Patent Description:
The use of struts to support the wings of an aircraft can significantly reduce the spanwise bending moment in the wings. Struts are typically attached to a lower portion of the fuselage, and extend up to the wings at an angle. Aircraft that operate at high cruise speeds typically have swept wings to reduce shock waves and wave drag. The aerodynamic performance of an aircraft can be improved by increasing the aspect ratio of the wings.

When struts are implemented on a swept-wing aircraft with high-aspect-ratio wings, the strut-fuselage joint (where the strut attaches to the fuselage) is located aft of the wing-fuselage joint (where the wing attaches to the fuselage). As a result of the aft offset of the strut-fuselage joint relative to the wing-fuselage joint, the lower portion of the struts are non-overlapped by the wings when the aircraft is viewed from above. The non-stacked or non-overlapping relation of the wings and struts reduces interference drag, which significantly improves the aerodynamic performance of the aircraft.

However, the aft offset of the strut-fuselage joint results in a relatively large moment about a vertical axis on the wings and struts. More specifically, the lifting force generated by each wing is reacted by tension load in the strut that supports the wing. Due to the aft offset of the strut-fuselage joint, the tension load in the strut induces a large bending moment about the vertical axis at the wing root and strut root, referred to as a vertical moment. The large vertical moment has the undesirable effect of urging the wings to pivot in an aft direction.

As can be seen, there exists a need in the art for a structural arrangement for a strut-braced, swept-wing aircraft that is capable of counteracting a large vertical moment in a structurally efficient manner.

<CIT>, which falls under Article <NUM>(<NUM>) EPC such that it is not relevant to the question of inventive step, in accordance with its abstract, states an aircraft has a fuselage, a wing assembly, and a pair of struts. The wing assembly has a center wing structure and a pair of outer wing structures. The center wing structure is coupled to the fuselage at a wing-fuselage joint, and has a pair of engine mounting locations respectively on opposite sides of a wing centerline. Each of the struts is coupled to the fuselage at a strut-fuselage joint, and to one of the outer wing structures at a strut-wing joint. Each strut-fuselage joint is located below and aft of the wing-fuselage joint. Each outer wing structure is coupled to the center wing structure at a mid-wing joint located no further inboard than the engine mounting location, and no further outboard than the strut-wing joint.

Document <CIT>, according to its abstract, discloses an aircraft including a body, a wing coupled to and extending from the body, and a strut. The wing includes a wing thickest region bounded by a wing thickest region leading boundary' and a wing thickest region trailing boundary. The strut includes a strut thickest region bounded by a strut thickest region leading boundary and a strut thickest region trailing boundary. In a planform view, the wing thickest region overlaps the strut thickest region at an overlap region, where the overlap region including less than fifteen percent of the strut thickest region.

The above-noted needs associated with structural arrangements for strut-braced, swept-wing aircraft is addressed by the present disclosure.

There is described herein, an aircraft, comprising: a fuselage; a wing coupled to the fuselage at a wing-fuselage joint, wherein the wing generates a lifting force when air passes over the wing; and a strut coupled to the fuselage at a strut-fuselage joint and coupled to the wing at a strut-wing joint, the strut-fuselage joint located below and at least partially aft of the wing-fuselage joint, wherein the strut comprises an A-frame structure having a strut front spar and a strut rear spar, each having a strut spar inboard end and a strut spar outboard end, wherein the strut spar outboard ends converge at the strut-wing joint; wherein: the lifting force induces a vertical moment about the wing-fuselage joint due to the location of the strut-fuselage joint below and at least partially aft of the wing-fuselage joint; the strut front spar and the strut rear spar are respectively configured to carry tension load and compression load in response to the vertical moment induced by the lifting force; the strut spar inboard ends are spaced apart from each other at the strut-fuselage joint, and are configured to transfer the tension load and the compression load into the fuselage at a strut front attach point and a strut rear attach point of the strut-fuselage joint; and at least one of the wing and the strut has a structural arrangement configured to counteract the vertical moment.

There is also described herein a method of enhancing the performance of an aircraft, comprising: generating, using a wing, a lifting force when air passes over the wing, wherein, the wing is coupled to a fuselage at a wing-fuselage joint, and is supported by a strut coupled to the fuselage at a strut-fuselage joint located below and at least partially aft of the wing-fuselage joint; inducing a vertical moment about the wing-fuselage joint in response to the lifting force; and counteracting the vertical moment using a structural arrangement of at least one of the wing and the strut, comprising: carrying tension load and compression load respectively in a strut front spar and a strut rear spar of an A-frame structure of the strut, the strut front spar and strut rear spar each having a strut spar inboard end and a strut spar outboard end, the strut spar outboard ends converge at a strut-wing joint, the strut spar inboard ends are spaced apart from each other at the strut-fuselage joint; and transferring the tension load and the compression load into the fuselage at a strut front attach point and a strut rear attach point of the strut-fuselage joint.

The features, functions and advantages that have been discussed can be achieved independently in various examples of the present disclosure or may be combined in yet other examples, further details of which can be seen with reference to the following description and drawings below.

These and other features of the present disclosure will become more apparent upon reference to the drawings wherein like numbers refer to like parts throughout and wherein:.

Disclosed versions will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all of the disclosed versions are shown. Indeed, several different versions may be provided and should not be construed as limited to the versions set forth herein. Rather, these versions are provided so that this disclosure will be thorough and fully convey the scope of the disclosure to those skilled in the art.

This specification includes references to "one version" or "a version. " Instances of the phrases "one version" or "a version" do not necessarily refer to the same version. Similarly, this specification includes references to "one example" or "an example. " Instances of the phrases "one example" or "an example" do not necessarily refer to the same example.

As used herein, "comprising" is an open-ended term, and as used in the claims, this term does not foreclose additional structures or steps.

As used herein, "configured to" means various parts or components may be described or claimed as "configured to" perform a task or tasks. In such contexts, "configured to" is used to connote structure by indicating that the parts or components include structure that performs those task or tasks during operation. As such, the parts or components can be said to be configured to perform the task even when the specified part or component is not currently operational (e.g., is not on).

As used herein, the phrase "at least one of," when used with a list of items, means different combinations of one or more of the listed items may be used, and only one of each item in the list may be needed. In other words, "at least one of" means any combination of items and number of items may be used from the list, but not all of the items in the list are required. The item may be a particular object, a thing, or a category.

Referring now to the drawings which illustrate preferred and various examples of the disclosure, shown in <FIG> is a strut-braced, high-wing aircraft <NUM>. The aircraft <NUM> has a fuselage <NUM> having a fuselage upper portion <NUM> and a fuselage lower portion <NUM>. The fuselage <NUM> has a nose and a tail section, and a longitudinal axis <NUM> (<FIG>) extending between the nose and the tail section. In the example shown, the tail section includes a vertical tail <NUM> and a pair of horizontal tails <NUM> mounted on top of the vertical tail <NUM>. However, the vertical tail <NUM> and horizontal tails <NUM> may be arranged in alternative configurations.

The aircraft <NUM> includes a pair of wings <NUM>, and a pair of engines <NUM> suspended from the wings <NUM>. However, the engines may be mounted at alternative locations on the aircraft <NUM>. For example, the engines <NUM> may be mounted on the fuselage <NUM>, such as on an aft portion (not shown) of the fuselage <NUM>. Each wing <NUM> has a wing leading edge <NUM>, a wing trailing edge <NUM>, a wing root <NUM>, and a wingtip <NUM>. The wingspan of the aircraft <NUM> is measured between the wingtips <NUM>. Each wing root <NUM> is coupled to the fuselage <NUM> at a wing-fuselage joint <NUM> at the fuselage upper portion <NUM>. In the example shown, the wing-fuselage joint <NUM> for each wing <NUM> is covered by a wing root fairing <NUM>. Each wing <NUM> is swept aftwardly, and each wing <NUM> is a high-aspect-ratio wing, having a relatively long span and a relatively short chord. In the example shown, each wing <NUM> is swept at an angle of up to <NUM> degrees relative to a lateral axis (not shown), which is perpendicular to the longitudinal axis <NUM> (<FIG>). In other examples, each wing <NUM> may be swept at an angle of between <NUM>-<NUM> degrees.

In <FIG>, each wing <NUM> has less than <NUM> degrees of anhedral, such that each wing <NUM> is slightly downwardly angled. However, in other examples, the wings <NUM> may have no anhedral, or the wings <NUM> may have dihedral, wherein the wings <NUM> are angled upwardly. In the example shown, the aircraft <NUM> is configured for transonic airspeeds, wherein the aircraft <NUM> may have a free stream Mach number of between <NUM>-<NUM>. However, the presently-disclosed structural arrangements may be implemented on aircraft configured for subsonic speeds, and/or on aircraft configured for supersonic speeds.

Referring still to <FIG>, on each side of the aircraft <NUM> is a strut <NUM>. Each strut <NUM> has a strut leading edge <NUM>, a strut trailing edge <NUM>, a strut root <NUM>, and a strut outboard end <NUM>. The strut root <NUM> is coupled to the fuselage <NUM> at a strut-fuselage joint <NUM> at the fuselage lower portion <NUM>. In the example shown, the aircraft <NUM> includes a fuselage stub <NUM> protruding laterally from each side of the fuselage <NUM>. The strut root <NUM> is coupled to the fuselage stub <NUM> at the strut-fuselage joint <NUM>. The strut-fuselage joint <NUM> is covered by a strut root fairing <NUM>.

Each strut <NUM> extends at an upward angle from the strut-fuselage joint <NUM>, and is coupled to the wing <NUM> at a strut-wing joint <NUM>. Although not shown, the strut-wing joint <NUM> may be covered by a strut-wing-joint fairing. In the example shown, each strut-wing joint <NUM> is located at a distance of <NUM>-<NUM> percent of the distance from the wing root <NUM> to the wingtip <NUM>.

Notably, each strut-fuselage joint <NUM> is located at least partially aft of the wing-fuselage joint <NUM> when the aircraft <NUM> is viewed from the side, as shown in <FIG>, or when viewed from the top, as shown in <FIG>. When viewed from a top-down perspective (e.g., <FIG> or <FIG>), the wing <NUM> and the strut <NUM> may be described as having a vertically unstacked arrangement, as opposed to a stacked arrangement (not shown) in which the wing <NUM> is vertically stacked directly above the strut <NUM>. <FIG> is a schematic sectional view of an example of a wing <NUM> and a strut <NUM> in a vertically stacked arrangement. <FIG> is a schematic sectional view taken along line <NUM>-<NUM> of <FIG>, illustrating an unstacked arrangement of the wing <NUM> and strut <NUM>. As a result of the unstacked arrangement, when the aircraft <NUM> is viewed from a top-down perspective, at least a portion of the strut leading edge <NUM> is aft of the wing trailing edge <NUM>. More specifically, at locations proximate the strut root <NUM>, the strut leading edge <NUM> is located aft of the wing trailing edge <NUM>. In the present disclosure, the strut-fuselage joint <NUM> is defined as being located aft of the wing-fuselage joint <NUM> if the strut leading edge <NUM> at the strut root <NUM> is located aft of the wing front spar <NUM> at the wing root <NUM>, although the aerodynamics are unfavorable if the strut leading edge <NUM> is located forward of the wing trailing edge <NUM>.

Advantageously, the unstacked arrangement of the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM> allows each strut <NUM> (at least an inboard portion of the strut <NUM> - e.g., <FIG>) to contribute to lift and thereby enhance aircraft performance, while reducing loading on the wing <NUM>. In contrast, for a vertically stacked arrangement (not shown) of the wing-fuselage joint <NUM> and strut-fuselage joint <NUM>, low-pressure flow coming off each strut <NUM> acts on the underside of the wing <NUM>, reducing pressure and diminishing the lift contribution of the wing <NUM>. An additional benefit of the unstacked arrangement is a reduction in drag that would otherwise occur in the stacked arrangement due to strong shocks from high local flow Mach numbers caused by flow interference between the strut <NUM> and the wing <NUM>.

Referring to <FIG>, shown respectively are perspective, top, front, and side views of a portion (e.g., one-half) of the aircraft <NUM> of <FIG>. Shown in each view is a wing axis <NUM> extending between the wing-fuselage joint <NUM> and the strut-wing joint <NUM>. Also shown is a strut axis <NUM> extending between the strut-fuselage joint <NUM> and the strut-wing joint <NUM>. The wing <NUM> generates a lifting force <NUM>, which is distributed along the wingspan. The lifting force <NUM> is the vertical force supporting the mass of the aircraft <NUM> during flight, and is generated by the wing <NUM> when air passes over the wing <NUM>.

Referring to <FIG>, shown are schematic diagrams respectively corresponding to <FIG>. <FIG> schematically illustrate the wing <NUM> and the wing axis <NUM>, and the strut <NUM> and the strut axis <NUM>. Also shown in <FIG> and subsequent schematic diagrams is a reference coordinate system <NUM>, to aid in identifying the orientation of each drawing figure. In addition, the wing-fuselage joint <NUM> is identified by reference character A, the strut-wing joint <NUM> is identified by reference character B, and the strut-fuselage joint <NUM> is identified by reference character C. Furthermore, shown is wing-joint/strut-joint axis <NUM> extending the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM>.

Referring to <FIG>, shown are schematic diagrams respectively similar to <FIG>, but without the aircraft <NUM>. <FIG> schematically illustrate the lifting force <NUM> applied to the strut-wing joint <NUM>. The lifting force <NUM> is shown as a vertical load vector at the strut-wing joint <NUM>, and represents the typical summation of spanwise distribution of lift along the wingspan that is carried by the strut <NUM>, as shown in <FIG>. A typically smaller portion of the wing spanwise distribution of lift is also transmitted by the wing <NUM> to the wing-fuselage joint <NUM>, and which does not contribute to a vertical moment Mz caused by the unstacked arrangement of the wing <NUM> and strut <NUM>.

As described herein, the vertical moment Mz is due to the aft offset of the strut-fuselage joint relative to the wing-fuselage joint <NUM>, and is a relatively large moment about a vertical or substantially vertical axis on the wings <NUM> and struts <NUM>. As mentioned above, the lifting force generated by each wing <NUM> is reacted by tension load in the strut <NUM> that supports the wing <NUM>. Due to the aft offset of the strut-fuselage joint, the tension load in the strut <NUM> induces the vertical moment Mz about a vertical or substantially vertical axis (i.e., parallel to the Z axis of the reference court system <NUM>) at the wing root <NUM> and strut root <NUM>. Also shown in <FIG> are reaction forces <NUM> at the wing-fuselage joint <NUM> and at the strut-fuselage joint <NUM>, and which area also in response to the lifting force <NUM>. As can be seen, the wing <NUM> is under compression load <NUM>, and the strut <NUM> is under tension load. The reaction force <NUM> at the wing-fuselage joint <NUM> is compression, and the reaction force <NUM> at the strut-fuselage joint <NUM> is tension.

As mentioned above, the reaction forces <NUM> include the vertical moment Mz, which is induced by the lifting force <NUM> about the wing-fuselage joint <NUM>. The vertical moment Mz is due to the location of the strut-fuselage joint <NUM> at least partially aft of the wing-fuselage joint <NUM> (e.g., see <FIG>). Stated another way, the vertical moment Mz is created as a result of the non-parallel relationship between the wing axis <NUM> and the strut axis <NUM> (e.g., see <FIG>) when the aircraft <NUM> is viewed from a top-down direction. The vertical moment Mz tends to urge the wing <NUM> to pivot about the wing root <NUM> in an aftward direction. The vertical moment Mz is in addition to the moment (not shown) generated by engine thrust, and in addition to moment (not shown) generated by aerodynamic drag on the wing <NUM>, the engine <NUM>, and the strut <NUM>, and/or in addition to yawing moments (not shown). Typically (e.g., for commercial airliners), the vertical moments resulting from engine thrust, aerodynamic drag, and yawing moments are much smaller than the vertical moment Mz created by the angle between the wing <NUM> and the strut <NUM> (e.g., <FIG>). Also shown in <FIG> is a reaction force <NUM> (i.e., parallel to the Y axis of the reference court system <NUM>) in the fore-aft direction (i.e., shear load into the fuselage <NUM>). The reaction force <NUM> in the fore-aft direction is also a result of the location of the strut-fuselage joint <NUM> below and at least partially aft of the wing-fuselage joint <NUM>.

In the present disclosure, the aircraft <NUM> is configured such that the wing <NUM> and/or the strut <NUM> on each side of the aircraft <NUM> has a structural arrangement configured to counteract or resist the vertical moment Mz. The structural arrangement of the wing <NUM> and/or the strut <NUM> prevents the vertical moment Mz from pivoting the wing <NUM> in an aftward direction, at least to an extent causing plastic deformation of the structural members of the aircraft <NUM>. The below discussion describes various examples of structural arrangements of the wing <NUM> and/or the strut <NUM> for counteracting the vertical moment Mz.

Referring to <FIG>, shown are schematic diagrams respectively similar to <FIG>, and illustrating an example of a structural arrangement of a strut <NUM> configured as a cantilevered beam <NUM> for resisting the vertical moment Mz induced by the lifting force <NUM>. The cantilevered beam <NUM> of the strut <NUM> is non-rotatably or fixedly coupled to the fuselage <NUM> via a fixed joint <NUM> at the strut-fuselage joint <NUM>, and is configured to carry tension and bending load to counteract the vertical moment Mz induced by the lifting force <NUM>. For the moment My (not shown) about a horizontal axis parallel to the Y axis at the strut-fuselage joint <NUM>, the strut <NUM> can be either fixedly coupled or pivotably coupled to the fuselage <NUM>. <FIG> show the bending (i.e., exaggerated for illustration purposes) of the cantilevered beam <NUM> of the strut <NUM> in response to the lifting force <NUM>. Also shown is the wing <NUM> under compression load <NUM>, and the reaction force <NUM> (i.e., pure axial load, and no bending load) at the wing-fuselage joint <NUM>. In addition, shown is the strut <NUM> (i.e., the cantilevered beam <NUM>) in bending, and the reaction force <NUM> at the strut-fuselage joint <NUM>, comprising tension in combination with bending moment from the vertical moment Mz,s. Additionally, shown is a reaction force <NUM> in the fore-aft direction (i.e., shear load, parallel to the Y axis) at the strut-fuselage joint <NUM>. Configuring the strut <NUM> as a cantilevered beam <NUM> for resisting the vertical moment Mz,s may favor an arrangement in which the strut <NUM> has a relatively large chord at the strut root <NUM>.

Referring to <FIG>, shown are schematic diagrams respectively similar to <FIG>, and illustrating an example of a structural arrangement of a wing <NUM> configured as a cantilevered beam <NUM> for resisting the vertical moment Mz induced by the lifting force <NUM>. In such an arrangement, for the vertical moment Mz,w, the cantilevered beam <NUM> of the wing <NUM> is non-rotatably or fixedly coupled via a fixed joint <NUM> to the fuselage <NUM>, and is configured to carry compression and bending. <FIG> show exaggerated bending of the cantilevered beam <NUM> of the wing <NUM> in response to the lifting force <NUM>. The reaction forces <NUM> in <FIG> are similar to the reaction forces <NUM> described above for <FIG>, with the exception that the wing <NUM> is in bending, and the strut <NUM> is under tension load <NUM>. The reaction forces <NUM> at the strut-fuselage joint <NUM> comprise pure tension, and no bending load. The reaction forces <NUM> at the wing-fuselage joint <NUM> comprise compression in combination with the above-mentioned vertical moment Mz,w. In addition, a reaction force <NUM> in the fore-aft direction (i.e., parallel to the Y axis) is induced at the wing-fuselage joint <NUM>.

Referring to <FIG>, shown is an example of a structural arrangement in which both the wing <NUM> and the strut <NUM> are configured as cantilevered beams <NUM> for counteracting the vertical moment Mz induced by the lifting force <NUM>. The strut <NUM> and the wing <NUM> share in resisting the vertical moment Mz. More specifically, the portion of the vertical moment Mz,w counteracted by the wing <NUM>, in combination with the portion of the vertical moment Mz,s counteracted by the strut <NUM>, is equivalent to the total magnitude of the vertical moment Mz for the unstacked arrangement of the wing <NUM> and strut <NUM>. The loads in the wing <NUM> and strut <NUM>, and the reaction forces <NUM> at the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM>, are similar to the above-described corresponding loads and reaction forces <NUM> in <FIG>.

In one example of the arrangement shown in <FIG>, the strut <NUM> is configured to counteract more than <NUM> percent of the vertical moment Mz, and the wing <NUM> is configured to counteract a remaining portion of the vertical moment Mz. The apportionment of vertical moment Mz between the wing <NUM> and the strut <NUM> may be based in part on the amount of upward load on the wing <NUM> carried by the strut <NUM>. In this regard, the relative stiffness (i.e., in the horizontal direction) of the wing <NUM> and the strut <NUM> measured at the strut-wing joint <NUM> may dictate the distribution of the vertical moment Mz. In some examples, the wing <NUM> (and the wing-fuselage joint <NUM>) may be configured to counteract <NUM> percent (e.g., <NUM>-<NUM> percent) of the vertical moment Mz, and the strut <NUM> (and the strut-fuselage joint <NUM>) may be configured to counteract <NUM> percent (i.e., or a remaining portion) of the vertical moment Mz.

Advantageously, configuring the strut <NUM> and the wing <NUM> such that each carries a portion of the vertical moment Mz allows for a reduction in the structural mass of the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM>, since neither joint is required to carry <NUM> percent of the vertical moment Mz. In addition, such an arrangement provides structural redundancy. For example, if the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM> are each designed to carry <NUM> percent of the vertical moment Mz, then if one of the joints is ineffective, the remaining joint can carry the vertical moment Mz due to a built-in safety factor typical of structural design. Thus, a degree of fail-safety is provided for an arrangement in which the vertical moment Mz is shared between the wing <NUM> and the strut <NUM> in equal or approximately equal proportions.

Referring to <FIG>, shown are structural arrangements in which the strut <NUM> is configured to carry the entirety of the vertical moment Mz induced by the lifting force <NUM>. In the example of <FIG>, the structural arrangement is based on the concept that the structural efficiency and stiffness of the strut <NUM> increases as the strut chord increases. In the examples shown, the strut <NUM> is configured as an strut A-frame structure <NUM> having a strut front spar <NUM> and a strut rear spar <NUM>. The combination of the wing <NUM> (i.e., the wing axis <NUM>) and the strut A-frame structure <NUM> (i.e., the strut front spar <NUM> and the strut rear spar <NUM>) defines a lower tetrahedron configuration <NUM>.

In <FIG>, the strut front spar <NUM> and the strut rear spar <NUM> each have a strut spar inboard end <NUM> and a strut spar outboard end <NUM>. Reference character D represents the location of the strut front attach point <NUM> (<FIG>), and reference character E represents the location of the strut rear attach point <NUM> (<FIG>). As mentioned above, reference character C represents the strut-fuselage joint <NUM>. The strut spar outboard ends <NUM> (<FIG>) of the strut front spar <NUM> and strut rear spar <NUM> converge at the strut-wing joint <NUM>. The strut front spar <NUM> and the strut rear spar <NUM> are respectively configured to carry tension load <NUM> (<FIG>) and compression load <NUM> (<FIG>) in response to the vertical moment Mz induced by the lifting force <NUM>. The strut spar inboard ends <NUM> are spaced apart from each other at the strut-fuselage joint <NUM>, and are configured to transfer tension load <NUM> and compression load <NUM> into the fuselage <NUM> at a strut front attach point <NUM> and a strut rear attach point <NUM>.

<FIG> illustrate the loads and reaction forces <NUM> on the wing <NUM> and the strut <NUM> as a result of the lifting force <NUM> at the strut-wing joint <NUM>. As can be seen, the wing <NUM> is subjected to compression load <NUM>, and the reaction force <NUM> at the wing-fuselage joint <NUM> is compression. The strut front spar <NUM> is subjected to tension load <NUM>, and the reaction force <NUM> at the strut front attach point <NUM> is tension. The strut rear spar <NUM> is typically subjected to compression load <NUM>, and the reaction force <NUM> at the strut rear attach point <NUM> is compression.

<FIG> are magnified top-down views showing the strut-fuselage joint <NUM>, and the resolution of the reaction forces <NUM> at the strut front attach point <NUM> and the strut rear attach point <NUM> into reaction forces <NUM> in the lateral direction (i.e., tension and compression, oriented perpendicular to the longitudinal axis <NUM>) and reaction forces <NUM> (i.e., shear load) in the fore-aft direction (i.e., parallel to the longitudinal axis <NUM>).

<FIG> is a chart of the reaction forces <NUM> at the strut front and rear attach points <NUM>, <NUM> due to tension load T and vertical moment Mz for four different configurations of the strut <NUM>. As shown in the chart, each of the four strut <NUM> configurations has a different attach point spacing between the strut front attach point <NUM> (reference character D) and the strut rear attach point <NUM> (reference character E). The difference in attach point spacing ("DE" - e.g., <FIG>) may be due to different angular spacings of the strut front spar <NUM> and the strut rear spar <NUM> and/or due to different configurations of the strut root <NUM>.

In <FIG>, the magnitude of the reaction forces <NUM> is represented by the length of the arrows. Although the reaction forces <NUM> due to the tension load T are of the same magnitude for each of the four strut configurations, the reaction forces <NUM> due to the vertical moment Mz are significantly different. For example, for the strut configuration on the extreme left-hand side of the chart, the attach point spacing between the strut front and rear attach points <NUM>, <NUM> is the smallest of the four configurations, and which results in relatively large magnitude reaction forces <NUM> at the strut front and rear attach points <NUM>, <NUM>. In contrast, for the strut configuration on the extreme right-hand side of the chart, the attach point spacing is the largest of the four strut configurations, and which results in relatively small reaction forces <NUM> at the strut front and rear attach points <NUM>, <NUM>.

Referring still to <FIG>, the chart shows the summation of the reaction forces <NUM> due to the tension load T and the vertical moment Mz for each of the four strut configurations. In general, the chart shows that the structural efficiency and bending stiffness of the strut <NUM> increases as the attach point spacing ("DE") increases between the strut front attach point <NUM> and the strut rear attach point <NUM>. Increased structural efficiency represents reduced reaction forces at D and E due to the vertical moment Mz at the strut front attach point <NUM> and the strut rear attach point <NUM>, which translates into reduced structural mass of the aircraft <NUM>. <FIG> also shows that the reaction force <NUM> at the rear strut attach point <NUM> can be compression, tension, or even zero, depending upon the attach point spacing.

Referring back to <FIG>, shown is an example of a strut A-frame structure <NUM> having an inboard end connector <NUM> interconnecting the strut spar inboard end <NUM> of the strut front spar <NUM> with the strut spar inboard end <NUM> of the strut rear spar <NUM>. The inboard end connector <NUM> is configured to transfer shear load into the fuselage <NUM> at the strut-fuselage joint <NUM>. The shear load (i.e., parallel to the Y axis) is a reaction force <NUM> to the tension load <NUM> and the compression load <NUM> respectively carried by the strut front spar <NUM> (<FIG>) and the strut rear spar <NUM> (<FIG>).

In <FIG>, the inboard end connector <NUM> is shown coupled to the fuselage <NUM> at a single location for transferring the shear load as a single reaction force <NUM> into the fuselage <NUM>. The inboard end connector <NUM> is either a separate connector beam (not shown), or the inboard end connector <NUM> is integrated into the structure of the fuselage <NUM> portion between the strut spar inboard end <NUM> of the strut front spar <NUM> and the strut spar inboard end <NUM> of the strut rear spar <NUM>. Although <FIG> shows the inboard end connector <NUM> coupled to the fuselage <NUM> at a single location midway or approximately midway between the strut front attach point <NUM> and strut rear attach point <NUM>, the inboard end connector <NUM> allows the reaction force <NUM> (i.e., the shear reaction) to be transferred into the fuselage <NUM> at any location between the strut front attach point <NUM> and the strut rear attach point <NUM>. Alternatively, the shear load can be distributed along the entire length of the inboard end connector <NUM>.

Referring to <FIG>, shown is an example of the strut <NUM> having a strut front spar <NUM> and a strut rear spar <NUM> encapsulated within the airfoil shape of the strut <NUM>. As shown in <FIG>, the airfoil shape is defined by a strut upper skin panel <NUM> and a strut lower skin panel <NUM>. The strut <NUM> includes a strut leading edge <NUM> and a strut trailing edge <NUM>, each extending from the strut root <NUM> at the strut-fuselage joint <NUM>, to the strut outboard end <NUM> at the strut-wing joint <NUM>. The strut leading edge <NUM> and the strut trailing edge <NUM> define a tapered shape for the strut <NUM>. Advantageously, the tapered shape of the strut <NUM> is complementary to the strut A-frame structure <NUM> of the strut front spar <NUM> and the strut rear spar <NUM>. The aerodynamic properties of the strut A-frame structure <NUM> are favorable, in that a progressively smaller strut chord near the strut-wing joint <NUM> minimizes interference drag between the strut <NUM> and the wing <NUM>. Furthermore, the relatively large strut chord at the strut-fuselage joint <NUM> enables the strut <NUM> to handle a large portion (e.g., an entirety) of the vertical moment Mz induced by the lifting force <NUM>.

Referring to <FIG>, shown in <FIG> are plots of the aerodynamic penalty <NUM>, structural penalty <NUM>, and structural benefit <NUM> as a function of the geometry of the lower tetrahedron configuration <NUM> of <FIG>. As described above, the lower tetrahedron configuration <NUM> of <FIG> is defined by the wing axis <NUM>, and by the strut A-frame structure <NUM>, as shown in <FIG>. In <FIG>, reference character O is at the same longitudinal location as the wing-fuselage joint <NUM>, and reference character C represents the longitudinal location of the strut-fuselage joint <NUM>. As mentioned above, reference character D represents the longitudinal location of the strut front attach point <NUM>, and reference character E represents the longitudinal location of the strut rear attach point <NUM>. Reference character C represents the strut-fuselage joint <NUM>, and in <FIG>, reference character C may be described as being located at the midpoint between the strut front attach point <NUM> (D) and the strut rear attach point <NUM> (E).

<FIG> is a moment diagram <NUM> illustrating a direct proportional relationship between distance OC and the magnitude of the vertical moment Mz. As can be seen, the structural penalty <NUM> (i.e., aircraft weight) increases as distance OC increases. <FIG> also illustrates the decrease in aerodynamic penalty <NUM> (e.g., decreased interference drag) that occurs with an increase in distance OC. <FIG> is a plot of structural benefit <NUM> as a function of the attach point spacing ("DE") between the strut front spar <NUM> and the strut rear spar <NUM>. As can be seen, the structural benefit <NUM> (i.e., reduction in aircraft weight) increases as the distance DE increases. In addition, <FIG> illustrates that distance DE is directly proportional to the ability of the strut <NUM> to resist the vertical moment Mz. The larger the distance DE, the greater the ability of the strut <NUM> to resist the vertical moment Mz.

Referring to <FIG>, shown are examples of an aircraft <NUM> in which the wing <NUM> includes a wing-A-frame structure <NUM>. The wing A-frame structure <NUM> extends from the wing-fuselage joint <NUM> at least to the strut-wing joint <NUM>. The wing A-frame structure <NUM> includes a wing front member <NUM> and a wing rear member <NUM>. The wing front member <NUM> and the wing rear member <NUM> may be alternatives to, or in addition to, the primary load-carrying structures of the wing <NUM>, which typically comprises a wing front spar <NUM> (<FIG>) and a wing rear spar <NUM> (<FIG>).

At the wing-fuselage joint <NUM>, the wing front member <NUM> has a wing front attach point <NUM>, which is identified by reference character G. The wing rear member <NUM> has a wing rear attach point <NUM>, which is identified by reference character H. As mentioned earlier, the strut-wing joint <NUM> is identified by reference character B, and the strut-fuselage joint <NUM> is identified by reference character C. The combination of the wing front member <NUM>, the wing rear member <NUM>, and the strut <NUM> form an upper tetrahedron configuration <NUM>.

In <FIG>, the wing front member <NUM> and the wing rear member <NUM> each have a wing member inboard end <NUM> and a wing member outboard end <NUM>. The wing member inboard end <NUM> of the wing front member <NUM>, and the wing member inboard end <NUM> of the wing rear member <NUM>, are spaced apart from each other at the wing-fuselage joint <NUM>. The wing member outboard end <NUM> of the wing front member <NUM> and the wing member outboard end <NUM> of the wing rear member <NUM> converge proximate the strut-wing joint <NUM>.

<FIG> illustrate the loads on the wing front member <NUM>, wing rear member <NUM>, and strut <NUM>, and the reaction forces <NUM> at the wing-fuselage joint <NUM> and the strut-fuselage joint <NUM>. The wing front member <NUM> and the wing rear member <NUM> are respectively sized and configured to respectively carry at least a portion of the tension load <NUM> and the compression load <NUM>, to thereby counteract the vertical moment Mz induced by the lifting force <NUM>. In some examples, the wing A-frame structure <NUM> may be configured to carry an entirety of the vertical moment Mz induced by the lifting force <NUM>. The structural efficiency of the wing <NUM> in resisting the vertical moment Mz is improved as the spacing increases between the wing front attach point <NUM> and the wing rear attach point <NUM>. To avoid interference of the wing front and rear members <NUM>, <NUM> with the wing front and rear spars <NUM>, <NUM> (<FIG>), or with the wing fuel tanks (not shown), the wing front member <NUM> and wing rear member <NUM> may each be provided as two separate members (not shown), with one member located proximate the upper surface of the wing <NUM>, and the other member located proximate the lower surface of the wing <NUM>.

Referring to <FIG>, shown is an example of a double tetrahedron configuration in which the wing <NUM> has a wing A-frame structure <NUM>, and the strut <NUM> has a strut A-frame structure <NUM>. The loads and reaction forces <NUM> associated with the wing A-frame structure <NUM> and the strut A-frame structure <NUM> are similar to the loads and reaction forces <NUM> described above. The structural efficiency of the double tetrahedron configuration increases as the distance between the wing front and rear attach points <NUM>, <NUM> (e.g., reference characters G and H) increases, and/or as the distances between the strut front and rear attach points <NUM>, <NUM> (e.g., reference characters D and E) increases.

Referring to <FIG>, shown in <FIG> is a plot of the conceptual weight <NUM> of a wing <NUM> vs. wingspan, for two different wing configurations. The area under the phantom line represents the weight of a typical cantilevered wing <NUM>. The area under the solid line represents the weight of a strut-braced-wing <NUM>, similar to the wing <NUM> of <FIG>. The weight of each wing <NUM> is the structural mass required to react the wing bending moment due primarily to aerodynamic loading on the wing <NUM>. The dashed line represents a cut-off for the weight of the wing <NUM> due to a minimum gauge limitation <NUM>, which recognizes that even at a bending moment near zero, the wing structural elements cannot have zero thickness and/or zero cross-sectional area.

As can be seen in <FIG>, the shape of the plot for the strut-braced-wing <NUM> is significantly different than the shape of the plot for the typical cantilevered wing <NUM>. For example, the strut-braced-wing <NUM> has an up-bending moment at the wing root <NUM> that is very small, and may even be negative, depending on the wing configuration. For most of the wing <NUM> between the wing root <NUM> and the strut-wing joint <NUM>, the vertical bending moment is small. The crossed-hatched area in <FIG> represents the structural weight savings achieved with the strut-braced-wing <NUM> of <FIG>.

<FIG> is a plot of conceptual weight <NUM> vs. wingspan for the vertical moment Mz reacted by the wing <NUM>. Due to the aft offset of the strut-fuselage joint <NUM> relative to the wing-fuselage joint <NUM>, the vertical moment Mz can be relatively large, resulting in correspondingly large wing weight (i.e., structural mass) to carry the vertical moment Mz.

<FIG> is a combination of the plots of <FIG>. The structural mass required to carry the vertical moment Mz detracts from the weight savings that would otherwise be achieved from using the strut-braced wing <NUM>. The remaining weight savings is represented by the crosshatched area between the curve of the typical cantilevered wing <NUM>, and the curve of the strut-braced-wing <NUM>. As a result, a larger portion of the vertical moment Mz is preferably carried by the strut <NUM> rather than the wing <NUM>, such that the weight savings of the strut-braced wing <NUM> can be preserved.

Referring to <FIG>, shown in <FIG> is a top-down view of a portion of the aircraft <NUM> illustrating an example of a strut A-frame structure <NUM>. <FIG> show an example of the strut <NUM> for which the strut front attach point <NUM> and the strut rear attach point <NUM> are at the same longitudinal location as the inboard ends of the strut front spar <NUM> and strut rear spar <NUM>. In this regard, the attach point spacing ("DE") is dictated by the spacing between the inboard ends of the strut front spar <NUM> and the strut rear spar <NUM>. <FIG> shows the relatively large reaction forces <NUM> at the strut front attach point <NUM> and strut rear attach point <NUM>. <FIG> is a plot of the bending moment Ms of the strut <NUM> (i.e., due the vertical moment Ms) as a function of strut length, illustrating that the highest bending moment occurs at the strut root <NUM>.

<FIG> illustrate an example of a strut A-frame structure <NUM> in which the strut front attach point <NUM> is located forward of the strut front spar <NUM> and aft of the strut leading edge <NUM>, and the strut rear attach point <NUM> is located aft of the strut rear spar <NUM> and forward of the strut trailing edge <NUM>, thereby increasing the attach point spacing. As mentioned above, increasing the attach point spacing results in a decrease in loads at the strut-fuselage joint <NUM>. In this regard, the magnitude of the reaction forces <NUM> at the strut front and rear attach points <NUM>, <NUM> in <FIG> is lower than the magnitude of the reaction forces <NUM> in <FIG>. The arrangement shown in <FIG> takes advantage of the volume of space within the strut leading edge portion and within the strut trailing edge portion, to thereby reduce the size and/or structural mass of the strut-fuselage joint <NUM> as a result of the reduced magnitude of the reaction forces <NUM>.

<FIG> represent different configurations of the strut <NUM> for decreasing the magnitude of the reaction forces <NUM> at the strut-fuselage joint <NUM>. <FIG> represent an arrangement in which the strut front spar <NUM> and the strut rear spar <NUM> are each contiguous from the strut-fuselage joint <NUM> to the strut-wing joint <NUM>, and each have at least one kink <NUM> located proximate the strut-fuselage joint <NUM>. In the example shown, the strut front spar <NUM> and the strut rear spar <NUM> each have a single kink <NUM> dividing the strut spar <NUM>, <NUM> into a strut spar inboard section <NUM> and a strut spar outboard section <NUM>. However, the strut <NUM> may be provided in an arrangement (not shown) wherein each strut spar <NUM>, <NUM> has multiple kinks <NUM>. At each kink <NUM>, a kick load (not shown) is generated due to the non-alignment of the spar sections <NUM>, <NUM>. The upper and lower strut skin panels <NUM>, <NUM> and/or other structural members (not shown) may be configured to react the kick loads.

In <FIG>, the strut spar inboard section <NUM> of the strut front spar <NUM> is angled forwardly relative to the strut spar outboard section <NUM> of the strut front spar <NUM>, and the strut spar inboard section <NUM> of the strut rear spar <NUM> is angled aftwardly relative to the strut spar outboard section <NUM> of the strut front spar <NUM>, to thereby increase the distance between the strut spar inboard ends <NUM>. In the strut <NUM> includes a kink connector beam <NUM> extending between and interconnecting the kinks <NUM> respectively of the strut front spar <NUM> and the strut rear spar <NUM>. In addition, the strut <NUM> includes an inboard end connector <NUM> connecting the strut spar inboard ends <NUM> of the strut spar inboard sections <NUM> of the strut front spar <NUM> and the strut rear spar <NUM>. The inboard end connector <NUM> is configured to transfer shear load from the strut <NUM> to the fuselage <NUM>, as described above.

Referring still to <FIG>, the strut <NUM> may alternatively or additionally include a kink plate <NUM> extending between and interconnecting the strut spar inboard section <NUM> of the strut front spar <NUM> to the strut spar inboard section <NUM> of the strut rear spar <NUM>. As shown in <FIG>, the kink plate <NUM> is located at the neutral axis of the strut front spar <NUM> and the strut rear spar <NUM>. Although not shown, the strut front spar <NUM> and the strut rear spar <NUM> may each include spar slots <NUM> (e.g., <FIG>) for receiving the kink plate <NUM>. The kink plate <NUM> is configured to facilitate load transfer into the fuselage <NUM>.

Alternatively or additionally, the strut <NUM> includes a pair of diagonal members <NUM>, each extending from one of the strut spar inboard ends <NUM> of one of the strut spars <NUM>, <NUM>, to the kink <NUM> of the other one of the strut spars <NUM>, <NUM>, as shown in <FIG>. The pair of diagonal members <NUM> are respectively configured to transfer tension load <NUM> and compression load <NUM>. The diagonal members <NUM> can be rods configured to resist axial load, as the diagonal members <NUM> are not subjected to bending. In <FIG>, the diagonal members <NUM> are shown crossing each other. However in other examples, one diagonal member <NUM> may be located on an upper surface of the kink plate <NUM>, and the other diagonal member <NUM> may be located a lower surface of the kink plate <NUM>.

Referring to <FIG>, shown is a further example of a strut A-frame structure <NUM> comprising a strut leading edge member <NUM> and a strut trailing edge member <NUM> respectively defining the strut leading edge <NUM> and the strut trailing edge <NUM> of the strut <NUM>. The strut leading edge member <NUM> and the strut trailing edge member <NUM> are interconnected by a strut upper skin panel <NUM> and a strut lower skin panel <NUM>, and the strut leading edge member <NUM> and strut trailing edge member <NUM> each have a strut member inboard end <NUM> and a strut member outboard end <NUM>. As shown in <FIG>, the strut member inboard ends <NUM> of the strut leading edge member <NUM> and strut trailing edge member <NUM> are spaced apart from each other proximate the strut-fuselage joint <NUM>. The strut member outboard ends <NUM> converge at the strut-wing joint <NUM>. The strut leading edge member <NUM> and the strut trailing edge member <NUM> are respectively sized and configured to carry tension load and compression load resulting from the vertical moment Mz induced by the lifting force <NUM>.

The strut leading edge member <NUM> and the strut trailing edge member <NUM> are configured respectively such that the strut leading edge <NUM> and the strut trailing edge <NUM> are each concavely curved when the aircraft <NUM> is viewed from a top-down perspective. The curved shape of the strut leading edge member <NUM> and strut trailing edge member <NUM> increases the distance between the strut member inboard ends <NUM>, relative to the distance between the strut member inboard ends <NUM> if the strut leading edge member <NUM> and the strut trailing edge member <NUM> were straight. In addition, the curvature of the strut leading edge <NUM> minimizes the amount of overlap between the strut leading edge <NUM> and the wing trailing edge <NUM> when the aircraft <NUM> is viewed from a top-down perspective, as shown in <FIG>.

The strut leading edge member <NUM> and the strut trailing edge member <NUM> may be formed of a durable material for damage resistance during the service life of the aircraft <NUM>, such as damage during ground operations, or in-flight damage from bird strikes or erosion, such as from hail or debris. In some examples, the strut <NUM> leading and trailing edge members may be machined from a metallic material such as aluminum, steel, or titanium. The strut upper skin panel <NUM> and the strut lower skin panel <NUM> function as shear webs for transferring shear load as the strut <NUM> is subjected to bending load from the vertical moment Mz. The strut leading edge and trailing edge members <NUM>, <NUM> and the strut upper and lower skin panels <NUM>, <NUM> may be interconnected in a manner to avoid steps, jumps, or discontinuities in the outer surfaces, particularly near the strut leading edge <NUM>, to promote laminar flow over the strut <NUM>. The interior of the strut <NUM> may include material or structural members to improve buckling load capability. Due to the continuous curvature in the strut leading and trailing edge members <NUM>, <NUM> of <FIG>, instead of a concentrated kick load in the kinked strut spar configuration of <FIG>, the kick load in <FIG> would be distributed along the length of the strut leading and trailing edge members <NUM>, <NUM>. As mentioned above, structure (not shown) would be provided between the strut leading and trailing edge members <NUM>, <NUM> to carry such distributed kick loads.

Referring to <FIG>, shown is an example of a strut <NUM> in which the strut front spar <NUM> and the strut rear spar <NUM> each have a channel-shaped cross-section comprised of an upper cap <NUM> and a lower cap <NUM> interconnected by a spar web <NUM>, although other cross-sectional shapes may be implemented. The strut front spar <NUM> and the strut rear spar <NUM> may be formed of fiber-reinforced polymer matrix material (i.e., composite material, such as graphite-epoxy). The strut front spar <NUM> and/or the strut rear spar <NUM> include reinforcing fibers <NUM> extending continuously from the strut root <NUM> to the strut outboard end <NUM>. The reinforcing fibers <NUM> increase the load-carrying capability of the strut spars <NUM>, <NUM>. Each reinforcing fiber <NUM> is comprised of a bundle of filaments. The filaments may be formed of any one of a variety of materials including, but not limited to, polymeric material (e.g., carbon fibers) or non-polymeric material such as metallic fibers. In some examples, the filaments may be formed of a lightweight and stiff material, such as boron, to increase the tension-load carrying capability of the strut front spar <NUM>. An alternative material may be used for improving the compression load carrying capability of the strut rear spar <NUM>. In some examples, the reinforcing fibers <NUM> are embedded within the material of the strut front spar <NUM> and/or the strut rear spar <NUM>. In other examples, the reinforcing fibers <NUM> may be bonded or attached by other means to the strut front spar <NUM> and/or the strut rear spar <NUM>. As mentioned above, the strut front spar <NUM> and/or the strut rear spar <NUM> are not limited to a channel-shaped cross-section as shown, but may be provided in alternative cross-sectional shapes, such as an I-shaped cross section.

Referring to <FIG>, shown is a still further example of a strut A-frame structure <NUM> comprising a strut front fitting <NUM> and a strut rear fitting <NUM>. The strut front fitting <NUM> extends forward of (i.e., toward the strut leading edge <NUM>) the strut front spar <NUM>. The strut front fitting <NUM> is coupled to the strut front spar <NUM> proximate the strut root <NUM>, and is configured to distribute load from the strut front spar <NUM> into the fuselage <NUM> at the strut front attach point <NUM> of the strut-fuselage joint <NUM>. The strut rear fitting <NUM> extends aft of (i.e., toward the strut trailing edge <NUM>) the strut rear spar <NUM>. The strut rear fitting <NUM> is coupled to the strut rear spar <NUM> proximate the strut root <NUM>, and is configured to distribute load from the strut rear spar <NUM> into the fuselage <NUM> at the strut rear attach point <NUM> of the strut-fuselage joint <NUM>. By increasing the spacing between the strut front attach point <NUM> and strut rear attach point <NUM>, the strut front fitting <NUM> and the strut rear fitting <NUM> increase the structural efficiency of the strut-fuselage joint <NUM>, thereby reducing the magnitude of the reaction forces <NUM> (e.g., <FIG>), which translates into reduced structural mass of the strut-fuselage joint <NUM>.

In <FIG>, the strut front fitting <NUM> and the strut rear fitting <NUM> are each configured as plates. In the example shown, the plates are located at the neutral axis of the strut front spar <NUM> and the strut rear spar <NUM>. The strut front fitting <NUM> and the strut rear fitting <NUM> may be bonded, mechanically fastened, welded, or integrally machined respectively with the strut front spar <NUM> and the strut rear spar <NUM>. The strut front spar <NUM> and the strut rear spar <NUM> are straight in <FIG>. However, in other examples not shown, the strut front spar <NUM> and strut rear spar <NUM> may be kinked similar to the strut front and rear spars <NUM>, <NUM> of <FIG>.

Referring to <FIG>, shown is an arrangement for attaching the strut front fitting <NUM> and strut rear fitting <NUM> respectively to the strut front spar <NUM> and strut rear spar <NUM>. The strut front spar <NUM> and the strut rear spar <NUM> each have the above-described channel-shaped cross-section. However, the strut front spar <NUM> and strut rear spar <NUM> may have an alternative cross-sectional shape, such as an I-beam cross-sectional shape (not shown). The strut rear spar <NUM>, the strut upper skin panel <NUM>, and the strut lower skin panel <NUM> collectively form a strut box, which provides bending stiffness and torsional stiffness for the strut <NUM>. The strut front fitting <NUM> extends vertically between, and interconnects, the upper cap <NUM> and the lower cap <NUM> of the strut front spar <NUM>. The strut rear fitting <NUM> extends vertically between, and interconnects, the upper cap <NUM> and the lower cap <NUM> of the strut rear spar <NUM>.

In <FIG>, the strut front fitting <NUM> and the strut rear fitting <NUM> have a cross-sectional shape that is complementary to the cross-sectional shape respectively of the strut front spar <NUM> and strut rear spar <NUM>, which improves the transfer of tension load <NUM> and compression load <NUM> respectively from the strut front spar <NUM> and strut rear spar <NUM> into the strut-fuselage joint <NUM> (<FIG>). The strut front fitting <NUM> and the strut rear fitting <NUM> may be adhesively bonded and/or mechanically fastened respectively to the strut front spar <NUM> and strut rear spar <NUM>. The strut upper skin panel <NUM> and the strut lower skin panel <NUM> may optionally be stiffened by skin stiffeners <NUM> on an interior side of the strut <NUM>. In the example shown, each skin stiffener <NUM> has a T-shaped cross-section. However, the skin stiffeners <NUM> may have other cross-sectional shapes (e.g., a Z-shaped or hat-shaped cross section). The skin stiffeners <NUM> may be adhesively bonded and/or mechanically fastened to the strut upper skin panel <NUM> and the strut lower skin panel <NUM>. In another configuration, instead of skin stiffeners, one or more full-depth spars (not shown) may be installed, with each full-depth spar extending between the strut upper and lower skin panels <NUM>, <NUM>.

Referring to <FIG>, shown is an example of a strut A-frame structure <NUM> in which the strut spar inboard end <NUM> of the strut front spar <NUM> and the strut rear spar <NUM> has a spar slot <NUM> formed in the spar web <NUM> at the strut root <NUM> end. Each spar slot <NUM> extends along the neutral axis of the respective strut front spar <NUM> and strut rear spar <NUM>. The strut A-frame structure <NUM> includes a lug plate <NUM> (i.e., a shear plate) inserted within the spar slot <NUM> in the strut front spar <NUM> and the strut rear spar <NUM>. The lug plate <NUM> interconnects the strut front spar <NUM> and the strut rear spar <NUM>. As shown in <FIG>, the lug plate <NUM> extends forward of the strut front spar <NUM>, and extends aft of the strut rear spar <NUM>, thereby providing increased spacing between the strut front attach point <NUM> and strut rear attach point <NUM>.

In <FIG>, the lug plate <NUM> is coupled (e.g., via mechanical fasteners <NUM>) to the strut front spar <NUM> and strut rear spar <NUM> via a plurality of angle brackets <NUM>. The strut A-frame structure <NUM> further includes a plurality of strut lugs <NUM> extending in an inboard direction from the lug plate <NUM>. As shown in <FIG>, a plurality of strut lugs <NUM> are located forward of the strut spar inboard end <NUM> of the strut front spar <NUM>, and a plurality of strut lugs <NUM> are located aft of the strut spar inboard end <NUM> of the strut rear spar <NUM>. The strut lugs <NUM> are parallel to each other, and are spaced apart complementary to the spacing of a plurality of fuselage lugs <NUM> (e.g., <FIG>) protruding from the fuselage <NUM>.

Referring to <FIG>, shown is an example of a pinned joint <NUM> for coupling a strut <NUM> to the fuselage <NUM>. As mentioned above, the fuselage <NUM> has a plurality of parallel and spaced apart fuselage lugs <NUM> protruding in an outboard direction at the strut front attach point <NUM> (<FIG>) and at the strut rear attach point <NUM> (<FIG>). The strut lugs <NUM> are coupled to the fuselage lugs <NUM> via one or more pins <NUM>. For example, a pin <NUM> may be installed at the strut front attach point <NUM> and a pin <NUM> may be installed at the strut rear attach point <NUM>. Alternatively, a single common pin <NUM> may extend through the strut lugs <NUM> and fuselage lugs <NUM> of the strut front attach point <NUM> and strut rear attach point <NUM>. In other examples, the one or more pins <NUM> may each be configured in a coaxial pin arrangement (not shown) consisting of an inner pin within an outer pin, for fail-safety.

In <FIG>, the one or more pins <NUM> allow rotation or pivoting of the strut <NUM> about an axis parallel to the longitudinal axis <NUM> (<FIG>) of the aircraft <NUM>. The pinned joint <NUM> allows the strut <NUM> to pivot slightly in an upward and downward direction during changes in loading on the wing <NUM> (e.g., during takeoff, maneuvering, turbulence, landing, etc.), thereby reducing or eliminating bending loads at the strut-fuselage joint <NUM>. In contrast, <FIG> show an example of a fixed joint <NUM> for fixedly or non-rotatably coupling the strut <NUM> to the fuselage <NUM>, as described in greater detail below. As shown in <FIG>, the pinned joint <NUM> allows for larger amount of buckling <NUM> (<FIG>) of the strut <NUM>, relative to the magnitude of buckling <NUM> (<FIG>) of the strut <NUM> attached to the fuselage <NUM> via the fixed joint <NUM>. In this regard, the fixed joint <NUM> provides higher bucking load capability for the strut <NUM> relative to the pinned joint <NUM>. In addition, the fixed joint <NUM> may provide greater resistance to lateral torsional buckling of the strut <NUM>, as described below.

Referring to <FIG>, shown is an example of a pinned joint <NUM> coupling the strut <NUM> to the fuselage <NUM>. The strut <NUM> has the strut A-frame structure <NUM> described above and shown in <FIG>. In this regard, the strut A-frame structure <NUM> includes the above-described lug plate <NUM> that interconnects the strut front spar <NUM> and the strut rear spar <NUM>. The lug plate <NUM> extends through the spar slot <NUM> (<FIG>) formed in the inboard end of the strut front spar <NUM> and strut rear spar <NUM>. Angle brackets <NUM> are used for mechanically fastening the lug plate <NUM> to the strut front spar <NUM> and the strut rear spar <NUM>.

The lug plate <NUM> includes a plurality of the above-described strut lugs <NUM>, which are located forward of the strut front attach point <NUM>, and aft of the strut rear attach point <NUM>. The strut lugs <NUM> may be integrally formed (e.g., machined) with the lug plate <NUM>, or the strut lugs <NUM> may separate components that are attached (e.g., mechanically fastened, welded) to the lug plate <NUM>. As shown in <FIG>, the strut <NUM> includes a lug bracket <NUM> at the inboard edge of the lug plate <NUM>. The lug bracket <NUM> is shown oriented vertical or substantially vertical, or normal to the strut axis <NUM> and the strut chord. In addition, the lug bracket <NUM> extends parallel to the joint rotational axis defined by the pin <NUM>. The lug bracket <NUM> stabilizes the strut lugs <NUM>, and facilitates the transfer of load from the lug plate <NUM> into the strut lugs <NUM>. The lug plate <NUM>, lug plate <NUM>, and strut lugs <NUM> transfer into the fuselage <NUM> tension load <NUM> from the strut front spar <NUM>, and compression load <NUM> from the strut rear spar <NUM>. In addition, the lug plate <NUM> and strut lugs <NUM> facilitate the transfer of shear load between the strut <NUM> and the fuselage <NUM>.

Referring to <FIG>, shown in <FIG> is an example of net tension load <NUM> (i.e., pure axial load) applied by the strut <NUM> at the strut-fuselage joint <NUM>, as a result of the vertical moment Mz induced by the lifting force <NUM> (<FIG>) at the strut-wing joint <NUM>. <FIG> shows the vertical moment Mz on the strut <NUM> as a result of the lifting force <NUM>. For most flight conditions, the ratio of the vertical moment Mz to the axial load will be constant or generally constant. <FIG> is an axial load profile <NUM> of the tension load <NUM> on the plurality of strut lugs <NUM> at the strut front attach point <NUM>, and at the strut rear attach point <NUM>. As can be seen, the most highly loaded strut lugs <NUM> at each attach point <NUM>, <NUM> are those that are located in the middle of the plurality of strut lugs <NUM>.

<FIG> is a moment profile <NUM> of the moment at the strut front attach point <NUM> and at the strut rear attach point <NUM>. As can be seen, the moment peaks or generally peaks at the extreme ends of the strut-fuselage joint <NUM> (i.e., at the forward end, and at the aft end). The configuration of the strut lugs <NUM> at the strut front attach point <NUM> and strut rear attach point <NUM> can be tailored to achieve uniform or substantially uniform loads in the strut lugs <NUM> and fuselage lugs <NUM>, thereby providing an opportunity for increasing the structural efficiency of the strut-fuselage joint <NUM>, which may translate to reduce structural mass of the aircraft <NUM>.

Referring to <FIG>, shown is an example of a strut A-frame structure <NUM> having a lug plate <NUM> and strut lugs <NUM> similar to the above-described arrangement shown in <FIG>. In <FIG>, the lug plate <NUM> extends from the strut spar inboard end <NUM> a further distance outboard along the strut front spar <NUM> than the distance that the lug plate <NUM> extends along the strut rear spar <NUM>. Additional angle brackets <NUM> are included along the strut front spar <NUM> to facilitate the transfer of a higher tension load <NUM> from the strut front spar <NUM> into the lug plate <NUM>, relative to the tension load <NUM> in the strut front spar <NUM> of the arrangement shown in <FIG>.

Referring to <FIG>, shown is an example of a fixed joint <NUM> coupling a strut A-frame structure <NUM> to the fuselage <NUM>. The strut A-frame structure <NUM> includes a lug plate <NUM> coupled to the strut front spar <NUM> and strut rear spar <NUM> via angle brackets <NUM>, as described above. In addition, the strut A-frame structure <NUM> includes a strut end plate <NUM>. The strut end plate <NUM> is coupled to the strut spar inboard end <NUM> of the strut front spar <NUM> and the strut rear spar <NUM>. In the example shown, the strut end plate <NUM> extends across the edge of the lug plate <NUM>, and interconnects the strut front spar <NUM> and the strut rear spar <NUM>. The strut end plate <NUM> is attached (e.g., via mechanical fasteners <NUM>) to the fuselage <NUM>, thereby non-rotatably coupling the strut spar <NUM>, <NUM> to the fuselage <NUM>, such that the strut <NUM> is a cantilevered beam <NUM>, as shown in the above-described <FIG>. As mentioned above with regard to <FIG>, non-rotatably coupling the strut spars <NUM>, <NUM> to the fuselage <NUM> may improve the buckling load capability of the strut <NUM>, and may also suppress lateral-torsional buckling of the strut <NUM>, as described below.

Referring to <FIG>, shown is an example of a structural arrangement for attaching the strut <NUM> to the wing <NUM> at the strut-wing joint <NUM>, for the aircraft <NUM> of <FIG> show the structural arrangement as a pinned joint <NUM> between the strut <NUM> and the wing <NUM>. <FIG> illustrate the pinned joint <NUM> in the assembled state. <FIG> illustrate the configuration of the individual components that make up the pinned joint <NUM>.

As shown in <FIG>, the strut outboard ends <NUM> of the strut front spar <NUM> and strut rear spar <NUM> respectively have a front spar plate <NUM> and a rear spar plate <NUM>. The front spar plate <NUM> and the rear spar plate <NUM> each extend in an outboard direction and overlap each other, and are coupled together via mechanical fasteners <NUM>. Advantageously, the arrangement of the front spar plate <NUM> and the rear spar plate <NUM> provides a means for resolving the tension load <NUM> in the strut front spar <NUM> and the compression load <NUM> in the strut rear spar <NUM> into axial tension and shear load between the strut <NUM> and the wing <NUM>.

As shown in <FIG>, the front spar plate <NUM> is inserted into a spar slot <NUM> formed along the neutral axis in the strut outboard end <NUM> of the strut front spar <NUM>. <FIG> show the rear spar plate <NUM> inserted into a spar slot <NUM> formed along the neutral axis in the strut outboard end <NUM> of the strut rear spar <NUM>. <FIG> show an example where a spar plate doubler <NUM> is included with the rear spar plate <NUM> to facilitate compression load transfer between the strut rear spar <NUM> and the rear spar plate <NUM>. Although not shown, a similar spar plate doubler <NUM> may be included with the front spar plate <NUM> to facilitate tension load transfer between the strut front spar <NUM> and the front spar plate <NUM>. Use of spar plate doublers <NUM> may reduce the diameter and/or quantity of mechanical fasteners <NUM>, due to the increased (i.e., double) shear capacity of the mechanical fasteners <NUM> as a result of adding the spar plate doubler <NUM>.

In <FIG>, angle brackets <NUM> are used for mechanically fastening the front spar plate <NUM> to the strut front spar <NUM>. Similarly, angle brackets <NUM> are used to couple the rear spar plate <NUM> to the strut rear spar <NUM>. However the front and rear spar plates <NUM>, <NUM> may be respectively coupled to the strut front and rear spars <NUM>, <NUM> in any one of a variety of means. For example, the front and rear spar plates <NUM>, <NUM> may be integrally formed (e.g., machined) respectively with the strut front and rear spars <NUM>, <NUM>.

As shown in <FIG>, the front spar plate <NUM> has a plurality of strut lugs <NUM> protruding in an outboard direction. Likewise, <FIG> show a plurality of strut lugs <NUM> protruding from the rear spar plate <NUM>. The strut lugs <NUM> of the front spar plate <NUM> and the rear spar plate <NUM> are vertically or generally vertically oriented. As shown in <FIG>, the strut lugs <NUM> are spaced apart from each other complementary to the spacing of the wing lugs <NUM>, which protrude in an inboard direction from the underside of the wing <NUM>. The wing lugs <NUM> may be directly or indirectly coupled to the wing front spar <NUM> (not shown) and/or the wing rear spar <NUM> (not shown). The strut lugs <NUM> are rotatably coupled to the wing lugs <NUM> via a pin <NUM>, which is oriented parallel or approximately parallel to the longitudinal axis <NUM>. The pin <NUM> allows for upward and downward pivoting of the strut <NUM> during changes in loading on the wing <NUM>.

Referring back to <FIG>, the strut-wing joint <NUM> further includes at least one drag link <NUM> for accommodating shear loads between the wing <NUM> and the strut <NUM>. In the example shown, the spar front plate is coupled to the wing <NUM> via a front drag link <NUM>. The front drag link <NUM> extends in a forward direction from a plate front portion of the front spar plate <NUM>. Similarly, the rear spar plate <NUM> is coupled to the wing <NUM> via a rear drag link <NUM>. The rear drag link <NUM> extends in an aft direction from a plate aft portion of the rear spar plate <NUM>. As mentioned above, the coupling of the front spar plate <NUM> to the rear spar plate <NUM> resolves the tension load <NUM> and compression load <NUM> respectively in the strut front spar <NUM> and strut rear spar <NUM> into tension load <NUM> in the wing lugs <NUM>, and compression and tension respectively in the front drag link <NUM> and rear drag link <NUM>. The pin <NUM> transfers axial load (e.g., tension load <NUM>) between the strut lugs <NUM> and the wing lugs <NUM>.

Referring to <FIG>, shown are examples of a jury strut <NUM> that may be included with the strut-braced aircraft <NUM>. The jury strut <NUM> extends between the strut <NUM> and the wing <NUM>, and is included to suppress buckling <NUM> (<FIG>) of the strut <NUM> at high compression loads. When the aircraft <NUM> is viewed from the front as shown in <FIG>, the jury strut <NUM> is oriented perpendicularly or approximately (e.g., within <NUM> degrees) perpendicular to the strut <NUM>. The jury strut <NUM> is coupled to the strut <NUM> at a distance from the strut-fuselage joint <NUM> of two-thirds of the distance between the strut-fuselage joint <NUM> and the strut-wing joint <NUM> or approximately (e.g., within <NUM> percent) two-thirds of the distance between the strut-fuselage joint <NUM> and the strut-wing joint <NUM>.

As shown in <FIG>, the jury strut <NUM> may be coupled to the strut <NUM> proximate the strut front spar <NUM>. Such an arrangement may allow for lateral pivoting movement of the strut <NUM>, as shown in <FIG>. Because the strut rear spar <NUM> is in compression, it may have a tendency to buckle via lateral-torsional buckling. <FIG> illustrate an arrangement in which the jury strut <NUM> has a width that is at least as wide as the distance between the strut front spar <NUM> and the strut rear spar <NUM> at the location wherein the jury strut <NUM> is coupled to the strut <NUM>. As a result, the jury strut <NUM> couples both the strut front spar <NUM> and the strut rear spar <NUM> to the wing <NUM>, and thereby has the capability to suppress lateral-torsional buckling of the strut <NUM>.

Referring to <FIG>, shown is an example of a wing-wing joint <NUM> at the location where the wings <NUM> attach to the fuselage <NUM>. As shown in <FIG>, each wing <NUM> includes the above-mentioned wing front spar <NUM> and wing rear spar <NUM>. In addition, the wing <NUM> also has a wing upper skin panel <NUM> (<FIG>) and a wing lower skin panel <NUM> (<FIG>). The wing front spar <NUM>, the wing rear spar <NUM>, the wing upper skin panel <NUM>, and the wing lower skin panel <NUM> collectively form a wing box, which provides bending stiffness and torsional stiffness for the wings <NUM>.

The wing front spar <NUM> and the wing rear spar <NUM> of each wing <NUM> have a wing spar inboard end <NUM>. A spar slot <NUM> is formed in the wing spar inboard end <NUM> of the wing front spar <NUM> and the wing rear spar <NUM>. Each wing <NUM> further includes a wing shear plate <NUM> interconnecting the wing spar inboard ends <NUM> of the wing front spar <NUM> and the wing rear spar <NUM>. The wing shear plate <NUM> is received within the spar slots <NUM>, and is mechanically coupled to the wing front spar <NUM> and the wing rear spar <NUM> via angle brackets <NUM> or other suitable means.

In addition, each wing <NUM> includes one or more wing lugs <NUM> protruding in an inboard direction from the wing shear plate <NUM>. In the example shown, a plurality of wing lugs <NUM> are located forward of the wing front spar <NUM>, and a plurality of wing lugs <NUM> are located aft of the wing rear spar <NUM>. Coupled to the inboard edge of each wing shear plate <NUM> is a lug bracket <NUM> for interconnecting and mechanically stabilizing the wing lugs <NUM>. On each wing <NUM>, the lug bracket <NUM> is connected to the wing front spar <NUM> and the wing front spar <NUM> respectively at the wing front attach point <NUM> and at the wing rear attach point <NUM>. The wing lugs <NUM> of one wing <NUM> are spaced apart complementary to the wing lugs <NUM> of the opposite wing <NUM>. The wing lugs <NUM> of the opposing wings <NUM> are configured to be rotatably coupled via one or more pins <NUM>, similar to the pins described above for a pinned joint <NUM> configuration of the strut-fuselage joint <NUM>. In the example shown, the wing-wing joint <NUM> includes a separate pin <NUM> at the wing front attach point <NUM>, and a separate pin <NUM> at the wing rear attach point <NUM>. The pins <NUM> allow the wings <NUM> to pivot in response to various loading conditions, while resisting the tension load <NUM> in the wing front spars <NUM>, the compression load <NUM> in the wing rear spars <NUM>, and the vertical moment Mz resulting from the lifting force <NUM> on each wing <NUM>.

Referring to <FIG>, shown is a method <NUM> of enhancing the performance of an aircraft <NUM> configured as shown in <FIG>. Step <NUM> of the method <NUM> includes generating, using a wing <NUM>, a lifting force <NUM> when air passes over the wing <NUM>. As described above, each wing <NUM> of the aircraft <NUM> is coupled to the fuselage <NUM> at a wing-fuselage joint <NUM>, and each wing <NUM> is supported by a strut <NUM> coupled to the fuselage <NUM> at a strut-fuselage joint <NUM> located below and at least partially aft of the wing-fuselage joint <NUM>, as shown in <FIG>, and described above.

Step <NUM> of the method <NUM> includes the wing-strut arrangement inducing a vertical moment Mz about the wing-fuselage joint <NUM> in response to the lifting force <NUM>. As described above, the lifting force <NUM> is generated as a result of air moving over the wing <NUM>. The vertical moment Mz is created due to the non-parallel relationship between the wing axis <NUM> and the strut axis <NUM> (<FIG>), and tends to urge the wing <NUM> to pivot in an aftward direction.

Step <NUM> of the method <NUM> includes counteracting the vertical moment Mz using the structural arrangement of the wing <NUM> and/or using the structural arrangement of the strut <NUM>. In some examples, counteracting the vertical moment Mz comprises counteracting a portion of the vertical moment Mz using the structural arrangement of the wing <NUM>, and counteracting a portion of the vertical moment Mz using the structural arrangement of the strut <NUM>. The combination of the vertical moment Mz counteracted by the wing <NUM> and the vertical moment Mz counteracted by the strut <NUM> is equivalent to the total magnitude of the vertical moment Mz.

The above-described <FIG> illustrate a structural arrangement wherein the wing <NUM> and the strut <NUM> are each configured as a cantilevered beam <NUM> capable of resisting a portion of the vertical moment Mz. In other examples, <FIG> illustrate a structural arrangement wherein the wing <NUM> has a wing A-frame structure <NUM>, and the strut <NUM> has a strut A-frame structure <NUM>. The combination of the wing A-frame structure <NUM> and the strut A-frame structure <NUM> defines a double tetrahedron structure, and each of the wing A-frame structure <NUM> and the strut A-frame structure <NUM> is capable of resisting a portion of the vertical moment Mz.

In some examples, step <NUM> comprises counteracting equivalent or substantially equivalent portions (e.g., <NUM> percent) of the vertical moment Mz using the wing <NUM> and the strut <NUM>. In other examples, step <NUM> comprises counteracting more than <NUM> percent of the vertical moment Mz using the strut <NUM>, and counteracting a remaining portion of the vertical moment Mz using the wing <NUM>. Referring to the example of <FIG>, step <NUM> of counteracting the vertical moment Mz comprises carrying tension load <NUM> and bending load in the strut <NUM>, which is configured as a single cantilevered beam <NUM> fixedly coupled to the fuselage <NUM> at the strut-fuselage joint <NUM>.

Referring to <FIG>, step <NUM> of counteracting the vertical moment Mz comprises carrying tension load <NUM> and compression load <NUM> respectively in the strut front spar <NUM> and the strut rear spar <NUM> of the above-mentioned strut A-frame structure <NUM>. As described above, the strut front spar <NUM> and strut rear spar <NUM> each have a strut spar inboard end <NUM> and a strut spar outboard end <NUM>. The strut spar outboard ends <NUM> converge at the strut-wing joint <NUM>, and the strut spar inboard ends <NUM> are spaced apart from each other at the strut-fuselage joint <NUM>. Step <NUM> additionally includes transferring the tension load <NUM> and the compression load <NUM> into the fuselage <NUM> at the strut front attach point <NUM> and the strut rear attach point <NUM> of the strut-fuselage joint <NUM>.

Referring still to the arrangement shown in <FIG>, the method <NUM> further comprises reacting shear load at the strut-fuselage joint <NUM> (e.g., at the strut front attach point <NUM> and the strut rear attach point <NUM>) using an inboard end connector <NUM> interconnecting the strut spar inboard ends <NUM>. As described above, the shear reaction results from the tension load <NUM> and the compression load <NUM> in the strut front spar <NUM> and the strut rear spar <NUM>. As shown schematically in <FIG>, the step of transferring the shear reaction into the fuselage <NUM> comprises reacting the shear load at a single location along the inboard end connector <NUM>.

Referring to the arrangement of <FIG>, the steps of carrying the tension load <NUM> and carrying the compression load <NUM> comprise, carrying the tension load <NUM> and the compression load <NUM> respectively in the strut front spar <NUM> and the strut rear spar <NUM> of the strut <NUM> having a strut leading edge <NUM> and a strut trailing edge <NUM>. As shown in the figures, the strut front spar <NUM> and the strut rear spar <NUM> each extend from the strut root <NUM> at the strut-fuselage joint <NUM>, to the strut outboard end <NUM> at the strut-wing joint <NUM>. As described above, the strut leading edge <NUM> and the strut trailing edge <NUM> define a tapered shape of the strut <NUM> from the strut root <NUM> to the strut outboard end <NUM>. As shown in <FIG>, the tapered shape is complementary to the A-frame structure of the strut front spar <NUM> and the strut rear spar <NUM>. At least a portion of the strut leading edge <NUM> is aft of a wing trailing edge <NUM> of the wing <NUM>.

Referring to the arrangement of <FIG>, the steps of carrying the tension load <NUM> and carrying the compression load <NUM> respectively comprise carrying the tension load <NUM> and the compression load <NUM> respectively in the strut front spar <NUM> and the strut rear spar <NUM>, each of which is contiguous, and each has at least one kink <NUM> dividing the strut front spar <NUM> and the strut rear spar <NUM> into a strut spar inboard section <NUM> and a strut spar outboard section <NUM>. As described above, the strut spar inboard section <NUM> of the strut front spar <NUM> is angled forwardly relative to the strut spar outboard section <NUM> of the strut front spar <NUM>, and the strut spar inboard section <NUM> of the strut rear spar <NUM> is angled aftwardly relative to the strut spar outboard section <NUM> of the strut front spar <NUM>, to thereby increase the distance between the strut spar inboard ends <NUM>.

Referring still to <FIG>, carrying the tension load <NUM> and carrying the compression load <NUM> respectively comprise distributing the tension load <NUM> and the compression load <NUM> respectively into the strut front attach point <NUM> and the strut rear attach point <NUM> using a kink connector beam <NUM>, a kink plate <NUM>, and/or a pair of diagonal members <NUM>. As shown and described above, the kink connector beam <NUM> extends between and interconnects the kinks <NUM> respectively of the strut front spar <NUM> and the strut rear spar <NUM>. The kink plate <NUM> extends between and interconnects the strut spar inboard section <NUM> of the strut front spar <NUM> to the strut spar inboard section <NUM> of the strut rear spar <NUM>. Each one of the diagonal members <NUM> extends from one of the strut spar inboard ends <NUM> of one of the strut spars <NUM>, <NUM>, to the kink <NUM> of the remaining strut spar <NUM>, <NUM>.

Referring to the arrangement of <FIG>, the method <NUM> may further include distributing the tension load <NUM> into the strut front attach point <NUM> using a strut front fitting <NUM> extending forward of, and coupled to, the strut front spar <NUM> proximate the strut root <NUM>. In addition, the method <NUM> may include distributing the compression load <NUM> into the strut rear attach point <NUM> using a strut rear fitting <NUM> extending aft of, and coupled to, the strut rear spar <NUM> proximate the strut root <NUM>. As described above, the steps of distributing the tension load <NUM> and distributing the compression load <NUM> are respectively performed by the strut front fitting <NUM> and the strut rear fitting <NUM> configured as plates. In the example of <FIG>, the plates of the strut front fitting <NUM> and the strut rear fitting <NUM> are located at the neutral axis respectively of the strut front spar <NUM> and the strut rear spar <NUM>.

Referring to the arrangement of <FIG>, the steps of distributing the tension load <NUM> and distributing the compression load <NUM> are respectively performed by the strut front fitting <NUM> and the strut rear fitting <NUM> extending between and interconnecting the upper cap <NUM> and the lower cap <NUM> respectively of the strut front spar <NUM> and the strut rear spar <NUM>. As described above, the strut front spar <NUM> and the strut rear spar <NUM> each have a channel-shaped cross-section in which the upper cap <NUM> and the lower cap <NUM> are interconnected by a web. As shown in <FIG>, the strut front fitting <NUM> is nested within the channel-shaped cross-section of the strut front spar <NUM>, and is mechanically fastened to the strut front spar <NUM>. The strut rear fitting <NUM> is coupled to the strut rear spar <NUM> in a similar manner.

For the arrangement of <FIG>, the method <NUM> further comprises distributing the tension load <NUM> into the strut front attach point <NUM>, and distributing the compression load <NUM> into the strut rear attach point <NUM>, using a lug plate <NUM> insertable within a spar slot <NUM> in the strut front spar <NUM> and the strut rear spar <NUM>. As described above, the lug plate <NUM> interconnects the strut front spar <NUM> and the strut rear spar <NUM>. To increase the spacing between the strut front attach point <NUM> and strut rear attach point <NUM>, the lug plate <NUM> extends forward of the strut front spar <NUM>, and aft of the strut rear spar <NUM>. The lug plate <NUM> has one or more strut lugs <NUM> located forward of the strut front spar <NUM>, and one or more strut lugs <NUM> located aft of the strut rear spar <NUM>. The strut lugs <NUM> are rotatably coupled, via one or more pins <NUM>, to a plurality of fuselage lugs <NUM> protruding from the fuselage <NUM> at the strut front attach point <NUM> and the strut rear attach point <NUM>, as shown in <FIG> and described above.

Referring to <FIG>, in an alternative structural arrangement of the strut A-frame structure <NUM>, step <NUM> of counteracting the vertical moment Mz comprises carrying tension load <NUM> and compression load <NUM> respectively in a strut leading edge member <NUM> and a strut trailing edge member <NUM> respectively defining the strut leading edge <NUM> and the strut trailing edge <NUM> of the strut <NUM>. As shown in the above-described <FIG>, the strut leading edge member <NUM> and the strut trailing edge member <NUM> are interconnected by the strut upper skin panel <NUM> and the strut lower skin panel <NUM>. As shown in <FIG>, the strut leading edge member <NUM> and the strut trailing edge member <NUM> each have a strut member inboard end <NUM> and a strut member outboard end <NUM>. The strut member inboard ends <NUM> are spaced apart from each other at the strut-fuselage joint <NUM>, and the strut member outboard ends <NUM> converge at the strut-wing joint <NUM>. Referring to <FIG> showing a still further structural arrangement of the strut A-frame structure <NUM>, the steps of carrying the tension load <NUM> and carrying the compression load <NUM> respectively comprise carrying the tension load <NUM> and carrying the compression load <NUM> using reinforcing fibers <NUM> (e.g., boron fibers) extending continuously between the strut root <NUM> and the strut outboard end <NUM> of the strut front spar <NUM> and the strut rear spar <NUM>.

As an alternative to the pinned joint <NUM> of <FIG>, the steps of transferring the tension load <NUM> and transferring the compression load <NUM> respectively comprise transferring the tension load <NUM> and transferring the compression load <NUM> via a fixed joint <NUM>, coupling the strut <NUM> to the fuselage <NUM> at the strut front attach point <NUM> and the strut rear attach point <NUM>. Transferring the tension load <NUM> and transferring the compression load <NUM> are performed via a strut end plate <NUM>. As described above, the strut end plate <NUM> is coupled to the strut spar inboard end <NUM> of the strut front spar <NUM> or the strut rear spar <NUM>. In the example shown, the strut end plate <NUM> is attached to the fuselage <NUM> via mechanical fasteners <NUM>.

Referring to the example of the strut-wing joint <NUM> shown in <FIG>, the method <NUM> further comprises transferring the tension load <NUM> and the compression load <NUM> into the wing <NUM> using a front spar plate <NUM> and a rear spar plate <NUM> respectively extending from the strut front spar <NUM> and the strut rear spar <NUM>. As described above, the front spar plate <NUM> and rear spar plate <NUM> are coupled together in overlapping relation. The front spar plate <NUM> and the rear spar plate <NUM> each have one or more strut lugs <NUM> protruding in an outboard direction. The method <NUM> additionally includes resolving, via the front spar plate <NUM> and the rear spar plate <NUM>, the tension load <NUM> and the compression load <NUM> respectively in the strut front spar <NUM> and strut rear spar <NUM> into axial tension transmitted into a plurality of wing lugs <NUM>. As described above, the wing lugs <NUM> protrude in an inboard direction, and are rotatably coupled to the strut lugs <NUM> via a pin <NUM>. The resolution of the tension load <NUM> and compression load <NUM> respectively in the strut front spar <NUM> and strut rear spar <NUM> also includes transmitting shear between the wing <NUM> and strut <NUM> via at least one drag link. In the example shown, compression load <NUM> and tension load <NUM> are respectively transferred via the front drag link <NUM> and the rear drag link <NUM>. As shown in <FIG>, the front drag link <NUM> and the rear drag link <NUM> are oriented in a forward-aft direction. The front drag link <NUM> and the rear drag link <NUM> couple the wing <NUM> respectively to the front spar plate <NUM> and the rear spar plate <NUM>.

Referring to <FIG>, the method <NUM> further comprises suppressing buckling of each strut <NUM> using a jury strut <NUM> extending between the strut <NUM> and the wing <NUM>. As described above, each jury strut <NUM> suppresses buckling of the strut <NUM> (i.e., the main strut) at high compression load. The step of suppressing the buckling of the strut <NUM> is performed with the jury strut <NUM> coupled to the strut <NUM> at a distance from the strut-fuselage joint <NUM> of two-thirds or approximately two-thirds of the distance between the strut-fuselage joint <NUM> and the strut-wing joint <NUM>. In some examples, suppressing the buckling of the strut <NUM> comprises suppressing lateral-torsional buckling of the strut <NUM> using the jury strut <NUM> having a jury strut <NUM> width that is at least as wide as the distance between the strut front spar <NUM> and the strut rear spar <NUM>.

Referring to <FIG>, the method <NUM> may comprise counteracting at least a portion of the vertical moment Mz using the wing <NUM>, by carrying tension load <NUM> and compression load <NUM> respectively in the wing front spar <NUM> and the wing rear spar <NUM>. As described above, the wing front spar <NUM> and the wing rear spar <NUM> each have a wing spar inboard end <NUM> at the wing-fuselage joint <NUM>. Each wing <NUM> includes a wing shear plate <NUM> interconnecting the wing spar inboard ends <NUM> of the wing front spar <NUM> and the wing rear spar <NUM>. The wing shear plates <NUM> each have protruding wing lugs <NUM> that are interconnected via a pinned joint <NUM> using one or more pins <NUM>.

Claim 1:
An aircraft (<NUM>), comprising:
a fuselage (<NUM>);
a wing (<NUM>) coupled to the fuselage (<NUM>) at a wing-fuselage joint (<NUM>), wherein the wing (<NUM>) generates a lifting force (<NUM>) when air passes over the wing (<NUM>); and
a strut (<NUM>) coupled to the fuselage (<NUM>) at a strut-fuselage joint (<NUM>) and coupled to the wing (<NUM>) at a strut-wing joint (<NUM>), the strut-fuselage joint (<NUM>) located below and at least partially aft of the wing-fuselage joint (<NUM>), wherein the strut (<NUM>) comprises an A-frame structure (<NUM>) having a strut front spar (<NUM>) and a strut rear spar (<NUM>), each having a strut spar inboard end (<NUM>) and a strut spar outboard end (<NUM>), wherein the strut spar outboard ends (<NUM>) converge at the strut-wing joint (<NUM>);
wherein:
the lifting force (<NUM>) induces a vertical moment about the wing-fuselage joint (<NUM>) due to the location of the strut-fuselage joint (<NUM>) below and at least partially aft of the wing-fuselage joint (<NUM>);
the strut front spar (<NUM>) and the strut rear spar (<NUM>) are respectively configured to carry tension load (<NUM>) and compression load (<NUM>) in response to the vertical moment induced by the lifting force (<NUM>);
the strut spar inboard ends (<NUM>) are spaced apart from each other at the strut-fuselage joint (<NUM>), and are configured to transfer the tension load (<NUM>) and the compression load (<NUM>) into the fuselage (<NUM>) at a strut front attach point (<NUM>) and a strut rear attach point (<NUM>) of the strut-fuselage joint (<NUM>); and
at least one of the wing (<NUM>) and the strut (<NUM>) has a structural arrangement configured to counteract the vertical moment.