CN111828529A - Buffer for aircraft tail skid - Google Patents

Abstract

The invention relates to a buffer for an aircraft tail skid, which comprises an outer cylinder, a first inner sleeve, a second inner sleeve, an elastic membrane and a piston. The first inner sleeve and the second inner sleeve are arranged in the cavity of the outer barrel from inside to outside along the radial direction. The wall surfaces of the first inner sleeve and the second inner sleeve are respectively provided with a plurality of first through holes and second through holes. The elastic membrane is disposed between the second inner sleeve and the outer sleeve, and an air chamber filled with high-pressure gas is formed between the elastic membrane and the inner wall of the outer sleeve. The piston pressurizes the hydraulic fluid under the influence of ambient pressure, thereby forcing the hydraulic fluid through the through-holes in each inner sleeve into a second hydraulic chamber located between the flexible membrane and the second inner sleeve. The buffer according to the invention enables the impact load to which the aircraft body is subjected to be reduced.

Description

Buffer for aircraft tail skid

Technical Field

The invention relates to the technical field of aircraft construction and design, in particular to a buffer for an aircraft tail skid.

Background

The tail is at risk of touchdown when the aircraft is performing a minimum ground clearance test. For this purpose, the tail of the aircraft is usually provided with a tail skid. When the airplane is lifted off the ground, the tail sledge at the tail part of the airplane touches the ground, so that the impact energy generated by collision between the tail part of the airplane and the ground due to an overlarge head-up angle of the airplane is absorbed and dissipated.

Fig. 1 shows a conventional aircraft tail skid device, which includes components such as bumpers, rocker arms, friction blocks, etc. The buffer comprises an outer cylinder, a piston rod and the like. The lower end of the outer barrel is hinged with the rocker arm, and the inner base is provided with a variable cross-section oil needle. The piston rod is of a hollow structure, and an oil hole matched with the variable-section oil needle is formed in the end face, facing the outer cylinder, of the piston rod. And a single lug joint is arranged at one end of the piston rod, which is back to the outer cylinder. Two ends of the tail sledge device are respectively hinged on the machine body structure through a rocker arm and a single-lug joint.

Referring to fig. 2, the buffer device of the tail skid is a single-cavity variable-section oil-gas type buffer, and energy generated by collision and friction generated by collision between the tail of the aircraft and the ground is mainly absorbed by the buffer device. After the airplane leaves the ground, a friction block facing the ground is arranged at one end of the rocker arm connected with the buffer, and the friction block collides with the ground to enable the outer cylinder to drive the variable-section oil needle to move upwards. Along with the compression of the buffer, the variable cross-section oil needle on the outer cylinder base penetrates through the oil fixing hole on the piston rod to extrude oil into the piston rod from the outer cylinder. The cooperation of the variable cross-section oil needle and the oil fixing hole enables the oil fixing hole of the buffer to form the function of the oil changing hole, so that proper oil liquid damping is provided for the tail skid, and energy is dissipated. During the oil entering the piston rod, the gas in the piston rod is compressed at the same time, which may also absorb a part of the energy.

According to the above, the variable cross-section oil-gas type buffer has the air cavity, so that the piston rod can automatically rebound, however, the stroke of the buffer is uncontrollable, and the requirement on the internal space is high due to the built-in variable cross-section oil needle.

Disclosure of Invention

In view of the above-mentioned situation of the tail skid bumper, an object of the present invention is to provide a bumper for an aircraft tail skid, which can efficiently absorb and dissipate impact energy generated by collision between an aircraft tail and the ground due to an excessive aircraft nose-up angle.

This object is achieved by the following form of the apparatus of the invention. The buffer comprises an outer cylinder, a first inner sleeve, a second inner sleeve, an elastic membrane and a piston. Wherein the interior of the outer barrel defines a cavity. The first inner sleeve is arranged in the cavity and comprises a first hydraulic cavity filled with hydraulic fluid, and a plurality of first through holes are formed in the wall surface of the first inner sleeve. The second inner sleeve is arranged in the cavity and located between the first inner sleeve and the outer barrel, and a plurality of second through holes are formed in the wall surface of the second inner sleeve. The elastic membrane is disposed between the second inner sleeve and the outer sleeve, and a gas chamber filled with high-pressure gas is formed between the elastic membrane and an inner wall of the outer sleeve. One end of the piston can extend into the first hydraulic cavity of the first inner sleeve under the action of external pressure so as to pressurize the hydraulic fluid, so that the hydraulic fluid is enabled to sequentially pass through the first through hole and the second through hole to enter the second hydraulic cavity between the elastic membrane and the second inner sleeve.

The arrangement of the inner sleeve in multiple layers helps to reduce the flow rate of the high pressure hydraulic fluid. This allows the damper to satisfy the damping action while preventing the oil from being damaged by being sprayed at a high speed against the elastic film.

According to a preferred embodiment of the present invention, the second through hole and the first through hole are offset from each other in a radial direction of the damper. The hydraulic fluid flowing out of the first through hole rushes to the inner wall surface of the second inner sleeve, and the second inner sleeve plays a role in reducing the speed and delaying the hydraulic fluid. Thanks to the first through holes and the second through holes which are arranged in a staggered manner, the second inner sleeve can avoid high-speed hydraulic fluid from directly impacting the elastic membrane.

According to a preferred embodiment of the present invention, the damper further includes a third inner sleeve disposed between the second inner sleeve and the first inner sleeve, and a plurality of third through holes having a cross section not smaller than that of the first through holes are formed in a wall surface of the third inner sleeve, thereby facilitating dispersion of the hydraulic fluid.

According to a preferred embodiment of the invention, the first, third through hole are arranged to enable a flow of the hydraulic fluid in a radial direction of the first inner sleeve. By means of the guiding effect of the third through holes, the hydraulic fluid can flow dispersedly and uniformly to the respective second through holes located downstream of the third through holes.

According to a preferred embodiment of the present invention, the first through holes and the third through holes correspond one to one.

According to a preferred embodiment of the invention, the axis of each third through hole is coaxial with the axis of the corresponding first through hole.

According to a preferred embodiment of the invention, the third through hole comprises a straight pipe section and a conical pipe section.

According to a preferred embodiment of the invention, the first end of the conical section has the same cross-sectional dimensions as the straight section, and the second end of the conical section has cross-sectional dimensions greater than the straight section.

According to a preferred embodiment of the invention, the straight tube section is opposite to the first through hole and the tapered tube section is opposite to the second through hole.

According to a preferred embodiment of the invention, the hydraulic fluid discharged from the third through hole comprises a plurality of second through holes in the alluvial area formed by the second inner sleeve.

According to a preferred embodiment of the invention, an edge of at least a part of the second through holes is tangent to an edge of the third through holes, seen in a radial direction of the first inner sleeve.

According to a preferred embodiment of the present invention, the first inner sleeve and the third inner sleeve are capable of being fitted to each other, and a plurality of sets of first through holes having different apertures are provided alternately in the circumferential direction of the first inner sleeve, wherein the first through holes in the same set have the same aperture.

According to a preferred embodiment of the present invention, the first through hole and the third through hole are arranged from sparse to dense in a moving direction in which the piston pressurizes the hydraulic fluid. The first through holes which are specifically arranged are formed in the first inner sleeve in the outer barrel, when the piston rod moves in the axial direction after being compressed, the oil holes in the first hydraulic cavity gradually become fewer, the effective oil hole area gradually becomes smaller, and the damping coefficient becomes larger along with the effective oil hole area, so that the implementation mode of the arrangement mode can play a role in adjusting the oil holes.

According to a preferred embodiment of the present invention, the damper includes an upper cover closing an upper end surface of the damper, a lower cover closing a lower end surface of the damper, and a guide rod fixed to the upper cover, wherein the piston has a through hole adapted to the guide rod.

According to a preferred embodiment of the present invention, the upper cover and/or the lower cover is formed with a hydraulic pressure adjusting hole, and the shock absorber further includes a hydraulic pressure adjusting circuit communicating with the hydraulic pressure adjusting hole, the hydraulic pressure adjusting circuit being configured to be able to adjust the hydraulic pressure in the first hydraulic pressure chamber.

According to a preferred embodiment of the present invention, the outer cylinder is formed with a gas adjusting hole, and the damper further includes a gas pressure adjusting circuit communicating with the gas pressure adjusting hole, the gas pressure adjusting circuit being configured to be capable of adjusting a gas pressure within the gas chamber so that the piston is returned.

According to a preferred embodiment of the present invention, the upper end surfaces of the third inner sleeve and the second inner sleeve are each formed with a groove, and the damper further includes a fixing pin which can be seated in the groove and prevents the third inner sleeve and the second inner sleeve from rotating relative to the outer sleeve.

On the basis of the common general knowledge in the field, the preferred embodiments can be combined randomly to obtain the preferred examples of the invention. Other systems, methods, features and advantages of the invention will be or will become apparent to one with skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features and advantages be included within this description and this summary, be within the scope of the invention, and be protected by the accompanying claims.

Drawings

For a better understanding of the above and other objects, features, advantages and functions of the present invention, reference should be made to the preferred embodiments illustrated in the accompanying drawings. Like reference numerals in the drawings refer to like parts. It will be appreciated by persons skilled in the art that the drawings are intended to illustrate preferred embodiments of the invention without any limiting effect on the scope of the invention, and that the various components in the drawings are not drawn to scale.

FIG. 1 is a schematic diagram of a prior art aircraft tail skid.

FIG. 2 is a schematic cross-sectional view of the damper of FIG. 1.

FIG. 3 is a schematic structural view of an aircraft tail skid according to a preferred embodiment of the present invention.

Fig. 4 is a schematic cross-sectional view of a bumper according to a preferred embodiment of the present invention.

Figure 5 is a schematic view of the inner sleeve of figures 2 and 3.

Figure 6 is an exploded view of the inner sleeve of figure 5.

Fig. 7 is an enlarged sectional view of a portion a of fig. 4.

Fig. 8 is a partial enlarged view in the left-hand direction of fig. 7.

Fig. 9 is a partial enlarged view of a lower portion of the damper of fig. 4.

Figure 10 is a top view of the first inner sleeve.

Fig. 11 is a plan view of the lower cover (upper cover).

Detailed Description

The inventive concept of the present invention will be described in detail below with reference to the accompanying drawings. What has been described herein is merely a preferred embodiment in accordance with the present invention and other ways of practicing the invention will occur to those skilled in the art and are within the scope of the invention. In the following detailed description, directional terms, such as "upper", "lower", "inner", "outer", "longitudinal", "lateral", and the like, are used with reference to the orientation depicted in the accompanying drawings. Components of embodiments of the present invention can be positioned in a number of different orientations and the directional terminology is used for purposes of illustration and is in no way limiting.

Referring to FIG. 3, an aircraft tail skid employing the bumpers of the present disclosure is shown. The aircraft tail skid is composed of a rocker arm 200, a buffer 100 and the like which are hinged with each other. Compared to the tail skid shown in fig. 1, the area of the outer cylinder 110 is relatively small under the condition of similar size.

Referring to FIG. 4, a cross-sectional schematic view of the bumper 100 of the aircraft tail skid of FIG. 3 is shown. The damper 100 includes an outer cylinder 110, an inner sleeve 120, an elastic membrane 130, and a piston 140. The outer cylinder 110, the elastic membrane 130, and the inner sleeve 120 are arranged in the bumper 100 from the outside to the inside in a radial direction. In the embodiment of fig. 4, the inner sleeve 120 comprises a first inner sleeve 122, a third inner sleeve 124 and a second inner sleeve 126 arranged radially from the inside to the outside.

The interior of the outer tub 110 defines a cavity. As a primary support structure, the outer barrel 110 has a relatively thick wall thickness that can resist axial impact forces and radial shear forces generated by the ground during liftoff of the aircraft.

Referring to fig. 5 and 6 in conjunction with fig. 4, fig. 5 shows the inner sleeve 120 inside the outer sleeve 110, and fig. 6 shows an exploded view of the inner sleeve 120. As shown in the above figures, the first inner sleeve 122 is disposed in the cavity of the outer cylinder 110. The first hydraulic chamber S1 defined by the first inner sleeve 122 is filled with hydraulic fluid, and has a plurality of first through holes 123 formed in a wall surface thereof.

Similar to the first inner sleeve 122, a second inner sleeve 126 is also disposed within the cavity of the outer barrel 110. The second inner sleeve 126 is disposed between the first inner sleeve 122 and the outer sleeve 110. A plurality of second through holes 127 are formed in the wall surface of the second inner sleeve 126. Preferably, the second through hole 127 and the first through hole 123 are misaligned with each other in a radial direction of the bumper.

The third inner sleeve 124 is disposed between the first inner sleeve 122 and the second inner sleeve 126, and has a plurality of third through holes 125 formed in a wall surface thereof with a cross section not smaller than that of the first through holes 123.

An elastic membrane 130 such as a rubber balloon is disposed between the second inner sleeve 126 and the outer cylinder 110, and an air chamber S3 filled with a certain pressure gas is formed between the elastic membrane 130 and the inner wall of the outer cylinder 110.

One end of the piston 140 (i.e., the piston head) is movably inserted into the first hydraulic chamber S1 of the first inner sleeve 122 and is movable under the influence of an external pressure to pressurize the hydraulic fluid within the first hydraulic chamber S1, thereby urging the hydraulic fluid to sequentially pass through the first through-hole 123, the third through-hole 125, the second through-hole 127 and into the second hydraulic chamber S2 between the elastic membrane 130 and the second inner sleeve 126. Specifically, with reference to FIG. 3, after the aircraft is lifted off the ground, the ground directly contacts the friction block on the rocker arm 200 and impacts the piston rod of the piston 140 upward. The piston rod moves upward so that the piston 140 head presses the hydraulic fluid of the first hydraulic chamber S1 into the second hydraulic chamber S2. The shock absorber 100 achieves the purpose of cushioning by the damping action of the first through hole 123 having a smaller aperture. And the volume occupied by the piston rod entering the first hydraulic chamber S1 is supplemented by the compressed elastic membrane 130. The hydraulic fluid flowing at a high speed performs deceleration hysteresis through the second through hole 127 and the third through hole 125 to prevent the high-speed hydraulic fluid from being injected into the inner wall of the outer tube to damage the elastic membrane 130.

In the case where the piston 140 has not started to be compressed, the gas pressure in the gas chamber S3 is about 1 atmosphere, 1.5 atmospheres, or 2 atmospheres.

When the piston 140 starts to move upward to perform a compression stroke, the hydraulic fluid flowing out of the first through hole 123 directly rushes toward the third through hole 125 of the third inner sleeve 124. The hydraulic fluid guided by the third through hole 125 can be better spread to the inner wall surface of the second inner sleeve 126 and the second through hole 126.

It will be appreciated that, as an alternative, the third inner sleeve 126 need not be provided within the damper 100. At this time, since the second through hole 127 and the first through hole 123 are misaligned with each other, the hydraulic fluid flows out of the first through hole 123 and at least partially rushes toward the inner wall surface of the second inner sleeve 126. This also prevents the hydraulic fluid from directly impacting the elastomeric membrane 130 at high velocity.

According to the present disclosure, the upper and lower covers 141 and 142 for closing the upper and lower end surfaces of the outer cylinder 110, the first inner sleeve 122, the third inner sleeve 124, the second inner sleeve 126, and the elastic membrane 130, respectively, may be provided in the form as shown in fig. 3, 4, and 11. The upper cover 141 and the lower cover 142 are respectively provided with corresponding through holes, and the fastening rod 146 is fastened by a bolt 151 after passing through the corresponding through holes.

Referring to fig. 7, 8, wherein fig. 7 shows an enlarged view of the detail a according to fig. 4, fig. 8 shows a left side view of fig. 7. In the preferred embodiment, the first and third through holes 123 and 125 are arranged to allow hydraulic fluid to flow in a radial direction of the damper. This can appropriately reduce the flow rate of the hydraulic fluid during the flow to the second hydraulic chamber S2 while guiding the hydraulic fluid flowing through one third through hole 125 uniformly and dispersedly to the inner wall surface of the second inner sleeve 126 and 1 or more second through holes 127 corresponding to the third through hole 125. According to the present disclosure, since the hole position of the second through hole 127 and the first through hole 123 are radially offset from each other, it is ensured that the hydraulic fluid is at least partially sprayed toward the inner wall surface of the second inner sleeve 126 after flowing out from the third through hole 125, and thus direct impact of the hydraulic fluid on the elastic membrane 130 can be avoided.

Preferably, the first through holes 123 and the third through holes 125 correspond one to one. The cross-sectional dimensions of the third through hole 125 and the first through hole 123 at the position opposite to each other are set to be substantially equal on the premise that the hydraulic fluid can flow in the radial direction along the damper 100, thereby preventing the damping effect of the damper 100 from being affected by the severe fluctuation of the hydraulic fluid during the flow from the first inner sleeve 122 to the third inner sleeve 124.

In the embodiment of fig. 7, 8, the first through-hole 123 has a cylindrical configuration. The third through hole 125 is composed of a straight pipe section 125A and a tapered pipe section 125B. The conical section 125B is formed in a trumpet shape by the straight section 125A after smooth transition and radial diffusion. The first end of the tapered tube section 125B has the same cross-sectional dimensions as the straight tube section 125A, and the second end of the tapered tube section 125B has cross-sectional dimensions greater than the straight tube section 125A. The straight tube section 125A of the third through hole 125 is opposite to the first through hole 123, and the tapered tube section 125B is opposite to the second through hole 127. It is to be understood that the through holes are "opposite" to each other, meaning that hydraulic fluid can flow in a radial direction directly from a through hole at one location to a through hole at another location, the axes of the two through holes not necessarily being coaxial.

The diameter D2 of the straight tube section 125A may be set slightly larger than the diameter D1 of the first through hole 123, for example, D2 is 1.05 times, 1.1 times, 1.15 times, 1.2 times, etc. of D1, except that the diameter D2 of the straight tube section 125A of the third through hole 125 is set to be the same as the diameter D1 of the first through hole 123.

Referring to FIG. 8 in conjunction with FIG. 7, the hydraulic fluid discharged from the third through-hole 125 includes 4 second through- holes 127 or 3, 5, etc., not shown, within the alluvial area formed by the second inner sleeve 126. Preferably, an edge of at least a portion of the plurality of second through holes 127 is tangent to an edge of the third through hole 125, as viewed in a radial direction of the first inner sleeve 122.

More preferably, referring to fig. 8, the edges of the third through hole 125 are respectively tangent to the inner edge of the first through hole 123 (the straight tube section 125A of the third through hole 125) and the outer edge of the tapered tube section 125B of the second through hole.

Referring to fig. 4 and 7, after the damper 100 is assembled, the first inner sleeve 122 and the third inner sleeve 124 can be attached to each other. In this case, referring to fig. 6 and 10, a plurality of sets of first through holes 123 having different apertures are provided alternately in the circumferential direction of the first inner sleeve 122, wherein the first through holes 123 in the same set have the same aperture. For example, 5 sets of first through holes 123 having different apertures are provided in the circumferential direction of the first inner sleeve 122, wherein the first through holes 123 of each set are provided in pairs at radially opposite ends of the first inner sleeve 122, and the circumferential coverage θ' of the first through holes 123 of each set is 36 °. For the sake of clarity, only one set of areas a1, a2 having the first through hole 123 is shown in black shading in the first inner sleeve 122 of fig. 10. As for the areas a1, a2, a plurality of first through holes 123 extending in the radial direction are actually distributed.

A slight radial gap for temporarily containing a small amount of hydraulic fluid is formed between the second inner sleeve 126 and the third inner sleeve 124. The radial clearance is, for example, 0.2mm, 0.5mm, 1mm, 2mm, etc.

Referring to fig. 9 and 11, fig. 9 is a partially enlarged view of the vicinity of the lower end of the bumper 100, and fig. 11 is a plan view of the lower cover 142 (upper cover 141). In order to facilitate the worker to accurately align the sets of first through holes 123 with the third through holes 127, a plurality of first positioning holes as shown in fig. 9 are formed in the circumferential direction of the lower end surface of the first inner sleeve 122, and a plurality of second positioning holes 142A (fig. 11) corresponding to the first positioning holes are formed in the lower cover 142. The first positioning holes are aligned with the circumferential ends and the circumferential ends of the first through holes 123. For example, with respect to the embodiment shown in fig. 10 in which 5 sets of the first through holes 123 having different apertures are arranged in the circumferential direction, the first through holes 123 are arranged at equal intervals in the circumferential direction such that the central angle θ "is 36 °. The installer first inserts the positioning pins 148 into the second positioning holes 142A, then rotates the first inner sleeve 122 to the desired position and then docks the first inner sleeve into the positioning pins 148.

It should be understood that, according to the above disclosure, those skilled in the art can know the embodiments in which the number of sets of the first through holes 123 different from those shown in fig. 10 and 11 is provided, and the first positioning holes and the second positioning holes 142A to be arranged in the embodiments. These aspects are also intended to be within the scope of the present disclosure.

In order to position the third inner sleeve 124 and the second inner sleeve 126 relative to each other, grooves 128 are formed in the upper end surfaces of the third inner sleeve and the second inner sleeve. The outer cylinder 110, the upper cover 141, or the lower cover 142 may be marked with a mark corresponding to the groove 128. When the third inner sleeve 124, 126 are positioned, the groove 128 is aligned with the indicia. The installer then places the securing pins in the grooves 128, which prevent the first inner sleeve 122, the third inner sleeve 124, and the second inner sleeve 126 from rotating relative to the outer barrel 110.

The first and third through holes 123 and 125 are arranged from sparse to dense in the moving direction in which the piston 140 pressurizes the hydraulic fluid (i.e., in the compression stroke direction of the piston 140). As can be seen from mechanical analysis, in this case, the piston 140 can move from a fast speed to a slow speed in the compression stroke, and the shock absorber 100 can provide a relatively uniform damping force during the process.

Referring further to fig. 4, preferably, the buffer 100 may be further provided with a guide rod 150 fixed to the upper cover 141. The piston 140 has a through hole formed therein to be fitted with the guide rod 150. By virtue of the guiding action of the guide rod 150, the piston 140 does not strike the wall surface of the first inner sleeve 122 obliquely with respect to the axial direction of the damper 100 after the striking action.

Referring further to fig. 4, the upper and lower covers 141 and 142 are formed with hydraulic pressure adjusting holes, not shown. The hydraulic pressure adjusting hole communicates with a hydraulic pressure adjusting circuit fixed on the upper cover 141 or other not-shown position. By means of the hydraulic pressure regulation circuit, the hydraulic pressure in the first hydraulic pressure chamber S1 can be adaptively regulated, thereby facilitating the return of the piston 140.

Similarly, the outer cylinder 110 is formed with a gas adjustment hole. The damper 100 is provided with an air pressure adjusting circuit (not shown) communicating with the air pressure adjusting hole. The gas pressure regulating circuit is configured to be able to regulate the gas pressure within the gas chamber S3 such that the piston 140 is retracted.

The scope of the invention is limited only by the claims. Persons of ordinary skill in the art, having benefit of the teachings of the present invention, will readily appreciate that alternative structures to the structures disclosed herein are possible alternative embodiments, and that combinations of the disclosed embodiments may be made to create new embodiments, which also fall within the scope of the appended claims.

Description of reference numerals:

a buffer: 100.

rocker arm: 200.

an outer cylinder: 110.

inner sleeve: 120.

a first inner sleeve: 122.

a first through-hole: 123.

a third inner sleeve: 124.

a third through hole: 125.

a straight pipe section: 125A.

A conical pipe section: 125B.

A second inner sleeve: 126.

a second through hole: 127.

groove: 128.

an elastic film: 130.

a piston: 140.

and (4) covering: 141.

and a lower cover 142.

A second positioning hole: 142A.

A single-lug joint: 144.

fastening the rod: 146.

positioning pins: 148.

Claims (18)

1. a bumper for an aircraft tail skid, the bumper comprising:

an outer barrel, the interior of the outer barrel defining a cavity;

a first inner sleeve disposed in the cavity and including a first hydraulic chamber filled with hydraulic fluid, a wall surface of the first inner sleeve being formed with a plurality of first through holes;

the second inner sleeve is arranged in the cavity and positioned between the first inner sleeve and the outer cylinder, and a plurality of second through holes are formed in the wall surface of the second inner sleeve;

an elastic membrane disposed between the second inner sleeve and the outer sleeve and forming a gas chamber filled with gas between the elastic membrane and an inner wall of the outer sleeve; and

and one end of the piston can extend into the first hydraulic cavity of the first inner sleeve under the action of external pressure so as to pressurize the hydraulic fluid, so that the hydraulic fluid is enabled to enter the second hydraulic cavity between the elastic membrane and the second inner sleeve through the first through hole and the second through hole in sequence.

2. The damper of claim 1, wherein the second through-hole and the first through-hole are offset from each other in a radial direction of the damper.

3. The damper according to claim 2, further comprising a third inner sleeve disposed between the second inner sleeve and the first inner sleeve, and a plurality of third through holes having a cross section not smaller than that of the first through holes are formed in a wall surface of the third inner sleeve.

4. A buffer according to claim 3 wherein the first, third through holes are arranged to enable the hydraulic fluid to flow in a radial direction of the first inner sleeve.

5. The damper of claim 4, wherein the first through holes and the third through holes correspond one-to-one.

6. A damper according to claim 4 in which the axis of each third through-hole is coaxial with the axis of the corresponding first through-hole.

7. A damper as claimed in any one of claims 3 to 6 wherein the third aperture comprises a straight tube section and a tapered tube section.

8. A damper as claimed in claim 7 wherein the first end of the tapered tube section has the same cross-sectional dimensions as the straight tube section and the second end of the tapered tube section has cross-sectional dimensions greater than the straight tube section.

9. The damper of claim 8, wherein the straight tube section opposes the first through-hole and the tapered tube section opposes the second through-hole.

10. The damper of claim 5, wherein the hydraulic fluid discharged from the third through-hole includes a second plurality of through-holes in a lash region formed by the second inner sleeve.

11. A damper as claimed in claim 10 wherein, viewed radially of the first inner sleeve, an edge of at least a portion of the plurality of second through holes is tangential to an edge of the third through hole.

12. A buffer according to claim 4 wherein the first and third inner sleeves are conformable to one another and wherein circumferentially spaced sets of first through holes of different apertures are provided, wherein the first through holes in a same set have the same aperture.

13. The damper according to claim 1, wherein the first through hole and the second through hole are arranged from sparse to dense in a moving direction in which the piston pressurizes the hydraulic fluid.

14. The damper according to claim 1, comprising an upper cover closing an upper end surface of the damper, a lower cover closing a lower end surface of the damper, and a guide rod fixed to the upper cover, wherein the piston has a through hole adapted to the guide rod.

15. The damper of claim 14, wherein the upper and/or lower covers are formed with a hydraulic adjustment bore, the damper further comprising a hydraulic adjustment circuit in communication with the hydraulic adjustment bore, the hydraulic adjustment circuit configured to be capable of adjusting hydraulic pressure within the first hydraulic chamber.

16. The damper of claim 1, wherein the outer cylinder is formed with a gas adjustment aperture, the damper further comprising a gas pressure adjustment circuit in communication with the gas pressure adjustment aperture, the gas pressure adjustment circuit configured to adjust a gas pressure within the gas chamber to return the piston.

17. The damper of claim 3, wherein the upper end surfaces of the second and third inner sleeves are each formed with a groove, the damper further comprising a fixing pin capable of being seated in the groove and preventing the second and third inner sleeves from rotating relative to the outer sleeve.

18. An aircraft tail skid, wherein the aircraft tail skid has a buffer as defined in any one of claims 1 to 17.

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