Landing gear sled puller device and method of designing the same

Abstract

The application provides a landing gear sled pull rod device, and belongs to the technical field of helicopter landing gear design. The device comprises an outer cylinder, a piston rod, a spring and a limiting joint. The outer cylinder is arranged on a landing gear buffer, the piston rod is arranged on a landing gear sled, one end of the piston rod extends into a hole in the outer cylinder, the limiting joint is arranged at the connection between the outer cylinder and the piston rod, the limiting joint, the inner wall of the outer cylinder and the outer wall of the piston rod jointly form a closed space, and the spring is sleeved on the outer side of the piston rod body and located in the closed space. The device can keep the posture of the helicopter sled. Meanwhile, the design of the pull rod device can keep the sled in an upward posture at all times, which is beneficial to the helicopter landing on snow or sliding, so that the sled cannot be inserted into the snow, and the helicopter can smoothly slide above the snow.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of helicopter landing gear design, and particularly relates to a landing gear snowshoe pull rod device and a design method thereof. BACKGROUND

[0002] In extremely cold environments, most landing sites are covered with ice and snow. The helicopter landing gear may sink due to excessive wheel pressure, making it impossible to take off or land safely. In addition, the helicopter cannot move normally when it is parked on a snow-covered road because the wheels sink.

[0003] Therefore, it is necessary to design a helicopter landing gear snowshoe device to solve the problem that traditional helicopter landing gears cannot take off or land on ice, snow, mud and other low-load-bearing ground. At the same time, the helicopter can move on a snow-covered road to improve its adaptability in different complex environments. For the design of the snowshoe device, the front and rear ends of the spring rope are usually used to pull the snowshoe to ensure the horizontal position of the snowshoe. However, this method has the disadvantages of easy aging of the spring rope, insufficient safety and poor reliability. SUMMARY

[0004] To solve the technical problems of easy aging of the spring rope, insufficient safety and poor reliability of the snowshoe device in the prior art, the present application provides a pull rod device that can effectively limit the snowshoe and a design method thereof to achieve the purpose of maintaining the posture of the helicopter snowshoe. At the same time, for the design of the pull rod device, the snowshoe can always be kept in an upward posture, which is beneficial to the helicopter landing on snow or sliding, and the snowshoe will not be inserted into the snow, so the helicopter can smoothly slide above the snow. The technical solution is as follows:

[0005] In a first aspect, a landing gear snowshoe pull rod device is provided, comprising: an outer cylinder, a piston rod, a spring, and a limiting joint.

[0006] The outer cylinder is arranged on the landing gear buffer, the piston rod is arranged on the landing gear snowshoe, and one end of the piston rod extends into the inner hole of the outer cylinder. The limiting joint is arranged at the connection between the outer cylinder and the piston rod, and the limiting joint, the inner wall of the outer cylinder and the outer wall of the piston rod form a closed space together. The spring is sleeved outside the piston rod body and located in the closed space.

[0007] Further, the device further comprises: an upper mounting shaft, a lower mounting bolt, a lower threaded joint, and a joint bearing.

[0008] The lower threaded joint is arranged on the landing gear snowshoe, and the end of the piston rod away from the outer cylinder 1 is provided with a threaded segment threadedly connected with the lower threaded joint.

[0009] The joint bearing is installed in the ear piece of the lower threaded joint, and the lower mounting bolt is installed in the inner hole of the joint bearing.

[0010] The upper mounting shaft is connected with the steel cable, the upper mounting shaft is installed in the two lugs at the end of the outer cylinder away from the piston rod through a nut, a support sleeve is arranged between the upper mounting shaft and the lug, the length of the support sleeve is greater than h, h=(L-M) / 2, wherein L is the outer diameter of the outer cylinder, and M is the span of the two lugs, so that the upper mounting shaft can be prevented from moving up and down in the axial direction, and the steel cable can be prevented from colliding with the outer cylinder.

[0011] Further, the device further comprises a limiting bolt, the limiting bolt sequentially penetrating the outer cylinder and the limiting joint.

[0012] Optionally, the limiting bolt 4 is three, and is uniformly distributed in the circumferential direction of the outer cylinder; an arc-shaped washer is arranged between the limiting bolt and the outer cylinder, and the arc-shaped washer is used to keep the limiting bolt in close contact with the outer cylindrical surface of the outer cylinder.

[0013] Further, the inner wall of the outer cylinder is coated with lubricating grease, so that the spring can smoothly slide in the closed space, and the spring can be prevented from being stuck and severely worn.

[0014] In the second aspect, a design method for the landing gear sled pull rod device of any one of the first aspect is provided,

[0015] The design process of the spring is as follows:

[0016] The maximum deformation f1 of the spring is determined as H0-H1, and the minimum deformation f2 is determined as H0-H2, wherein H1 is the minimum length of the spring, H2 is the maximum length of the spring, and H0 is the free length of the spring;

[0017] The outer diameter D1 of the spring is determined according to the size of the outer cylinder section, and the diameter d of the spring is determined, so that the middle diameter D2 of the spring is obtained;

[0018] The pitch t of the spring is determined according to the diameter d of the spring by the relationship t>d;

[0019] The effective working turns n of the spring are determined as (H0-2d) / t;

[0020] The total turns n0 of the spring are determined as n+2 according to the effective working turns n;

[0021] The maximum working load P1 of the spring is determined as (f1*G*d 4 ) / (8n0*D2 3 ), and the minimum working load P2 of the spring is determined as (f2*G*d 4 ) / (8n0*D2 3 ); wherein G is the shear modulus of the spring material;

[0022] The stiffness K of the spring is determined as (P1-P2) / (f1-f2);

[0023] determine the spring winding ratio C=D2 / d; and the curvature coefficient M=(4*C-1) / (4*C-4)+0.615 / C; and obtain the spring allowable load P=(3.14*d 3 *G) / (8*D2*M);

[0024] determine the single-turn deformation f3 of the spring under the maximum working load f1 / n0, and the single-turn deformation f4 of the spring under the minimum working load f2 / n0;

[0025] The design process of the outer cylinder, the piston rod and the limiting joint is as follows:

[0026] According to the flight state of the helicopter landing gear, the longest value S1 of the outer cylinder mounting point and the piston rod mounting point is determined; according to the parking state of the helicopter landing gear, the shortest value S2 of the outer cylinder mounting point and the piston rod joint mounting point is determined; S1, S2, the structure length S3 of the outer cylinder and the structure length S4 of the piston rod satisfy the constraint condition: S3<S2; S4<S2; S1<S3+S4;

[0027] According to the strength calculation result, the outer circle diameter O3 of the piston rod body and the inner hole diameter O4 of the limiting joint satisfy the relationship: O3+0.02<O4<O3+0.05; the outer circle diameter O5 of the limiting joint satisfies the relationship: O1-0.05<O5<O1-0.02, and O1 is the inner hole diameter of the outer cylinder.

[0028] Such design can ensure the cooperation relationship among the outer cylinder 1, the limiting joint 12 and the piston rod 2.

[0029] Further, the method further comprises:

[0030] The design parameters of the spring are verified, and if P2<P1<P; f4<f3<t-d; n0<(H1 / d) are satisfied, the verification is passed.

[0031] Optionally, the minimum value H1 of the spring length, the maximum value H2 of the spring length and the free state length H0 of the spring are determined according to the buffer length change amount of the helicopter landing gear after landing and taking off.

[0032] The present application has at least the following beneficial effects:

[0033] 1. The pull rod device extends the reverse compression spring, so that the landing gear sled always has a clockwise moment, and the sled will not insert into the snow road surface when the helicopter lands and slides;

[0034] 2. The limiting bolt perpendicular to the outer cylinder cylindrical surface is installed at the joint of the outer cylinder and the piston rod, and the limiting bolt is installed through the arc washer and the outer cylinder cylindrical surface, so that the outer cylinder and the limiting joint form a closed cavity, and the end of the piston rod can move in the closed cavity without falling out;

[0035] 3. The spring design method can reasonably determine the spring parameters so that the spring has a designable spring force corresponding to different length positions of the pull rod;

[0036] 4. The installation position of the lower threaded joint can be fine-tuned by screwing the thread length of the lower threaded joint and the piston rod body, which is convenient for assembly;

[0037] 5. The spring pull rod has the function of shock absorption. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 A schematic diagram of a landing gear sled pull rod device provided by an embodiment of the present invention;

[0039] Figure 2 A cross-sectional view of a landing gear ski pull rod assembly provided by an embodiment of the present invention;

[0040] Figure 3 This is a cross-sectional view of the device taken along line AA provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below through specific implementation methods and drawings.

[0042] One embodiment of the present invention provides a landing gear sled pull rod device, see Figure 1 , including: outer tube 1, piston rod 2, spring 9, limit joint 12;

[0043] The outer tube 1 is arranged on the landing gear buffer, the piston rod 2 is arranged on the landing gear sled, and one end of the piston rod 2 extends into the inner hole of the outer tube 1; the limit joint 12 is arranged at the connection between the outer tube 1 and the piston rod 2, and the limit joint 12, the inner wall of the outer tube 1, and the outer wall of the piston rod 2 jointly form a closed space, and the spring 9 is sleeved on the outside of the rod body of the piston rod 2 and is located in the closed space.

[0044] In another embodiment, see Figure 2 The device also includes: an upper mounting shaft 5, a lower mounting bolt 8, a lower threaded joint 3, and a spherical bearing 10.

[0045] The lower threaded joint 3 is provided on the landing gear sled, and the end of the piston rod 2 away from the outer tube 1 is provided with a threaded section threadedly connected to the lower threaded joint 3;

[0046] The spherical bearing 10 is installed in the ear piece of the lower threaded joint 3, and the lower mounting bolt 8 is installed in the inner hole of the spherical bearing 10;

[0047] The upper mounting shaft 5 is installed in the two lugs on the outer cylinder 1 far from the piston rod 2 through a nut 7; the upper mounting shaft 5 is connected with a steel cable, and a supporting sleeve 6 is arranged between the upper mounting shaft 5 and the lug, and the length of the supporting sleeve 6 is greater than h, h=(L-M) / 2, L is the outer diameter of the outer cylinder 1, and M is the span of the two lugs, so that the upper mounting shaft 5 can not move up and down along the axial direction, and the steel cable can not collide with the outer cylinder 1.

[0048] In another embodiment, referring to Figure 2 The inner wall of the outer cylinder 1 can be coated with lubricating grease, so that the spring 9 can smoothly slide in the closed space, and the jamming and severe wear can be avoided.

[0049] Referring to Figure 3 The device further comprises a limiting bolt 4 which passes through the outer cylinder 1 and the limiting connector 12 in sequence.

[0050] In an embodiment, referring to Figure 3 The limiting bolt 4 is three, and is distributed in the circumferential direction of the outer cylinder 1; an arc-shaped washer 11 is arranged between the limiting bolt 4 and the outer cylinder 1, and the arc-shaped washer 11 keeps the limiting bolt 4 in close contact with the outer cylindrical surface of the outer cylinder 1.

[0051] An embodiment of the application provides a design method of a landing gear sled pull rod device, which comprises the following steps:

[0052] (1) The length of the buffer of the helicopter landing gear changes after landing and taking off, which causes the length of the sled pull rod to change, and the length of the spring changes due to the different lengths of the pull rods, so there is a minimum spring length H1, a maximum spring length H2, and a spring free state length H0, the maximum spring deformation f1 is obtained as H0-H1, and the minimum deformation f2 is obtained as H0-H2.

[0053] (2) The spring outer diameter D1 can be determined according to the size of the outer cylinder cross section; the spring diameter d is determined according to the strength load estimation, and the spring middle diameter D2=D1-d is obtained.

[0054] (3) t is the spring pitch, that is, the axial distance of the corresponding points of the adjacent two coils of the spring on the middle diameter, and the size should satisfy t>2d, that is, the relationship t>d, so that the t value is preliminarily determined.

[0055] (4) According to the geometric shape of the spring structure, the total number of spring coils n0=(H0-2d) / t is obtained.

[0056] (5) According to the general compression spring, the number of support coils is 1 / 4, 1 / 2 or a whole coil, and in this case, one coil at each end of the spring is taken as a support coil, so the number of support coils is 2, and thus the effective working coil number n=n0-2 is obtained.

[0057] (6) According to the selected spring material, the shear modulus G of the spring material is a constant value. Calculate the maximum working load of the spring P1 = (f1 * G * d 4 ) / (8n0 * D2 3 ), and the minimum working load of the spring P2 = (f2 * G * d4) / (8n0 * D2 3 );

[0058] (7) The spring stiffness is the ratio of the load change value to the spring length change value. Therefore, the spring stiffness K = (P1 - P2) / (f1 - f2) can be calculated;

[0059] (8) Calculate the spring pitch ratio C = D2 / d; calculate the curvature coefficient M = (4 * C - 1) / (4 * C - 4) + 0.615 / C; thus obtain the allowable load of the spring P = (3.14 * d 3 * G) / (8 * D2 * M);

[0060] (9) Calculate the single - loop deformation of the spring under the maximum working load f3 = f1 / n0, and calculate the single - loop deformation of the spring under the minimum working load f4 = f2 / n0.

[0061] When designing the outer cylinder 1, piston rod 2, and limit joint 12 of the sled pull rod device,

[0062] Define the inner - hole cavity diameter of the outer cylinder 1 as O1, the outer - circle diameter of the wall thickness at the mating part of the outer cylinder 1 and the limit joint 12 as O2, the outer - circle diameter of the piston - rod 2 as O3, the inner - hole diameter of the limit joint 12 as O4, and the outer - circle diameter of the limit joint 12 as O5;

[0063] According to the strength calculation results, determine the outer - circle diameter of the piston - rod 2 as O3, and then design the inner - hole diameter dimension O4 of the limit joint 12 to satisfy the relationship: O3 + 0.02 < O4 < O3 + 0.05; this ensures that the outer - circle of the piston - rod 2 can be closely fitted with the inner - hole of the limit joint 12, and the piston - rod 2 can be smoothly inserted into the inner - hole of the limit joint 12 without excessive clearance between the piston - rod 2 and the inner - hole of the limit joint 12.

[0064] Similarly, design the outer - circle diameter O5 of the limit joint 12 to satisfy the relationship O1 - 0.05 < O5 < O1 - 0.02; this ensures that the inner - hole O1 of the outer cylinder 1 can be closely fitted with the outer - circle of the wall thickness at the mating part of the limit joint 12 (O5), and the limit joint 12 can be smoothly inserted into the inner - hole of the outer cylinder 1 without excessive clearance between the outer - circle wall of the limit joint 12 and the inner - hole of the outer cylinder 1.

[0065] Furthermore, the design parameters of the spring can also be verified:

[0066] The design results should satisfy the relational inequality P2 < P1 < P; f4 < f3 < t - d; n0 < (H1 / d).

[0067] P2 is the minimum working load, P1 is the maximum working load, P is the spring allowable load, thus P2 < P1 < P should be met;

[0068] f3 is the single coil deformation of the spring under the maximum working load, f4 is the single coil deformation of the spring under the minimum working load, thus f4 < f3 naturally, and t refers to the axial distance of the corresponding points of the adjacent two coils of the spring on the center line, the spring is a compression spring, and f3 should be less than t minus the value of twice 1 / 2 spring diameter d in the certain geometric relationship, thus the relationship f4 < f3 < t-d is obtained; similarly, from the geometric relationship, the total number of coils n0 of the spring should be less than the minimum length H1 of the spring divided by the spring diameter d, otherwise the adjacent coils of the spring will interfere with each other, which is not consistent with the actual situation, thus the relationship n0 < (H1 / d) is obtained.

[0069] The above only expresses the embodiments of the present application, which are described in detail and specifically, but cannot be understood as the limitation of the patent scope. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, which all belong to the protection scope of the present application. In addition, the non-exhaustive parts of the present application are all conventional technologies.

Claims

1. A landing skid puller device, characterized by, The device comprises an outer cylinder, a piston rod, a spring, and a limiting joint. The outer cylinder is arranged on a landing gear buffer, the piston rod is arranged on a landing gear ski, and one end of the piston rod extends into a hole in the outer cylinder. The device further comprises an upper mounting shaft, a lower mounting bolt, a lower threaded joint, and a joint bearing. The lower threaded joint is arranged on the landing gear ski, and a threaded segment of the piston rod away from the outer cylinder is threadedly connected to the lower threaded joint. The joint bearing is mounted in an ear of the lower threaded joint, and the lower mounting bolt is mounted in a hole in the joint bearing. The upper mounting shaft is connected to a steel cable, and the upper mounting shaft is mounted in two ears at an end of the outer cylinder away from the piston rod via a nut. A support sleeve is arranged between the upper mounting shaft and the ears, and the length of the support sleeve is greater than h, where h=(L-M) / 2, L is the outer diameter of the outer cylinder, and M is the span of the two ears. The device further comprises a limiting bolt, which passes through the outer cylinder and the limiting joint in sequence. There are three limiting bolts, which are evenly distributed in the circumferential direction of the outer cylinder.

2. The apparatus of claim 1, wherein, An arc-shaped washer is arranged between the limiting bolt and the outer cylinder to ensure that the limiting bolt is in close contact with the outer cylindrical surface of the outer cylinder. The inner wall of the outer cylinder is coated with lubricating grease.

3. A design method for the landing gear ski pull rod device of claim 1 or 2, characterized in that The design process of the spring is as follows: Determine the maximum deformation f1=H0-H1 and the minimum deformation f2=H0-H2 of the spring, where H1 is the minimum length of the spring, H2 is the maximum length of the spring, and H0 is the free length of the spring. Determine the outer diameter D1 of the spring according to the size of the outer cylinder cross section, and determine the diameter d of the spring to obtain the middle diameter D2 of the spring. Determine the pitch t of the spring according to the diameter d of the spring. Determine the effective working turns n of the spring as (H0-2d) / t. determining a maximum working load P1 of the spring = (f1*G*d 4 ) / (8n0*D2 3 ), and a minimum working load P2 of the spring = (f2*G*d 4 ) / (8n0*D2 3 ); wherein G is a shear modulus of the spring material; Determine the total turns n0 of the spring as n+2 according to the effective working turns n. determining the spring winding ratio C = D2 / d; and the curvature factor M = (4*C - 1) / (4*C - 4) + 0.615 / C; and from this the spring allowable load P = (3.14*d 3 G) / (8*D2*M); Determine the spring stiffness K as (P1-P2) / (f1-f2). Determine the single-turn deformation f3 of the spring under the maximum working load as f1 / n0, and the single-turn deformation f4 of the spring under the minimum working load as f2 / n0. The design process of the outer cylinder, the piston rod, and the limiting joint is as follows: Determine the maximum length S1 of the outer cylinder mounting point and the piston rod mounting point according to the flight state of the helicopter landing gear, and determine the minimum length S2 of the outer cylinder mounting point and the piston rod joint mounting point according to the parking state of the helicopter landing gear.

4. The method of claim 3, wherein, S1, S2, the structure length S3 of the outer cylinder, and the structure length S4 of the piston rod satisfy the constraint conditions: S3<S2; S4<S2; and S1<S3+S4. Determine the outer diameter O3 of the piston rod body and the inner hole diameter O4 of the limiting joint according to the strength calculation results, and the limiting joint outer diameter O5 satisfies the relationship: O1-0.05 <O5< O1-0.02, where O1 is the inner hole diameter of the outer cylinder. The method further comprises The design parameters of the spring are verified, if P2 5. The method of claim 3, wherein, The minimum spring length H1, the maximum spring length H2, and the free state spring length H0 are determined according to the change of the bumper length after the landing and the taking off of the helicopter landing gear.

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