Strength calculation method for hull floating frame of amphibious aircraft without shear sheet

Abstract

The invention provides a shear-piece-free amphibious aircraft hull floating frame strength calculation method, a fuselage and a hull of an amphibious aircraft are of a shear-piece-free structure, a hull bulkhead on the lower portion of the fuselage of the amphibious aircraft is of a floating frame form, and the floating frame is not directly connected with hull skin. According to the scheme of the ship body floating frame structure without the shear sheet, the manufacturing and assembling cost and the weight cost of an aircraft can be reduced, meanwhile, the provided similar ship body floating frame strength calculation method can be used for guiding design and strength calculation of the aircraft bulkhead structure, and the method has high practical application value. According to the method provided by the invention, the external load borne by the floating frame is simplified into a plurality of concentrated forces, so that stress analysis and subsequent failure analysis and structural optimization can be performed on the floating frame by adopting a classical engineering beam theory, and the method is used for guiding structural design and strength calculation of hull bulkheads of amphibious aircrafts and seaplane; design work can be effectively simplified, and efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of aircraft structure strength design, and in particular to a method for calculating the strength of an amphibious aircraft hull floating frame without shear plates. Background Art

[0002] Traditional aircraft fuselage bulkheads are generally connected to the skin through shear plates, which transfer loads between the fuselage bulkheads and the skin through their own shear stiffness. The lower hull of an amphibious aircraft needs to withstand a large bottom water load pressure. For hull bulkheads with traditional designs, the water load directly acting on the hull skin will be transmitted to the bulkheads through the hull long spars and shear plates. At the same time, after the bulkheads are deformed by load, they will also transfer and diffuse part of the load to the hull wall panels through the shear plates, and the other part will be transferred and diffused to the upper fuselage wall panels. Therefore, the load transfer path of the entire fuselage hull is very complex, and it is difficult to accurately calculate its strength using existing engineering methods, which brings great difficulty to the design work. Summary of the invention

[0003] In order to solve the problems existing in the traditional aircraft fuselage bulkhead, the purpose of the present invention is to provide a strength calculation method for an amphibious aircraft hull floating frame without shear plates, which has simple structure, good assembly processability and light weight.

[0004] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0005] A method for calculating the strength of a floating frame of an amphibious aircraft hull without shear plates, wherein the fuselage hull of the amphibious aircraft adopts a shear plate-free structure, and the hull bulkhead of the amphibious aircraft fuselage lower part adopts a floating frame form, and the floating frame is not directly connected to the hull skin. The method comprises the following steps:

[0006] Step S1, determining the size, direction and action point of the external load according to the station arrangement of the aircraft hull buoyancy frame and the long stringer, and the bottom water load pressure distribution;

[0007] Step S2, determining the main internal force distribution of the buoyancy frame according to the preliminary configuration size of the aircraft hull buoyancy frame and the load input determined in step S1;

[0008] Step S3, determining the working stress of different parts of each cross section of the buoyancy frame according to the internal force of the aircraft hull buoyancy frame and the preliminary cross-sectional dimensions;

[0009] Step S4, determining the allowable stress of each part of the aircraft hull buoyancy frame according to the aircraft design requirements, material selection and cross-sectional dimensions;

[0010] Step S5, determining the safety margin of each section of the aircraft hull buoyancy frame by comparing the working stress and the allowable stress;

[0011] Step S6, for the cross section with insufficient or excessive safety margin, adjusting and optimizing the corresponding cross section size according to the comparison result;

[0012] Step S7, repeating steps S3 to S5 according to the adjusted cross-sectional dimension parameters;

[0013] Step S8, verifying the strength of the aircraft hull buoyancy frame; wherein, the stress conditions of the amphibious aircraft in actual use are simulated to check whether the strength of the buoyancy frame meets the design requirements.

[0014] According to a method for calculating the strength of an amphibious aircraft hull float frame without shear plates provided by the present invention, no direct load transfer occurs between the aircraft hull float frame and the hull skin.

[0015] According to the strength calculation method of the amphibious aircraft hull floating frame without shear plates provided by the present invention, when the amphibious aircraft takes off and lands on the water surface or glides on the water, the bottom of the hull will be subjected to water pressure. These pressure loads act directly on the hull skin, and the hull skin transmits the water pressure load to the long stringer through its connection with the long stringer. The long stringer further transmits the load to the aircraft hull floating frame through its connection point with the aircraft hull floating frame, and finally transmits it from the hull floating frame to the upper frame of the fuselage and diffuses it to the fuselage wall plate.

[0016] According to a method for calculating the strength of an amphibious aircraft hull floating frame without shear plates provided by the present invention, the aircraft hull wall plate only serves as a bottom plate structure to bear the bottom water load pressure and does not participate in the load diffusion and transfer between bulkheads.

[0017] According to a shear-sheet-free amphibious aircraft hull float frame strength calculation method provided by the present invention, when performing strength calculation analysis, a strength calculation analysis model is constructed, and the model only includes a single fuselage lower hull float frame, and does not include other fuselage structures.

[0018] According to a method for calculating the strength of an amphibious aircraft hull float frame without shear plates provided by the present invention, in step S1, the external load on the aircraft hull float frame is a number of concentrated forces F=Pc×B×L, and the concentrated force F acts at the intersection of the aircraft hull float frame and the axis of the long girder, and points to the inside of the hull along the normal direction of the outer surface of the hull skin.

[0019] Among them, Pc is the distributed pressure of water load on the bottom of the ship, B is the spacing between hull bulkheads, and L is the spacing between hull long girders.

[0020] According to a method for calculating the strength of an amphibious aircraft hull floating frame without shear plates provided by the present invention, in step S2, the main internal forces of the aircraft hull floating frame include section bending moment M and shear force Q, which are determined by engineering beam theory.

[0021] According to a method for calculating the strength of an amphibious aircraft hull floating frame without a shear sheet provided by the present invention, in step S3, when determining the working stress of different parts of each cross section of the aircraft hull floating frame, the selection of the cross section position is determined by the position of the long stringer, and the working stress f of the flange and the working stress fs of the web are calculated respectively, and the calculation formula is as follows:

[0022] f=My / I;fs=Q / ht;

[0023] Wherein, I is the bending inertia moment of the floating frame section, y is the distance from the edge of the flange to the neutral axis of the floating frame section, h is the height of the floating frame web, and t is the thickness of the floating frame web.

[0024] According to a method for calculating the strength of an amphibious aircraft hull float frame without shear plates provided by the present invention, in step S4, factors determining the allowable stress of the float frame include the allowable value of the material, stability control, and the service life of the aircraft.

[0025] According to a method for calculating the strength of an amphibious aircraft hull float frame without shear plates provided by the present invention, in step S8, the verified test piece only includes a single lower fuselage hull float frame, and the verification method includes: test loading, support method and consistency verification.

[0026] It can be seen that for amphibious aircraft and seaplanes, the shear-free hull floating frame structure provided by the present invention has the advantages of simple structure, good assembly process and light weight. At the same time, the present invention provides a strength calculation method based on this floating frame structure, the mechanical model is simple and clear, the calculation process is complete and clear, and it can be used to guide the structural design and strength calculation of the hull bulkhead of amphibious aircraft and seaplanes, which can effectively simplify the design work and improve efficiency.

[0027] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The utility model is a typical hull schematic diagram of an amphibious aircraft in the prior art.

[0029] Figure 2 The present invention is a structural schematic diagram of a conventional hull bulkhead containing shear plates in the prior art.

[0030] Figure 3 The present invention is a flow chart of an embodiment of a method for calculating the strength of an amphibious aircraft hull floating frame without shear plates.

[0031] Figure 4 The present invention is a schematic structural diagram of an aircraft hull buoyancy frame without shear plates in an embodiment of a method for calculating the strength of an amphibious aircraft hull buoyancy frame without shear plates.

[0032] Figure 5 The present invention is a simplified flow chart of an embodiment of a method for calculating the strength of an amphibious aircraft hull floating frame without shear plates. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0035] See also Figures 1 to 5 The present invention provides a method for calculating the strength of an amphibious aircraft hull floating frame without a shear plate, the method comprising the following steps:

[0036] Step S1, according to the station arrangement of the aircraft hull buoy frame and the long stringer, and the bottom water load pressure distribution, determine the size, direction and action point of the external load. Because the external load is the main basis and input for the design of the buoy frame structure, its size, direction and action point will directly affect the stress and deformation of the buoy frame.

[0037] Step S2, determining the main internal force distribution of the floating frame according to the preliminary configuration size of the aircraft hull floating frame and the load input determined in step S1. The internal force distribution is the interaction force generated at various locations inside the floating frame structure to resist external response when the floating frame is subjected to external load.

[0038] Step S3, according to the internal force of the aircraft hull buoyancy frame and the preliminary cross-sectional dimensions, determine the working stress of different parts of each cross section of the buoyancy frame. The working stress is the concentration of internal forces borne by each part of the material of the buoyancy frame structure under normal working conditions, which reflects the specific stress conditions and severity of different parts of the buoyancy frame.

[0039] Step S4, according to the aircraft design requirements, material selection and cross-sectional dimensions, determine the allowable stress of each part of the aircraft hull buoyancy frame. The allowable stress is the maximum stress value that different parts of the buoyancy frame can withstand under specific load conditions, which takes into account factors such as material static strength performance, fatigue performance, and structural stability.

[0040] Step S5, by comparing the working stress and the allowable stress, determine the safety margin of each section of the aircraft hull floating frame. The safety margin is a quantitative index of the strength reserve of the floating frame, which reflects whether the strength reserve of the floating frame is sufficient when subjected to external loads.

[0041] Step S6, for the cross section with insufficient or excessive safety margin, the corresponding cross section size is adjusted and optimized according to the comparison result. The stress distribution and strength reserve of the floating frame, as well as the structural weight, can be improved by adjusting the cross section size.

[0042] Step S7, the adjusted cross-sectional dimension parameters need to be verified again, and steps S3 to S5 are repeated according to the adjusted cross-sectional dimension parameters to ensure that the adjusted floating frame design meets the safety requirements and weight indicators.

[0043] Step S8, verifying the strength of the aircraft hull buoyancy frame; wherein the load conditions of the amphibious aircraft in actual use are simulated to check whether the strength of the buoyancy frame meets the design requirements.

[0044] Among them, in the traditional fuselage hull, shear plates are often used to connect the skin and the frame to transmit shear force. However, in the design of the amphibious aircraft of this embodiment, in order to simplify the structure, reduce weight and improve the overall performance, a structure without shear plates is adopted, which means that the floating frame is not directly connected to the skin, but other means are used to maintain the integrity and stability of the structure. This design reduces the assembly nail holes and load effects between the skin and the floating frame, reducing the risk of cracking or damage to the skin. At the same time, it also enables the floating frame to adapt to deformation more flexibly when subjected to external loads, thereby protecting the entire fuselage hull from damage.

[0045] In this embodiment, there is no direct load transfer between the aircraft hull float frame and the hull skin. Specifically, when the amphibious aircraft takes off and lands on the water or glides on the water, the bottom of the hull will be subjected to water pressure, and these pressure loads act directly on the hull skin. As the part directly in contact with the water, the hull skin will transfer the water pressure load it bears to the long stringer through its connection with the long stringer. As a longitudinal reinforcing member, the long stringer can effectively disperse and transfer these loads; the load it bears will be further transferred to the aircraft hull float frame by the long stringer through its connection point with the aircraft hull float frame, and finally transmitted from the hull float frame to the upper fuselage frame and diffused to the fuselage wall panel.

[0046] Among them, the hull floating frame is an important part of the lower hull frame of amphibious aircraft, designed to maintain the shape of the fuselage and provide support for the longitudinal structural parts. At the same time, it is also an important structure for bearing and transmitting bottom water loads and other loads; the hull skin is a thin shell structure covering the hull floating frame, which is in direct contact with water and bears water pressure loads. The skin needs to be strong enough to resist water pressure and effectively transfer these loads to the internal support structure. The long stringer is a longitudinal reinforcement member inside the hull, which is used to support the skin and transfer loads. They are connected to the skin and the floating frame to form a stable structural system; the upper fuselage frame is located on the upper part of the aircraft fuselage and is effectively connected to the hull floating frame to further disperse and transfer loads; the fuselage wall panel is one of the main structural parts of the aircraft fuselage, responsible for bearing and dispersing loads from all directions.

[0047] In this embodiment, the aircraft hull wall plate only serves as a bottom plate structure to bear the bottom water load pressure and does not participate in the load diffusion and transfer between bulkheads, which effectively simplifies the load transmission path of the aircraft fuselage hull.

[0048] In this embodiment, when performing strength calculation and analysis, a strength calculation and analysis model is constructed, and the model only includes a single lower hull buoyancy frame of the fuselage, and does not include other fuselage structures.

[0049] In the above step S1, according to the aircraft hull bulkhead spacing B, the hull long stringer spacing L, and the bottom water load distribution pressure Pc, the concentrated force F acting on the buoyant frame is calculated by the formula F=Pc×B×L. The point of action is located at the intersection of the buoyant frame and the long stringer axis, and the direction is along the normal of the outer surface of the hull skin pointing to the inside of the hull.

[0050] In the above step S2, according to the span size of the hull buoyancy frame, the engineering beam model and its theory supported at both ends and subjected to multiple concentrated forces are adopted to calculate the bending moment M and shear force Q at each section. The calculation method and formula can refer to structural mechanics or related aircraft structure design manuals.

[0051] Among them, the section bending moment M is the moment that describes the rotation of the beam section around its neutral axis. In the aircraft hull pontoon, when the pontoon is subjected to the bottom water pressure load or other lateral loads, it will produce bending deformation, thereby generating a bending moment on the section. The magnitude and direction of the bending moment depend on the magnitude and distribution of the load, as well as the geometry and support conditions of the beam. In engineering beam theory, the bending moment can be obtained by integrating the distributed load on the beam.

[0052] Shear force Q is an internal force perpendicular to the beam axis, which causes the beam section to have a tendency to move relative to each other. In aircraft hull buoyancy frames, shear forces are generated on the beams when the buoyancy frames are subjected to concentrated loads or distributed loads. The magnitude and direction of the shear force depend on the type and location of the load. Similar to the bending moment, the shear force can also be determined by methods in engineering beam theory. For simple structures such as simply supported beams, the shear force value can be directly calculated by static equilibrium conditions.

[0053] In the above step S3, according to the bending moment M and the shear force Q, the moment of inertia of the floating frame section and other dimensional parameters, the working stress of the flange and the web at each section of the floating frame is calculated according to the given formula; when determining the working stress of different parts at each section of the aircraft hull floating frame, the selection of the section position is determined by the position of the long stringer, and the working stress f of the flange and the working stress fs of the web are calculated respectively, and the calculation formula is as follows:

[0054] f=My / I;fs=Q / ht;

[0055] Wherein, I is the bending inertia moment of the floating frame section, y is the distance from the edge of the flange to the neutral axis of the floating frame section, h is the height of the floating frame web, and t is the thickness of the floating frame web.

[0056] In the above step S4, the factors determining the allowable stress of the floating frame include the allowable value of the material, stability control and the service life of the aircraft. The allowable stress of the floating frame flange and the web is determined according to the design service life of the aircraft, the service environment, the material characteristics of the floating frame and the stability control requirements. The calculation of the critical stability value is mainly based on the material parameters and the specific size parameters of the components, and the relevant aircraft structure design manual can be referred to.

[0057] In this embodiment, the material allowable value specifically includes:

[0058] Mechanical properties of materials: Mechanical properties of materials used for floating frames, including yield limit, strength limit and fatigue limit, etc.

[0059] Calculation of allowable stress: Allowable stress is the maximum stress value that a material is allowed to withstand under specific conditions. It is usually obtained by dividing the failure stress of the material (such as yield limit, strength limit or fatigue limit) by a safety factor. The choice of safety factor depends on factors such as the reliability of the design requirements, the variability of the material and the severity of the working environment.

[0060] For plastic materials (such as most structural steels and aluminum alloys), the allowable stress is usually calculated based on the yield limit.

[0061] For brittle materials (such as cast iron and high-strength steel), the allowable stress is calculated based on the ultimate strength.

[0062] In addition, the material allowable value can be obtained from the data sheet provided by the material manufacturer, industry standards or relevant design specifications.

[0063] In this embodiment, the stability control specifically includes:

[0064] Structural stability analysis: The stability of the floating frame refers to its ability to maintain its original stable shape and load-bearing characteristics when subjected to external loads. The stability requirements of the floating frame must be considered when determining the allowable stress.

[0065] Critical stress calculation: Through stability analysis, the critical stress of the floating frame can be calculated, that is, the minimum stress value that causes structural instability. This value is crucial to determine the allowable stress, because the allowable stress must be less than the critical stress to ensure the stability of the structure.

[0066] Stability control measures: In order to improve the stability of the floating frame, a series of measures can be taken, such as adding support structures, optimizing cross-sectional shapes, using reinforcing ribs, etc. These measures will affect the determination of allowable stress.

[0067] In this embodiment, the aircraft service life specifically includes:

[0068] Fatigue life considerations: The aircraft hull float frame will be subjected to alternating loads during use, resulting in fatigue damage. When determining the allowable stress, the fatigue life requirements must be considered to ensure that the float frame can work safely and reliably throughout the service life of the aircraft.

[0069] Design life and fatigue limit: The design life of an aircraft is usually determined through fatigue testing and damage calculation. When determining the allowable stress of the float frame, it is necessary to refer to the design life and fatigue limit of the aircraft to ensure that the float frame will not suffer fatigue damage during the service life of the aircraft.

[0070] Maintenance and inspection: In order to extend the service life of the floating frame and ensure its safety, regular maintenance and inspection are required.

[0071] In the above step S6, for the cross section with a safety margin less than 0 or greater than 0.2, the relevant cross section dimension parameters, such as flange width, thickness, web thickness, etc., are adjusted according to the result.

[0072] In the above step S7, steps S3 to S5 are repeated according to the adjusted cross-sectional dimension parameters until a safety margin result that is reasonable in engineering is obtained.

[0073] In the above step S8, the verified test piece only includes a single lower hull buoyancy frame of the fuselage, and the verification method includes: test loading, support method and consistency verification.

[0074] In this embodiment, the test loading method includes:

[0075] Simulation of actual loads: The test loading should simulate as much as possible the loads to which the buoyancy frame is subjected in the actual working environment, including bottom water pressure loads, other possible lateral or longitudinal loads, and any dynamic loads caused by aircraft movement or waves.

[0076] Loading devices: Loading devices are designed and manufactured to ensure that the required loads can be accurately applied. These devices may include hydraulic cylinders, pneumatic systems or mechanical loading mechanisms, depending on the type and size of the load.

[0077] Loading control: The loading process should be strictly controlled to ensure that the load is applied smoothly and evenly and in accordance with the loading conditions in the calculation model. Sensors, control systems and data logging equipment are needed to monitor and record various parameters during the loading process.

[0078] In this embodiment, the support methods include:

[0079] Simulate actual constraints: The support method in the test should simulate the actual constraints of the float frame on the aircraft, including the connection method with the fuselage, the location and stiffness of the supporting structure, etc.

[0080] Fixtures: Design and install appropriate fixtures to ensure that the floating frame remains stable during the test and does not cause unnecessary movement or deformation due to loading.

[0081] Boundary conditions: Ensure that the boundary conditions in the test are consistent with those in the computational model, including the stiffness of the supporting structure, load diffusion, and any other factors that may affect the response of the floating frame.

[0082] In this embodiment, consistency verification includes:

[0083] Loading history comparison: During the test, the loading history is recorded and compared with the loading history in the calculation model to ensure consistency in time and magnitude.

[0084] Response monitoring: Use sensors to monitor the response of the floating frame during the test, such as stress, strain, displacement, etc., and compare these responses with the predictions in the computational model.

[0085] Data analysis: The test data should be analyzed in detail to evaluate whether the performance of the floating frame meets the design requirements. If any significant differences are found, an in-depth investigation should be carried out to find out the reasons, such as errors in the calculation model, deviations in the test conditions, or deficiencies in the floating frame design.

[0086] Therefore, by ensuring that the test loading and support methods are consistent with those in calculation, the accuracy and reliability of the test verification can be improved, providing strong support for the design and optimization of the aircraft hull buoyancy frame.

[0087] Specifically, when building a strength calculation and analysis model, it includes:

[0088] Analyze the stress distribution, deformation, etc. of the hull buoyancy frame under specific water pressure.

[0089] Determine the support method, external loads (such as bottom water pressure load) and constraints of the hull buoyancy frame.

[0090] Create a floating frame geometry model: Use CAD software (such as SolidWorks, Catia, etc.) to create a three-dimensional geometric model of the hull floating frame according to the design drawings or actual measurement data, ensuring that the size, shape and details of the model are consistent with the actual structure.

[0091] Remove details that have little impact on the analysis, such as small holes and small chamfers, to reduce the amount of calculation and improve analysis efficiency. If the analysis only focuses on the hull buoyancy frame itself, there is no need to include other structures such as the upper fuselage bulkhead.

[0092] According to the actual material used, define its physical properties such as elastic modulus, Poisson's ratio, density, etc. in the model. According to the analysis needs, select the appropriate material model, such as linear elastic model, elastic-plastic model, etc.

[0093] Determine mesh density: Determine the appropriate mesh density based on the analysis accuracy and computing resource requirements. Usually, denser meshes are used in areas of stress concentration and large deformation.

[0094] Meshing: Use finite element analysis software (such as ANSYS, Abaqus, etc.) to mesh the floating frame geometry model to ensure good mesh quality without distorted or overly distorted elements.

[0095] Apply external loads: According to the analysis objectives, apply corresponding external loads to the model, such as bottom water pressure loads. Ensure that the size, direction, and point of action of the loads are consistent with the actual situation.

[0096] Apply constraints: According to the boundary conditions, apply corresponding constraints on the model, such as fixed constraints, displacement constraints, etc., to ensure that the constraints can accurately reflect the actual working status of the floating frame.

[0097] Finite element analysis software is used to solve and calculate, and the stress distribution, deformation and other results of the floating frame are obtained.

[0098] Post-process the solution results, extract key data and analyze them.

[0099] The analysis results are presented using charts, cloud diagrams, etc., so as to more intuitively understand the stress conditions of the floating frame.

[0100] Verify the accuracy and reliability of the model by comparing it with experimental results or other reliable data.

[0101] Based on the analysis results, evaluate whether the strength of the floating frame meets the design requirements.

[0102] If the requirements are not met, the model needs to be adjusted or optimized and the analysis performed again.

[0103] In summary, the strength calculation method of the amphibious aircraft hull float frame without shear plates provided in this embodiment is for strength analysis and design of the hull float frame with a shear plate-free structure, and has the following advantages:

[0104] This embodiment can more accurately simulate the stress conditions of the floating frame in actual use through detailed load analysis and internal force distribution calculation, thereby improving the accuracy and reliability of the design.

[0105] This method allows the cross-sectional dimensions of the floating frame to be finely adjusted and optimized after the preliminary design based on the comparison results of the working stress and the allowable stress. This helps to achieve structural optimization while meeting the strength requirements, reduce unnecessary material use, reduce weight, and improve structural efficiency.

[0106] This embodiment can ensure that the floating frame can maintain sufficient safety margin under various working conditions through multiple rounds of stress analysis and safety margin verification, avoid the problem of insufficient strength in actual use, and thus improve the overall safety of the aircraft.

[0107] This method adopts a systematic design process, from load analysis to strength verification, with clear goals and methods for each step. This helps designers complete the design work quickly and accurately, shorten the design cycle, and improve design efficiency.

[0108] This embodiment can avoid repeated modifications and re-manufacturing due to improper design through detailed load analysis and structural optimization, thereby reducing design and verification costs. At the same time, since unnecessary material use is reduced, manufacturing costs are also reduced.

[0109] The method is not only applicable to the amphibious aircraft hull floating frame without shear plates, but can also be appropriately modified and expanded according to specific needs to adapt to the design of amphibious aircraft fuselages of different types and specifications.

[0110] In step S8, by simulating the stress conditions of the amphibious aircraft in actual use, it is possible to check whether the strength of the floating frame meets the design requirements. This simulation verification method helps to discover and solve potential problems in advance and reduce the risk of flight tests.

[0111] In summary, the shear-sheet-free amphibious aircraft hull float frame strength calculation method provided in this embodiment has significant advantages in improving design accuracy, optimizing structural design, improving safety, shortening design cycle, reducing design cost and enhancing adaptability.

[0112] The technical features of the above embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A method for calculating the strength of an amphibious aircraft hull floating frame without shear plates, characterized in that: The fuselage hull of the amphibious aircraft adopts a shear-free structure, and the hull bulkhead of the lower fuselage of the amphibious aircraft adopts a floating frame form, and the floating frame is not directly connected to the hull skin. The method comprises the following steps: Step S1, determining the size, direction and action point of the external load according to the station arrangement of the aircraft hull buoy frame and the long stringer, and the bottom water load pressure distribution; Step S2, determining the main internal force distribution of the buoyancy frame according to the preliminary configuration size of the aircraft hull buoyancy frame and the load input determined in step S1; Step S3, determining the working stress of different parts of each cross section of the buoyancy frame according to the internal force of the aircraft hull buoyancy frame and the preliminary cross-sectional dimensions; Step S4, determining the allowable stress of each part of the aircraft hull buoyancy frame according to the aircraft design requirements, material selection and cross-sectional dimensions; Step S5, determining the safety margin of each cross section of the aircraft hull buoyancy frame by comparing the working stress and the allowable stress; Step S6, for the cross section with insufficient or excessive safety margin, adjusting and optimizing the corresponding cross section size according to the comparison result; Step S7, repeating steps S3 to S5 according to the adjusted cross-sectional dimension parameters; Step S8, verifying the strength of the aircraft hull buoyancy frame; wherein, the stress conditions of the amphibious aircraft in actual use are simulated to check whether the strength of the buoyancy frame meets the design requirements.

2. The method according to claim 1, characterized in that: There is no direct load transfer between the aircraft hull buoyancy frame and the hull skin.

3. The method according to claim 2, characterized in that: When an amphibious aircraft takes off and lands on the water or glides on the water, the bottom of the hull will be subjected to water pressure. These pressure loads act directly on the hull skin. The hull skin transfers the water pressure load to the long spars through its connection with the long spars. The long spars further transfers the load to the aircraft hull buoyancy frame through its connection point with the aircraft hull buoyancy frame, and finally transmits it from the hull buoyancy frame to the upper fuselage frame and diffuses it to the fuselage wall panel.

4. The method according to claim 3, characterized in that: The aircraft hull wall panels only serve as the bottom plate structure to bear the bottom water load pressure and do not participate in the load diffusion and transfer between bulkheads.

5. The method according to claim 1, characterized in that: When performing strength calculation and analysis, a strength calculation and analysis model is constructed, which only includes a single lower hull buoyancy frame of the fuselage and does not include other fuselage structures.

6. The method according to claim 1, characterized in that: In step S1, the external load on the aircraft hull buoyancy frame is a number of concentrated forces F=Pc×B×L, and the concentrated force F acts on the intersection of the aircraft hull buoyancy frame and the long stringer axis, and points to the inside of the hull along the normal direction of the outer surface of the hull skin. Among them, Pc is the distributed pressure of water load on the bottom of the ship, B is the spacing between hull bulkheads, and L is the spacing between hull long girders.

7. The method according to claim 1, characterized in that: In step S2, the main internal forces of the aircraft hull buoyancy frame include section bending moment M and shear force Q, which are determined by engineering beam theory.

8. The method according to claim 1, characterized in that: In step S3, when determining the working stress of different parts of each cross section of the aircraft hull floating frame, the cross section position is selected by the long stringer station position, and the working stress f of the flange and the working stress fs of the web are calculated respectively, and the calculation formula is as follows: f=My / I;fs=Q / ht; Wherein, I is the bending inertia moment of the floating frame section, y is the distance from the edge of the flange to the neutral axis of the floating frame section, h is the height of the floating frame web, and t is the thickness of the floating frame web.

9. The method according to claim 1, characterized in that: In step S4, factors determining the allowable stress of the floating frame include material allowable value, stability control and aircraft service life.

10. The method according to claim 1, characterized in that: In step S8, the verified test piece only includes a single lower hull buoyancy frame of the fuselage, and the verification method includes: test loading, support method and consistency verification.

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