Patent Description:
During landing, the truck beam is typically maintained in a predetermined "toe up" or "toe down" position just prior to touchdown. Touchdown is detected by sensors that sense rotation of the truck beam that occurs subsequent to the first wheel contacting the ground. That is, after the first wheel makes contact, the truck beam rotates into a generally horizontal position in which all of the wheels are in contact with the ground. It is also necessary to maintain the truck beam in the predetermined position when the aircraft is airborne to ensure that the main landing gear will fit within the landing gear bay when the gear is retracted.

Known truck beam positioners include active positioners, which utilize various types of actuators to control the position of the truck beam. <CIT> discloses one such active truck beam positioner, wherein an auxiliary actuator is connected to the landing gear strut and the truck beam. The auxiliary actuator is hydraulically energized to selectively change length, thereby controlling the angle of the truck beam relative to the strut.

Other truck beam positioner configurations are passive positioners, which rely on biasing elements, such as springs, and/or aerodynamic loads to position the truck beam. A passive positioner is disclosed in <CIT>. The position of the truck beam is maintained by a spring loaded-telescopic link in combination with limiter incorporated in the torque link. The telescopic link extends between the shock strut and the truck beam and urges the forward end of the truck beam to rotate downward. At the same time, the limiter includes an abutment that bears against the shock strut to limit the downward rotation of the truck beam to lock the torque link and the landing gear in a bottom limit position.

Known passive and active truck beam positioners add weight, cost, complexity, and maintenance requirements to the aircraft.

<CIT> discloses that a wheel-supporting piston of the strut is rotated relative to the cylinder by an adjustable torque arm interconnection of the two to eliminate vertical friction, the adjustment being made by a hydraulic actuator, and a pressure readout of the internal strut pressure provides indication of the vertical weight load on the gear after such friction elimination.

<CIT> discloses a hydraulic control cylinder used to swing the upper part of a two part wheel strut about an axis of rotation established at the upper end of the upper strut part and at an upper central location within a stowage compartment. A folding drag brace assembly is connected between the strut and a lower rear portion of the stowage compartment. During use of the control cylinder for swinging the upper strut part rearwardly and upwardly, the drag brace folds automatically in the manner of a pantographic device, and functions to fold the lower strut part up against the upper strut part within the stowage compartment. A mechanism is provided for rotating the wheel assembly W, relative to the lower strut part, for the purpose of properly positioning the wheel assembly W for movement into the stowage compartment.

<CIT> discloses a semi-levered landing gear that includes a shock strut, a truck beam pivotally connected to the shock strut and a semi-levered landing gear mechanism including at least three links configured to angularly orient the truck beam and a truck pitch actuation system operatively connected to at least one of the three links. The landing gear mechanism may be configured to cooperate with an extension of a shock strut by positioning the truck pitch actuator in a retracted position, thereby positioning a forward end of the truck beam in a raised position relative to the aft end of the truck beam. The landing gear mechanism may also be configured to cooperate with a retraction of the shock strut into the wheel well by extending the truck pitch actuator to position a forward end of the truck beam in a lower position relative to the aft end of the truck beam.

The disclosed technology relates to landing gear that utilizes a simplified, lightweight passive truck beam positioner that reduces cost, weight, and maintenance, while also increasing reliability as compared known positioning systems. The disclosed aircraft landing gear includes a shock strut having a rod with a first end slidably disposed within a cylinder. A beam is rotatably coupled to a second end of the rod. The beam is configured to have at least a forward wheel and an aft wheel rotatably mounted thereto. The landing gear further includes a link assembly that has an upper link and a lower link. The upper link has a first end rotatably connected to the cylinder, and the lower link has a first end rotatably connected to the beam. The second end of the lower link is rotatably coupled to the second end of the upper link by a limiter joint. The limiter joint includes a first stop associated the upper link and a second stop associated with the lower link. The stops are configured such that the first stop engages the second stop to limit rotation of the upper link relative to the lower link.

The limiter is selectively adjustable to provide a predetermined maximum distance between the first end of the upper link and the first end of the lower link.

In an embodiment, the first stop comprises a first tab extending from the first leg, and the second stop comprises a second tab extending from the second leg.

In another embodiment, the first stop further comprises a first contact fitting coupled to the first tab, the first contact fitting having a first contact surface configured to contact the second stop, wherein a position of the first contact surface is selectively adjustable relative to the first tab.

In another embodiment, the first contact fitting is a first threaded fastener threadedly coupled to the first tab.

In another embodiment, the second stop further comprises a second contact fitting coupled to the second tab, the second contact fitting having a second contact surface configured to contact the first stop, wherein the position of the second contact surface is selectively adjustable relative to the second tab.

In another embodiment, the second contact fitting is a second threaded fastener threadedly coupled to the second tab.

In another embodiment, the second stop further comprises a second contact fitting coupled to the second tab, the second contact fitting having a second contact surface configured to contact the first stop, wherein a position of the second contact surface is selectively adjustable relative to the second tab.

In another embodiment, a torque link assembly is positioned on one of a leading (forward) edge and trailing (aft) edge of the shock strut. The torque link assembly includes an upper torque link with a first end rotatably coupled to the cylinder and a lower torque link with a first end rotatable coupled to the rod. The second end of the lower torque link is rotatably coupled to the second end of the upper torque link. The link assembly is positioned on the other of the leading edge and the trailing edge of the shock strut.

In another embodiment, the link assembly is located forward of the shock strut.

In another embodiment, the torque link assembly is positioned aft of the shock strut.

In another embodiment, the biasing element comprises a tension spring having a first end coupled to the cylinder and a second end coupled to the lower link of the truck beam positioner.

The foregoing aspects and many of the attendant advantages of the disclosed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:.

<FIG> illustrate a first representative embodiment of a landing gear <NUM> in accordance with the present disclosure. The landing gear <NUM> includes a shock strut <NUM> rotatably connected to structure of an aircraft (not shown).

As used herein, "rotatably" coupled, mounted, connected, etc., indicates that the referenced components are associated in such a way that rotational movement of one component relative to the other component is provided. Typically this rotation is about an axis of rotation that has a fixed position relative to the two components, however, embodiments in which the axis of rotation is moveable relative to one or both components are possible. It will also be appreciated that in some contemplated embodiments, the connection of the components may allow for relative rotational movement between the components that is about a point rather than about an axis of rotation, i.e., the components pivot relative to each other.

An actuation system (not shown) is connected to the shock strut <NUM> to reciprocate the shock strut, and thus the landing gear, between a gear-up, i.e., stowed, position, employed during flight, and a gear-down, i.e., deployed, position, used during takeoff (<FIG>), landing (<FIG>), and ground operations (<FIG>).

As best shown in <FIG> and <FIG>, the shock strut <NUM> includes a cylinder <NUM> and a rod <NUM>, a portion of which is slidably disposed within the cylinder along centerline <NUM>. That is, the cylinder <NUM> and the rod <NUM> share a common centerline <NUM>, with the rod extending from the cylinder. The interior wall of the cylinder <NUM> engages the outer surface of the rod <NUM> to restrict translational movement of the rod relative to the cylinder in all directions except along the centerline <NUM>. As a result, the rod <NUM> is capable of sliding translational movement relative to the cylinder <NUM> along the direction of the centerline <NUM>. The cylinder <NUM> and rod <NUM> cooperate to act as a shock absorber.

The landing gear <NUM> also includes a truck beam <NUM> that is rotatably coupled to a lower end of the rod <NUM> about an axis <NUM>. A plurality of wheels <NUM> are rotatably attached to the each end of the truck beam <NUM>.

The landing gear <NUM> further includes a link assembly <NUM> connecting the cylinder <NUM> to the truck beam <NUM>. As will be described in further detail, the link assembly <NUM> acts as a truck beam positioner that ensures the truck beam <NUM> and wheels <NUM> maintain a predetermined position relative to the shock strut <NUM> when the aircraft is airborne and, in particular, in a gear-down condition.

The link assembly <NUM> includes an elongate upper link <NUM> rotatably coupled at an upper end to the cylinder <NUM> about an axis <NUM>, and an elongate lower link <NUM> rotatably coupled at a lower end to the truck beam <NUM> about an axis <NUM>. In the embodiment shown, the lower end of the upper link <NUM> is rotatably coupled to the upper end of the lower link <NUM> by a limiter joint <NUM> about an axis <NUM>. Axes <NUM>, <NUM>, and <NUM> are generally horizontal and parallel to each other. As a result, as the rod <NUM> moves out of the cylinder <NUM>, the link assembly <NUM> moves in a scissoring motion so that an angle α between the upper link <NUM> and lower link <NUM> increases. Similarly, the angle α decreases as the rod <NUM> moves further into the cylinder <NUM>.

Referring now to <FIG>, the limiter joint <NUM> will be described in more detail. As shown in <FIG>, the limiter joint <NUM> includes a first stop <NUM> associated with the upper link <NUM> and a second stop <NUM> associated with the lower link <NUM>. In the embodiment shown, the first stop <NUM> is formed by a first tab <NUM> that extends outwardly in a radial direction from the upper link <NUM> and a first contact fitting <NUM> extending through the first tab toward the second stop <NUM>. The second stop <NUM> is similarly formed, having a second tab <NUM> that extends outwardly in a radial direction from the lower link <NUM> and a second contact fitting <NUM> extending through the second tab <NUM> toward the first stop <NUM>.

As the upper link <NUM> and the lower link <NUM> rotate relative to each other about axis <NUM> such that the angle α increases, the first stop <NUM> moves toward the second stop <NUM>. In this regard, the first stop <NUM> and the second stop <NUM> contact each other when the angle α reaches the predetermined maximum value, at which point the contact between the stops prevents further rotation of the links <NUM>, <NUM> relative to each other.

In the illustrated embodiment, contact between the first and second stops <NUM>, <NUM> occurs when a first contact surface <NUM> of the first contact fitting <NUM> contacts the second tab <NUM> and a second contact surface <NUM> of the second contact fitting <NUM> contacts the first tab <NUM>. In some embodiments, the contact fittings <NUM> and <NUM> may include threaded bodies. The threaded engagement of the contact fittings with their respective tabs provides for adjustment of the position of the contact surfaces relative to their respective tabs by rotating the contact fittings. This adjustability allows for selective adjustment of the angle α between the upper and lower links <NUM>, <NUM> achieved when the first and second stops <NUM>, <NUM> contact each other. This adjustability also enables an operator to ensure that both contact surfaces <NUM>, <NUM> are in contact with the opposing tab <NUM>, <NUM> when the upper link <NUM> and lower link <NUM> are at the maximum predetermined angle α relative to each other.

In the illustrated embodiment, the contact fittings are a pair of threaded fasteners. It will be appreciated that variations in the number and location of the contact fittings are possible. Further, alternate embodiments that utilize alternate structure to limit the maximum angle between the upper link <NUM> and lower link <NUM> are possible, and such alternatives may be adjustable or fixed. In this regard, any suitable configuration that limits the maximum angle between the upper link <NUM> and lower link <NUM> may be utilized, and such configurations should be considered within the scope of the present disclosure.

Referring back to <FIG>, when the aircraft is on the ground, the wheels <NUM> are in contact with the ground <NUM>, which establishes the position of the truck beam <NUM>. The weight of the airplane compresses the shock strut <NUM> so that the rod <NUM> is in a retracted position relative to the cylinder <NUM>. In this position, the link assembly <NUM> acts as a typical torque link to restrict rotation of the truck beam <NUM> and, thus, the wheels <NUM> and rod <NUM>, relative to the cylinder <NUM> about axis <NUM>.

<FIG> shows the aircraft airborne and traveling in the direction of arrow T, with the landing gear <NUM> in a gear-down position. With the weight of the aircraft off of the shock strut <NUM>, the weight of the truck beam <NUM> and wheels <NUM>, as well as the energy stored in the shock strut <NUM>, cause the rod <NUM> to move downward relative to the cylinder <NUM> into an extended position. As the rod <NUM> moves toward the extended position, the angle α between the upper link <NUM> and the lower link <NUM> increases as a result of the increase in the distance between axis <NUM>, which remains fixed relative to the cylinder <NUM>, and axis <NUM>, which moves downward with the truck beam <NUM>. The angle α increases until it reaches a predetermined maximum value, at which point the limiter joint <NUM> prevents further rotation of the upper link <NUM> and the lower link <NUM> relative to each other. This, in turn, effectively fixes the maximum length of the link assembly <NUM>, i.e., the distance between axis <NUM> and axis <NUM>. With this length effectively fixed, further downward extension of the rod <NUM> causes the truck beam <NUM> to rotate into a "toe down" position, in which the forward end of the truck beam <NUM> is lower than the aft end of the truck beam <NUM>.

In the airborne gear-down position, the link assembly <NUM> positions the truck beam <NUM> relative to the shock strut <NUM> so that the landing gear <NUM> can be received within the landing gear bay of the aircraft. Aerodynamic loads act on the wheels <NUM> of the landing gear to bias the forward end of the truck beam <NUM> counter-clockwise as viewed in <FIG> and <FIG>, biasing the landing gear <NUM> toward the toe down position. These loads help to maintain the truck beam <NUM> in the airborne deployed position (<NUM>) when the aircraft is landing but the wheels have not yet touched down, and (<NUM>) as the landing gear retracts into the landing gear bay.

As previously noted, <FIG> and <FIG> show a landing gear <NUM> with a toe down configuration and with the airplane traveling from right to left. Thus the link assembly <NUM> is located aft of the shock strut <NUM>. In some aircraft, landing gear bay limitations and landing gear configurations make it necessary for the landing gear to have a "toe up" configuration in which the truck beam <NUM> is angled relative to the shock strut <NUM> so that the forward end of the truck beam is higher than the aft end. Such a configuration is possible with the present landing gear configuration by repositioning the link assembly <NUM> to be located forward of the shock strut <NUM>, i.e., a mirror image of the link assembly positioning shown in <FIG> and <FIG>.

Referring now to <FIG> and <FIG>, a second representative embodiment of a landing gear <NUM> according to the present disclosure will be described. For the sake of brevity, unless specifically noted, previously described features of the first embodiment shown in <FIG> and <FIG> that are also present in <FIG> and <FIG> will not be described again. For such features, a reference number indicated by 1XX or 3XX in <FIG> and <FIG> corresponds to a reference number 2XX or 4XX, respectively, in <FIG> and <FIG>. For example, except as otherwise noted, the shock strut <NUM> and the axis <NUM> shown in <FIG> and <FIG> correspond to the shock strut <NUM> and the axis <NUM>, respectively, shown in <FIG> and <FIG>.

In the illustrated embodiment, the landing gear <NUM> includes a link assembly <NUM> positioned aft of the shock strut <NUM>. An elongate upper link <NUM> of the link assembly <NUM> is rotatably coupled at an upper end to the cylinder <NUM> about an axis <NUM>, and an elongate lower link <NUM> of the link assembly <NUM> is rotatably coupled at a lower end to the truck beam <NUM> about an axis <NUM>. The lower end of the upper link <NUM> is rotatably coupled to the upper end of the lower link <NUM> by a limiter joint <NUM> about an axis <NUM>.

In the embodiment shown, biasing element <NUM> biases the link assembly <NUM> toward the maximum effective length, i.e. towards the position in which the angle α is its maximum value as determined by the limiter joint <NUM>. That is, the biasing element urges the axis <NUM> toward the shock strut <NUM>. In the illustrated embodiment, the biasing element is a tension spring <NUM> coupled at one end to a lug <NUM> on the lower link <NUM> of the link assembly <NUM>. A second end of the spring <NUM> is coupled to a lug <NUM> on the shock strut <NUM>.

Although the illustrated biasing element <NUM> is shown as a tension spring, it will be appreciated that any number of configurations may be employed to urge the axis <NUM> toward the shock strut <NUM>. In one contemplated embodiment, the biasing element is a torsion spring that biases the upper link <NUM> to rotate relative to the shock strut <NUM> about axis <NUM> or the lower link <NUM> relative to the truck beam <NUM> about axis <NUM>. Additional, embodiments are also contemplated in which multiple biasing elements are utilized, such as various combinations of one or more tension springs and/or torsion springs. These and other configurations to urge axis <NUM> toward the shock strut <NUM> are contemplated and should be considered within the scope of the present disclosure.

Still referring to <FIG> and <FIG>, a torque link assembly <NUM> can be provided and is positioned forward of the shock strut <NUM>. The torque link assembly <NUM> includes an elongate upper torque link <NUM> rotatably coupled at an upper end to cylinder <NUM> about an axis <NUM> and an elongate lower torque link <NUM> rotatably coupled at lower end to a truck beam fitting <NUM> about an axis <NUM>. The lower end of the upper torque link <NUM> is rotatably coupled to the upper end of the lower torque link about an axis <NUM>. The truck beam fitting <NUM> is fixedly coupled to the rod <NUM> and rotatably coupled to the truck beam <NUM> about axis <NUM>.

As with known torque link assemblies, axes <NUM>, <NUM>, and <NUM> are generally parallel, allowing the torque link assembly <NUM> to move in a scissoring motion to accommodate movement of the rod <NUM> as the rod extends from and retracts into the cylinder <NUM>. At the same time, the torque link assembly <NUM> prevents rotation of the rod <NUM>, and therefore the truck beam <NUM>, about axis <NUM> relative to the cylinder <NUM>.

It will be appreciated that the inclusion of the torque link assembly <NUM> on the forward side of the shock strut <NUM> allows for a more lightweight and compact link assembly <NUM> on the aft side of the shock strut. Because the torque link assembly <NUM> reacts most of the forces tending to rotate the rod <NUM> and truck beam <NUM> about axis <NUM>, the link assembly <NUM> can be sized and configured mainly for maintaining the orientation of the truck beam <NUM> when the aircraft is airborne. It will be further appreciated that alternate embodiments are possible in which the torque link assembly <NUM> is omitted, similar to the embodiment of <FIG>, so that the link assembly <NUM> maintains the orientation of the truck beam <NUM> while also preventing rotation of the rod <NUM> about axis <NUM>.

As shown in <FIG>, when the aircraft is on the ground, the ground <NUM> establishes the position of the truck beam <NUM>, and the shock strut <NUM> is compressed under the weight of the aircraft. The torque link assembly <NUM>, and to a much lesser extent the link assembly <NUM>, restrict rotation of the truck beam <NUM> relative to the cylinder <NUM> about axis <NUM>.

As shown in <FIG>, when the aircraft is airborne and traveling in the direction of arrow T with the landing gear <NUM> in a gear-down position, the shock strut <NUM> is in an extended position. The link assembly <NUM> and the associated limiter joint <NUM> operate to position the truck beam in a toe down position, similar to the embodiment of <FIG>. However, the embodiment of <FIG> and <FIG> uses the biasing element <NUM> in addition to the aerodynamic loads acting on the wheels <NUM> to bias the forward end of the truck beam <NUM> counter-clockwise as viewed in <FIG> and <FIG>, thereby biasing the landing gear <NUM> toward the toe down position.

Similar to the embodiment of <FIG>, the landing gear <NUM> shown in <FIG> and <FIG> can be configured to provide a toe up position by positioning the link assembly <NUM> forward of the shock strut <NUM> and the torque link assembly <NUM> aft of the shock strut.

In the description above, specific details are set forth to provide a thorough understanding of representative embodiments of the present disclosure. It will be apparent to one skilled in the art, however, that the embodiments disclosed herein may be practiced without embodying all of the specific details. In some instances, well-known process steps have not been described in detail in order not to unnecessarily obscure various aspects of the present disclosure. Further, it will be appreciated that embodiments of the present disclosure may employ any combination of features described herein.

It should be noted that for purposes of this disclosure, terminology such as "upper," "lower," "vertical," "horizontal," "inwardly," "outwardly," "inner," "outer," "forward," "rear," etc., should be construed as descriptive and not limiting the scope of the claimed subject matter. Further, the use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter as well as additional items. Unless limited otherwise, the terms "connected," "coupled," and "mounted" and variations thereof herein are used broadly and encompass direct and indirect connections, couplings, and mountings.

The present application may also reference quantities and numbers. Unless specifically stated, such quantities and numbers are not to be considered restrictive, but exemplary of the possible quantities or numbers associated with the present application. Also in this regard, the present application may use the term "plurality" to reference a quantity or number. In this regard, the term "plurality" is meant to be any number that is more than one, for example, two, three, four, five, etc. The terms "about," "approximately," "near," etc., mean plus or minus <NUM>% of the stated value. For the purposes of the present disclosure, the phrase "at least one of A, B, and C," for example, means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C), including all further possible permutations when greater than three elements are listed.

Claim 1:
An aircraft landing gear (<NUM>), comprising:
a shock strut (<NUM>) including a rod (<NUM>) with a first end slidably disposed within a cylinder (<NUM>);
a beam (<NUM>) rotatably coupled to a second end of the rod, the beam being configured to have a forward wheel and an aft wheel rotatably mounted thereto; and
a link assembly (<NUM>), comprising:
an upper link (<NUM>) having a first end rotatably connected to the cylinder(<NUM>); and
a lower link (<NUM>) having a first end rotatably connected to the beam, a second end of the lower link (<NUM>) being rotatably coupled to a second end of the upper link (<NUM>); and
a limiter (<NUM>),
characterised in that
the limiter comprises a first stop (<NUM>) associated with the upper link and a second stop (<NUM>) associated with the lower link, the first stop engaging the second stop to limit rotation of the upper link relative to the lower link, wherein the limiter is selectively adjustable to provide a predetermined maximum distance between the first end of the upper link and the first end of the lower link.