail fins use point restraint through reinforcing ribs. Furthermore, to maintain a flat tail fin shape with lower longitudinal stress than lateral stress, a further longitudinal layer is installed on the tail fin.

[0044] It is understood that the circumferential direction of the tail fin refers to a direction substantially perpendicular to the longitudinal direction. Preferably, the circumferential section of the tail fin is parallel to the axis of the main airbag.

[0045] In one embodiment of this application, the bottom of the tail fin leaves space for the expansion of the main airbag bulge, so that the bottom of the tail fin conforms to the radial bulge of the main airbag.

[0046] In one embodiment of this application, the tail fin is provided with multiple longitudinal reinforcing ribs, which are used to be fixed to the main airbag reinforcing ribs at the root of the tail fin.

[0047] It should be noted that, Figure 3 This is a schematic diagram of the tail fin structure, which is also the initial shape for the simulation calculation of the tail fin's deformable shape.

[0048] The bottom generatrix is ​​the generatrix after deformation of the main airbag's radial reinforcing ribs. The material at the bottom of the tail fin can be directly interpolated based on the shape of the main airbag bulge. The designed tail fin adopts a three-airbag structure (upper, middle, and lower). The bottom airbag smooths the uneven tail area of ​​the main airbag in the height direction, facilitating the design and installation of the upper and middle airbags. The bottom contains eight small bulges, corresponding to the two large bulges of the main airbag. Since the tail fin also needs to fit circumferentially with the main airbag bulges, the bottom airbag uses a triangular structure at its leading and trailing edges. Here, the circumferential direction of the main airbag is the direction surrounding the main airbag's axis. The base of the triangle is the circumferential length of the main airbag bulge, and the vertices of the triangle are the straight lines of the leading and trailing edges of the upper and middle airbags. The upper and middle airbags need to function as the hypotenuse of the tail fin's leading edge; therefore, the leading edge bulge is no longer a quadrilateral structure but a triangular bulge shape, and the upper airbag has only seven bulges. Additionally, the top of the tail fin also needs to be sealed. Its initial shape is planar, but it only has 6 bulges (including 1 triangular bulge). Therefore, the tail fin structure has a total of (8+2)+8+7+6=31 small bulges. The discrete points of a single tail fin bulge are reduced to 7×7. For the reinforcing rib structure, the cross nodes are fixed in the simulation, and the stiffness and diameter of the mass segment representing the reinforcing rib are increased. In one embodiment of this application, the spherical membrane deforms when subjected to an internal and external pressure difference, with the maximum force on the interlayer occurring at the middle position of the bottom of the tail fin. The deformed tail fin after being subjected to a pressure difference of 300Pa is as follows... Figure 4.a Figure ~c shows the shape of the airship's tail fin after deformation, and its shape after assembly onto the airship. The forces acting on the tail fin membrane and the longitudinal diaphragm are as follows... Figure 5 and Figure 6 As shown.

[0049] Figure 5 The stress of each diaphragm is shown to indicate that the stress on the diaphragm is much less than the yield strength of the membrane. It can be seen that the maximum stress on the spherical membrane is 2.5 MPa at the bottom center. The maximum stress on the diaphragm is in the middle and upper airbags, reaching only 0.01 MPa, indicating that the stress on the diaphragm membrane is significantly reduced compared to when only longitudinal diaphragms are used without reinforcing ribs to constrain the tail fin. In the figure, the horizontal axis represents the selected discrete node number, and the vertical axis represents the diaphragm stress (Pa). The location of each diaphragm is shown in the figure below, based on its number. Figure 3 .

[0050] Figure 6The circumferential and meridional stress distribution of the membrane including the top airbag. Fourteen curves correspond to the seven bulges formed by the longitudinal stiffeners of the top airbag. The five curves in each graph represent the stress at the intersection of the five circumferential stiffeners and the longitudinal stiffeners. It can be concluded that the stress on the membrane is much less than the yield strength stress (10MPa).

[0051] In one embodiment of this application, the partition is rectangular, isosceles trapezoidal, or isosceles triangle in shape.

[0052] In one embodiment of this application, the tail fin film has longitudinal wrinkles. During processing, the cutting pattern of the three large air bubbles is as follows: Figure 7.a As shown in ~c. This figure shows the cutting pattern of the tail fin membrane, corresponding to the three large air bubbles at the top, middle, and bottom.

[0053] Since the designed tail fin is an assembled structure, the upper, middle, and lower airbags need to be welded and sealed separately during processing. The method for obtaining the planar cut-out shape of the tail fin is still determined by the solved transverse and longitudinal mass segment lengths. Taking the most complex bottom airbag cut-out shape as an example, the cut-out pattern is shown in Figure 7. Since the tail fin is a front-to-back symmetrical structure, the upper center line of the bottom airbag is taken as the axis of symmetry of the cut-out pattern. From the upper center line downwards, the spherical membrane material passes through half of the upper surface, the front surface of the airbag, and half of the bottom surface of the airbag in sequence. Calculate from the first longitudinal line of the first small bulge on the right to the left. First, calculate the length y(n) of the current longitudinal line, where n is the current longitudinal line number. Then, calculate the distance x(n,i) between each mass point on the current longitudinal line and the corresponding mass point on the next longitudinal line, where i is the mass point number on the current longitudinal line, i = 1 to 7. The longest distance max(x(n,i)) is added to the current longitudinal line position to obtain the position of the next cut-out longitudinal line. Finally, the shapes of the eight small bulges are derived, as shown by the thin black lines along the vertical axis in the figure. In addition, the bottom airbag requires the addition of triangular cutout patterns at the front and rear. Here, the vertical lines are line segments originating from the vertices of the triangles, and the lateral distances are equivalent to deflection angles, i.e., the maximum vertices deflection angle corresponding to the distance between the mass points of each line segment. The middle and upper airbags use the same cutout method, but it should be noted that the diagonal line at the leading edge of the tail fin results in a triangular cutout shape for the head airbag.

[0054] The tail fin film cutting pattern after edge fitting is as follows: Figure 8 As shown, the tail fin membrane has excessive wrinkles. Specifically, during processing, the cut membrane shape is required to be as smooth as possible without any wavy appearance, necessitating edge fitting of the resulting cut membrane pattern. The fitting curve is shown in the figure, where the discrete points are... Figure 7.aThe required material for the longitudinal line obtained in ~c. The fitting curve used is of a low order, a quadratic and cubic polynomial curve. Unlike the main airbag trimming, the tail fin trimming requires fitting not only the edges but also the positions containing transverse reinforcing ribs. The excess material of the spherical membrane is calculated by subtracting the original position from the fitted position. The trimming curve shows that there is more excess material at the leading edge of the tail fin, especially at the bottom of the triangular leading edge. The excess material in the upper airfoil of each airbag is less than that in the lower airfoil. This means that after the tail fin is inflated and maintains the same pressure differential, the excess spherical membrane below the upper airbag may extend into the upper airbag of the middle airbag. Similarly, the excess spherical membrane below the middle airbag will extend into the upper airbag of the lower airbag.

[0055] Figure 2 This is a flowchart of an embodiment of the method of this application, which includes the following steps 210 to 250.

[0056] Step 210: Make a spherical membrane using polyethylene film.

[0057] Step 220: Use reinforcing ribs to tighten the spherical membrane to withstand the pressure difference between the inside and outside.

[0058] Preferably, the layout of the reinforcing ribs is analyzed using a three-dimensional triangular membrane element mass point discretization method to satisfy the maximum internal and external pressure difference of the tail fin.

[0059] Step 230: Weld a longitudinally extending septum into the spherical cavity.

[0060] Preferably, the layout of the partition is analyzed using the mass point discretization method of three-dimensional triangular membrane unit, and the partition is welded at the position where the longitudinal force is small, so that the longitudinal force is smaller than the lateral force when the tail fin is kept flat.

[0061] It should be noted that the optimization analysis method for the polyethylene tail fin structure employs a three-dimensional triangular membrane element mass point discretization method. Since the overall size of the tail fin is much smaller than the main airbag, even if designed according to the structure's inherent elastic modulus, it will not reach a yield strength of 10 MPa. In other words, while the tail fin's strength requirements are relatively easy to meet, maintaining its shape requires a reasonable arrangement of layers and reinforcing ribs.

[0062] It can be deduced that the maximum stress on the interlayer under an internal pressure of 300 Pa is 2.5 MPa at the bottom center. The maximum stress on the spherical membrane is also 2.5 MPa at the bottom center. Therefore, the maximum pressure difference of the tail fin is expected to reach 1000 Pa.

[0063] Step 240: Tail wing assembly and main airbag installation.

[0064] Furthermore, in one embodiment of this application, longitudinal reinforcing ribs are connected at designated points between adjacent cylindrical bubbles of the tail fin to maintain the geometry of the tail fin.

[0065] When the main airbag is installed, the tail wing is installed on the radial bulge at the rear of the main airbag. The installation method is that the tail wing reinforcing rib and the main airbag reinforcing rib are fixed at the bottom.

[0066] Preferably, the tail fin airfoil is a relatively wide NACA0024 symmetrical airfoil. For example, it is installed on the second and third radial bulges from the bottom of the main airbag. The installation method is that the tail fin reinforcing ribs and the main airbag reinforcing ribs are fixed at the bottom. At the same time, space is left at the bottom of the tail fin to allow for the full expansion of the second and third bulges of the main airbag.

[0067] Step 250: In one embodiment of this application, a stiffness test and a pressure test are performed on the tail fin.

[0068] This leads to the following conclusion: the shape of each longitudinally spaced membrane layer is as follows Figure 9 As shown, the shape and size of the 20 diaphragms determine the overall shape of the tail fin. The location of each diaphragm, based on its number, is shown below. Figure 3 The horizontal axis of each diaphragm image represents the diaphragm width, and the vertical axis represents the diaphragm height, in meters (m).

[0069] The completed polyethylene tail fin structure is as follows Figure 10 As shown, this image is a photograph of the actual tail fin shape produced.

[0070] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0071] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. The term “and / or” as used herein includes all or any units and all combinations of one or more associated listed items.

[0072] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical, terminological, and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0073] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A polyethylene film inflatable tail fin for an airship, characterized in that, include: A spherical membrane made of polyethylene film; The reinforcing ribs are used to hold the spherical membrane in place to withstand the pressure difference between the inside and outside. The tail fin is constructed by stacking columns longitudinally with multiple circumferential reinforcing ribs holding it in place, and longitudinal reinforcing ribs are connected at multiple designated points between adjacent columns in the longitudinal direction. And longitudinally extending partitions welded into the bulbous cavity, the longitudinal direction being from the root of the tail fin to the tip of the tail fin. There are multiple partitions arranged laterally along the tail fin. The shape of the partitions is rectangular, isosceles trapezoidal, or isosceles triangle. Multiple partitions are arranged laterally in the bulbous cavity. The bulbous membrane of the tail fin is provided with multiple bulges formed by the intersection of circumferential and longitudinal reinforcing ribs. The maximum stress position of the partitions is located at the middle of the bottom of the tail fin. And the bottom of the tail fin leaves space for the expansion of the main airbag bulge, so that the bottom of the tail fin is conformal to the radial bulge of the main airbag.

2. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The tail fin is an assembled structure, with the upper, middle and lower airbags welded and sealed respectively.

3. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The tail fins are mounted on the second and third radial bulges from the end of the main airbag.

4. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The tail fin is provided with multiple longitudinal reinforcing ribs, which are used to fix to the main airbag reinforcing ribs at the root of the tail fin.

5. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The edge fitting curves of the tail fin film pattern after edge fitting are quadratic and cubic polynomial curves.

6. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The tail fin membrane has longitudinal wrinkles.

7. The polyethylene film airship inflatable tail fin as described in claim 1, characterized in that, The maximum force on the spherical membrane is 2.5 MPa at the bottom center.

8. The method for manufacturing an inflatable tail fin for an ethylene film airship as described in any one of claims 1 to 7, characterized in that, The process includes the following steps: forming a spherical membrane from a polyethylene film; reinforcing the spherical membrane with reinforcing ribs to withstand the pressure difference between the inside and outside; and welding a longitudinally extending partition into the cavity of the spherical membrane.

9. The manufacturing method as described in claim 8, characterized in that, The layout of the partitions and stiffeners is analyzed using the mass point discretization method of three-dimensional triangular membrane elements, satisfying at least one of the following conditions: Maximum pressure difference between the inside and outside of the tail fin; Weld the partition layer in a location where the longitudinal stress is relatively small; When the tail fin maintains a flat shape, the longitudinal force is less than the lateral force.

10. The manufacturing method as described in claim 8, characterized in that, Longitudinal reinforcing ribs are connected at designated points between adjacent cylindrical air bubbles of the tail fin to maintain the geometry of the tail fin, and / or the tail fin is mounted on the radial bulge at the rear of the main airbag, with the tail fin reinforcing ribs and the main airbag reinforcing ribs being fixed at the bottom. Stiffness and pressure tests were conducted on the tail fin.

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