Design method of skid type landing gear

Abstract

The invention relates to a design method of a skid type undercarriage. The design method comprises the following steps: S1, confirming design parameters of an aircraft; s2, calculating ground bearing reaction of the front landing gear and the rear landing gear when the aircraft lands; s3, establishing an undercarriage finite element model, calculating stress and strain of the front undercarriage structure and the rear undercarriage structure, and calculating vertical displacement and transverse displacement of the front undercarriage structure and the rear undercarriage structure; s4, calculating the gravity center vertical displacement of the aircraft by adopting interpolation; s5, calculating a vertical speed theoretical value when the aircraft lands; and S6, comparing the vertical velocity theoretical value with a design value, judging whether the aircraft landing requirement is met or not, and determining whether iterative optimization needs to be carried out or not according to a judgment result. Compared with explicit dynamics simulation analysis, the design method has the advantages of high project iterative optimization speed and high efficiency.

Description

Technical Field

[0001] The invention relates to the field of aircraft design, and in particular to a design method for a skid-type landing gear. Background Art

[0002] The skid-type landing gear is a form of landing gear with a simple structure and light weight. Its main function is to absorb the kinetic energy generated by the vertical speed of the aircraft when landing, reduce the vertical overload during landing, and provide support when the aircraft is parked.

[0003] There is currently no mature and reliable static mechanical design and calculation method for skid-type landing gear, and the design is difficult. At present, the design work mainly starts from static strength design, and the static strength analysis of the landing gear is performed by artificially assuming an overload coefficient and applying ground loads. Because the overload coefficient is an artificially assumed value and may deviate greatly from the actual value, this method also needs to adjust the structural parameters through the results of explicit dynamics simulation analysis and repeatedly calculate to achieve the ideal state. However, the display dynamics analysis time cycle is long, the project iteration speed is slow, and the efficiency is low, which will affect the overall progress of the project. Summary of the invention

[0004] In view of the above technical problems, the present invention provides a design method for a skid-type landing gear. The landing gear is analyzed during the landing of the aircraft by an energy method to obtain corresponding indicators such as stress, strain, vertical speed, etc. that the landing gear meets during the landing of the aircraft. The method can quickly determine whether the landing gear meets the performance requirements of the aircraft during landing, and quickly perform iterative optimization as needed. The method is efficient and accurate, and is suitable for any form of landing gear design that absorbs energy through structural deformation.

[0005] In view of the above problems, the present application provides a design method for a skid-type landing gear, comprising: S1. Confirm the aircraft design indicators, including: the total mass m; the center of gravity position of the entire aircraft; the design value of the aircraft landing vertical speed v; the aircraft landing rotor lift L; the maximum vertical overload of the aircraft landing ng, where g is the acceleration of gravity and n is any number ≥ 1; the distance between the front landing gear and the center of gravity d1; the distance between the rear landing gear and the center of gravity d2; the ground friction coefficient μ; S2. Calculate the vertical ground support reaction force of the front and rear landing gears when the aircraft lands. The calculation formula is as follows: ; in: F1 is the ground support reaction force of the front landing gear; F2 is the ground support reaction force of the rear landing gear; S3. Establish a landing gear finite element model and calculate the stress, strain, vertical displacement and lateral displacement of the front and rear landing gears; S4. Use interpolation to calculate the vertical displacement h of the center of gravity of the aircraft. The calculation formula is as follows: ; Where: h1 is the vertical displacement of the front landing gear; h2 is the vertical displacement of the rear landing gear; S1 is the lateral displacement of the front landing gear; S2 is the lateral displacement of the rear landing gear; S5, calculating the theoretical vertical velocity value V1 of the aircraft when landing; S6. Compare the theoretical vertical landing speed value V1 of the aircraft with the speed design value V to determine: (1) If V1 ≥ V, the aircraft landing requirements are met; (2) If V1<V, the landing requirements of the aircraft are not met.

[0006] Further, the step S3 specifically includes: using finite element software to establish a finite element model of the landing gear, under the finite element model, constraining the connection joint between the landing gear and the fuselage, loading a vertical load of 0.5F1 and a horizontal load of 0.5μF1 on the left and right contact points between the front landing gear and the ground, respectively, loading a vertical load of 0.5F2 and a horizontal load of 0.5μF2 on the left and right contact points between the rear landing gear and the ground, respectively, and then starting to perform a static analysis on the landing gear to calculate the structural stress and strain of the landing gear, as well as the vertical displacement h1 and lateral displacement S of the front landing gear. 1， The vertical displacement h2 and lateral displacement S2 of the rear landing gear; Furthermore, the finite element software may be Nastran, Abaqus, ANSYS, etc.

[0007] Furthermore, the step S5 specifically includes: based on the finite element model, according to the law of conservation of energy when the aircraft is landing, calculating the theoretical value of the vertical velocity of the aircraft when landing, the calculation formula is as follows: .

[0008] Furthermore, when it is determined that the aircraft landing requirements are not met, the following steps are also included: S7, iteratively optimizing the landing gear, wherein the optimization iteration specifically includes: re-executing step S3, adjusting the design parameters of the landing gear, re-establishing the landing gear finite element model, and re-calculating the theoretical value of the vertical velocity of the aircraft when landing for judgment.

[0009] Beneficial effects of the present invention: The present invention mainly analyzes the landing gear during the landing of the aircraft by the energy method, obtains the corresponding indicators such as the landing gear stress and strain satisfied by the landing gear during the landing of the aircraft, and further calculates the theoretical value of the vertical velocity of the landing gear. This method can quickly determine whether the landing gear meets the performance requirements of the aircraft during landing, and confirm whether optimization iteration is required based on the judgment result. The design method is efficient and accurate, and the iterative optimization is simple, and is applicable to any form of landing gear that absorbs energy through structural deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0011] Attached Figure 1 The present invention is a flow chart of the skid-type landing gear design method; Attached Figure 2 This is a schematic diagram of the skid-type landing gear structure of Example 1; Among them: 1-restraint point; 2-front landing gear loading point; 3-rear landing gear loading point. DETAILED DESCRIPTION

[0012] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments 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 those skilled in the art without creative work are within the scope of protection of the present invention.

[0013] As attached Figure 1 As shown, a design method of a skid-type landing gear comprises: S1. Confirm the aircraft design indicators, including: the total aircraft mass m; the center of gravity position of the entire aircraft; the aircraft landing vertical speed design value v; the aircraft landing rotor lift L; the aircraft landing maximum vertical overload ng, where g is the gravity acceleration and n is any number ≥ 1; the distance between the front landing gear and the center of gravity in the heading direction d1, the distance between the rear landing gear and the center of gravity in the heading direction d2, and the ground friction coefficient μ; S2. Calculate the vertical ground support reaction force of the front and rear landing gears when the aircraft lands. The calculation formula is as follows: ; in: F1 is the ground support reaction force of the front landing gear; F2 is the ground support reaction force of the rear landing gear; S3. Establish a finite element model of the skid-type landing gear, and calculate the stress, strain, vertical displacement and lateral displacement of the front and rear landing gear structures, specifically including: using finite element software to establish a finite element model of the landing gear, under the finite element model, constrain the connection joint between the landing gear and the fuselage, load a vertical load of 0.5F1 and a horizontal load of 0.5μF1 at the left and right contact points between the front landing gear and the ground, respectively, and load a vertical load of 0.5F2 and a horizontal load of 0.5μF2 at the left and right contact points between the rear landing gear and the ground, respectively, and then start a static analysis of the landing gear to calculate the stress and strain of the landing gear structure, as well as the vertical displacement h1 and lateral displacement S of the front landing gear. 1， The vertical displacement h2 and lateral displacement S2 of the rear landing gear; S4. Use interpolation to calculate the vertical displacement h of the center of gravity of the aircraft. The calculation formula is as follows: ; S5. Calculate the theoretical vertical velocity value V1 of the aircraft when landing, specifically including: based on the finite element model, calculate according to the law of conservation of energy when the aircraft lands, and the calculation formula is as follows: ; S6. Compare the theoretical vertical landing velocity V1 of the aircraft with the velocity design value V: (1) If V1 ≥ V, the aircraft landing requirements are met; (2) If V1<V, the landing requirements of the aircraft are not met.

[0014] Furthermore, when it is determined that the aircraft landing requirements are not met, the following steps are also included: S7, when iteratively optimizing the landing gear, the optimization iteration specifically includes: re-executing step S3, adjusting the design parameters of the landing gear, re-establishing the landing gear finite element model, and re-calculating the theoretical value of the vertical velocity of the aircraft when landing for judgment.

[0015] Example 1 The design method of the skid-type landing gear of a certain type of vertical take-off and landing aircraft includes: S1. Confirm the aircraft design indicators, including: the aircraft mass m is 150kg, the X-coordinate position of the aircraft center of gravity is 1700mm, the X-coordinate position of the front landing gear center is 747mm, the X-coordinate position of the rear landing gear center is 2547mm, the maximum vertical overload of the aircraft landing is 3g, the vertical speed design value v of the aircraft landing is 0.5m / s, the rotor lift is 0.66mg according to CCAR27, and the ground friction coefficient μ is 0.25 according to CCAR27; The distance between the front landing gear and the center of gravity is d1=1700-747=953mm; The distance between the rear landing gear and the center of gravity is d2 = 2547-1700 = 847mm; S2. Calculate the ground support reaction force of the front and rear landing gear when the aircraft lands. The calculation formula is as follows:

[0016] in: F1 is the vertical support reaction force of the front landing gear on the ground; F2 is the vertical support reaction force of the rear landing gear on the ground; According to the above formula, the vertical support reaction force of the front landing gear is 2075.15N; the vertical support reaction force of the rear landing gear is 2334.85N; S3. Establish a landing gear finite element model and calculate the stress, strain, vertical displacement and lateral displacement of the front and rear landing gears. Specifically, the finite element model of the landing gear is established using finite element software. Under the finite element model, as shown in the attached figure, Figure 2 As shown, the landing gear is constrained at the connection joint with the fuselage (i.e., constraint point 1), a vertical load of 0.5F1 (i.e., 1037.575N) and a horizontal load of 0.5μF1 (i.e., 259.394N) are respectively applied to the left and right contact points between the front landing gear and the ground (i.e., front landing gear loading point 2), a vertical load of 0.5F2 (i.e., 1167.425N) and a horizontal load of 0.5μF2 (i.e., 291.856N) are respectively applied to the left and right contact points between the rear landing gear and the ground (i.e., rear landing gear loading point 3), and then the landing gear is subjected to static analysis, and the vertical displacement h1 of the front landing gear is calculated to be 42mm and the lateral displacement S1 is 75.2mm, and the vertical displacement h2 of the rear landing gear is 63.3mm and the lateral displacement S2 is 102mm; S4. Use interpolation to calculate the vertical displacement h of the center of gravity of the aircraft. The calculation formula is as follows: ; According to the above formula, the vertical displacement of the center of gravity of the aircraft is 53.277mm; S5. Calculate the theoretical vertical velocity value V1 of the aircraft when landing, specifically including: based on the finite element model, calculate according to the law of conservation of energy when the aircraft lands, and the calculation formula is as follows: ; Right now, ; According to the formula, the theoretical vertical velocity of the aircraft during landing is: ; S6. Compare and judge the theoretical vertical velocity value V1 of the aircraft during landing with the velocity design value V: V1>V, meeting the landing requirements of the aircraft.

[0017] The above is only a specific embodiment of the present invention, and the present invention is described in detail. The unexplained part is a conventional technology. However, the protection scope of the present invention is not limited to this. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. The protection scope of the present invention shall be based on the protection scope of the claims.

Claims

1. A method for designing a skid-type landing gear, characterized in that include: S1. Confirm the design indicators of the aircraft, including: the mass of the whole aircraft m; the position of the center of gravity of the whole aircraft; the design value of the vertical speed of the aircraft landing v; the lift of the aircraft landing rotor L; the maximum vertical overload of the aircraft landing ng, where g is the acceleration of gravity and n is any number ≥ 1; the distance between the front landing gear and the center of gravity d1; the distance between the rear landing gear and the center of gravity d2; the ground friction coefficient μ; S2. Calculate the vertical ground support reaction force of the front and rear landing gears when the aircraft lands. The calculation formula is as follows: ； Where: F1 is the ground support reaction force of the front landing gear; F2 is the ground support reaction force of the rear landing gear; S3. Establish a landing gear finite element model and calculate the stress, strain, vertical displacement and lateral displacement of the front and rear landing gears; S4. Use interpolation to calculate the vertical displacement h of the center of gravity of the aircraft when it lands. The calculation formula is as follows: ; Where: h1 is the vertical displacement of the front landing gear; h2 is the vertical displacement of the rear landing gear; S1 is the lateral displacement of the front landing gear; S2 is the lateral displacement of the rear landing gear; S5, calculating the theoretical vertical velocity value V1 of the aircraft when landing; S6. Compare the theoretical vertical velocity value V1 of the aircraft during landing with the velocity design value V to determine: If V1 ≥ V, the aircraft landing requirements are met; If V1<V, the landing requirements of the aircraft are not met.

2. The design method of a skid-type landing gear according to claim 1, characterized in that: The step S3 specifically includes: using finite element software to establish a finite element model of the landing gear, under the finite element model, constraining the connection joint between the landing gear and the fuselage, loading a vertical load of 0.5F1 and a horizontal load of 0.5μF1 at the left and right contact points between the front landing gear and the ground, respectively, loading a vertical load of 0.5F2 and a horizontal load of 0.5μF2 at the left and right contact points between the rear landing gear and the ground, respectively, and then starting to perform a static analysis on the landing gear, calculating the stress and strain of the landing gear, and calculating the vertical displacement h1 and lateral displacement S1 of the front landing gear, and the vertical displacement h2 and lateral displacement S2 of the rear landing gear.

3. The design method of a skid-type landing gear according to claim 1, characterized in that: The step S5 calculates the theoretical vertical velocity value V1 of the aircraft when landing, specifically including: based on the finite element model, according to the law of conservation of energy when the aircraft lands, the calculation formula is as follows: 。 4. The design method of a skid-type landing gear according to claim 1, characterized in that: When it is determined that the aircraft landing requirements are not met, it also includes: S7, iteratively optimizing the landing gear, specifically including: re-executing step S3, adjusting the landing gear design parameters, re-establishing the landing gear finite element model, and recalculating the theoretical value of the vertical velocity of the aircraft during landing under the new finite element model, and then making a judgment.

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