LANDING GEAR WITH ARTICULATED LENGTH EXTENSION MECHANISM

Related Application

This application claims priority of U.S. Provisional Application No. 60/657,961 filed March 2, 2005, which is hereby incorporated herein by reference in its entirety.

Field of the Invention

The invention herein described relates generally to landing gear for large aircraft and more particularly to a landing gear including an articulated length extension mechanism.

Background

Landing gear for large aircraft heretofore have employed a telescoping shock-absorbing strut to which a multi-wheel truck (bogie beam) is attached. Such landing gear usually are equipped with some form of positioning mechanism to orientate the truck when the strut is fully extended and aircraft weight is removed. This provides a predictable position of the assembly to ensure internal and external landing gear clearances are respected during and after landing gear extension and retraction.

Some landing gear applications require an articulated truck position relative to landing gear retraction angle to optimize the clearances within the aircraft landing gear bay. In order to achieve this relationship, pitch trimmers have been employed to provide a desired pitch angle of the truck when deployed and/or retracted. Prior art designs have used complex hydraulics in association with the pitch trimmer in order to obtain an actuation solution that can accommodate shock absorber stroke rates during aircraft landing/take-off phases.

Summary of the Invention

The present invention enables a landing gear to be equipped with a mechanism that isolates a hydraulic pitch trimmer outside of the landing loop thereby eliminating the need for complex hydraulics normally associated with articulated landing gear designs equipped with pitch or trimmers or other articulating actuators.

According to one aspect of the invention, a landing gear for an aircraft comprises a shock strut including a cylinder and a piston telescopically movable in the cylinder, a multi-axle bogie beam connected to the lower end of the shock strut piston at a first pivot connection, an articulated strut connected between the bogie beam and shock strut cylinder for controlling the pitch of the bogie beam, an over-center linkage connected between the articulated strut and the shock strut cylinder, and an externally powered actuator connected to the over-center linkage for moving the over-center linkage between the over-center locked position and other another position articulating the bogie beam from an end of take-off position to a stowage position, whereby the bogie beam can be properly angularly positioned relative to the shock strut for retraction into an aircraft landing gear bay. The articulated strut includes a lower strut pivotally connected at its lower end to the bogie beam at a location spaced from the first pivot connection between the bogie beam and shock strut piston, and an upper strut connected at one end to the lower strut at a second pivot connection and at its other end to the shock strut cylinder that allows for movement of the upper strut whereby the position of the second pivot connection between the upper and lower struts can be changed relative to the shock strut cylinder. The over-center linkage includes first and second links pivotally connected to one another for movement into and out an over-center locked position, the over-center linkage, when in the over-center locked position, cooperating with the upper strut to restrain movement of the second pivot connection relative to the shock strut cylinder, whereby the bogie beam will be caused to pivot when the shock strut piston extends out of the shock strut cylinder during take-off, and the over-center linkage, when not in the over-center locked position, allowing movement of the second pivot connection whereby the bogie beam can be pivoted relative to the

shock strut piston without corresponding extension or retraction of the shock strut piston.

The upper strut may be pivotally connected to the shock strut cylinder and may form a fixed triangular structure with the over-center linkage when the over-

5 center linkage is in its over-center locked position. At least one of the first and second links of the over-center linkage may include an extendible member biased toward a retracted position, which biased extendible member compensates for rocking movement of the bogie beam during landing and takeoff when the over-center linkage is in its over-center condition. The extendible 0 member may include an actuator pressured to its retracted position.

The externally powered actuator may be connected to the first and second links at a pivot connection therebetween, and may include an end-of- stroke stop that defines the over-center stop position of the over-center linkage. The over-center linkage, when in its over-center locked position, may be s cooperative with the lower strut to rotate the bogie beam to a forward axle up position as the shock strut piston is extended during take-off of the aircraft.

According to another aspect of the invention, a landing gear is characterized by a mechanism that isolates an actuator used to position the bogie beam for stowage outside of the landing loop, thereby eliminating the o need for complex hydraulics normally associated with articulated landing gear equipped with pitch trimmers or other articulating actuators. The mechanism may comprise an articulated strut connected between a bogie beam and a shock strut cylinder for controlling the pitch of the bogie beam, an over-center linkage connected between the articulated strut and the shock strut cylinder, and 5 an externally powered actuator connected to the over-center linkage for moving the over-center linkage between the over-center locked position and other another position articulating the bogie beam from an end of take-off position to a stowage position, whereby the bogie beam can be properly angularly positioned relative to the shock strut for retraction into an aircraft landing gear bay. o According to a further aspect of the invention, a method of articulating a landing gear of an aircraft, comprises the steps of isolating outside of the takeoff/landing loop an> actuator used to position a landing gear bogie beam for

stowage, thereby eliminating the need for complex hydraulics normally associated with articulated landing gear equipped with pitch trimmers or other articulating actuators; and after take-off of the aircraft with the landing gear shock strut extended, operating the actuator to move the bogie beam to its position for stowage thereby allowing the landing gear to be retracted into a landing gear bay of the aircraft. The isolating step may include using an linkage connected between an articulated strut and cylinder of the shock strut to isolate the actuator from the take-off/landing loop.

The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.

Brief Description of the Drawings

Fig. 1 is a side elevational view of a landing gear according to the invention, shown during take-off.

Fig. 2 is a view similar to Fig. 1 , showing the landing gear during landing. perspective view of the landing gear of Fig. 1 , shown in a retracted position.

Fig. 3 is a view similar to Fig. 1 , showing the landing gear during forward wheel removal.

Fig. 4 is a view similar to Fig. 1 , showing the landing gear in an extended articulated position.

Detailed Description

In Fig. 1 , a main landing gear according to the invention is indicated generally at 10. The illustrated landing gear is particularly intended for large multi-wheel aircraft comprising nose landing gear, fuselage-mounted, multi-wheeled landing gears, and/or wing-mounted, multi-wheeled landing gears. The landing gear system arrangement may perform one or more of the following basic functions: (a) to distribute aircraft loads onto the ground ¹ , (b) to carry the

aircraft during ground maneuvers, (c) to enable effective braking, (d) to contribute to a clean aerodynamic shape in flight, (e) to ensure safe aircraft transition from flight to ground and from ground to flight, and (f) to achieve an acceptable passenger and crew comfort during take-off, landing and ground maneuvers.

The landing gear 10 may be a cantilever-type with a shock strut 14 fitted with a multi-wheel truck 16, also referred to herein as a bogie. The truck 16 includes a truck (bogie) beam 18 that carries two or more axles 20 for respective pairs of wheels 22. In the illustrated embodiment, two axles are employed to provide a four wheel truck. The number of wheels and/or axles may be varied as desired for a given application.

The shock strut 14 may be of any suitable construction. For example, the shock strut may be a single-stage oleo-pneumatic type in which nitrogen gas and oil are unseparated and perform gas spring and shock dampening functions as is conventional in the art. The shock strut, as is typical, may comprise a single piece outer cylinder 24 into which a piston 26 (sliding member) strokes. The shock strut preferably is inclined with an aftward angled rake in the gear down position as shown in Fig. 1. The upper end of the shock strut may be attached by any suitable means to the frame structure of the aircraft, usually in a manner that allows the gear to rotate upwardly into a landing gear bay of the aircraft. For this purpose the landing gear typically will be equipped with a retraction actuator, such as the retraction actuator 30 (Fig. 4), for retracting the landing gear into the bay and also for extending the gear, i.e., for moving the gear between stowed and unstowed positions. The landing gear is equipped with torque links 32 and 34 that are attached by suitable pivot connections between the outer cylinder 24 of the shock strut 14 and the bogie beam 18, for example, on the aft side of the shock strut. The torque links transmit pivoting torque from the strut piston 26 and bogie beam to the outer cylinder 24, and into the aircraft. The torque links are articulated to accommodate shock strut stroking. If desired, other means may be employed for transferring torque from the bogie beam to the outer cylinder and/or to the aircraft frame structure.

The strut piston 26 at its lower end forms a fork 56 to which the bogie beam 18 is attached with a pivot pin 58. The fork is provided with lugs for attachment of brake rods (one shown at 62) for reacting brake torque from brakes (not shown) associated with the wheels. In accordance with the invention, the landing gear 10 is equipped with an articulated length extension mechanism 66. The exemplary articulated length extension mechanism shown in Fig. 1 generally comprises an articulated strut 68 connected between the bogie beam 18 and shock strut cylinder 24 for controlling the pitch of the bogie beam, an over-center linkage 70 connected between the articulated strut 68 and the shock strut cylinder 24, and an externally powered actuator 72 connected to the over-center linkage for moving the over-center linkage between the over-center locked position (Fig. 1) and other another position (Fig. 4) articulating the bogie beam from an end of takeoff position to a stowage position, whereby the bogie beam can be properly angularly positioned relative to the shock strut for retraction into an aircraft landing gear bay.

In the illustrated exemplary landing gear, the articulated strut 68 includes a lower (vertical) strut 76 pivotally connected at its lower end to the bogie beam 18 at a location 78 spaced from the first pivot connection 58 between the bogie beam and shock strut piston, and an upper (horizontal) strut 80 connected at one end to the lower strut at a second pivot connection 82 and at its other end to the shock strut cylinder 24 that allows for movement of the upper strut whereby the position of the second pivot connection 82 between the upper and lower struts can be changed relative to the shock strut cylinder. The illustrated vertical and horizontal struts are links that are attached by suitable pivot connections between the outer cylinder 24 of the shock strut 14 and the bogie beam 18. As seen in Fig. 1 , the pivot connection 78 between the vertical strut and the bogie beam is proximate the end of the bogie beam opposite the end to which the lower torque link 34 is attached, i.e., at the forward side of the shock strut. In the illustrated exemplary landing gear, the over-center linkage 70 includes first and second links 86 and 88 pivotally connected to one another for movement into and out an over-center locked position seen in Fig. 1. The over-

center linkage, when in the over-center locked position, cooperates with the upper strut 80 to restrain movement of the second pivot connection 82 relative to the shock strut cylinder 24, whereby the bogie beam 18 will be caused to pivot when the shock strut piston 26 extends out of the shock strut cylinder during take-off, and the over-center linkage. When not in the over-center locked position, the over-center linkage allows movement of the second pivot connection 82 whereby the bogie beam can be pivoted relative to the shock strut piston without corresponding extension or retraction of the shock strut piston. The second link 88 of the over-center linkage includes an extendible member biased toward a retracted position, which biased extendible member compensates for rocking movement of the bogie beam during landing and takeoff when the over-center linkage is in its over-center condition. The extendible member may include, as shown, an actuator pressured to its retracted position, which may be referred to as a rocking bogie actuator. The pivot connection 82 between the vertical and horizontal struts may provide the pivotal connection of the first link 86 to the strut link assembly (the "first link" is also referred to herein as the "articulation over-center link"). The other end of the first link is pivotally connected to one end of the rocking bogie actuator 88 and to one end of the articulation actuator 72. The other ends of the rocking bogie actuator and articulation actuators are pivotally connected to the shock strut cylinder 24 at different points along the length of the shock strut cylinder.

In the illustrated embodiment, hydraulic pressure from an external source, such as an aircraft's hydraulic system, is applied to the articulation actuator 72 for extension or retraction, such actuator being, for example, a hydraulic cylinder and piston assembly. The rocking bogie actuator 88, which may also be a piston and cylinder assembly, is always pressured (biased) to retract in the illustrated embodiment.

Aircraft Take-Off

For aircraft take-off, the articulation actuator 72 receives a constant hydraulic pressure to the fully retracted position. This creates a fixed

triangulated structure being supported vertically by the rocking bogie actuator 88. In the illustrated embodiment, the rocking bogie actuator is always pressured to retract as above mentioned. An over-center condition is created between the rocking bogie actuator and the articulation over-center link, with mechanical stops between the components serving to support the structure.

The fixed triangular structure is connected to the bogie beam 18 via the vertical strut 76. The structure can react against the shock strut gas spring to support and pivot the aircraft around the aft wheels.

As the aircraft lifts during take-off, the shock strut 14 will extend as the weight of the aircraft is lifted off the shock strut. As the shock strut extends, the bogie beam 18 will rotate and maintain the rear wheels of the truck in contact with the runway for a longer period of time, as is often desired, as is depicted in Fig. 1. The articulation actuator 88 is effectively taken out of the loop by the over-center condition of the rocking bogie actuator 88 and the articulation over- center link 86. The fixed triangular structure, vertical strut, bogie beam and shock strut function as a four-bar linkage with three revolute joints and one prismatic or slide joint. Linear movement of the shock strut piston effects rotation of the bogie beam between the positions seen in Figs. 1 and 2.

Aircraft Landing

Upon full extension of the landing gear 10 in preparation for landing (as substantially shown in Fig. 1), hydraulic pressure is applied to the articulation actuator to create the locked triangulated structure previously mentioned. As the aircraft lands and the aft wheels engage the ground, the aft wheels will react against the gas spring of the shock strut 14 and rotate the bogie beam to horizontal (parallel to the ground). The triangulated structure does not change position during this stage. Once the bogie beam 18 is at horizontal the mechanism accommodates the compression stroke of the shock strut by utilizing the extension of the rocking bogie actuator via the vertical strut. That is, further compression of the shock strut beyond the position shown in Fig. 2 is accommodatedi by extension of the rocking bogie actuator.

Forward Wheel Removal

As illustrated in Figure 3, the articulated length extension mechanism 66 allows for jacking of the forward wheels to replace a flat tire without compressing the shock strut. The angular movement of the bogie beam 18 is accommodated through extension of rocking bogie actuator 88.

Landing Gear Articulation

After aircraft take-off hydraulic pressure may be applied to extend the articulation actuator 72 to its full length. This causes, through the vertical strut 76, the bogie beam to pivot the forward wheels downwardly to optimize and reduce the necessary landing gear bay envelope. The angle of movement is directly proportional to the length ratios of the mechanism components.

As will be appreciated from the foregoing discussion, hydraulic damping can be applied to the extension and retraction strokes of the articulation actuator. This will reduce inertia loads and noise at stroke extremes. The articulation actuator can be located outside of landing loop thereby to reduce complex hydraulic systems necessary for previously proposed designs. This also reduces cost and weight. The articulated length extension mechanism can be applied to all types of aircraft including multi-axle bogies.

Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described integers (components, assemblies, devices, compositions, etc.), the terms (including a reference to a "means") used to describe such integers are intended to correspond, unless otherwise indicated, to any integer which performs the specified function of the described integer (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated ¹ exemplary embodiment or embodiments of

the invention. In addition, while a particular feature of the invention may have been described above with respect to only one of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.