Aircraft main landing gear structure and folding and unfolding method

Abstract

The aircraft main landing gear structure comprises a fuselage connecting assembly, a supporting column assembly, an oil injection valve assembly, a shimmy damping assembly and a wheel assembly, the fuselage connecting assembly is arranged on the upper section of the supporting column assembly, the top end of the supporting column assembly is connected with a fuselage, the lower end of the supporting column assembly is connected with the wheel assembly, and the supporting column assembly is fixedly connected with the fuselage through the fuselage connecting assembly; the oil injection valve assembly is arranged on the supporting column assembly and higher than the horizontal position of the machine body connecting assembly, the upper portion of the shimmy damping assembly is connected with the supporting column assembly, the lower portion of the shimmy damping assembly is connected with the wheel assembly, the two ends of the retracting and releasing control assembly are connected with the supporting column assembly and the machine body respectively, and the wheel assembly comprises a scraper device, a scraper mounting frame and a tire. And the mud scraper device is arranged on the mounting frame and is positioned above the tire, and an annular gap which is symmetrical to the external size of the tire is reserved. The design of the mud scraping plate device of the wheel group can prevent runway foreign matters from entering an airplane wheel cabin, and the lifting of a gravel roadbed is met.

Description

Technical Field

[0001] The present invention relates to the field of aircraft landing gears, and particularly to an aircraft main landing gear structure and a retracting and extending method thereof. Background Art

[0002] The landing gear is one of the most common landing devices of an aircraft and is one of the important load-bearing components of the aircraft. It bears a large load and the force is relatively complex, bearing the ground reaction forces generated during landing impact, ground taxiing, and various maneuvering movements (such as braking, turning, etc.). Moreover, both the landing impact and the ground taxiing impact loads have obvious dynamic characteristics. The landing gear includes a nose landing gear and a main landing gear. The main landing gear is located near the center of gravity of the aircraft and bears about 85%-92% of the load when the aircraft is parked, taxiing, taking off, and landing on the ground. It disperses the aircraft weight to multiple wheels through a strut and axle system made of high-strength alloy materials (such as titanium alloy or aviation aluminum). For example, the main landing gear of a large airliner often adopts a multi-wheel design (such as dual-wheel or four-wheel) to reduce the pressure on the runway per unit area.

[0003] The existing main landing gears usually have difficulty in taking off and landing on gravel roads, and the fuselage layout is unreasonable. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide an aircraft main landing gear structure and a retracting and extending method thereof.

[0005] To solve the above technical problems, the present invention provides the following technical solutions: An aircraft main landing gear structure of the present invention includes a fuselage connection assembly, a strut assembly, an oil injection valve assembly, a shock absorber assembly, and a wheel assembly. The fuselage connection assembly is arranged at the upper section of the strut assembly. The top of the strut assembly is connected to the fuselage, and the bottom end is connected to the wheel assembly and is fixedly connected to the fuselage through the fuselage connection assembly. The oil injection valve assembly is arranged on the strut assembly and is at a horizontal position higher than the fuselage connection assembly. The upper part of the shock absorber assembly is connected to the strut assembly, and the lower part is connected to the wheel assembly. Both ends of the retracting and extending control assembly are respectively connected to the strut assembly and the fuselage. The wheel assembly includes a mudguard device, a mudguard mounting bracket, and a tire. The mudguard device is arranged on the mounting bracket and has an annular gap symmetrical to the outer dimension of the tire above the tire.

[0006] As a preferred technical solution of the present invention, the fuselage connection assembly includes a landing gear bracket and a fixing pin. The landing gear bracket is arranged in a triangle shape. The fixing pin is used to fix the landing gear bracket and is sleeved on the strut assembly. The fuselage connection assembly is an overall transverse bracket and is fixedly connected to the fuselage through bolts at both ends. As a preferred technical solution of the present invention.

[0007] As a preferred technical solution of the present invention, the strut assembly includes a main landing gear strut and a filling and inflation sign. The main landing gear strut is hollow inside, provided with an oil chamber filled with hydraulic oil. A piston rod is arranged below the main landing gear strut, and the filling and inflation sign is arranged on the main landing gear strut.

[0008] As a preferred technical solution of the present invention, the oil injection valve assembly includes an actuating cylinder, an inlet liquid pipe joint, an outlet liquid pipe joint and an inlet and outlet hydraulic pipe. One end of the actuating cylinder is fixed on the main landing gear strut. The inlet liquid pipe joint and the outlet liquid pipe joint are fixed on the outer wall of the actuating cylinder. Both the inlet liquid pipe joint and the outlet liquid pipe joint are externally connected to hydraulic pipes, and the hydraulic pipes are connected to the fuselage oil pressure system.

[0009] As a preferred technical solution of the present invention, the anti-shimmy assembly includes a scissors link. An anti-shimmy damper is arranged on the upper section of the scissors link. The anti-shimmy damper is sleeved on the main landing gear strut, and the lower end of the scissors link is sleeved on the wheel assembly.

[0010] As a preferred technical solution of the present invention, the lower part of the anti-shimmy assembly is sleeved on the piston rod.

[0011] As a preferred technical solution of the present invention, the wheel assembly further includes a front fork, a mounting shaft, a wheel hub guard, a spacer, a wheel, a sleeve pipe part, a sleeve pipe anchoring ear, a connecting plate, a first spring, a limiting device, a connecting rod, a spring anchoring ear and a shaft plug. The upper end of the front fork is connected to the piston rod, and the lower end is connected to the mounting shaft on both sides. The mounting shaft is sleeved with the wheel through the upper part, and the wheel is sleeved with a tire. The wheel hub guard is arranged on both sides of the wheel. The shaft plugs are arranged on both sides of the mounting shaft. The connecting rod and the sleeve pipe part are fixedly connected to the front fork through the sleeve pipe anchoring ear. The sleeve pipe anchoring ear is used to fix the relative positions of the connecting rod and the sleeve pipe part with the front fork. The connecting rod is slightly longer than the diameter of the tire. A mud scraping plate device mounting bracket is arranged at the end of the connecting rod. A spring anchoring ear is arranged below the front fork. The spring anchoring ear is connected to the connecting rod through a spring. A limiting device is also arranged between the two sleeve pipe anchoring ears of the connecting rod and is connected to the front fork.

[0012] As a preferred technical solution of the present invention, the landing gear support includes a connecting block, a support block, a stop block, a pivot pin, and a spring anchoring bolt. The right side of the connecting block is connected to the main landing gear strut. The stop block is arranged on the left side of the connecting block. The support block is arranged in a wing shape on the stop block. One pivot pin is arranged at each of the left and right ends of the support block, and one spring anchoring bolt is arranged at each of the left and right ends of the support block. The spring anchoring bolt is fixed to the fuselage through a spring.

[0013] As a preferred technical solution of the present invention, the retraction and extension of the main landing gear strut are realized by controlling the retraction and extension of the actuator by a hydraulic system. When the piston of the actuator shortens, the main landing gear retracts upward into the wing wheel well; When the piston of the actuator extends, the main landing gear lowers.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. The design of the mudguard device of the wheel set can prevent foreign objects on the runway from entering the wheel well and meet the takeoff and landing on a gravel subgrade; 2. The design adopts a simple strut-type, single-wheel landing gear and uses a better wide-section tire.

[0015] 3. The triangular fuselage connection bracket disperses the load through geometric stability and avoids stress concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings: Figure 1 is a schematic diagram of the overall structure of the present invention; Figure 2 is a schematic diagram of the first partial structure of the present invention; Figure 3 is a schematic diagram of the second partial structure of the present invention; Figure 4 is a schematic diagram of the third partial structure of the present invention; Figure 5 is a schematic diagram of the fourth partial structure of the present invention; In the figure: 1. Fuselage connection assembly; 2. Strut assembly; 3. Main landing gear strut; 4. Oil injection valve assembly; 5. Shimmy damper assembly; 6. Wheel assembly; 11. Piston rod; 13. Front fork; 14. Mounting shaft; 15. Spacer; 18. Scissor link; 19. Filling and inflation identification plate; 20. Wheel; 22. Tire; 23. Connecting rod; 231. Connecting plate; 24. Mudguard mounting bracket; 25. Sleeve pipe fitting; 26. Sleeve pipe anchor ear; 28. Spring anchor ear; 30. Mudguard device; 31. Hub guard; 32. Axial plug; 33. Landing gear support; 331. Connecting block; 332. Support block; 333. Stopper; 334. Pivot pin; 335. Spring anchor bolt; 34. First spring; 35. Fixed pin; 36. Landing gear bracket; 37. Limiting device; 38. In and out hydraulic pipe; 39. Actuator; 40. Inlet liquid pipe joint; 41. Outlet liquid pipe joint. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The preferred embodiments of the present invention will be described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0018] Among them, the same reference numerals in the drawings all refer to the same components.

[0019] As Figures 1-5 shown, the present invention provides an aircraft main landing gear structure, including a fuselage connection assembly 1, a strut assembly 2, an oil filling valve assembly 4, a damping assembly 5, and a wheel assembly 6. The fuselage connection assembly 1 is provided at the upper section of the strut assembly 2. The top of the strut assembly 2 is connected to the fuselage, and the bottom end is connected to the wheel assembly 6 and is fixedly connected to the fuselage through the fuselage connection assembly 1. The oil filling valve assembly 4 is provided on the strut assembly 2 and is higher than the horizontal position of the fuselage connection assembly 1. The upper part of the damping assembly 5 is connected to the strut assembly 2, and the lower part is connected to the wheel assembly 6. Both ends of the retraction and extension control assembly are respectively connected to the strut assembly 2 and the fuselage. The wheel assembly 6 includes a mudguard device 30, a mudguard mounting bracket 24, and a tire 22. The mudguard device 30 is provided on the mounting bracket and is located above the tire 22, leaving an annular gap symmetrical to the outer dimension of the tire 22.

[0020] In the present invention, the fuselage connection assembly 1 serves as the interface between the landing gear and the fuselage and needs to withstand the impact load during takeoff and landing. Its design needs to balance strength and lightweight. The strut assembly 2 is the main load-bearing structure, usually made of high-strength alloy materials (such as titanium alloy or aviation aluminum). The hydraulic oil in the internal oil cavity is used to absorb the landing impact energy and transmit the load through the piston rod 11. The oil filling valve assembly 4 is connected to the fuselage oil pressure system through a hydraulic pipeline to ensure the dynamic balance of the hydraulic oil during the retraction and extension process, and at the same time needs to have good sealing performance to prevent leakage. The damping assembly 5 suppresses the lateral vibration (shimmy phenomenon) of the wheel 20 during the taxiing process through the scissors link 18 and the damper, improving the ground handling stability. The mudguard device 30 of the wheel assembly 6 is designed to prevent foreign objects on the runway from entering the wheel 20 compartment. Its annular gap needs to be dynamically adjusted according to the wear of the tire 22 to avoid excessive friction or failure due to too large a gap. The material of the mudguard device 30 needs to be heat-resistant and corrosion-resistant, such as carbon fiber composite material, to cope with the heat load during high-speed taxiing.

[0021] In an alternative embodiment, the fuselage connection assembly 1 includes a landing gear bracket 36 and a fixing pin 35. The landing gear bracket 36 is triangularly arranged. The fixing pin 35 is used to fix the landing gear bracket 36 and is sleeved on the strut assembly 2. The fuselage connection assembly 1 is an overall transverse bracket and is fixedly connected to the fuselage through bolts at both ends.

[0022] It should be noted that the triangular fuselage connection bracket disperses the load through geometric stability to avoid stress concentration. The fixing pin 35 is made of high-strength steel (such as 30CrMnSiA) and is surface-chromed or nitrided to enhance wear resistance. The bolt connection between the bracket and the fuselage requires pre-tightening force control to prevent loosening caused by vibration.

[0023] The triangular layout of the bracket can improve the torsional stiffness, especially suitable for the dynamic load during the retraction and extension of the landing gear of high-speed aircraft.

[0024] The installation of the fixing pin 35 requires tolerance analysis to ensure that the thermal expansion under extreme temperatures does not affect the structural integrity.

[0025] In an optional embodiment, the strut assembly 2 includes the main landing gear strut 3 and the filling and inflation sign 19. The main landing gear strut 3 is hollow inside, provided with an oil chamber filled with hydraulic oil. A piston rod 11 is arranged below the main landing gear strut 3, and the filling and inflation sign 19 is arranged on the main landing gear strut 3.

[0026] It should be noted that the main landing gear strut 3 adopts a hollow design, and the internal oil chamber realizes buffering through hydraulic oil. Its volume needs to be calculated according to the weight and landing speed of the aircraft. The filling and inflation sign 19 is used to indicate the nitrogen pressure (usually 300 - 500 psi) to ensure that the shock absorber is in normal working condition. The surface of the piston rod 11 needs to be treated with a hard coating (such as a ceramic coating) to reduce friction with the seal.

[0027] The hydraulic oil needs to have low-temperature fluidity (can still work at -50°C) and anti-foaming characteristics. The common grades are Skydrol or Hyjet5.

[0028] The inflation sign may integrate a pressure sensor to transmit data to the cockpit monitoring system in real time.

[0029] In an optional embodiment, the oil injection valve assembly 4 includes an actuating cylinder 39, an inlet pipe joint 40, an outlet pipe joint 41, and an inlet and outlet hydraulic pipe 38. One end of the actuating cylinder 39 is fixed on the main landing gear strut 3. The inlet pipe joint 40 and the outlet pipe joint 41 are fixed on the outer wall of the actuating cylinder 39. Both the inlet pipe joint 40 and the outlet pipe joint 41 are externally connected to hydraulic pipes, and the hydraulic pipes are connected to the fuselage oil pressure system.

[0030] It should be noted that the actuating cylinder 39, as a hydraulic actuator, needs to meet a high-frequency response (the retraction and extension time is usually < 15 seconds). The inlet / outlet pipe joint 41 adopts a self-sealing quick-release structure to prevent hydraulic oil leakage. The hydraulic pipeline is composed of a titanium alloy braided hose and can withstand a pulse pressure of more than 200 bar. A buffer valve is arranged inside the actuating cylinder 39 to avoid hydraulic shock when the retraction and extension are in place.

[0031] The system needs to be configured with emergency cold air or electric drive backup, such as the "gravity release" mechanism of the A320.

[0032] In an alternative embodiment, the anti-shimmy assembly 5 includes a scissors link 18. A shimmy damper is provided on the upper section of the scissors link 18, and the lower end of the scissors link 18 is sleeved on the wheel assembly 6.

[0033] It should be noted that the scissors link 18 amplifies the damping force of the shimmy damper through the lever principle to suppress the lateral swing of the wheel 20. The shimmy damper usually adopts the form of friction damping or hydraulic damping. This design is closer to the friction type, and the damping coefficient is controlled by adjusting the pre-tightening force of the tightening bolt. The hinge points of the scissors link 18 need to be lubricated regularly to prevent looseness caused by wear. The friction disc of the shimmy damper uses copper-based powder metallurgy material, taking into account both wear resistance and heat dissipation.

[0034] In an alternative embodiment, the lower part of the anti-shimmy assembly 5 is sleeved on the piston rod 11.

[0035] It should be noted that the split semi-circular part design facilitates disassembly, installation and maintenance. The tightening bolt adopts anti-loosening threads (such as Spirol threads) to ensure long-term stability. The thickness of the friction disc needs to be detected regularly, and it needs to be replaced when the wear exceeds 1 mm. The shimmy damper can be integrated with a temperature sensor to monitor the friction heat generation situation. The torque of the tightening bolt needs to be calibrated strictly according to the manual (such as 50 - 70 N·m) to avoid deformation caused by over-tightening.

[0036] In an alternative embodiment, the wheel assembly 6 further includes a front fork 13, a mounting shaft 14, a wheel hub guard plate 31, a spacer 15, a wheel 20, a sleeve member 25, a sleeve anchoring ear 26, a connecting plate 231, a first spring 34, a limiting device 37, a connecting rod 23, a spring anchoring ear 28 and a shaft plug 32. The upper end of the front fork 13 is connected to the piston rod 11, and the lower end of the front fork 13 is connected to the mounting shaft 14 on both sides. The mounting shaft 14 is sleeved with the wheel 20 through the upper part, and a tire 22 is sleeved on the wheel 20. The wheel hub guard plate 31 is arranged on both sides of the wheel 20. The shaft plugs 32 are arranged on both sides of the mounting shaft 14. The connecting rod 23 and the sleeve member 25 are fixedly connected to the front fork 13 through the sleeve anchoring ear 26. The sleeve anchoring ear 26 is used to fix the relative positions of the connecting rod 23 and the sleeve member 25 with the front fork 13. The length of the connecting rod 23 is slightly longer than the diameter of the tire 22. A mud scraper device 30 mounting bracket is arranged at the end of the connecting rod 23. A spring anchoring ear 28 is arranged below the front fork 13. The spring anchoring ear 28 is connected to the connecting rod 23 through a spring. A limiting device 37 is also arranged between the two sleeve anchoring ears 26 of the connecting rod 23 and is connected to the front fork 13.

[0037] It should be noted that the sludge scraper mounting bracket 24 adapts to the wear of the tire 22 through springs and the limiting device 37 to keep the gap constant. The sleeve anchor ear 26 is cast from 7075-T6 aluminum alloy, and the carbon fiber material of the connecting rod 23 can reduce the mass and improve the fatigue resistance. The bearing of the wheel 20 needs to adopt an oil-gas lubrication system to adapt to high-speed operating conditions. The design of the shaft plug 32 needs to prevent lubricating oil from seeping into the braking system.

[0038] In an alternative embodiment, the landing gear support 33 includes a connecting block 331, a support block 332, a stop block 333, a pivot pin 334, and a spring anchor bolt 335. The right side of the connecting block 331 is connected to the main landing gear strut 3. The stop block 333 is arranged on the left side of the connecting block 331. The support block 332 is wing-shaped and arranged on the stop block 333. One pivot pin 334 is arranged at each of the left and right ends of the support block 332, and one spring anchor bolt 335 is arranged at each of the left and right ends of the support block 332. The spring anchor bolt 335 is fixed to the fuselage through a spring.

[0039] It should be noted that the installation angle of the pivot pin 334 (angle a < 90°) optimizes the retraction and extension trajectory and avoids interference with the fuselage structure. The stiffness of the spring anchor bolt 335 needs to match the fuselage skin to prevent resonance. The wing-shaped design of the support block 332 can reduce the aerodynamic drag. The spring is made of silicon manganese steel, and the pre-pressure is adjusted according to the position of the aircraft's center of gravity.

[0040] As Figures 1-5 shown, the retraction and extension of the main landing gear strut 3 are realized by controlling the retraction and extension of the actuator 39 by a hydraulic system. When the piston of the actuator 39 shortens, the main landing gear retracts upward into the wing wheel well; when the piston of the actuator 39 extends, the main landing gear is lowered.

[0041] It should be noted that: The hydraulic system realizes stepless adjustment of the retraction and extension speed through a proportional valve, and gives priority to closing the hatch during retraction to reduce aerodynamic drag. The system integrates a position sensor (such as a Hall sensor) to real-time feedback the landing gear status to the cockpit. A mechanical lock (such as a strut lock or a hook lock) needs to be set on the retraction and extension actuator 39 to prevent accidental movement in case of hydraulic failure. Modern aircraft (such as the A350) adopt an electro-hydrostatic actuator (EHA) to improve the control accuracy.

[0042] The working principle of the present invention is as follows: The landing gear strut passes through the fixing pins 35 at both ends of the landing gear bracket 36 and inserts into the mounting holes of the fixing blocks in the wing wheel well. Limited by the interval size between the front and rear beams of the wing, the fixing pins 35 can be firmly inserted into the mounting holes. The piston rod 11 is connected to the front fork 13, and the wheel 20 and the tire 22 are fixed through the mounting shaft 14. When the landing gear is loaded, during the compression and extension movement of the landing gear strut, resistance is generated by the oil in the strut. At the same time, the tire 22 can also bear a part of the energy.

[0043] The scissors link 18 connects the landing gear strut and the front fork 13 by bolts, effectively controlling the rising height of the landing gear strut and preventing the strut from bouncing when the internal pressure is too high, which may cause the overall upward movement of the wing and damage the wing and the connection between the wing and the fuselage.

[0044] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An aircraft main landing gear structure, characterized in that, It includes a fuselage connection component (1), a strut component (2), an oil filling valve component (4), a shock absorber component (5), and a wheel component (6). The fuselage connection component (1) is arranged on the upper section of the strut component (2). The top of the strut component (2) is connected to the fuselage, and the bottom end is connected to the wheel component (6) and is fixedly connected to the fuselage through the fuselage connection component (1). The oil filling valve component (4) is arranged on the strut component (2) and is higher than the horizontal position of the fuselage connection component (1). The upper part of the shock absorber component (5) is connected to the strut component (2), and the lower part is connected to the wheel component (6). Both ends of the retraction and extension control component are respectively connected to the strut component (2) and the fuselage. The wheel component (6) includes a mud scraper device (30), a mud scraper mounting bracket (24), and a tire (22). The mud scraper device (30) is arranged on the mounting bracket and is located above the tire (22) with an annular gap symmetrical to the outer dimension of the tire (22).

2. The main landing gear structure of an aircraft according to claim 1, characterized in that, The fuselage connection component (1) includes a landing gear bracket (36) and a fixing pin (35). The landing gear bracket (36) is arranged in a triangle shape. The fixing pin (35) is used to fix the landing gear bracket (36) and is sleeved on the strut component (2). The fuselage connection component (1) is an overall horizontal bracket, and both ends are fixedly connected to the fuselage through bolts.

3. The main landing gear structure of an aircraft according to claim 1, characterized in that, The strut component (2) includes a main landing gear strut (3) and a filling and inflation sign (19). The main landing gear strut (3) is hollow inside, provided with an oil cavity filled with hydraulic oil. A piston rod (11) is arranged below the main landing gear strut (3). The filling and inflation sign (19) is arranged on the main landing gear strut (3).

4. The structure of an aircraft main landing gear according to claim 3, characterized in that, The oil filling valve component (4) includes an actuating cylinder (39), a liquid inlet pipe joint (40), a liquid outlet pipe joint (41), and an inlet and outlet hydraulic pipe (38). One end of the actuating cylinder (39) is fixed on the main landing gear strut (3). The liquid inlet pipe joint (40) and the liquid outlet pipe joint (41) are fixed on the outer wall of the actuating cylinder (39). Both the liquid inlet pipe joint (40) and the liquid outlet pipe joint (41) are externally connected to hydraulic pipes, and the hydraulic pipes are connected to the fuselage oil pressure system.

5. The main landing gear structure of an aircraft according to claim 3, characterized in that, The shock absorber component (5) includes a scissors link (18). A shock absorber is arranged on the upper section of the scissors link (18) and is sleeved on the main landing gear strut (3). The lower end of the scissors link (18) is sleeved on the wheel component (6).

6. The main landing gear structure of an aircraft according to claim 5, characterized in that, The lower part of the shock absorber component (5) is sleeved on the piston rod (11).

7. The structure of an aircraft main landing gear according to claim 1, characterized in that, The wheel assembly (6) further includes a front fork (13), a mounting shaft (14), a wheel guard (31), a spacer (15), a wheel (20), a sleeve member (25), a sleeve anchoring ear (26), a connecting plate (231), a first spring (34), a limiting device (37), a connecting rod (23), a spring anchoring ear (28) and a shaft plug (32). The upper end of the front fork (13) is connected to the piston rod (11), and the lower ends on both sides are connected to the mounting shaft (14). The mounting shaft (14) is sleeved with the wheel (20) from above. A tire (22) is sleeved on the wheel (20). The wheel guard (31) is arranged on both sides of the wheel (20). The shaft plugs (32) are arranged on both sides of the mounting shaft (14). The connecting rod (23) and the sleeve member (25) are fixedly connected to the front fork (13) through the sleeve anchoring ear (26). The sleeve anchoring ear (26) is used to fix the relative positions of the connecting rod (23) and the sleeve member (25) with respect to the front fork (13). The connecting rod (23) is slightly longer than the diameter of the tire (22). A mounting bracket for a mud scraping device (30) is arranged at the end of the connecting rod (23). A spring anchoring ear (28) is arranged below the front fork (13). The spring anchoring ear (28) is connected to the connecting rod (23) through a spring. A limiting device (37) is also arranged between the two sleeve anchoring ears (26) of the connecting rod (23) and is connected to the front fork (13).

8. The main landing gear structure of an aircraft according to claim 3, characterized in that, The landing gear support (33) includes a connecting block (331), a support block (332), a stop block (333), a pivot pin (334), and a spring anchoring bolt (335). The right side of the connecting block (331) is connected to the main landing gear strut (3). The stop block (333) is arranged on the left side of the connecting block (331). The support block (332) is arranged in a wing shape on the stop block (333). One pivot pin (334) is arranged at each of the left and right ends of the support block (332). One spring anchoring bolt (335) is arranged at each of the left and right ends of the support block (332). The spring anchoring bolts (335) are fixed to the fuselage through springs.

9. A method for retracting and extending the main landing gear of an aircraft, characterized in that, The retraction and extension of the main landing gear strut (3) are achieved by controlling the retraction and extension of the actuator (39) of the hydraulic system. When the piston of the actuator (39) shortens, the main landing gear retracts upward into the wing wheel well; When the piston of the actuator (39) extends, the main landing gear lowers.

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