A method of designing a rocker-armed tail landing gear on-board joint and support structure

Abstract

The application belongs to the field of structure design, and relates to a rocker arm type tail landing gear on-machine joint and support structure design method. The method comprises the following steps: determining the front joint position and the rear joint position according to the overall layout of the helicopter, the tail landing gear structure and the intersection data; the front joint comprises a front joint B and a front joint A which are the same in structure and symmetrical; designing the front joint structure and the front frame position according to the front joint position and the front joint load; designing the rear joint structure and the rear frame position according to the rear joint position and the rear joint load; and creating an initial finite element model of the front joint, the rear joint and the fuselage support structure according to the front joint structure and the front frame position, the rear joint structure and the rear frame position and the load transmission path of the front joint and the rear joint.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of structural design, and relates to a rocker arm type tail landing gear on-machine joint and a support structure design method. BACKGROUND

[0002] In the past, when determining the structure of the on-machine joint of a helicopter landing gear, the load conditions of the on-machine joint under all landing and ground conditions were not considered, and unreasonable design of the structure of the on-machine joint directly leads to more weight cost. In addition, when designing the strength of the on-machine joint and the connection structure of the helicopter tail landing gear, the traditional design idea is to separately take the on-machine joint as the research object, create a finite element model of the actual unit, and will not take the on-machine joint and the support structure of the fuselage as a whole. The stiffness of the support structure of the fuselage directly affects the load distribution of the on-machine joint and the load size of the connecting bolts. If the stiffness of the support structure of the fuselage is not designed, the load calculation accuracy of the connecting bolts between the on-machine joint and the support structure of the fuselage will be directly affected, and the accuracy and reliability of the strength calculation of the connecting bolts, the on-machine joint and the support structure of the fuselage cannot be guaranteed, which finally affects the safety of the helicopter. SUMMARY

[0003] The application aims to provide a standardized process for the integrated design of the static strength and fatigue strength of a rocker arm type landing gear on-machine joint and support structure.

[0004] TECHNICAL SCHEME

[0005] The application provides a rocker arm type tail landing gear on-machine joint and support structure design method, which comprises the following steps:

[0006] Step 1: determining the position of the front joint and the position of the rear joint according to the overall layout of the helicopter, the structure of the tail landing gear and the intersection data; the front joint comprises a front joint B and a front joint A which are the same in structure and symmetrical;

[0007] Step 2: designing the structure of the front joint and the position of the front frame according to the position of the front joint and the load of the front joint;

[0008] Step 3: designing the structure of the rear joint and the position of the rear frame according to the position of the rear joint and the load of the rear joint;

[0009] Step 4: creating an initial finite element model of the front joint, the rear joint and the support structure of the fuselage according to the structure of the front joint, the position of the front frame, the structure of the rear joint, the position of the rear frame and the load transmission path of the front joint and the rear joint.

[0010] Further, the method further comprises:

[0011] Step 5, the load of the mounting bolt of the front and rear joints and the tail section structure of the fuselage is obtained by applying the initial finite element model, the structure form of the front and rear frames in the connecting area in the support structure is determined as a double-angle joint, the strength of the double-angle joint is calculated by applying an engineering method, and the size of the double-angle joint is determined after repeated iteration and optimization;

[0012] Step 6, the stress distribution of the front and rear joints is obtained by applying the initial finite element model, whether the front and rear joint structures meet the strength design requirements is judged according to the stress failure criterion, and the size and material of the front and rear joints are finally determined after multiple rounds of optimization iteration, and the size definition is completed;

[0013] Step 7, the strength of the bolt shank and the thread small diameter is calculated according to the fourth strength theory respectively, the strength safety margin of the connecting bolt is calculated according to the stress failure criterion and considering the joint coefficient 1.15, and at least 20% of the design principle is reserved to determine the bolt diameter and material.

[0014] Further, the method further comprises:

[0015] Step 8, the swing-arm tail landing gear and the support structure obtained after the static strength design of steps 1-7 are taken as the initial model of the fatigue strength design;

[0016] Step 9, the size of the initial model of the fatigue strength design is corrected, and the static strength and fatigue strength integration design of the swing-arm tail landing gear on-board joint and the support structure is completed.

[0017] Further, according to the position of the front joint and the load of the front joint, the front joint structure and the front frame position are designed, including:

[0018] A coordinate system is established, wherein the positive direction of the X axis is the direction from the midpoint between the front left joint and the front right joint to the rear joint, the positive direction of the Z axis is the vertical upward direction, and the positive direction of the Y axis is the right direction perpendicular to the XOZ plane according to the right-hand rule;

[0019] It is determined that each of the two front joints has three direction loads (F x , F y , F z ), for any front joint, the X-direction load F x of a front joint in all landing and ground conditions exists in positive and negative directions, the Z-direction load F z of the front joint is always positive, so according to the ratio of the Z-direction load F z to the X-direction load F x , two boundaries are obtained when determining the boundary of the front joint, which are named as boundary 1 and boundary 2;

[0020] Front joint bottom surface design: the front joint bottom surface needs to be attached to the tail section skin, and the bottom surface, boundary 1 and boundary 2 enclose the front joint ear region, and the front joint bottom surface is designed according to the skin shape; the length of the front joint bottom surface is determined according to the boundary 1 and the boundary 2 of the front joint; the width of the front joint bottom surface is determined according to the preset row number of the mounting bolt on the bottom surface, the general row spacing, and the edge distance;

[0021] Front joint mounting bolt number design: the number of single-row bolts is determined according to the length of the front joint bottom surface and the general spacing of the bolts;

[0022] Since the connecting bolt located on the front joint ear and connected to the tail landing gear rocker arm needs to bear the Y-direction load F y , and there is a distance between the front joint connecting point a and the root of the front joint ear, which generates a bending moment on the root of the front joint ear, therefore the cross section of the root of the front joint ear needs to be strengthened;

[0023] According to the principle that the line between the connecting point a and the middle surface of the front frame web is parallel to the boundary 1, the position of the front frame is determined.

[0024] Further, according to the position of the rear joint and the load of the rear joint, the rear joint structure and the rear frame position are designed, including:

[0025] According to the same axial direction of the single ear of the rear joint and the axial compression direction of the buffer strut, and the position of the tail landing gear rear intersection, the height of the rear joint is determined;

[0026] According to the principle that the position of the middle surface of the rear frame web is located on the extension line of the axial direction of the single ear of the rear joint, the position of the rear frame is determined.

[0027] Further, an initial finite element model of the front joint, the rear joint and the fuselage support structure is created, including:

[0028] According to the load size of the tail landing gear front and rear intersection in all landing and ground conditions, the working conditions of the front joint and the rear joint under severe load are selected;

[0029] The shell element is used to simulate the fuselage support structure, the solid element is used to simulate the front joint and the rear joint, the beam element and MPC are used to simulate the bolt connection in the connection area between the front joint, the rear joint and the fuselage support structure, and the rivet element is used to simulate the connection between the fuselage support structures;

[0030] The three translational degrees of freedom of the node at the front end of the tail section structure are constrained;

[0031] The working conditions of the front joint and the rear joint under severe load are created, and the corresponding load of the tail landing gear front and rear intersection is applied.

[0032] Further, considering the installation bolt pre-tightening force, the bolt shank and the thread minor diameter strength are calculated respectively according to the fourth strength theory, the bolt strength safety margin is calculated according to the stress failure criterion and considering the joint coefficient 1.15, and the bolt diameter and material are determined according to the design principle that at least 20% safety margin is reserved, including:

[0033] The axial load of the installation bolt not considering the pre-tightening force is defined as P ext , and the shear load of the installation bolt is defined as Q.

[0034] The bolt pre-tightening force P0 is calculated according to the relationship expression between the tightening torque and the pre-tightening force.

[0035] The tightening torque is composed of two parts: M = M T + M P , M P is the torque generated by overcoming the thread friction force, and M T is the torque generated by the friction force of the nut bearing surface.

[0036] The bolt connection stiffness coefficient is k, and the separation load of the installation bolt is P sep = P0 / (1-k); the actual axial load of the bolt under the working state of the bolt pre-tightening force is P b = P0+kP ext (P ext <P sep ), P b = P ext (P ext >P sep ).

[0037] The bolt shank stress includes the normal stress σ1 generated by the actual axial load P b of the bolt, the shear stress τ1 generated by the shear load Q of the bolt, and the shear stress τ2 generated by the torque M P , the cross-sectional area is the cross-sectional area of the bolt shank, and the equivalent stress σ eq1 of the bolt shank is calculated according to the fourth strength theory.

[0038] The thread minor diameter stress includes the normal stress σ2 generated by the actual axial load P b of the bolt, the shear stress τ'2 generated by the torque M P , and the cross-sectional area is the cross-sectional area of the thread minor diameter, and the equivalent stress σ eq2 of the thread minor diameter is calculated according to the fourth strength theory.

[0039] Further, considering the joint coefficient 1.15, the bolt strength safety margin is calculated according to the design principle that at least 20% safety margin is reserved, and the bolt diameter and material are determined, including:

[0040] According to the stress failure criterion, and considering the joint coefficient 1.15, the bolt diameter and material are determined according to the principle of reserving at least 20% of the design safety margin of the bolt strength.

[0041] Advantages:

[0042] A standardized process for integrated design of static strength and fatigue strength of a rocker-type on-board joint and support structure of a landing gear is provided. The on-board joint and support structure designed according to the present patent are more reasonable, avoiding more weight cost, and making the helicopter body structure more easily meet the minimum weight design principle. A static strength calculation method for connecting bolts is provided, which calculates the strength of the bolt shank and the small diameter of the thread after considering the bolt pretightening force. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 is a schematic diagram of the intersection of the tail landing gear and the fuselage.

[0044] Figure 2 is a schematic diagram of the double-angle joint structure of the front and rear frame connection area. DETAILED DESCRIPTION

[0045] The present application determines the joint load envelope and joint structure form according to the tail landing gear and on-board joint connection point load under all landing and ground conditions. In order to accurately simulate the actual stress state, load transmission path and diffusion form of the tail landing gear on-board joint in actual installation, the on-board joint and the connected fuselage structure are integrated as a research object to create a finite element model. According to the tail landing gear and on-board joint connection point load under all landing and ground conditions, the most severe working conditions of the on-board joint are selected. The finite element model is used to calculate the connecting bolt load, and the strength of the bolt shank and the small diameter of the thread is calculated considering the bolt pretightening force. Based on the connecting bolt load, the support structure form of the fuselage is determined, and the static strength evaluation is completed by using the engineering method. After several rounds of calculation and iteration, the structure that meets the static strength design requirements is determined, which is used as the initial structure for fatigue strength calculation and iteration. The on-board joint and support structure that meet the static strength and fatigue strength design requirements are determined, achieving the purpose of integrated design.

[0046] The present application provides a design method for a rocker-type tail landing gear on-board joint and support structure, comprising:

[0047] [1] on-board joint and support structure design;

[0048] A certain type of machine rocker arm type tail landing gear is connected with the tail section structure of the fuselage through the front left joint, the front right joint and the rear joint, and the connection points are defined as a, b and c respectively. The tail section structure between the front joint and the rear joint is defined as the support structure, which includes the front frame, the rear frame, the left longitudinal beam, the right longitudinal beam, the intermediate angle bar and the skin. According to the overall layout of the helicopter and the intersection data, the front left joint, the front right joint, the rear joint and the front and rear frame positions of the tail landing gear connected with the fuselage are determined. In order to ensure the continuous and effective transmission of the X-direction load of the connection joint, the left longitudinal beam, the right longitudinal beam and the intermediate angle bar are contained in the fuselage connecting structure; the Y-direction load is transmitted and diffused by the frame flange; and the Z-direction load is borne and diffused by the frame longitudinal rib. According to the load size and direction of the tail landing gear and the fuselage joint points a, b and c (as shown in Table 1), the structure form of the front left joint, the front right joint and the rear joint and the positions of the front and rear frames are determined, as shown in Figure 1 and Figure 2

[0049] Table 1 shows the load of the tail landing gear and the joint on the machine

[0050]

[0051] The specific steps are as follows:

[0052] 1) According to the overall layout of the helicopter, the tail landing gear structure and the intersection data, the positions of the front left joint, the front right joint and the rear joint are determined;

[0053] 2) Front joint structure design and front frame position design:

[0054] Front joint boundary design: there are three direction loads (F x , F y , F z ) at the connection points a and b of the front left and right joints respectively, wherein the X-direction load F x of each front joint in all landing and ground working conditions exists in positive and negative directions, and the Z-direction load F z is always positive, therefore, taking the front left joint A as an example, according to the ratio of the Z-direction load F z to the X-direction load F x , two boundaries of the joint A will be obtained when the joint A boundary is determined, which are named as boundary 1 and boundary 2; the front left joint A and the front right joint B have the same structure and are arranged symmetrically along the Y axis;

[0055] Joint A bottom surface design: the bottom surface of the joint A needs to be fitted with the tail section skin, therefore, the bottom surface of the joint A is designed according to the shape of the skin. According to the boundary 1 and the boundary 2 of the joint S, the length of the bottom surface of the joint A is determined. According to the preset row number of the mounting bolt, the general row spacing and the margin, the width of the bottom surface of the joint A is determined;

[0056] ​Front joint mounting bolt number design: according to the length of the front joint A bottom surface and the general pitch of the mounting bolt, the number of single row mounting bolt is determined;

[0057] Since the connecting bolt at the connection point a of the front joint A needs to bear the Y direction load F y , and there is a distance between the connection point a of the front joint A and the root of the front joint A ear, which generates bending moment on the root of the front joint A ear, the cross section of the root of the front joint A ear needs to be strengthened;

[0058] According to the principle that the line between the center point of the connecting bolt hole and the middle surface of the front frame web is parallel to the boundary 1, the position of the front frame is determined.

[0059] 3) rear joint structure design and rear frame position design:

[0060] Rear joint ear structure design: the rear joint C is the tail landing gear buffer strut and the fuselage connection joint, and the rear joint connection point c only has X and Z direction loads (F x , F z ) in all landing and ground conditions, and the resultant force direction is always along the axial compression direction of the buffer strut, so the axial direction of the rear joint single ear is the axial compression direction of the buffer strut. According to the position of the tail landing gear rear intersection, the height of the rear joint is determined;

[0061] According to the principle that the middle surface position of the rear frame web is located on the extension line of the axial direction of the rear joint single ear, the position of the rear frame is determined.

[0062] [2] create a finite element model of the front and rear joints and the fuselage support structure, the specific steps are as follows:

[0063] 1) According to the load size of the tail landing gear front and rear intersection in all landing and ground conditions, the working conditions of the front joint and the rear joint are screened;

[0064] 2) shell element is used to simulate the fuselage support structure, solid element is used to simulate the front and rear joints, beam element and MPC are used to simulate the bolt connection in the connection area of the front and rear joints and the fuselage support structure, and rivet element is used to simulate the connection between the fuselage support structure;

[0065] 3) constrain the 3D translational freedom of the front end node of the tail section structure;

[0066] 4) create the front and rear joints in the first step of [2] screened under severe load, and apply the corresponding load of the working condition to the tail landing gear front and rear intersection.

[0067] [3] the finite element model created in step [2] is used to obtain the load of the joint and the fuselage tail section structure connection bolt, so as to determine the structure form of the front and rear frames in the connection area of the support structure as double angle joint, such as Figure 2The application engineering method is used to calculate the strength of the double-angle joint, and the size of the double-angle joint is determined after repeated iteration and optimization.

[0068] [4] The finite element model created in step [2] is used to obtain the stress distribution of the front and rear joints. According to the stress failure criterion, it is determined whether the front and rear joint structures meet the strength design requirements. After multiple rounds of optimization and iteration, the joint size and material are finally determined, and the size definition is completed.

[0069] [5] Considering the bolt pretightening force, the bolt shank and thread diameter strength are calculated according to the fourth strength theory, and the bolt strength safety margin is calculated according to the stress failure criterion and considering the joint coefficient 1.15, which is at least 20% of the design principle to determine the bolt diameter and material. The specific process is as follows:

[0070] 1) Define the axial load of the connecting bolt as P ext , and the shear load of the connecting bolt as Q.

[0071] 2) According to the relationship expression between the tightening torque and the pretightening force, the bolt pretightening force P0 is calculated and obtained.

[0072] 3) The tightening torque is composed of two parts: M = M T + M P , M P is the torque generated to overcome the friction of the thread; M T is the torque generated by the friction of the nut bearing surface.

[0073] 4) The separation load of the connecting bolt is P sep = P0 / (1-k); considering the working state of the bolt pretightening force, the actual axial load of the bolt is P b = P0+kP ext (P ext <P sep ), P b = P ext (P ext >P sep ).

[0074] 5) The bolt shank stress includes the normal stress σ1 generated by the actual axial load P b of the bolt, the shear stress τ1 generated by the bolt shear load Q, and the shear stress τ2 generated by the torque M P . The cross-sectional area is the cross-sectional area of the bolt shank. The equivalent stress σ eq1 of the bolt shank is calculated according to the fourth strength theory.

[0075] 6) The thread diameter stress includes the normal stress σ2 generated by the actual axial load P b of the bolt, and the shear stress τ2 generated by the torque M PThe generated shear stress τ'2, the cross-sectional area is the cross-sectional area of the small diameter thread, and the equivalent stress σ of the small diameter thread is calculated according to the fourth strength theory eq2 ;

[0076] 7) According to the stress failure criterion, and considering the joint coefficient 1.15, the bolt diameter and material are determined according to the design principle of reserving at least 20% of the safety margin of the bolt strength.

[0077] [6] The rocker arm type tail landing gear and support structure obtained after static strength design are used as the initial model for fatigue strength design. According to the fatigue load spectrum, the fatigue strength of the connecting bolt, the on-machine joint and the fuselage support structure is evaluated, unreasonable structures are changed, and through multiple rounds of iterative calculation, the on-machine joint and the support structure that meet the static strength and fatigue strength design requirements are determined.

[0078] [7] Through the above steps, the static strength and fatigue strength integrated design of the on-machine joint and support structure of the rocker arm type tail landing gear is finally completed.

Claims

1. A method of designing a rocker-armed tail landing gear on-board joint and support structure, characterized in that, The method comprises the following steps: Step 1, determining the front joint position and the rear joint position according to the overall layout of the helicopter, the structure of the tail landing gear and the intersection data; the front joint comprises a front joint B and a front joint A which are the same in structure and symmetrical; Step 2, designing the front joint structure and the front frame position according to the front joint position and the front joint load, comprising: establishing a coordinate system, wherein the positive direction of the X axis is the direction from the midpoint between the front left joint and the front right joint to the rear joint, the positive direction of the Z axis is the vertically upward direction, and the positive direction of the Y axis is the right direction perpendicular to the XOZ plane according to the right-hand rule; It is determined that each of the two front joints has three directional loads (F x , F y , F z ), for any one front joint, the X-direction load F x of the front joint in all landing and ground working conditions has positive and negative directions, the Z-direction load F z of the front joint is always positive, therefore, according to the ratio of the Z-direction load F z to the X-direction load F x , two boundaries of the front joint are determined, which are named as boundary 1 and boundary 2; front joint bottom surface design: the front joint bottom surface needs to be attached to the tail section skin, the bottom surface and the boundary 1 and the boundary 2 form the front joint ear piece area, and the front joint bottom surface is designed according to the skin shape; the length of the front joint bottom surface is determined according to the boundary 1 and the boundary 2 of the front joint; the width of the front joint bottom surface is determined according to the preset row number of the mounting bolts, the general row spacing and the edge distance on the bottom surface; front joint mounting bolt number design: the number of bolts in a single row is determined according to the length of the front joint bottom surface and the general spacing of the bolts; Since the connecting bolt of the front joint ear and the tail landing gear rocker arm needs to bear the Y direction load F y , and the front joint connecting point a is away from the root of the front joint ear, a bending moment is generated on the root of the front joint ear, so the cross section of the root of the front joint ear needs to be reinforced. determining the front frame position according to the principle that the connecting line between the connecting point a and the middle surface of the front frame web is parallel to the boundary 1; Step 3, designing the rear joint structure and the rear frame position according to the rear joint position and the rear joint load, comprising: determining the height of the rear joint according to the same axial direction of the rear joint single ear piece and the axial compression direction of the buffer strut, and the position of the rear intersection of the tail landing gear; determining the rear frame position according to the principle that the middle surface position of the rear frame web is located on the extension line of the axial direction of the rear joint single ear piece; Step 4, creating an initial finite element model of the front joint, the rear joint and the fuselage support structure according to the front joint structure and the front frame position, the rear joint structure and the rear frame position and the load transmission path of the front joint and the rear joint, comprising: screening the working conditions of the front joint and the rear joint under the severe load according to the load size of the front and rear intersection of the tail landing gear in all landing and ground conditions; simulating the fuselage support structure by shell element, simulating the front joint and the rear joint by solid element, creating beam element and MPC to simulate bolt connection in the connection area between the front joint, the rear joint and the fuselage support structure, and creating connecting rivet element to simulate the connection between the fuselage support structures; restricting the translational freedom of the front end node of the tail section structure in three directions; creating the working conditions of the front joint and the rear joint under severe load, and applying the corresponding load of the working condition to the front and rear intersection of the tail landing gear.

2. The method of claim 1, wherein, The method further comprises: Step 5, obtaining the load of the mounting bolts of the front joint and the rear joint and the tail section structure of the fuselage by applying the initial finite element model, determining that the structure form of the front frame and the rear frame in the connection area is a double-angle joint, calculating the strength of the double-angle joint by applying the engineering method, and repeatedly iterating and optimizing to determine the size of the double-angle joint; Step 6, obtaining the stress distribution of the front joint and the rear joint by applying the initial finite element model, judging whether the front joint structure and the rear joint structure meet the strength design requirements according to the stress failure criterion, and finally determining the size and material of the front joint and the rear joint through multiple rounds of optimization iteration to complete the size definition. Step 7, considering the installation bolt pre-tightening force, calculating the bolt light pole and thread small diameter strength according to the fourth strength theory, calculating the connecting bolt strength safety margin reserving at least 20% of the design principle according to the stress failure criterion and considering the joint coefficient 1.15 to determine the bolt diameter and material.

3. The method of claim 2, wherein, The method further comprises: Step 8, taking the swing arm type tail landing gear and support structure obtained after the static strength design of steps 1-7 as the initial model of the fatigue strength design; Step 9, performing size correction on the initial model of the fatigue strength design to complete the swing arm type tail landing gear on-machine joint and support structure static strength and fatigue strength integrated design.

4. The method of claim 1, wherein, Considering the installation bolt pre-tightening force, calculating the bolt light pole and thread small diameter strength according to the fourth strength theory, calculating the connecting bolt strength safety margin reserving at least 20% of the design principle according to the stress failure criterion and considering the joint coefficient 1.15 to determine the bolt diameter and material, including: The axial load of the mounting bolt, which is not considered the pretightening force, is defined as P ext , and the shear load of the mounting bolt is defined as Q. According to the relationship expression between the tightening torque and the pre-tightening force, the bolt pre-tightening force P0 is calculated and obtained. The tightening torque is composed of two parts: M = M T + M P , M P is the torque generated to overcome the friction of the thread; M T is the torque generated by the friction of the bearing surface of the nut. The bolt connection stiffness coefficient is k, the separation load of the mounting bolt: P sep =P0 / (1-k); considering the actual axial load of the bolt under the working state of the bolt pretightening force: P b =P0+kP ext (P ext <P sep )、P b = P ext (P ext >P sep ); The bolt light pole stress includes the axial stress generated by the actual axial load P of the bolt b The generated normal stress The shear stress generated by the bolt shear load Q The shear stress generated by the torque M P The generated shear stress The cross-sectional area of the bolt light pole is the cross-sectional area of the bolt light pole, and the equivalent stress of the bolt light pole is calculated according to the fourth strength theory ; The thread minor stress includes the stress generated by the actual axial load P of the bolt b The generated normal stress The shear stress generated by the torque M P The generated shear stress The equivalent stress of the thread minor calculated according to the fourth strength theory, with the cross-sectional area being the cross-sectional area of the thread minor .

5. The method of claim 4, wherein, Considering the joint coefficient 1.15, the connecting bolt strength safety margin reserving at least 20% of the design principle is calculated to determine the bolt diameter and material, including: According to the stress failure criterion and considering the joint coefficient 1.15, the bolt strength safety margin reserving at least 20% of the design principle is calculated to determine the bolt diameter and material.

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