A design method for a skid-type landing gear

Abstract

The present invention relates to a design method for a skid-type landing gear, including: S1, confirming the design parameters of the aircraft; S2, calculating the ground reaction forces of the front and rear landing gears when the aircraft lands; S3, establishing a finite element model of the landing gear, calculating the stress and strain of the front and rear landing gear structures, and calculating the vertical and lateral displacements of the front and rear landing gears; S4, using interpolation to calculate the vertical displacement of the aircraft's center of gravity; S5, calculating the theoretical value of the vertical speed when the aircraft lands; S6, comparing the theoretical value of the vertical speed with the design value to determine whether the requirements for the aircraft landing are met, and confirming whether iterative optimization is required according to the judgment result. Compared with explicit dynamic simulation analysis, this design method has a fast project iterative optimization speed and high efficiency.

Description

Technical Field

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

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

[0003] At present, there is no mature and reliable static mechanics design and calculation method for skid-type landing gears, 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 carried out by artificially assuming the overload coefficient and applying the ground load. Since the overload coefficient is an artificially assumed value, there may be a large deviation from the actual value. Therefore, this method still needs to adjust the structural parameters through explicit dynamic simulation analysis results and calculate repeatedly to make it reach the ideal state. However, the explicit dynamic analysis has a long time cycle, slow project iteration speed, low efficiency, and 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, which analyzes the landing gear during the landing process of the aircraft by the energy method, and obtains the corresponding indexes such as stress, strain, and vertical velocity of the landing gear when the aircraft lands. This method can quickly judge whether the landing gear meets the performance requirements during the landing of the aircraft, and can quickly perform iterative optimization according to needs, with high efficiency and accuracy, and is applicable to the design of any form of landing gear 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, including:

[0006] S1. Confirm the design indexes of the aircraft, including: the total mass m of the aircraft; the position of the center of gravity of the whole aircraft; the designed value V of the vertical velocity of the aircraft during landing; the lift L of the rotor of the aircraft during landing; the maximum vertical overload ng during the landing of the aircraft, where g is the acceleration due to gravity and n is any number greater than or equal to 1; the distance d between the nose landing gear and the center of gravity in the course direction 1 ; the distance d between the rear landing gear and the center of gravity in the course direction 2 ; the ground friction coefficient μ;

[0007] S2. Calculate the vertical ground reaction forces of the front and rear landing gears when the aircraft lands. The calculation formulas are as follows:

[0008]

[0009] Where:

[0010] F 1 is the ground reaction force of the nose landing gear;

[0011] F 2 is the ground reaction force of the rear landing gear;

[0012] S3. Establish a finite element model of the landing gear, 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 aircraft's center of gravity, and the calculation formula is as follows:

[0013]

[0014] In the formula:

[0015] h 1 is the vertical displacement of the front landing gear;

[0016] h 2 is the vertical displacement of the rear landing gear;

[0017] S 1 is the lateral displacement of the front landing gear;

[0018] S 2 is the lateral displacement of the rear landing gear;

[0019] S5. Calculate the theoretical value V of the vertical speed when the aircraft lands 1 ;

[0020] S6. Compare and judge the theoretical value V of the vertical speed when the aircraft lands 1 with the designed value V of the vertical speed when the aircraft lands:

[0021] (1) If V 1 ≥V, it meets the requirements for the aircraft to land;

[0022] (2) If V 1 <V, it does not meet the requirements for the aircraft to land.

[0023] Furthermore, the specific steps of S3 include: using finite element software to establish a finite element model of the landing gear. Under this finite element model, the joints where the landing gear is connected to the fuselage are constrained. At the left and right contact points between the front landing gear and the ground, vertical loads of 0.5F 1 and horizontal loads of 0.5μF 1 are respectively applied. At the left and right contact points between the rear landing gear and the ground, vertical loads of 0.5F 2 and horizontal loads of 0.5μF 2 are respectively applied. Then, start the static analysis of the landing gear to calculate the structural stress, strain of the landing gear, as well as the vertical displacement h 1 and lateral displacement S 1 of the front landing gear, and the vertical displacement h 2 and lateral displacement S 2 of the rear landing gear;

[0024] Further, the finite element software may be nastran, abaqus, ansys, etc.

[0025] Further, the step S5 specifically includes: based on the finite element model, calculating the theoretical value of the vertical velocity of the aircraft during landing according to the law of conservation of energy during aircraft landing. The calculation formula is as follows:

[0026]

[0027] Further, when it is determined that the requirements for aircraft landing are not met, the following steps are also included:

[0028] S7. Iteratively optimize the landing gear. The specific optimization iteration includes: re-executing step S3, adjusting the design parameters of the landing gear, re-establishing the finite element model of the landing gear, and calculating the theoretical value of the vertical velocity of the aircraft during landing again for judgment.

[0029] Advantages of the present invention:

[0030] The present invention mainly analyzes the landing gear during the aircraft landing process by the energy method, obtains the corresponding indexes such as the stress and strain of the landing gear that meet the aircraft landing requirements, and further calculates the theoretical value of the vertical velocity of the landing gear. This method can quickly judge whether the landing gear meets the performance requirements during aircraft landing, and confirm whether iterative optimization is needed according to the judgment result. This design method is efficient and accurate, and the iterative optimization is simple, and it is applicable to any form of landing gear that absorbs energy through structural deformation. Description of the Drawings

[0031] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Att Figure 1 is the flowchart of the design method of the skid-type landing gear of the present invention;

[0033] Att Figure 2 is the structural schematic diagram of the skid-type landing gear in Embodiment 1;

[0034] Wherein: 1 - constraint point; 2 - front landing gear loading point; 3 - rear landing gear loading point. Specific Embodiments

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Apparently, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0036] As shown in the Figure 1 accompanying drawings, a design method for a skid-type landing gear includes:

[0037] S1. Confirm the design indicators of the aircraft, including: the total mass m of the aircraft; the position of the center of gravity of the whole aircraft; the designed value V of the vertical landing speed of the aircraft; the rotor lift L during the aircraft landing; the maximum vertical overload ng during the aircraft landing, where g is the acceleration due to gravity and n is any number greater than or equal to 1; the heading distance d between the nose landing gear and the center of gravity 1 , the heading distance d between the rear landing gear and the center of gravity 2 , and the ground friction coefficient μ;

[0038] S2. Calculate the vertical ground reaction forces of the front and rear landing gears when the aircraft lands. The calculation formula is as follows:

[0039]

[0040] Where:

[0041] F 1 is the ground reaction force of the nose landing gear;

[0042] F 2 is the ground reaction force of the rear landing gear;

[0043] 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, use finite element software to establish a finite element model of the landing gear. Under this finite element model, constrain the joints where the landing gear is connected to the fuselage, and apply a vertical load of 0.5F 1 and a horizontal load of 0.5μF 1 respectively at the left and right contact points between the nose landing gear and the ground, and apply a vertical load of 0.5F 2 and a horizontal load of 0.5μF 2 respectively at the left and right contact points between the rear landing gear and the ground. Then start the static analysis of the landing gear to calculate the stress and strain of the landing gear structure, as well as the vertical displacement h 1 and lateral displacement S 1 of the nose landing gear, and the vertical displacement h 2 and lateral displacement S 2 of the rear landing gear;

[0044] S4. Calculate the vertical displacement h of the aircraft's center of gravity using interpolation. The calculation formula is as follows:

[0045]

[0046] S5. Calculate the theoretical value V of the vertical velocity when the aircraft lands 1 , specifically including: calculating based on the finite element model according to the law of conservation of energy when the aircraft lands. The calculation formula is as follows:

[0047]

[0048] S6. Compare the theoretical value V of the vertical velocity when the aircraft lands 1 with the designed value V of the vertical velocity when the aircraft lands:

[0049] (1) If V 1 ≥V, the landing requirements of the aircraft are met;

[0050] (2) If V 1 <V, the landing requirements of the aircraft are not met.

[0051] Furthermore, when it is determined that the landing requirements of the aircraft are not met, it further includes the steps of:

[0052] S7. When performing iterative optimization on the landing gear, the specific optimization iteration includes: re - executing step S3, adjusting the design parameters of the landing gear, re - establishing the finite element model of the landing gear, and recalculating the theoretical value of the vertical velocity when the aircraft lands for judgment.

[0053] Embodiment 1

[0054] A design method for the skid - type landing gear of a certain type of vertical take - off and landing aircraft, including:

[0055] S1. Confirm the aircraft design indicators, including: the total mass m of the aircraft is 150 kg, the X - coordinate position of the center of gravity of the whole aircraft is 1700 mm, the X - coordinate position of the center of the front landing gear is 747 mm, the X - coordinate position of the center of the rear landing gear is 2547 mm, the maximum vertical overload during aircraft landing is 3g, the designed value V of the vertical velocity when the aircraft lands is 0.5 m / s, the rotor lift is taken as 0.66mg according to CCAR27, and the ground friction coefficient μ is taken as 0.25 according to CCAR27;

[0056] The heading distance d between the front landing gear and the center of gravity 1 =1700 - 747=953 mm;

[0057] The heading distance d between the rear landing gear and the center of gravity 2 =2547 - 1700=847 mm;

[0058] S2. Calculate the ground reaction forces of the front and rear landing gears when the aircraft lands. The calculation formula is as follows:

[0059]

[0060] Where:

[0061] F 1 is the vertical ground reaction force of the front landing gear;

[0062] F 2 is the vertical ground reaction force of the rear landing gear;

[0063] According to the above formula, the vertical ground reaction force of the front landing gear is 2075.15 N; the vertical ground reaction force of the rear landing gear is 2334.85 N;

[0064] S3. Establish a finite element model of the landing gear and calculate the stress, strain, vertical displacement, and lateral displacement of the front and rear landing gears. Specifically, use finite element software to establish a finite element model of the landing gear. Under this finite element model, as shown in the appendix Figure 2 constrain the joint where the landing gear is connected to the fuselage (i.e., constraint point 1). Apply a vertical load of 0.5F 1 (i.e., 1037.575 N) and a horizontal load of 0.5μF 1 (i.e., 259.394 N) at the left and right contact points between the front landing gear and the ground (i.e., front landing gear loading point 2). Apply a vertical load of 0.5F 2 (i.e., 1167.425 N) and a horizontal load of 0.5μF 2 (i.e., 291.856 N) at the left and right contact points between the rear landing gear and the ground (i.e., rear landing gear loading point 3). Then start the static analysis of the landing gear and calculate the vertical displacement h 1 of the front landing gear to be 42 mm and the lateral displacement S 1 to be 75.2 mm. The vertical displacement h 2 of the rear landing gear is 63.3 mm and the lateral displacement S 2 is 102 mm;

[0065] S4. Use interpolation to calculate the vertical displacement h of the aircraft's center of gravity. The calculation formula is as follows:

[0066]

[0067] According to the above formula, the vertical displacement of the aircraft's center of gravity is 53.277 mm;

[0068] S5. Calculate the theoretical value V 1 of the vertical speed when the aircraft lands. Specifically, calculate based on the finite element model according to the law of conservation of energy when the aircraft lands. The calculation formula is as follows:

[0069]

[0070] That is,

[0071] 0.5 × 150 kg × B 1 2 +(150 kg × 9.8 N / kg - 0.66 × 150 kg × 9.8 N / kg) 53.277 mm = 0.5 × 2075.15 N × 42 mm + 0.5 × 2334.85 N × 63.3 mm - 0.5 × 0.25 × 2075.15 N × 75.2 mm - 0.5 × 0.25 × 2334.85 N × 102 mm;

[0072] According to the formula, the theoretical value of the vertical velocity of the aircraft during landing is: V 1 = 0.74 m / s;

[0073] S6. Compare and judge the theoretical value V 1 of the vertical velocity of the aircraft during landing with the designed value V of the vertical velocity of the aircraft during landing: V 1 > V, meeting the requirements for the aircraft to land.

[0074] The above is only a specific embodiment of the present invention. The present invention has been described in detail, and the unelaborated parts are conventional techniques. However, the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. The protection scope of the present invention shall be subject to the protection scope of the said 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 greater than or equal to 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; 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: Where: S1 is the lateral displacement of the front landing gear; S2 is the lateral displacement of the rear landing gear; S6. Compare the theoretical value V1 of the vertical speed of the aircraft during landing with the design value V of the vertical speed of the aircraft during landing 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 joints 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 static analysis on the landing gear, calculating the stress and strain of the landing gear, as well as 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: 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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