Hydraulic strut assembly for semi-levered landing gear

A hydraulic strut assembly, for use in a semi-levered landing gear in an aircraft, comprising an actuator and a manifold associated with the actuator. The actuator comprises a housing, a first piston, a second piston, and a third piston. The first piston is positioned between outer and inner cylindrical structures of the housing. The outer and inner cylindrical structures and first piston form an outer chamber that receives a first fluid. The inner cylindrical structure, the first piston, and the second piston, which is nested within the first piston, form an inner chamber, which holds a second fluid comprising a gas. A volume of the inner chamber changes when at least one of the first and second pistons moves. The third piston is positioned between the outer cylindrical structure and the first piston. The first, second, and third pistons move in a direction parallel to an axis through the housing.

BACKGROUND INFORMATION

Embodiments of the present disclosure relate generally to landing gear and, more particularly, to a semi-levered landing gear and an associated method of positioning the bogie beam of the landing gear using a telescopic hydraulic actuator.

Many airplanes include landing gear to facilitate takeoff, landing and taxi. The landing gear of some aircraft includes a shock absorber that is pivotally attached to a bogie beam at a distal or lower end thereof. The shock absorber may also be referred to as a shock strut. The bogie beam includes two or more axles upon which tires are mounted. In this regard, the bogie beam may include a forward axle positioned forward of the shock absorber and an aft axle positioned aft of the shock absorber. Upon takeoff, an airplane having a conventional landing gear with forward and aft axles will pivot about the pin that attaches the bogie beam to the shock absorber such that all of the landing gear tires have an equal load distribution.

In order to provide additional ground clearance for rotation of the aircraft during takeoff, semi-levered landing gear mechanisms have been developed. A semi-levered landing gear fixedly positions the shock absorber and the forward end of the bogie beam during takeoff such that the forward axle is in a raised position relative to the aft axle when the airplane has left the ground. As such, the aircraft pivots about the aft axle, rather than the pin that pivotally connects the bogie beam to the shock absorber, provided that the extend pressure of the shock absorber has been increased sufficiently. By rotating about the aft axle, the landing gear height is effectively increased so as to provide additional ground clearance for rotation of the aircraft during takeoff. As a result, the takeoff field length (TOFL) of the aircraft may be reduced, the thrust used by the engines may be reduced, or the weight carried by the aircraft may be increased while maintaining the same takeoff field length.

In order to provide for rotation of the aircraft about the aft axle during takeoff, a semi-levered landing gear locks the bogie beam in a “toes-up” attitude such that the tires mounted upon the aft axle support the aircraft, while the tires mounted upon the forward axle are raised above the surface of the runway. Following takeoff, the landing gear is generally stowed in a location such as a wheel well. In order to fit within a conventional wheel well, the landing gear is typically unlocked and the bogie beam repositioned in a “stowed” attitude prior to retracting the landing gear into the wheel well. Thereafter, during landing, the landing gear is lowered and the bogie beam is repositioned such that the forward axle is higher than the aft axle. Upon touch down, all of the wheels, including both those on the forward axle and the aft axle, equally bear the weight of the aircraft. Typically, the locking and unlocking of a semi-levered gear system, and the resulting repositioning of the bogie beam relative to the shock absorber, occurs without input from the pilot or the flight control system.

One type of semi-levered landing gear utilizes a mechanical linkage to lock the bogie beam during takeoff, but uses a separate mechanical linkage, termed a shrink-link, to reposition the shock absorber for retraction into the wheel well. The use of a shrink-link increases the complexity, expense and weight of the resulting semi-levered landing gear more than desired. Mechanical linkages also may not provide sufficiently desired damping during landing or bogie beam pitch dampening while on the ground.

Another type of semi-levered landing gear includes a locking hydraulic strut to lock the bogie beam in the desired orientation for takeoff. The locking hydraulic strut is essentially a locking actuator, but has a number of additional chambers and an internal floating piston. While a semi-levered landing gear having a locking hydraulic strut is suitable for some aircraft, the landing gear of other aircraft may not have sufficient clearance or room for the hydraulic strut to be positioned between the shock absorber and the bogie beam in an efficient manner.

Accordingly, it would be desirable to provide an improved semi-levered landing gear hydraulic actuator that may be used on landing gears that do not have sufficient space for housing a conventional locking hydraulic strut configuration. In particular, it would be desirable to provide a semi-levered landing gear that is both weight and cost efficient and that is not overly complex, while still satisfying the various operational requirements of the semi-levered landing gear.

SUMMARY

In one illustrative embodiment, a hydraulic strut assembly comprises a housing, a first piston, a second piston, and a third piston. The housing comprises an outer cylindrical structure and an inner cylindrical structure. The first piston is positioned between the outer cylindrical structure and the inner cylindrical structure. An outer chamber is configured to receive a first fluid is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston. The second piston is nested within the first piston. The inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move. The inner chamber is configured to hold a second fluid comprising a gas. The third piston is positioned between the outer cylindrical structure and the first piston. The first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing.

In another illustrative embodiment, an actuator for use in a hydraulic strut assembly comprises a housing, a first piston, a second piston, and a third piston. The housing comprises an outer cylindrical structure and an inner cylindrical structure. The first piston is positioned between the outer cylindrical structure and the inner cylindrical structure. The outer chamber is configured to receive a first fluid that is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston in which the first fluid comprises a hydraulic liquid. The second piston is nested within the first piston. The inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move. The inner chamber is configured to hold a second fluid comprising the hydraulic liquid and a gas. The third piston is positioned between the outer cylindrical structure and the first piston. The first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing.

In yet another illustrative embodiment, a method for operating an aircraft to perform an alternate landing is present. The aircraft is operated to perform the alternate landing. An actuator in a landing gear assembly for the aircraft comprises a housing, a first piston, a second piston, and a third piston. The housing comprises an outer cylindrical structure and an inner cylindrical structure. The first piston is positioned between the outer cylindrical structure and the inner cylindrical structure. An outer chamber is configured to receive a first fluid that is formed between the outer cylindrical structure, the inner cylindrical structure, and the first piston. The second piston is nested within the first piston. The inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first piston and the second piston move. The inner chamber is configured to hold a second fluid comprising a gas. The third piston is positioned between the outer cylindrical structure and the first piston. The first piston, the second piston and the third piston are configured to move in a direction parallel to an axis through the housing. The second piston and the first piston are retracted in response to a load being applied to the second piston when the landing gear assembly contacts a ground on which the aircraft is landing. The gas in the inner chamber compresses when the second piston retracts.

The features and functions can be achieved independently in various illustrative embodiments of the present disclosure or may be combined in yet other illustrative embodiments in which further details can be seen with reference to the following description and drawings.

DETAILED DESCRIPTION

The present disclosure now will be described more fully hereinafter with reference to the accompanying drawings, in which preferred illustrative embodiments of the disclosure are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the illustrative embodiments set forth herein; rather, these illustrative embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout.

The illustrative embodiments recognize these issues and present a solution that is flexible, durable, relatively inexpensive compared to other struts, and lightweight. Additionally, the illustrative embodiments have added further value to aircraft operation in that the illustrative embodiments aid an aircraft in both landing and lift off. The illustrative embodiments aid an aircraft to lift off by increasing the angle of attack of the aircraft. The angle of attack is the angle at which an aircraft is attempting to lift off from the ground into the air. The illustrative embodiments aid an aircraft to land by providing additional bogie beam pitch dampening. Other illustrative embodiments are apparent from the following additional description.

Specifically, illustrative embodiments of the present disclosure relate generally to landing gear assemblies and, more particularly, to a semi-levered landing gear assembly and an associated method of positioning the bogie beam of the landing gear assembly using a telescopic actuator. However, the illustrative embodiments may also apply to other vehicles and may be used in other applications aside from vehicles. Thus, the illustrative embodiments are not limited to use in landing gears or landing gear assemblies.

FIG. 1is an illustration of a block diagram of an aircraft in which an illustrative embodiment may be implemented. WhileFIG. 1may be used to describe an aircraft incorporating the illustrative embodiments, aircraft100may also potentially be any other vehicle in which a hydraulic strut or hydraulic piston might be used.

Aircraft100includes fuselage102, which is connected to wing104. In a non-limiting illustrative embodiment, aircraft100may include engine106. In another illustrative embodiment, landing gear assembly108may be connected to one of wing104or fuselage102, or even possibly engine106, or possibly combinations thereof. Aircraft100may include many other components. In an illustrative embodiment, landing gear assembly108may include actuator110and other landing gear assembly components112.

Actuator110may include a nested series of hydraulic pistons sharing common outer wall114. Thus, for example, actuator110may include first hydraulic piston116, second hydraulic piston118, and third hydraulic piston120. In an illustrative embodiment, the three hydraulic pistons are concentric. In an illustrative embodiment, the three hydraulic pistons may actuate in a telescopic manner such that, when fully extended, second hydraulic piston118extends past a top of the third hydraulic piston120, and second hydraulic piston118extends past a top of first hydraulic piston116. Actuator110also includes manifold122. Manifold122may be contained within common outer wall114; however, manifold122may be connected in some other way to the first, second, and third hydraulic pistons. In any case, manifold122is disposed relative to the first, second, and third hydraulic pistons (116,118, and120) such that a fluid moving in manifold122can control positions of the first, second, and third hydraulic pistons (116,118, and120). Examples of such a fluid flow are detailed below with respect toFIGS. 2 through 5.

Other arrangements are also possible. In other illustrative embodiments, one or more of the hydraulic pistons might be replaced by some other kind of piston, such as an electromechanical piston.

In an illustrative embodiment, at least two of the first, second, and third hydraulic pistons may share a common fluid source. In other illustrative embodiments, all three hydraulic pistons share a common fluid source. In an illustrative embodiment, more or fewer hydraulic pistons may be present. Thus, for example, four or more nested hydraulic pistons might be provided, though in another illustrative embodiment only two nested hydraulic pistons might be provided.

In an illustrative embodiment, the different hydraulic pistons might have different operating pressures. Thus, for example, third hydraulic piston120might maintain a constant pressure having a first value, whereas the second hydraulic piston118might maintain a constant return pressure having a second value different than or the same as the first value. However, pressures may vary; for example, the first hydraulic piston116might be configured to operate at variable pressures between third and fourth values different than the first and second values. Other combinations of operating pressures are possible.

For example, first piston206may correspond to first hydraulic piston116, second piston202may correspond to second hydraulic piston118, third piston204may correspond to third hydraulic piston120, and common outer wall214may correspond to common outer wall114. Hydraulic actuator assembly200may also be referred to as a telescopic hydraulic strut assembly in some illustrative examples.

In the illustrative embodiment shown inFIG. 2, first piston206, second piston202, and third piston204are concentric to each other. Each hydraulic piston has a corresponding pressure chamber. Thus, for example, second piston202and third piston204share chamber208, and first piston206has chamber210. The space between common outer wall214and first piston206define chamber212. These chambers may operate at the same or different pressures, variable pressures, or a combination of constant and variable pressures, all of which may be the same or different.

In a non-limiting illustrative embodiment, the purpose of hydraulic actuator assembly200is to act as a fixed length tension member during takeoff, as shown inFIG. 8. In this configuration, hydraulic actuator assembly200may be referred to as a hydraulic strut. During takeoff roll, the load on the landing gear assembly is reduced as the wings generate lift. The reduced load on the landing gear shock absorber604may cause the lower portion802of the shock absorber604to extend such that the bogie beam602is forced to pivot about upper lug pivot612rather than about the main pivot616so as to provide a semi-levered function to the landing gear assembly600. As a result, the aircraft may experience a greater ground clearance, which in turn allows the airplane to rotate to a greater angle of attack on takeoff.

In a non-limiting illustrative embodiment, to perform the semi-levered function of a hydraulic actuator, chamber212is filled with fluid to an illustrative pressure greater than the fluid pressure in chamber210. This result is shown inFIGS. 3 and 4. The greater fluid pressure in chamber212causes the first piston206to be fully retracted inside the cylinder barrel215.FIG. 3shows the on-ground configuration where the first piston206is fully retracted, but the second piston202and the third piston204may move, allowing fluid to pass in and out of chambers210and208. This movement of fluid in and out of chambers210and208provides dampening, which is an illustrative function to resist bogie beam pitch about main pivot616ofFIGS. 6 through 8.

During takeoff roll, the load on the landing gear assembly is reduced as the wings generate lift. The reduced load on the landing gear shock absorber causes the lower portion of the shock absorber604to extend. The extending motion of the shock absorber causes the hydraulic actuator assembly200to extend to the position shown inFIG. 4. In this position, the second piston202is pulled against stops on the end of first piston206. This position achieves the semi-lever functionality of the hydraulic actuator and landing gear assembly.

Referring toFIG. 3in conjunction with the above description ofFIG. 2, in this illustrative embodiment, the hydraulic actuator assembly200passively transitions from position300to position400in response to the loads applied to the aircraft and landing gear assembly. This transition may not require any input from the pilots, crew, or any other mechanical or electrical device to achieve this desirable functionality. This passive operation reduces mechanical and hydraulic complexity and increases reliability.

Hydraulic actuator assembly200may have other functions. For example, hydraulic actuator assembly200may aid in positioning the bogie beam602ofFIGS. 6 through 8, to different positions of varying lengths, such as stow or landing positions. In typical large aircraft configurations, it is beneficial to position the bogie beam602ofFIG. 7in an attitude where the forward axle is lower than the aft axle for storage in a wheel well. In this instance, the hydraulic actuator assembly200can be lengthened to position500as shown inFIG. 5. This position is achieved by decreasing the fluid pressure in chamber212, which allows the pressure in chamber208to extend the hydraulic actuator assembly200. In this manner, passages in the manifold allow the fluid in chamber212to exit the chamber. In some instances it may be beneficial to integrate the command to assume position500with the landing gear assembly retraction command such that the hydraulic actuator commands position500automatically when the pilot commands the landing gear assembly to be retracted.

Hydraulic actuator assembly200may allow for extension during landing touchdown to allow a change in bogie beam pitch to facilitate air-ground sensing. In particular, hydraulic actuator assembly200may allow for extension during landing touchdown to allow a change in bogie beam pitch to provide even tire loading. Hydraulic actuator assembly200may provide damping during landing to limit loads into the other parts of the aircraft. Hydraulic actuator assembly200may provide bogie beam pitch damping, as shown further inFIG. 6.

Returning toFIG. 2, the second piston202may operate with a constant pressure, such as about 2000 pounds per square inch (psi) in one non-limiting illustrative embodiment (possibly more or fewer psi) by pressuring the fluid in chamber208accordingly. The constant pressure may be selected to provide sufficient force to position a bogie beam to stow, while not producing excessive force while on the ground, which could undesirably load the tires.

In an illustrative embodiment, the third piston204may maintain a constant downward force due to pressure in chamber208being greater than chamber210. This force may reduce the extend forces and reduce the areas that experience system pressure.

In an illustrative embodiment, the first piston206may operate at variable pressures by varying the pressure of the fluid in chamber212. The pressure in chamber212may be varied depending on the mode of operation of the hydraulic actuator assembly200. For example, a relatively low pressure of about 500 psi may be used in chamber212for landing to allow the bogie beam to move for air-ground sensing, though higher or lower pressure might be used for this purpose depending on the aircraft and design considerations. On the other hand, chamber212may operate at about 3000 to about 5000 psi, or greater, in order to lock the hydraulic actuator assembly200. In this case, the hydraulic actuator assembly200may act as a tension member during lift off rotation of the aircraft. Later, a reduced pressure of system return in chamber212may cause the strut to telescopically extend the nested hydraulic pistons206,204, and202while bringing the strut and bogie beam to a stow position.

In an illustrative embodiment, the second piston202may be referred to as a main piston, the first piston206may be referred to as a telescopic piston, and the third piston204may be referred to as a floating piston. In an illustrative embodiment, third piston204and guide tube238may define chamber239, which is common with chamber208and which may greatly reduce the hydraulic flow used to reposition the hydraulic actuator assembly200. As a result, the time used to extend the hydraulic actuator assembly200for stowing in the wheel well may be illustratively reduced since the flow into chamber208from system supply250is much less than if chamber210had to be filled using system supply250.

Attention is now turned to pressure ranges with respect to hydraulic actuator assembly200. In the illustrative embodiment shown, pressure ranges are for a system operating between about 500 psi and 5000 psi, though other ranges might be suitable and could vary by as much as about 0 psi to about 10,000 psi or more. These pressures are approximate and may vary with each specific operation or implementation. Seals are not shown, but conventional seals may be used in each groove shown in hydraulic actuator assembly200.

In an illustrative embodiment, multi-mode reducer216may provide three outlet pressures using a single valve, as shown. These pressures might be 0 psi, 500 psi, and 5000 psi, as indicated at dashed sensing line218. The single valve may provide three outlet pressures by using a standard pressure reducer and adding solenoid valve input220and solenoid valve input222to either end as shown. Solenoid valve input220and solenoid valve input222may be actuated to drive the valve to be fully on or fully off. When solenoid valve input220is on, then the pressure may be about 0 psi. When solenoid valve input222is on, then the pressure may be about 5000 psi. When both solenoid valve input220and solenoid valve input222are off, multi-mode reducer216may perform as a normal reducer, outputting about 500 psi in this example. The about 500 psi may be low enough to hold the bogie beam in a landing attitude but still allow the bogie beam to move at touchdown, allowing the aircraft to use initial bogie beam motion to trigger landing spoilers. In particular, pressure of about 500 psi may be low enough to hold the bogie beam in a landing attitude but still allow the bogie beam to move at touchdown, allowing the tires to be evenly loaded when the aircraft contacts the ground.

Multi-mode relief valve224may be an adaptation of a common relief valve with solenoid valve inputs, which may be the same valve inputs used in multi-mode reducer216. Thus, for example, solenoid valve input226may cause the relief valve to be opened, for use in the stow position, and solenoid valve input228may be used to put the relief valve into its high pressure setting. The solenoid valve input228may increase the cracking pressure from about 1000 psi to about 5500 psi by increasing the spring pre-load. A use for the multi-mode relief valve224may be to provide touchdown damping in order to reduce loads in the fuselage and other parts of the airframe, which saves weight. During touchdown, the first piston206and the second piston202may be pulled out rapidly. Fluid from the rod end of chamber212may exit through the multi-mode relief valve224, which may be sized to provide the proper damping rate.

A pressure sensor240may be used to verify that the hydraulic actuator assembly200is locked. If the pressure sensor senses that pressure is near maximum system pressure, then the hydraulic actuator assembly200may react to the full tension load expected during takeoff with a semi-levered landing gear. Note that if the seals are damaged, full pressure would not be achieved and/or sensed by pressure sensor240, thereby providing an illustrative method of testing the integrity of the hydraulic actuator assembly200.

Check valve230may be a check valve that may trap fluid in hydraulic actuator assembly200in order to hold the hydraulic actuator assembly200in the fully extended position. In an illustrative embodiment, the hydraulic pressure may be removed from system supply250after the landing gear is retracted, and check valve230also holds the bogie beam in position while the landing gear is tucked into the wheel well.

Reducer232may provide reduced pressure to the chamber208. This reduced pressure may be selected so as to avoid overloading the front tires while the aircraft is on the ground, but being sufficient pressure to power the actuator to the fully extended position when gear up is selected. A possible alternative illustrative embodiment may be to provide a solenoid input to reducer232in order to shut reducer232off while the aircraft is on the ground. In this illustrative embodiment, the tires may be equally loaded.

Check valve234may be used in an alternate extension case, such as where the landing gear assembly is extended by alternate means after hydraulic system loss. This use may leave the hydraulic actuator assembly200fully extended so that the aircraft may land with front tires down. This landing procedure may cause a rapid compression of the hydraulic actuator assembly200. The second piston202may move first, which may force fluid out of chamber210and back towards reducer232. In this case, the fluid in chamber208may also flow to system return242. In an illustrative embodiment, accumulator248may be provided for surge suppression.

In any case, relief valve236may allow the fluid in chamber208to flow into chamber212, forcing the first piston206down. This action starts the first piston206moving before the second piston202reaches the first piston206, which reduces impact loads. If the fluid flow from chamber210exceeds the return line capacity, then that flow may flow through the check valve234to chamber212, further aiding the motion of the first piston206. When the second piston202reaches the first piston206, the second piston202may contact stop244.

In an illustrative embodiment, the third piston204may be contained within the second piston202, in which case, guide tube238may extend from the head end of cylinder barrel215. In this case, the third piston204may have a stop246that prevents the third piston204from departing from guide tube238if the third piston204attempts to over-extend.

Thus,FIG. 2depicts one illustrative embodiment of hydraulic strut606ofFIGS. 6 through 8in greater detail. Hydraulic actuator assembly200includes a cylinder barrel215, a first piston206slidably received through an open end of the cylinder barrel215, and second piston202slidably received through an open end of first piston206. The second piston202may include at least one lug or other connecting member at its upper end for attachment to the landing gear assembly upper half, as shown inFIGS. 6 through 8. The cylinder barrel215may include at least one lug or other connecting member at its lower end for attachment to bogie beam602at upper lug pivot612, both ofFIGS. 6 through 8. The cylinder barrel215also contains a guide tube238that is fixed to the cylinder barrel215. A floating piston, third piston204, is contained within the second piston202and the guide tube238. The upper end of cylinder barrel215sealingly engages with the outer surface of first piston206. The lower end of the first piston206sealingly engages with the inner surface of the cylinder barrel215.

The cylinder barrel215includes fluid passages as shown inFIG. 2to supply chambers212,210, and208with pressurized fluid. These passages and chambers constitute a manifold contained within the common outer wall, the manifold is disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons. The features of the hydraulic manifold shown inFIG. 2allow the pressures in chamber212to be changed such that the first piston206may be forced in or out of the cylinder barrel215in a desirable manner. Note that the manifold may take other forms. For example, the manifold may be a series of possibly different (more or fewer than those shown) chambers connected in some other way to the first, second, and third hydraulic pistons. In any case, the manifold is disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons.

The upper end inside surface of first piston206sealingly engages with the outer surface of the second piston202. The inside surface of second piston202sealingly engages with the upper outside surface of third piston204. The upper end inside surface of the guide tube238sealingly engages with the outer surface of the third piston204. The cylinder barrel215includes fluid passages as shown inFIG. 2to supply chambers208,210, and212with pressurized fluid. The features of the hydraulic actuator assembly200shown inFIG. 2allow the pressures in chambers208and212to be changed such that the second piston may be forced out of the first piston206in a desirable manner and both second piston202and third piston204can be extended together.

As implied above, the nested pistons shown in hydraulic actuator assembly200may have different arrangements to achieve different functions. Furthermore, different valves, reducers, and other hydraulic components may be arranged to change how hydraulic fluids flow within the various fluid chambers of hydraulic actuator assembly200, again to achieve different functions. Thus, the illustrative embodiments are not limited by the particular arrangements described with respect toFIG. 2.

FIG. 3throughFIG. 5are illustrations of a hydraulic actuator in use, in accordance with an illustrative embodiment. The illustrative embodiments shown inFIG. 3throughFIG. 5correspond to the hydraulic actuator assembly200shown inFIG. 2. Therefore, reference numerals inFIG. 3throughFIG. 5sharing the same value as the reference numerals inFIG. 2may correspond to the same components and may have similar structure and functions. Not all components described with respect toFIG. 2are necessarily shown with respect toFIGS. 3 through 5; however, all such components may be present in some illustrative embodiments.

The illustrative embodiments shown inFIG. 3throughFIG. 5show hydraulic actuator assembly200in use. InFIG. 3, the hydraulic actuator assembly200has a position300for use while the aircraft is on the ground. InFIG. 4, the hydraulic actuator assembly200has a position400. InFIG. 5, the hydraulic actuator assembly200has a position500.

In the illustrative embodiment shown in position300, the chamber208may have a pressure of about 2000 psi, but that value may be more or less. The chamber210is at the return pressure, which may be a constant pressure of about 50 psi. The chamber212may have a pressure of about 500 psi. In this arrangement, third piston204and first piston206are held down by pressure in chambers208and212. Second piston202slides axially as the bogie beam moves.

This position300of hydraulic actuator assembly200may be beneficial when the airplane is on the ground. The position may be beneficial because the hydraulic actuator assembly200allows for normal bogie beam pitch motion without excessive loads in the hydraulic actuator. Furthermore, the hydraulic actuator may be arranged so as to avoid impact against a lockup position to avoid overloading the front tires. Additionally, the hydraulic actuator may be short enough to prevent overload of the hydraulic actuator in the event of an unexpected condition such as one or more tires on the aft landing gear axles experiencing lowered air pressure.

In position400, the pressure in chamber208and chamber210is maintained, but the pressure in chamber212may be increased so as to restrain first piston206in a fully compressed position. Position400is illustrative during takeoff. Position400is beneficial on takeoff because hydraulic actuator assembly200has a fixed length, which has the effect of pulling up on the front of the bogie beam as the landing gear shock absorber pushes down, which causes the rear tires to be forced down. As a result, the effective length of the landing gear assembly is longer at the point of rotation, which allows the airplane to rotate to a higher angle of attack.

During landing, position400causes hydraulic actuator assembly200to see an initial tension load. In this manner, position400may act as a damper during initial touchdown as fluid is forced out of chamber212.

In position500, the pressure in chamber212is removed so that the pressure in chamber208will fully extend second piston202. The extension of second piston202will pull third piston204to its full extended position. As a result, hydraulic actuator assembly200reaches maximum telescopic extension of each of the three hydraulic pistons such that the top of second piston202extends past the top of third piston204. Position500is illustrative because this position orients the bogie beam in the desirable attitude to fit inside the wheel well. No supply pressure is present and no single issue or change in the hydraulic actuator assembly configuration can cause large retraction forces.

FIGS. 6 through 8illustrate a landing gear assembly in three different positions in several illustrative embodiments.FIG. 6illustrates a landing gear assembly600in the ground position;FIG. 7illustrates landing gear assembly600in the stow position; andFIG. 8illustrates landing gear assembly600in a landing position. Reference numerals inFIGS. 6 through 8sharing the same value as the reference numerals may correspond to similar components and may have similar structure and functions. In one possible non-limiting illustrative embodiment, the same components amongFIGS. 6 through 8may be the same and have the same functions. The illustrative embodiments shown inFIGS. 6 through 8are non-limiting examples of one possible use of hydraulic actuator assembly200shown inFIGS. 2 through 5. A possible operation of landing gear assembly600in conjunction with hydraulic strut606is described with respect toFIGS. 2 through 5.

Turning first toFIG. 7, an illustration of a landing gear assembly in the stow position is shown, in accordance with an illustrative embodiment. Landing gear assembly600includes hydraulic strut606. Hydraulic strut606may be the same or similar to hydraulic actuator assembly200shown inFIG. 2throughFIG. 5. The illustrative embodiment shown inFIG. 7is a non-limiting example of one possible use of hydraulic actuator assembly200shown inFIGS. 2 through 5. A possible operation of landing gear assembly600in conjunction with hydraulic strut606is described with respect toFIGS. 2 through 5.

Turning now toFIG. 6, hydraulic strut606is shown in the ground configuration, which may correspond to position300shown inFIG. 3. Landing gear assembly600also shows other features, some of which are described above with respect toFIGS. 2 through 5. These features include bogie beam602attached to the lower portion of shock absorber604. Lug608is attached to the cylinder portion of shock absorber604. Plurality of wheels610are attached to bogie beam602. Plurality of wheels610may include forward wheels610B and aft wheels610A. Hydraulic strut606is pivotally attached to the upper portion of shock absorber604at lug608. Hydraulic strut606is pivotally attached to bogie beam602at lower lug pivot612. Shock absorber604is attached to bogie beam602by main pivot616. In use, lug608and lower lug pivot612allow hydraulic strut606to move in two different orientations with respect to shock absorber604and bogie beam602. In use, main pivot616allows the ends of bogie beam602to pivot upwardly and downwardly with respect to shock absorber604.

FIG. 7also depicts the hydraulic strut606with the second piston700(corresponding to second piston202ofFIG. 2) pivotally attached to the upper portion of the shock absorber604via lug608. The cylinder barrel607(corresponding to cylinder barrel215ofFIG. 2) of hydraulic strut606is pivotally attached to the bogie beam at the lower lug pivot612. In other illustrative embodiments, the hydraulic strut606may be reoriented such that the second piston (700/202) may be attached to the lower lug pivot612to the bogie beam602and the cylinder barrel (215/607) may be attached to the cylinder portion of the shock absorber604.

As shown inFIG. 7, hydraulic strut606is actuated such that second piston (700/202) and telescopic, first piston (702/206) are extended. In an embodiment, both are fully extended. In this orientation, one end of bogie beam602is forced downwardly about main pivot616. This orientation and operation is described further with respect toFIGS. 2 through 5.

After liftoff, the hydraulic strut606positions the landing gear assembly600at an angle, such that the forward axle is lower than the aft axle, as shown inFIG. 7. In an illustrative embodiment, the angle may be twelve degrees, though this value may be varied between less than a degree to eighty degrees or more. Hydraulic strut606may be repositioned quickly to stow position shown inFIG. 7using the small flow required to fill chamber208ofFIG. 2.

Later, the hydraulic strut606may be hydraulically de-energized. While in the wheel well, the hydraulic strut606may maintain the fully extended position with no supply pressure. The return pressure in chamber210may aid in this function. While in this position, no single failure may cause large retraction forces.

Turning now toFIG. 8, the hydraulic strut606is depicted with the second piston700(corresponding to second piston202ofFIG. 2) pivotally attached to the upper portion of the shock absorber604via lug608. The cylinder barrel607(corresponding to cylinder barrel215ofFIG. 2) of hydraulic strut606is pivotally attached to the lower lug pivot612which is attached to the bogie beam. In other illustrative embodiments, the hydraulic strut606may be reoriented such that the second piston (700/202) may be attached to the lower lug pivot612to the bogie beam602and the cylinder barrel (215/607) may be attached to the cylinder portion of the shock absorber604at lug608.

In an illustrative embodiment, the bogie beam angle with respect to the ground may be 23 degrees, though this value may be varied to suit the requirements of the vehicle. This orientation and operation is described further below, with respect toFIGS. 2 through 5.

Before landing, the hydraulic strut606positions the landing gear assembly from position500(FIG. 5) to position400(FIG. 4) by retracting the first piston206. This position tilts the bogie beam602for a landing position such that the forward axle is higher than the aft axle. In this position, the hydraulic strut606is restrained with a prescribed amount of force by pressure in chamber212ofFIG. 2.

During landing, the aft tires will contact the ground first, causing the bogie beam to rotate about main pivot616. This motion may cause hydraulic strut606to experience an initial high tension load. Hydraulic strut606may move with initial low resistance to allow an air-ground sensing system to detect the change in pitch of the bogie beam. As the shock absorber604compresses, the bogie beam will continue to rotate about main pivot616until the forward tires contact the ground. Once the forward tires touch the ground, the hydraulic strut606may experience rapid compression. Hydraulic strut606may act as a damper during initial touchdown. In an illustrative embodiment, hydraulic strut606may allow the aircraft to land when hydraulic strut606is in a fully extended position as shown inFIG. 7, if no hydraulic pressure is available, in order to provide for an alternate landing position.

While on the ground, the hydraulic strut606allows for normal pitch motion of bogie beam602around a main pivot616without excessive loads in the hydraulic strut606and without overloading the tires. In an illustrative embodiment, hydraulic strut606may collapse short enough to prevent any unexpected conditions from impairing landing gear assembly600or the aircraft.

ConsideringFIGS. 6 through 8together, a semi-levered landing gear assembly600in accordance with an illustrative embodiment of the disclosure is shown. The landing gear assembly600includes a shock absorber604of suitable construction to absorb and dampen transient loads exerted between the gear and the ground during ground operations of an aircraft, and to support the aircraft when stationary on the ground. The shock absorber604typically includes an upper portion800and a lower portion802that is telescopingly received in the upper portion such that the length of the shock absorber604can vary depending on the amount of the load applied to the landing gear assembly in a direction along the axis of the shock absorber. On initial touchdown, as shown inFIG. 8, the amount of load applied to the landing gear assembly600is relatively small and, accordingly, the length of the shock absorber604is about at a maximum.

The landing gear assembly600further includes a wheel truck804formed by at least one bogie beam602pivotally attached at main pivot616to a lower portion802of the shock absorber604. A plurality of wheels610are rotatably supported by the bogie beam602, including at least one forward wheel and at least one aft wheel respectively supported at a forward end and an aft end of the bogie beam602. In general, for most large aircraft, the wheel truck of a main landing gear assembly may include a plurality of wheels610, which may include a pair of forward wheels on an axle at the forward end of bogie beam602and a pair of aft wheels on an axle at the aft end of bogie beam602. Some illustrative embodiments may include a plurality of wheels on one or more additional axles between the forward and aft axles. However, the illustrative embodiments described herein are applicable to any wheel truck configuration having at least one wheel supported by a bogie beam at a location that is longitudinally displaced forward of a main pivot and at least one wheel supported by a bogie beam at a location that is longitudinally displaced aft of a main pivot.

The landing gear assembly600also includes a hydraulic strut606, which may be hydraulic actuator assembly200ofFIG. 2. Hydraulic strut606is pivotally connected at its upper end to the lug608at the shock absorber604and has its lower end pivotally connected at lower lug pivot612on the bogie beam602at a location forward of main pivot616. The hydraulic strut606is a variable-length device enabling the bogie beam602to pivot relative to the shock absorber604. Additionally, the hydraulic strut606is capable of locking up at a fixed length, when suitably controlled as further described above, such that the bogie beam602is forced to pivot about lower lug pivot612rather than about main pivot616, so as to provide a semi-levered function to the landing gear assembly600.

FIG. 9is an illustration of a block diagram of an aircraft, in accordance with an illustrative embodiment. Aircraft900shown inFIG. 9may be, for example, aircraft100shown inFIG. 1. The various components described with respect toFIG. 9may also be found inFIGS. 2 through 8, as described further below.

Aircraft900includes landing gear902, which may include a plurality of axles904upon which a plurality of tires905are disposed. Landing gear902may have, in other embodiments, one or more axles including one or more tires. Landing gear902may be, in some embodiments, landing gear assembly108ofFIG. 1or landing gear assembly600ofFIGS. 6 through 8. Plurality of axles904may be, for example, part of bogie beam602ofFIGS. 6 through 8. Plurality of tires905may be, for example, plurality of wheels610ofFIGS. 6 through 8.

Landing gear902may also include manifold906. An actuator910is disposed within manifold906. In an illustrative embodiment, the pressure of fluid908may be varied and then applied to the actuator910such that landing gear902is restrained in a landing position by actuator910with a force that is suitably low to also allow for air-ground sensing during touchdown of the aircraft900.

Fluid908may be, for example, the fluid that flows through a manifold disposed with respect to manifold906. In a particular example, fluid908may flow within chambers, such as chambers208,210, and212ofFIGS. 2 through 5. Actuator910may take other forms, as well, such as additional pistons in a nested piston arrangement.

In an embodiment, manifold906may include multi-mode relief valve914. Multi-mode relief valve914may be, for example, multi-mode relief valve224ofFIG. 2. Multi-mode relief valve914may be configured to allow fluid908to exit manifold906. In another embodiment, multi-mode relief valve914may be configured to reduce a pressure of fluid908while aircraft900is on the ground in order to balance loads among the plurality of axles904.

In an embodiment, an accumulator916may be disposed with respect to manifold906such that accumulator916absorbs pressure spikes during touchdown of the aircraft900. Accumulator916may be, for example, accumulator248ofFIG. 2.

In an embodiment, pressure sensor918may be connected to at least one of manifold906and actuator910. Pressure sensor918may be configured to monitor a health of landing gear902. Pressure sensor918may be, for example, pressure sensor240ofFIG. 2.

The different illustrative embodiments recognize and take into account that actuator110inFIG. 1, hydraulic actuator assembly200inFIGS. 2 through 5, hydraulic strut606inFIGS. 6 through 8, actuator910inFIG. 9, manifold906inFIG. 9, are examples of different implementations for a hydraulic actuator for a landing gear assembly. The different illustrative embodiments recognize and take into account that these hydraulic actuators use hydraulic fluid.

For example, the fluid flowing through manifold122inFIG. 1and fluid908flowing through manifold906inFIG. 9is hydraulic fluid. This hydraulic fluid may be, for example, without limitation, a liquid comprising, for example, without limitation, phosphate-ester hydraulic fluid.

The different illustrative embodiments recognize and take into account that the hydraulic actuator may have an alternate extension state when the aircraft performs an alternate landing. As used herein, an “alternate landing” is a landing performed when hydraulic system power is unavailable to control the landing gear for the aircraft. For example, an alternate landing may be an emergency landing.

During an alternate landing, a landing gear assembly for an aircraft may be configured with the wheeled truck assembly positioned with the forward axle lower than the aft axle. Consequently, the hydraulic actuator in the alternate extension state may need to compress more rapidly during an alternate landing as compared to a typical landing.

The different illustrative embodiments recognize and take into account that rapid compression of the hydraulic actuator may require that the hydraulic fluid be expelled from the hydraulic actuator. In some cases, this expulsion of hydraulic fluid from the hydraulic actuator may require higher flow rates than desired. Further, in some cases, managing these high flow rates may be more difficult and require larger and/or heavier components than desired.

The different illustrative embodiments recognize and take into account that a different configuration for the pistons used in actuator110inFIG. 1, hydraulic actuator assembly200inFIGS. 2 through 5, hydraulic strut606inFIGS. 6 through 8, and actuator910inFIG. 9and/or introducing a compressible gas into these hydraulic actuators may allow these hydraulic actuators to rapidly compress during an alternate landing. In particular, using a compressible gas in a hydraulic actuator may reduce the amount of hydraulic fluid that needs to be expelled from the hydraulic actuator.

Thus, the different illustrative embodiments provide a hydraulic actuator configured to also use a compressible gas that does not need to be expelled from the hydraulic actuator when the hydraulic actuator is rapidly compressed during an alternate landing. In one illustrative embodiment, a hydraulic strut assembly comprises a housing, a first piston, a second piston, and a third piston. The housing comprises outer and inner cylindrical structures. An outer chamber is formed between the outer cylindrical structure and the inner cylindrical structure and is configured to receive a first fluid. The first piston is positioned between the outer and inner cylindrical structures. The second piston is nested within the first piston. The inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first and second pistons move. The inner chamber is configured to hold a second fluid comprising a gas. The third piston is positioned between the outer cylindrical structure and the first piston. The first, second, and third pistons are configured to move in a direction parallel to an axis through the housing.

Turning now toFIG. 10, an illustration of a hydraulic strut assembly in the form of a block diagram is depicted in accordance with an illustrative embodiment. In these illustrative examples, hydraulic strut assembly1000may be part of landing gear assembly1002.

Hydraulic strut assembly1000may also be referred to as a strut assembly or a telescopic hydraulic strut assembly. Further, in some cases, hydraulic strut assembly1000may be referred to as an actuator assembly or a hydraulic actuator assembly.

Landing gear assembly1002is an example of one implementation for landing gear assembly108inFIG. 1. Landing gear assembly1002is a semi-levered landing gear assembly in these illustrative examples. As depicted, landing gear assembly1002may be part of aircraft1004in these examples. In other illustrative examples, landing gear assembly1002may be part of some other suitable type of aerospace vehicle.

As depicted, actuator1001comprises housing1006, first piston1008, second piston1010, and third piston1012. First piston1008, second piston1010, and third piston1012may be referred to as hydraulic pistons in some illustrative examples. In other illustrative examples, first piston1008, second piston1010, and third piston1012may be referred to as a telescopic piston, a main piston, and a floating piston, respectively.

In these illustrative examples, housing1006comprises outer cylindrical structure1014and inner cylindrical structure1016. Outer cylindrical structure1014may be formed by an outer wall having an inner surface and an outer surface. Inner cylindrical structure1016may be formed by an inner wall having an inner surface and an outer surface.

Inner cylindrical structure1016is located within outer cylindrical structure1014. Further, inner cylindrical structure1016may be associated with outer cylindrical structure1014. For example, housing1006has first end1020and second end1022. First end1020may be the bottom end of housing1006, while second end1022may be the top end of housing1006. Inner cylindrical structure1016may be associated with outer cylindrical structure1014at second end1022of housing1006.

Further, axis1024is an axis that runs through housing1006from first end1020of housing1006to second end1022of housing1006. In one illustrative example, axis1024is a center axis through actuator1001. For example, axis1024may be a center axis along which both inner cylindrical structure1016and outer cylindrical structure1014are aligned. In this manner, inner cylindrical structure1016and outer cylindrical structure1014may be concentric to each other with respect to axis1024. Movement in a direction parallel to axis1024may be considered linear movement.

First piston1008, second piston1010, and third piston1012are associated with housing1006. When one component is “associated” with another component, the association is a physical association in these illustrative examples. For example, a first component, such as first piston1008, may be considered to be associated with a second component, such as housing1006, by being secured to the second component, bonded to the second component, mounted to the second component, welded to the second component, fastened to the second component, and/or connected to the second component in some other suitable manner. Further, the first component may be movably connected to the second component such that at least one of these components may move relative to the other component.

Further, the first component also may be connected to the second component using a third component. The first component may also be considered to be associated with the second component by being formed as part of and/or an extension of the second component. For example, third piston1012is used to associate first piston1008with housing1006. Further, first piston1008is used to associate second piston1010with housing1006.

Additionally, the first component may be considered to be associated with the second component by being physically connected to the second component in a manner that physically constrains motion of the first component relative to the second component. For example, first piston1008may be associated with housing1006in a manner that causes motion of first piston1008to be constrained relative to housing1006. The movement of first piston1008may be constrained to movement substantially parallel to axis1024.

In particular, first piston1008, second piston1010, and third piston1012are a nested series of pistons. In these illustrative examples, these three pistons are concentric to each other with respect to axis1024. In particular, first piston1008may be disposed within third piston1012and second piston1010may be disposed within first piston1008. In this manner, first piston1008, second piston1010, and third piston1012may be substantially aligned with respect to axis1024in these illustrative examples.

First piston1008is positioned between outer cylindrical structure1014and inner cylindrical structure1016. In particular, first piston1008is located between an inner surface of outer cylindrical structure1014and an outer surface of inner cylindrical structure1016. Second piston1010is nested within first piston1008.

As depicted, first piston1008has first end1026and second end1028. First end1026may be the top end of first piston1008, while second end1028may be the bottom end of first piston1008. Further, second piston1010has first end1030and second end1032. First end1030may be the top end of second piston1010, while second end1032may be the bottom end of second piston1010.

In these illustrative examples, first piston1008is configured to move in a direction parallel to axis1024relative to first end1020of housing1006. In other words, first piston1008may move in a direction parallel to axis1024such that a position of first piston1008relative to first end1020of housing1006changes.

For example, a position of second end1028of first piston1008relative to first end1022of housing1006changes when first piston1008moves in a direction parallel to axis1024. When first piston1008moves in a direction towards second end1022of housing1006, first piston1008is considered to be retracting. When first piston1008moves in a direction away from second end1022of housing1006, first piston1008is considered to be extending.

In these illustrative examples, second piston1010is configured to move in a direction parallel to axis1024relative to second end1028of first piston1008. In other words, second piston1010may move in a direction parallel to axis1024such that a position of second piston1010relative to second end1028of first piston1008changes.

For example, the position of first end1030of second piston1010relative to second end1028of first piston1008changes when second piston1010moves in a direction parallel to axis1024. When second piston1010moves in a direction towards second end1022of housing1006, second piston1010is considered to be retracting. When second piston1010moves in a direction away from second end1022of housing1006, second piston1010is considered to be extending.

When actuator1001is part of landing gear assembly1002, second end1032of second piston1010may be connected to beam1034in landing gear assembly1002. Beam1034may be referred to as a “truck beam” or a “bogie beam” in some illustrative examples. Beam1034is connected to wheels1036for landing gear assembly1002.

In one illustrative example, beam1034may be configured to pivot about pivot point1035. For example, second end1032of second piston1010may be connected to beam1034such that movement of second piston1010in a direction parallel to axis1024causes rotation of beam1034about pivot point1035. Rotation of beam1034about pivot point1035may change the position of wheels1036relative to each other. Similarly, rotation of beam1034about pivot point1035may cause second piston1010to move in a direction parallel to axis1024.

As depicted, third piston1012is located between an inner surface of outer cylindrical structure1014of housing1006and first piston1008. Further, third piston1012may move in a direction parallel to axis1024.

In these illustrative examples, movement of first piston1008, second piston1010, and third piston1012is controlled by first fluid1038and second fluid1040in actuator1001. Outer chamber1048of actuator1001is configured to receive first fluid1038. Inner chamber1050of actuator1001is configured to receive second fluid1040.

Outer chamber1048is formed by the space between outer cylindrical structure1014and inner cylindrical structure1016. In particular, this space includes the space surrounded by at least one of the inner surface of outer cylindrical structure1014, the outer surface of inner cylindrical structure1016, and first piston1008.

In these illustrative examples, the volume of outer chamber1048that is configured to hold first fluid1038is determined by the position of first piston1008. For example, the volume of outer chamber1048changes when first piston1008moves in a direction parallel to axis1024.

Further, third piston1012is configured to move in a direction parallel to axis1024to cause outer chamber1048to divide into first sub-chamber1047and second sub-chamber1049. The volumes of first sub-chamber1047and second sub-chamber1049are determined by the position of third piston1012within outer cylindrical structure1014.

When third piston1012is located at first end1020of housing1006within outer cylindrical structure1014, the volume of second sub-chamber1049may be substantially zero. However, as third piston1012moves away from first end1020and towards second end1022of housing1006, the volume of second sub-chamber1049increases and the volume of first sub-chamber1047decreases.

Inner chamber1050is formed by inner cylindrical structure1016of housing1006, first piston1008, and second piston1010. In these illustrative examples, the volume of inner chamber1050configured to hold second fluid1040is determined by the position of first piston1008and the position of second piston1010. For example, the volume of inner chamber1050is changed when first piston1008and/or second piston1010moves in a direction parallel to axis1024.

As depicted in these examples, first fluid1038comprises hydraulic liquid1042, and second fluid1040comprises gas1044and hydraulic liquid1046. Gas1044is a compressible gas in these examples. For example, gas1044may comprise nitrogen. Of course, in other illustrative examples, gas1044may comprise air, helium, and/or some other suitable type of compressible gas.

Hydraulic liquid1042and hydraulic liquid1046may be the same type of hydraulic liquid in these illustrative examples. These hydraulic liquids may comprise water, oil, phosphate-ester fluid, and/or other suitable types of hydraulic liquids.

Hydraulic liquid1046in inner chamber1050may be used to lubricate any devices associated with movement between inner cylindrical structure1016, first piston1008, and/or second piston1010that are exposed in inner chamber1050. These devices may include, for example, without limitation, any number of bearings, seals, and/or other suitable types of mechanical devices.

The flow of first fluid1038into and out of outer chamber1048is controlled by manifold1005in hydraulic strut assembly1000, in these illustrative examples. Manifold1005is associated with actuator1001. Manifold1005is a structure comprising channels through which first fluid1038may flow. Any number of valves, ports, sensors, and/or other suitable components may be associated with this structure in manifold1005to control the flow of first fluid1038through manifold1005, as well as the flow of first fluid1038into and out of outer chamber1048.

The amount and pressure of first fluid1038in first sub-chamber1047and second sub-chamber1049in outer chamber1048may determine the position of third piston1012in outer chamber1048. For example, as first fluid1038enters second sub-chamber1049and exits first sub-chamber1047, third piston1012may float upwards through outer chamber1048in a direction parallel to axis1024.

Movement of third piston1012may cause movement of first piston1008. For example, the amount and/or pressure of first fluid1038in second sub-chamber1049may be increased such that third piston1012moves upwards, towards second end1022of housing1006, in a direction parallel to axis1024and pushes against first end1026of first piston1008. Third piston1012pushes against first end1026of first piston1008in a manner that moves first piston1008upwards in a direction parallel to axis1024. In other words, when third piston1012pushes against first end1026of first piston1008, first piston1008retracts until first end1026reaches second end1022of housing1006.

Further, in these illustrative examples, first piston1008may be fully extended when the amount and/or pressure of first fluid1038in second sub-chamber1049is not sufficient enough to cause third piston1012to push against first end1026of first piston1008. In other words, without third piston1012pushing against first end1026towards second end1022of housing1006, first piston1008may fully extend.

Second fluid1040may be introduced into inner chamber1050in a number of different ways. As one illustrative example, an operator may pour hydraulic liquid1046into inner chamber1050through an open port. The operator may subsequently pump gas1044into inner chamber1050. The operator may be, for example, a human operator, a robotic operator, or some other suitable type of operator.

When first piston1008and third piston1012are in retracted positions and a load is not being applied to second end1032of second piston1010by beam1034, the pressure of gas1044causes gas1044within inner chamber1050to push against first end1030of second piston1010in a direction away from second end1022of housing1006. In other words, the pressure of gas1044causes second piston1010to extend.

When the amount and/or pressure of first fluid1038in second sub-chamber1049is not sufficient enough to cause third piston1012and first piston1008to retract, the pressure of gas1044may cause second piston1010to fully extend. When second piston1010is fully extended, first end1030of second piston1010pushes against second end1028of first piston1008in the direction away from second end1022of housing1006. Further, when second piston1010is fully extended, the volume of inner chamber1050is increased as compared to when second piston1010is retracted. The extension of second piston1010causes gas1044to expand and fill the increased volume of inner chamber1050.

In these illustrative examples, when a compressive load is applied to second end1032of second piston1010by beam1034, second piston1010may retract. This retraction may occur even when first piston1008and third piston1012are in retracted positions. When second piston1010retracts, gas1044is compressed. Further, when second piston1010is fully retracted, the volume of inner chamber1050is decreased as compared to when second piston1010is extended.

When both first piston1008and second piston1010are fully extended, actuator1001is configured to be fully extended. When first piston1008is fully retracted and second piston1010is fully retracted, actuator1001is considered to be fully compressed. When first piston1008is fully retracted and second piston1010is fully extended, actuator1001is configured to be retracted.

As depicted, second piston1010may have an open end to increase the volume of inner chamber1050. Second piston1010may also have elongate member1052. Elongate member1052may be configured to divide inner chamber1050into first sub-chamber1051and second sub-chamber1053. First sub-chamber1051is located within inner cylindrical structure1016. Second sub-chamber1053is located within second piston1010.

In particular, elongate member1052may have open ends such that gas1044in inner chamber1050may move between first sub-chamber1051and second sub-chamber1053. In one illustrative example, elongate member1052may extend into first sub-chamber1051beyond a fluid line for hydraulic liquid1046in inner chamber1050. In this manner, the chances of hydraulic liquid1046entering the cavity inside second piston1010may be reduced. In another illustrative example, elongate member1052may extend into second sub-chamber1053to draw any hydraulic liquid1046from second sub-chamber1053into first sub-chamber1051. This action may occur when at least one of the second piston1010and the first piston1008extends.

In these illustrative examples, gas1044in inner chamber1050allows second piston1010to retract without the resistance of hydraulic liquid motion in response to wheels1036contacting ground with actuator1001in a fully extended state. Control of the positions and movement of first piston1008, second piston1010, and third piston1012using first fluid1038and second fluid1040is described in greater detail with respect to a particular implementation for hydraulic strut assembly1100inFIG. 11below.

For example, in some illustrative examples, pistons in addition to first piston1008, second piston1010, and third piston1012may be present in actuator1001. In other illustrative examples, manifold1005may include components not described above. For example, manifold1005may include valves not described inFIG. 10.

FIG. 11is an illustration of a cross-sectional view of a hydraulic strut assembly, depicted in accordance with an illustrative embodiment. In this illustrative example, hydraulic strut assembly1100is an example of one implementation for hydraulic strut assembly1000inFIG. 10. Hydraulic strut assembly1100may be used in a landing gear assembly, such as, for example, landing gear assembly1002inFIG. 10.

As depicted, hydraulic strut assembly1100comprises actuator1102and manifold1104. Actuator1102is an example of one implementation for actuator1001inFIG. 10. Manifold1104is an example of one implementation for manifold1005inFIG. 10.

In this illustrative example, actuator1102includes housing1106, first piston1116, second piston1118, and third piston1120. Housing1106, first piston1116, second piston1118, and third piston1120are examples of one implementation for housing1006, first piston1008, second piston1010, and third piston1012, respectively, inFIG. 10.

First piston1116, second piston1118, and third piston1120are associated with housing1106in this depicted example. First piston1116has first end1117and second end1119. Second piston1118has first end1121and second end1123.

First piston1116, second piston1118, and third piston1120are configured to move linearly in a direction parallel to axis1125. Axis1125is a center axis through actuator1102in this depicted example. In particular, first piston1116may move in a direction parallel to axis1125relative to first end1113of housing1106. Movement of first piston1116away from second end1115of housing1106is extension. Movement of first piston1116toward second end1115of housing1106is retraction.

Second piston1118may move in a direction parallel to axis1125relative to second end1119of first piston1116. Movement of second piston1118toward second end1115of housing1106is retraction. Movement of second piston1118away from second end1115of housing1106is extension. When second piston1118retracts, second end1123of second piston1118may contact spring system1127.

Spring system1127may comprise one or more springs associated with second end1119of first piston1116and/or second end1123of second piston1118. Spring system1127may comprise, for example, at least one of a mechanical spring, a coil spring, a ring spring, a leaf spring, an elastomeric spring, and some other suitable of spring device.

Spring system1127is configured to compress in response to a load applied to spring system1127by second end1123of second piston1118and/or second end1119of first piston1116. Spring system1127reduces the acceleration and/or force with which first piston1116retracts when second end1123of second piston1118contacts spring system1127.

Further, spring system1127prevents second end1123of second piston1118from directly contacting second end1119of first piston1116when second piston1118retracts. In this manner, undesired effects to second end1119of first piston1116that may be caused by second end1123of second piston1118contacting second end1119of first piston1116may be prevented.

In this illustrative example, third piston1120is located between first piston1116and the inner surface of outer cylindrical structure1108of housing1106. As depicted, third piston1120may move between first piston1116and outer cylindrical structure1108in a direction parallel to axis1125. When third piston1120moves upwards towards second end1115of housing1106, third piston1120may push first end1117of first piston1116towards second end1115of housing1106, causing first piston1116to retract. When third piston1120moves away from second end1115of housing1106, first piston1116is allowed to extend.

As depicted, outer chamber1122is formed in the space surrounded by outer cylindrical structure1108, inner cylindrical structure1112, and first piston1116. Third piston1120divides outer chamber1122into first sub-chamber1141and second sub-chamber1143. Movement of third piston1120in the direction parallel to axis1125causes the volumes of first sub-chamber1141and second sub-chamber1143to change.

Further, inner chamber1124is formed by inner cylindrical structure1112, first piston1116and second piston1118. Movement of second piston1118in a direction parallel to axis1125changes a volume of inner chamber1124. In particular, the volume of inner chamber1124increases when second piston1118extends, and the volume of inner chamber1124decreases when second piston1118retracts. Additionally, extension of first piston1116also may increase the volume of inner chamber1124.

In this illustrative example, second piston1118has tube1128. Tube1128is an example of one implementation for elongate member1052inFIG. 10. Both ends of tube1128are open in this example. In this manner, tube1128connects first sub-chamber1147of inner chamber1124to second sub-chamber1149of inner chamber1124. Second sub-chamber1149of inner chamber1124is formed by cavity1126inside second piston1118. In some illustrative examples, one or both ends of tube1128may be partially open or partially covered.

Charge valve1130and pressure sensor1132are associated with second end1115of housing1106in this depicted example. Charge valve1130provides a mechanism for adding fluid to inner chamber1124. In particular, both a hydraulic liquid and a compressible gas may be added to inner chamber1124through charge valve1130. Alternatively, a separate port may be used to fill and/or drain hydraulic liquid from inner chamber1124. Also, in some illustrative examples, port1139located near second end1123of second piston1118may be used for filling and/or draining fluid from inner chamber1124. Pressure sensor1132is configured to measure the pressure of a compressible gas held in inner chamber1124.

In this illustrative example, manifold1104of hydraulic strut assembly1100is associated with actuator1102. Manifold1104is depicted in the form of a schematic in this depicted example. As depicted, manifold1104has plurality of channels1131and plurality of valves1133through which a hydraulic liquid may flow within manifold1104.

The hydraulic liquid flowing through manifold1104may enter second sub-chamber1143of outer chamber1122through channel1135in plurality of channels1131. The hydraulic liquid in first sub-chamber1141of outer chamber1122may return to manifold1104through channel1137in plurality of channels1131.

Hydraulic liquid enters manifold1104from source1134. Source1134may be any suitable type of supply of hydraulic liquid. For example, source1134may be a container or tank filled with hydraulic liquid. The hydraulic fluid in source1134may have sufficient pressure to enable movement of fluid through manifold1104and into second sub-chamber1143of outer chamber1122to facilitate movement of third piston1120and first piston1116.

Hydraulic liquid flows from source1134into manifold1104through filter1136. Further, hydraulic liquid may flow from manifold1104into return1145. Return1145may take the form of, for example, without limitation, a storage container, a tank, or some other suitable component configured to hold hydraulic liquid received from manifold1104.

The flow of hydraulic liquid through manifold1104is controlled using plurality of valves1133. Plurality of valves1133includes valve1138, valve1140, valve1142, and valve1144. Valve1138may be a multi-mode pressure-reducing valve in this depicted example. Further, valve1140may be a first solenoid shut-off valve, and valve1142may be a second solenoid shut-off valve. Valve1144may be a multi-mode pressure-relief valve.

Spring1146indicates an “at rest” mode of operation for valve1138. As depicted, when valve1138is at rest, hydraulic liquid flowing from filter1136is allowed to flow through channel1135and into second sub-chamber1143of outer chamber1122. Valve1138is at rest when the pressure of hydraulic liquid at input1150has not reached a selected level and the pressure of hydraulic liquid at input1153has not reached a selected level.

When the actuator is to be placed in a retracted position, valve1138reduces pressure of source1134by sensing the outlet pressure at channel1135and compressing spring1146to adjust valve position and maintain a selected pressure level. Valve1138senses the pressure of channel1135as input1153into valve1138. In this manner, hydraulic liquid may have a pressure of about 800 psi and may flow into second sub-chamber1143of outer chamber1122through channel1135, retracting third piston1120and first piston1118.

Valve1138may change positions based on input1150, input1152, and input1153. When actuator1102is to be fully extended, the pressure of hydraulic liquid at input1150is increased to a selected level or greater. Consequently, the pressure level at input1150pushes against spring1146and valve1138changes position to allow the flow of hydraulic liquid from second sub-chamber1143of outer chamber1122into plurality of channels1131and valve1138. This hydraulic fluid may exit manifold1104at return1145. In this illustrative example, the outlet pressure for valve1138in channel1135may be about 70 psi.

The pressure of hydraulic liquid at the outlet of valve1138and channel1135is reduced such that third piston1120moves downwards freely. This movement of third piston1120allows first piston1116and second piston1118to extend such that actuator1102fully extends.

When the actuator is to be placed in a retracted position and locked, the pressure of hydraulic liquid at input1152is increased to a selected level or greater. Consequently, valve1138is blocked from moving to allow hydraulic liquid having a pressure substantially equal to source1134to flow through valve1138and into second sub-chamber1143of outer chamber1122through channel1135. Pressure of source fluid1134may be, for example, without limitation, about 5000 psi.

Further, spring1154for valve1140indicates an at rest mode of operation for valve1140. When valve1140is at rest, hydraulic liquid flowing from filter1136is allowed to pass through valve1140to input1150for valve1138and to input1162for valve1144. Valve1140is at rest when solenoid actuator1156associated with valve1140is not activated. Solenoid actuator1156may be activated in response to electrical signals. These electrical signals may be received from a control system located onboard the aircraft.

When solenoid actuator1156is activated, spring1154is compressed and valve1140changes position to allow hydraulic liquid to flow towards return1145to reduce pressure levels at input1162for valve1144and input1150for valve1138. Solenoid actuator1156may be activated when actuator1102is to be moved to the reacted position in which first piston1116is retracted and second piston1118is extended.

Spring1158for valve1142indicates an at rest mode of operation for valve1142. When valve1142is at rest, hydraulic liquid is blocked from flowing through valve1142. When actuator1102is to be retracted and locked, solenoid actuator1160associated with valve1142is activated. This activation causes spring1158to compress and valve1142to change position such that hydraulic liquid flowing from filter1136may flow through valve1142towards input1152for valve1138and input1155for valve1144. This flow of hydraulic liquid towards input1152for valve1138increases the pressure at input1152and blocks valve1138from moving out of the at rest state. Further, the flow of hydraulic liquid towards input1155for valve1144increases the pressure at input1155and changes the pressure level at which valve1144will open and allow hydraulic liquid to flow through valve1144.

Valve1144is configured to open to allow hydraulic liquid to flow from channel1129into channel1163when the pressure of the hydraulic liquid at channel1129reaches either a low pressure setting or a high pressure setting selected for valve1144. The low pressure setting for valve1144may be any pressure value that is between the pressure value for source1134and the pressure value for return1145. The high pressure setting for valve1144may be higher than the pressure value for source1134.

The pressure value for source1134may be referred to as the source pressure. The pressure value for return1145may be referred to as the return pressure. If the source pressure is about 5000 psi, and the return pressure is about 70 psi, then the low pressure setting for valve1144may be about 1000 psi and the high pressure setting for valve1144may be about 5500 psi.

When the pressure of the hydraulic liquid at channel1129decreases to a pressure value that is lower than the low pressure setting for valve1144, valve1144closes and blocks the flow of hydraulic liquid through valve1144into channel1163. Additionally, when the pressure of hydraulic liquid at input1162reaches the desired level of pressure, valve1144will open to allow hydraulic liquid to flow from channel1129into channel1163.

In this manner, plurality of valves1133controls the flow of hydraulic liquid through manifold1104as well as into and out of outer chamber1122. Further, pressure sensor1164is configured to measure the pressure of hydraulic liquid within outer chamber1122.

Additionally, seal system1165may be associated with first end1121of second piston1118. Seal system1165may comprise any number of seals configured to allow second piston1118to move relative to inner cylindrical structure1112and provide a seal for inner chamber1124. In particular, this seal for inner chamber1124is formed when second piston1118is retracted into inner cylindrical structure1112and seal system1165engages with the inner surface of inner cylindrical structure1112.

Seal system1165may be configured to divide first sub-chamber1147of inner chamber1124into a first portion and a second portion. The first portion may be the portion of first sub-chamber1147above seal system1165and the second portion may be the portion of first sub-chamber1147below seal system1165. As second piston1118is retracted into inner cylindrical structure1112, the volume of the first portion of first sub-chamber1147decreases and the volume of the second portion of first sub-chamber1147increases. Alternately, as second piston1118is extended, the volume of the first portion of first sub-chamber1147increases and the volume of the second portion of first sub-chamber1147decreases. The change in the volume of the first portion and the second portion of first sub-chamber1147causes the hydraulic liquid portion of the second fluid to be forced past seal system1165to provide resistance to the movement of the second piston1118.

Further, retraction of second piston1118causes the seal formed by seal system1165to be moved.

FIGS. 12 through 14are illustrations of different positions for the pistons in an actuator, depicted in accordance with an illustrative embodiment. InFIGS. 12 through 14, actuator1102fromFIG. 11is depicted in a compressed position, a retracted position, and an extended position, respectively.

FIG. 12is an illustration of actuator1102in a compressed position, depicted in accordance with an illustrative embodiment. In this illustrative example, actuator1102has compressed position1200. Actuator1102may have compressed position1200when, for example, the aircraft in which actuator1102is used is parked on the ground.

As depicted, third piston1120and first piston1116are in retracted positions1202and1204, respectively. In other words, third piston1120has moved upwards such that first piston1116is fully retracted such that first end1117of first piston1116is at second end1115of housing1106.

In this illustrative example, a compressive load has been applied to second end1123of second piston1118to cause second piston1118to partially retract. In particular, first end1121of second piston1118has moved upwards and away from second end1119of first piston1116. The load applied to second end1123of second piston1118may be a load transferred to second end1123of second piston1118in response to the landing gear assembly contacting the ground.

The positions of first piston1116, second piston1118, and third piston1120inFIG. 12may be determined by first fluid1206in outer chamber1122and second fluid1208in inner chamber1124. First fluid1206is a hydraulic liquid. This hydraulic liquid may be introduced into outer chamber1122by manifold1104inFIG. 11. Further, first fluid1206may flow out of outer chamber1122and return to manifold1104inFIG. 11.

Second fluid1208comprises both gas1210and hydraulic liquid1212. Gas1210is a compressible gas. When second piston1118retracts, gas1210compresses. The compressibility of gas1210allows for rapid compression of the second piston without the resistance of fluid flow. Second fluid1208may be introduced into inner chamber1124through charge valve1130inFIG. 11. Hydraulic liquid1212is used to lubricate seal system1165and reduce undesired effects to seal system1165in response to operation of actuator1102.

When first piston1116is fully retracted, seal system1165forms a seal between first end1121of second piston1118and a lower end of inner cylindrical structure1112. When second piston1118moves, second fluid1208will flow past seal system1165. Seal system1165may include a small fluid passage to allow the speed of movement of second piston1118to be reduced. In this manner, bogie beam motion may be dampened when the aircraft is traveling on the ground.

As depicted, tube1128extends into inner chamber1124above a fluid line for hydraulic liquid1212. In this manner, the possibility of hydraulic liquid1212entering cavity1126may be reduced. However, gas1210may be allowed to expand into cavity1126.

As depicted inFIG. 12, tube1128extends into inner chamber1124such that hydraulic liquid1212does not enter cavity1126. In some cases, a portion of hydraulic liquid1212may enter cavity1126through tube1128when actuator1102is compressed. In these examples, extension of second piston1118and/or first piston1116may cause gas1210to expand such that a pressure within inner chamber1124is reduced. The pressure in inner chamber1124may be reduced to a level below the pressure in cavity1126. Consequently, any gas1210and/or any hydraulic liquid1212in cavity1126may be expelled from cavity1126, having a higher pressure, into inner chamber1124, having a lower pressure, through tube1128.

FIG. 13is an illustration of actuator1102in a retracted position, depicted in accordance with an illustrative embodiment. In this illustrative example, actuator1102has retracted position1300. In particular, third piston1120has retracted position1202, first piston1116has retracted position1204, and second piston1118is fully extended when actuator1102has retracted position1300.

Actuator1102may be configured to have retracted position1300when actuator1102is to be in a landing position and/or a locked position. Actuator1102may be in a landing position when, for example, the aircraft has prepared the landing gear for landing onto the ground. Actuator1102may be in a locked position when, for example, the aircraft is traveling on a runway in preparation for takeoff.

FIG. 14is an illustration of actuator1102in a fully extended position depicted in accordance with an illustrative embodiment. In this illustrative example, actuator1102is considered to be in fully extended position1400. In particular, both first piston1116and second piston1118are fully extended when actuator1102is in fully extended position1400.

Actuator1102may be in fully extended position1400when the amount and/or pressure of first fluid1206fromFIGS. 12-13in second sub-chamber1143of outer chamber1122has been reduced such that pressure of second fluid1208forces gas1210to expand, first piston1116and second piston1118to extend, and third piston1120to move downwards.

FIG. 15is an illustration of a landing gear assembly with an actuator in a compressed position depicted in accordance with an illustrative embodiment. In this illustrative example, landing gear assembly600fromFIG. 6is depicted having hydraulic strut assembly1100fromFIG. 11instead of hydraulic strut606inFIG. 6. Manifold1104for hydraulic strut assembly1100may not be seen in this view. As depicted, landing gear assembly600is in a ground position. In this ground position, actuator1102has compressed position1200fromFIG. 12.

FIG. 16is an illustration of a landing gear assembly with an actuator in a retracted position depicted in accordance with an illustrative embodiment. In this illustrative example, landing gear assembly600fromFIG. 8is depicted having hydraulic strut assembly1100fromFIG. 11instead of hydraulic strut606inFIG. 8. As depicted, landing gear assembly600is in a landing position. In this landing position, actuator1102has retracted position1300fromFIG. 13.

FIG. 17is an illustration of a landing gear assembly with an actuator in a fully extended position depicted in accordance with an illustrative embodiment. In this illustrative example, landing gear assembly600fromFIG. 7is depicted having hydraulic strut assembly1100fromFIG. 11instead of hydraulic strut606inFIG. 7. As depicted, landing gear assembly600is in a stow position. In this stow position, actuator1102has fully extended position1400fromFIG. 14.

FIG. 18is an illustration of a flowchart of a method of operating a hydraulic actuator in an aircraft, in accordance with an illustrative embodiment. The process shown inFIG. 18may be implemented using a hydraulic actuator assembly200, such as that shown inFIG. 2throughFIG. 5, or may be implemented using a hydraulic strut606, such as that shown inFIGS. 6 through 8.

The process1800begins by operating a vehicle, the vehicle comprising: a fuselage; a wing connected to the fuselage; a landing gear assembly connected to one of the fuselage and the wing; an actuator connected to the landing gear assembly, wherein the actuator comprises: a first hydraulic piston; a second hydraulic piston disposed within the first hydraulic piston; and a third hydraulic piston disposed within both the first hydraulic piston and the second hydraulic piston, wherein the first, second, and third hydraulic pistons are contained within a common outer wall; and a manifold is contained within the common outer wall, the manifold disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons (operation1802). In an illustrative embodiment the method may include, during liftoff, passively pulling the second hydraulic piston (operation1804). In an illustrative embodiment, the method may further include, while stowing the landing gear assembly, extending the first, second, and third hydraulic pistons (operation1806).

In an illustrative embodiment, the method may further include, while positioning for landing, retracting the first hydraulic piston so that a bogie beam connected to the landing gear assembly is positioned such that a forward axle of the bogie beam is disposed upwardly relative to a rear axle of the bogie beam (operation1808). In an illustrative embodiment, the method may further include reacting to an overload condition by compressing the first, second, and third hydraulic pistons (operation1810). In an illustrative embodiment, the method may further include forcing fluid with respect to the second hydraulic piston such that the actuator acts as a dampener (operation1812). The process terminates thereafter.

Thus, the illustrative embodiments provide for an actuator. The actuator includes a first hydraulic piston, a second hydraulic piston disposed within the first hydraulic piston, and a third hydraulic piston disposed within both the first hydraulic piston and the second hydraulic piston. The first, second, and third hydraulic pistons are contained within a common outer wall.

The illustrative embodiments present provide for a nested piston actuator that is flexible, durable, light weight, and relatively inexpensive compared to other actuators. Additionally, the illustrative embodiments have added further value to aircraft operation in that the illustrative embodiments aid an aircraft in both landing and lift off. The illustrative embodiments aid an aircraft to lift off by increasing the height of the landing gear assembly at the time of initial take-off rotation, which allows a higher angle of attack. Other illustrative embodiments are apparent from the following additional description.

FIG. 19is an illustration of a process for operating a vehicle during an alternate landing in the form of a flowchart depicted in accordance with an illustrative embodiment. The process described inFIG. 19may be implemented using hydraulic strut assembly1000inFIG. 10. For example, this process may be used to operate aircraft1004inFIG. 10when aircraft1004performs an alternate landing.

The process begins by operating the aircraft during an alternate landing in which the aircraft comprises a landing gear assembly with an actuator comprising a housing, a first piston, and a second piston (operation1900). During an alternate landing, the landing gear assembly for the aircraft may be in a stow position. In particular, the actuator in the landing gear assembly may be in a fully extended position.

In this illustrative example, the housing of the actuator comprises an outer cylindrical structure and an inner cylindrical structure. The outer cylindrical structure and the inner cylindrical structure form an outer chamber configured to receive a first fluid. The first piston is configured to move in a direction parallel to an axis through the housing relative to a first end of the housing.

Further, the second piston is configured to move in the direction parallel to the axis through the housing relative to a second end of the first piston such that a volume of an inner chamber formed by the inner cylindrical structure and the second piston changes. The inner chamber is configured to hold a second fluid in which the second fluid comprises a gas that is compressible.

Thereafter, the process retracts the second piston and then the first piston in response to a load being applied to the second piston when the landing gear assembly contacts a ground on which the aircraft is landing (operation1902). The gas in the inner chamber compresses when the second piston and the first piston retract. In operation1902, the gas allows the second piston and the first piston to be retracted when the aircraft touches the ground during the alternate landing. Further, with the compressible gas in the inner chamber, the second fluid that is present in the inner chamber is not expelled from the inner chamber during the retraction of the second piston and the first piston.

The flowcharts and block diagrams in the different depicted illustrative embodiments illustrate the architecture, functionality, and operation of some possible implementations of apparatus and methods in different illustrative embodiments. In this regard, each block in the flowchart or block diagrams may represent a module, segment, function, and/or a portion of an operation or step. The illustrative embodiments may be manufactured or configured to perform one or more operations in the flowcharts or block diagrams.

In some alternative implementations, the function or functions noted in the block may occur out of the order noted in the figures. For example, in some cases, two blocks shown in succession may be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Also, other blocks may be added in addition to the illustrated blocks in a flowchart or block diagram.

Illustrative embodiments of the disclosure may be described in the context of aircraft manufacturing and service method2000as shown inFIG. 20and aircraft2100as shown inFIG. 21. Turning first toFIG. 20, an illustration of an aircraft manufacturing and service method is depicted in accordance with an illustrative embodiment. During pre-production, aircraft manufacturing and service method2000may include specification and design2002of aircraft2100inFIG. 21and material procurement2004.

During production, component and subassembly manufacturing2006and system integration2008of aircraft2100inFIG. 21takes place. Thereafter, aircraft2100inFIG. 21may go through certification and delivery2010in order to be placed in service2012. While in service2012by an operator, aircraft2100inFIG. 21is scheduled for routine maintenance and service2014, which may include modification, reconfiguration, refurbishment, and other maintenance or service.

Each of the processes of aircraft manufacturing and service method2000may be performed or carried out by a system integrator, a third party, and/or an operator. For the purposes of this description, a system integrator may include, without limitation, any number of aircraft manufacturers and major-system subcontractors; a third party may include, without limitation, any number of vendors, subcontractors, and suppliers; and an operator may be an airline, a leasing company, a military entity, a service organization, and so on.

With reference now toFIG. 21, an illustration of an aircraft is depicted in which an illustrative embodiment may be implemented. In this example, aircraft2100is produced by aircraft manufacturing and service method2000inFIG. 20and may include airframe2102with plurality of systems2104and interior2106. Examples of systems2104include one or more of propulsion system2108, electrical system2110, hydraulic system2112, environmental system2114, and landing gear system2116. Landing gear system2116may include one or more landing gear assemblies such as, for example, without limitation, landing gear assembly108inFIG. 1, landing gear assembly600inFIGS. 6 through 8, landing gear902inFIG. 9, landing gear assembly1002inFIG. 10, or landing gear assembly600inFIGS. 16 through 17. Any number of other systems may be included in systems2104, depending on the implementation.

Apparatus and methods embodied herein may be employed during at least one of the stages of aircraft manufacturing and service method2000inFIG. 20. For example, actuator110inFIG. 1, hydraulic actuator assembly200inFIGS. 2 through 5, hydraulic strut606inFIGS. 6 through 8, actuator910inFIG. 9, or hydraulic strut assembly1000may be formed and added to landing gear system2116for aircraft2100during at least one of component and subassembly manufacturing2206, system integration2208, and maintenance and service2014.

In one illustrative example, components or subassemblies produced in component and subassembly manufacturing2006inFIG. 20may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft2100is in service2012inFIG. 20. As yet another example, one or more apparatus embodiments, method embodiments, or a combination thereof may be utilized during production stages, such as component and subassembly manufacturing2006and system integration2008inFIG. 20. One or more apparatus embodiments, method embodiments, or a combination thereof may be utilized while aircraft2100is in service2012and/or during maintenance and service2014inFIG. 20. The use of a number of the different illustrative embodiments may substantially expedite the assembly of and/or reduce the cost of aircraft2100.

Thus, the illustrative embodiments provide for a guide tube and a floating piston disposed within the guide tube. The floating piston is configured within the guide tube such that a landing gear connected to the floating piston may extend rapidly to the stow position relative to a mechanical device for retracting a landing gear.

The illustrative embodiments also provide for an actuator including a first hydraulic piston, a second hydraulic piston disposed within the first hydraulic piston, and a third hydraulic piston disposed within both the first hydraulic piston and the second hydraulic piston. The first, second, and third hydraulic pistons are contained within a common outer wall. A manifold is connected to the first, second, and third hydraulic pistons. The manifold is disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons.

The embodiments also provide for a vehicle including a fuselage, a wing connected to the fuselage, and a landing gear assembly connected to at least one of the fuselage and the wing. The vehicle further includes a hydraulic actuator connected to the landing gear assembly. The hydraulic actuator includes a first hydraulic piston, a second hydraulic piston disposed within the first hydraulic piston, and a third hydraulic piston disposed within both the first hydraulic piston and the second hydraulic piston. The first, second, and third hydraulic pistons are contained within a common outer wall. The hydraulic actuator further includes a manifold connected to the first, second, and third hydraulic pistons. The manifold is disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons.

The embodiments also provide for a method for operating a vehicle. The vehicle includes a fuselage, a wing connected to the fuselage, and a landing gear assembly connected to one of the fuselage or the wing. An actuator is connected to the landing gear assembly. The actuator includes a first hydraulic piston, a second hydraulic piston disposed within the first hydraulic piston, and a third hydraulic piston disposed within both the first hydraulic piston and the second hydraulic piston. The first, second, and third hydraulic pistons are contained within a common outer wall. A manifold is connected to the first, second, and third hydraulic pistons. The manifold is disposed relative to the first, second, and third hydraulic pistons such that a fluid moving in the manifold can control positions of the first, second, and third hydraulic pistons.

Further, the different illustrative embodiments provide a hydraulic actuator, such as actuator1001inFIG. 10, configured to use a compressible gas that may not need to be expelled from the hydraulic actuator when the hydraulic actuator is rapidly compressed during an alternate landing. In one illustrative embodiment, a hydraulic strut assembly comprises a housing, a first piston, a second piston, and a third piston. The housing comprises outer and inner cylindrical structures. An outer chamber is configured to receive a first fluid that is formed between the outer cylindrical structure and the inner cylindrical structure. The first piston is positioned between the outer and inner cylindrical structures. The second piston is nested within the first piston. The inner cylindrical structure, the first piston, and the second piston form an inner chamber in which a volume of the inner chamber changes when at least one of the first and second pistons move. The inner chamber is configured to hold a second fluid comprising a gas. The third piston is positioned between the outer cylindrical structure and the first piston. The first, second, and third pistons are configured to move in a direction parallel to an axis through the housing.

The telescopic feature of the actuator in the telescopic hydraulic strut assembly provided by the different illustrative embodiments allows for a smaller overall package than the currently available and/or proposed systems. The valves within the manifold are configured to control pressure within the actuator, thereby allowing the telescopic hydraulic strut assembly to serve multiple functions. The more compact design has reduced weight as compared to currently available systems and may be used on aircraft landing gears that do not have sufficient space for some of the currently available semi-levered gear systems.

The actuator provided by the different illustrative embodiments comprises a fixed outer housing assembly with one closed end, the head end, one open end, and the rod end that houses three moveable pistons. The outer cylinder structure of the actuator is pivotally connected to the upper portion of the landing gear shock strut. One of the three pistons, the second piston, is pivotally connected to the forward end of the bogie beam of the landing gear. The three pistons slide axially within the outer housing. Movement of the piston may be controlled by the movement of fluids in or out of the actuator, as controlled by the valve module, or by the landing gear as it pushes or pulls against the attachment ends of the actuator. The valve manifold, when connected to a pressurized hydraulic fluid delivery system, will control fluid flow in and out of the actuator with the use of electrically commanded solenoid control valves, pressure reducing valves, pressure relief valves, and/or check valves.

In another illustrative embodiment, the hydraulic strut assembly comprises a housing, a first piston, a second piston, and a third piston. The housing comprises an outer cylindrical structure and an inner cylindrical structure. The inner cylindrical structure, the first piston, and the second piston form an inner chamber configured to hold a fluid comprising a gas and a hydraulic liquid. The inner chamber may have a first sub-chamber and a second sub-chamber. The gas is compressible such that at least one of the first piston and the second piston may be retracted without expelling the second fluid from the inner chamber.

Further, the hydraulic strut assembly may also include a seal system associated with at least one of the first piston and the second piston. The seal system may be configured to divide the first sub-chamber of the inner chamber into a first portion and a second portion and provide a seal between the first portion and the second portion of the first sub-chamber when the second piston retracts. When a volume of the first portion of the first sub-chamber increases and a volume of the second portion of the second sub-chamber decreases in response to the second piston extending, the hydraulic liquid of the second fluid may be moved past the seal system to provide resistance to the movement of the second piston. Additionally, the hydraulic liquid may provide lubrication for the seal system.

In one illustrative embodiment, the actuator is fully extended to position the landing gear bogie beam in a configuration with the forward axle lower than the aft axle, such as actuator1102in fully extended position1400inFIG. 14andFIG. 17. This position may facilitate stowage of the landing gear within an aircraft wheel well. The actuator achieves the fully extended position when the control valves open the outer chambers to the external hydraulic fluid return system. The inner chamber contains a compressible mixture of fluid that is charged to a predetermined pressure during maintenance of the hydraulic strut assembly. The pressure within the inner chamber forces the movement of the pistons to extend. Extension rate of the pistons is controlled by a variable restriction of the fluid that is expelled from the outer chamber of the actuator.

In another illustrative embodiment, the actuator is partially retracted to position the landing gear bogie beam in a configuration with the forward axle higher than the aft axle, such as actuator1102in retracted position1300inFIG. 13andFIG. 16. This position may position the bogie beam in the optimum touchdown configuration. The actuator achieves the partially retracted position when the manifold provides control of hydraulic fluid to and from the outer chambers. This action retracts the first and third pistons. The inner chamber contains a compressible fluid that is charged to a predetermined pressure during maintenance of the hydraulic strut assembly. The pressure within the inner chamber forces the movement of the second piston to extend.

The semi-levered function is enabled by forcibly holding the third piston retracted against the outer housing and thereby preventing the extension of the first and third pistons as the aircraft rotates for takeoff and the landing gear bogie beam tries to rotate the forward axle away from the aircraft reference. This motion will attempt to extend the actuator pistons. With highly pressurized hydraulic fluid applied by the control valves to the outer chamber, the fluid acts against the area of the third piston to resist the pulling force of the bogie beam and prevent extension of the first and third pistons. A pressure relief valve prevents over-pressurization of the fluid in the outer chamber.

In one illustrative embodiment, the aircraft is situated with all tires on the ground and the actuator position is controlled by the landing gear. The actuator may be in a compressed position, such as actuator1102in compressed position1200inFIG. 12andFIG. 15. The actuator length may be influenced by the angle of the bogie beam with respect to the landing gear shock strut and the extension amount of the landing gear shock strut. The desired response from the actuator in this condition is to minimize unequal load distribution on the tires and provide a resistive force that dampens rotations of the bogie beam. The pressure of the compressible fluid within the inner chamber and the pressure of the hydraulic fluid within the outer chambers are controlled to provide such motive force acting on the pistons to affect an insignificantly unbalanced load distribution on the tires. Another desired response from the actuator in this condition is to affect damping of the bogie beam rotations. To dampen bogie beam rotation, the fluid in the inner chamber is forced thru a fluid flow restricting device as the second piston is extended. Additionally, the inner chamber is partially filled with compressible gas and partially filled with hydraulic liquid.

The actuator provided by the different illustrative embodiments, such as actuator1001inFIG. 10and actuator1102inFIGS. 11-17, provides a dampening effect on the bogie beam during touchdown of the aircraft. Touchdown can cause rapid rotation of the bogie beam and therefore very rapid linear motion of the actuator pistons. A routine touchdown will affect extension of the first and third pistons that will force hydraulic fluid through a restrictive passage and resist motion of the bogie beam. A non-routine, or alternate, touchdown will affect compression of the first and second pistons that will compress the gas within the first fluid chamber. A mechanical spring placed between the first and second pistons provides control of accelerations during contact between the pistons.

The telescopic hydraulic strut assembly described by the different illustrative embodiments provides different types of functionality when installed on a conventional multi-axle landing gear and during typical operation of an aircraft. In particular, the telescopic hydraulic strut assembly described by the different illustrative embodiments provides the ability to position the bogie beam in two positions while the aircraft is in flight. The first position is for stowage of the landing gear within a wheel well, and the other position is a position appropriate for landing the aircraft.

Further, the telescopic hydraulic strut assembly described by the different illustrative embodiments provides the ability to inhibit extension of the actuator, known as lock-up, and hold the forward axle of the bogie beam at a constant distance from the aircraft reference, thereby causing the bogie beam to pivot about the forwardly located attachment of the telescopic hydraulic strut as the landing gear shock strut extends during takeoff. This effectively lengthens the main landing gear during takeoff.

Additionally, the telescopic hydraulic strut assembly described by the different illustrative embodiments provides the ability to deactivate the semi-levered landing gear functions when desired to ensure equal tire loading, maximum braking capability, and optimum damping performance. Still further, the telescopic hydraulic strut assembly described by the different illustrative embodiments provides the ability to dampen rotations of the bogie beam upon touchdown and taxiing.

The description of the different illustrative embodiments has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the illustrative embodiments in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art.

Further, different illustrative embodiments may provide different features as compared to other illustrative embodiments. The illustrative embodiment or embodiments selected are chosen and described in order to best explain the principles of the illustrative embodiments, the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various illustrative embodiments with various modifications as are suited to the particular use contemplated.