Patent Description:
Aircraft, including fixed-wing aircraft and rotary-wing aircraft, employ a variety of aerodynamic control surfaces, such as ailerons, air brakes, elevators, flaps, rudders, slats, spoilers and the like. By manipulating one or more of the aerodynamic control surfaces, a pilot may control the lift generated by the aircraft, such as during takeoff, climbing, descending and landing, as well as the aircraft's orientation about its pitch, roll, and yaw axes. For example, the trailing edge of a wing of a fixed-wing aircraft typically includes one or more flaps, with the flaps being moveable between retracted and extended positions. At cruise, the flaps are typically maintained in a retracted position. When extended, the flaps increase the camber of the wing. Therefore, during takeoff, climbing, descending, or landing, the flaps may be extended, either partially or fully, to increase the maximum lift coefficient and effectively reduce the stalling speed of the aircraft. Said aerodynamic control surfaces are typically airfoils formed of composite materials, and thus are referred to herein as structural composite airfoils.

In general, a composite material is a structure that is formed from two or more constituent component materials with different physical and/or chemical properties that, when combined, produce a composite material having characteristics that are different than the characteristics of the individual components materials. As an example, one type of composite material is carbon fiber reinforced plastic ("CFRP"). CFRP generally includes one or more composite layers or plies laminated together to form a sheet, laminate or layup. Each of the composite layers or plies can include a reinforcement material and a matrix material. The matrix material surrounds, binds and supports the reinforcement material. The reinforcement material provides structural strength to the matrix material and the CFRP. The matrix material is generally a non-conductive polymer such as an epoxy resin. The reinforcement material generally consists of strands of carbon fiber, which are electrically conductive.

Structural composite airfoils, such as flaps, have an aerodynamic cross-sectional profile that is typically formed by connecting an upper skin to a lower skin proximate both the leading edge and the trailing edge of the structural composite airfoil. In conventional construction of inboard and outboard flaps, for example, a primary structural element of the flap is defined by the upper and lower skins being coupled to three spars that extend the width of the flap. The leading edge of the structural composite airfoil (which typically includes a bullnose shape), and the trailing edge (which is tapered to a thin cross-section) are typically outside of the primary structural element, forming respective secondary structural elements of the flap. Various fasteners and components (e.g., splice straps and/or nutplates) are used to secure the upper and lower skins to the spars and other structures that form the flap. Large numbers of fasteners can increase costs, manufacturing cycle time, and weight of the resulting assemblies. Accordingly, those skilled in the art continue research and development efforts directed to improving structural composite airfoils and the manufacturing thereof.

<CIT>, in accordance with its abstract, states a closed-angle composite airfoil spar is provided for an airfoil assembly. The composite airfoil spar comprises a web portion having a thickness. The composite airfoil spar also comprises a flange portion having a thickness. The flange portion extends transverse to the web portion. The composite airfoil spar may further comprise a radius portion interconnecting the web and flange portions. The radius portion is an acceptable amount thinner relative to thickness of the web portion and thickness of the flange portion based on design requirements and material properties.

<CIT>, in accordance with its abstract, states an aerodynamic control surface including an upper panel having an upper panel aft end portion, a lower panel having a lower panel aft end portion, mechanical fasteners connecting the upper panel aft end portion to the lower panel aft end portion, and a fairing having a fairing forward end portion and a fairing aft end portion, wherein the fairing forward end portion is connected to either the upper panel or the lower panel, and wherein the fairing aft end portion is connected to the other of the upper panel or the lower panel.

Structural composite airfoils and related methods of forming said structural composite airfoils as disclosed herein may reduce fastener counts, improve airfoil aerodynamic surfaces, and/or simplify manufacturing processes for structural composite airfoils.

There is disclosed herein a structural composite airfoil having a leading edge and a trailing edge, the structural composite airfoil comprising: a primary structural element extending from a leading edge region to a trailing edge region, wherein the leading edge region is adjacent the leading edge of the structural composite airfoil, wherein the primary structural element comprises: an upper skin panel; a lower skin panel; an internal volume defined between the upper skin panel and the lower skin panel; and a front C-channel spar comprising an upper flange coupled to the upper skin panel, wherein the front C-channel spar further comprises a lower flange coupled to the lower skin panel, wherein a first channel of the front C-channel spar faces the leading edge of the structural composite airfoil, wherein the upper flange forms a first angle with an elongated span of the front C-channel spar, wherein the lower flange forms a second angle with the elongated span, and wherein the first angle is acute; a secondary structural element defining the trailing edge of the structural composite airfoil; a leading edge skin panel defining the leading edge of the structural composite airfoil and positioned adjacent the leading edge region of the primary structural element, wherein a first end region of the leading edge skin panel is coupled to the upper flange of the front C-channel spar, wherein a second end region of the leading edge skin panel is coupled to the lower flange of the front C-channel spar, and wherein the leading edge skin panel has a bullnose shape; and a trailing edge closeout cover, wherein: a first cover end region of the trailing edge closeout cover is bonded to the lower skin panel, and the first cover end region of the trailing edge closeout cover is recessed into the lower skin panel; and a second cover end region of the trailing edge closeout cover comprises an integral wedge coupled to the upper skin panel.

The upper flange may be angled with respect to the elongated span to be complementary to the first end region of the leading edge skin panel.

The lower flange may be angled to be complementary to the second end region of the leading edge skin panel.

The upper skin panel may be abutted to the leading edge skin panel.

The lower skin panel may be abutted to the leading edge skin panel.

The leading edge skin panel may interface with the upper skin panel without a splice strap.

The leading edge skin panel may interface with the lower skin panel (<NUM>) without a/the splice strap.

The structural composite airfoil may further comprise a plurality of fasteners coupling the front C-channel spar to the upper skin panel and the lower skin panel, wherein each fastener of the plurality of fasteners is not blind, such that each fastener of the plurality of fasteners is accessible while the front C-channel spar is secured to the upper skin panel and the lower skin panel.

The upper skin panel may be coupled to the upper flange of the front C-channel spar without a nutplate.

The lower skin panel may be coupled to the lower flange of the front C-channel spar without a/the nutplate.

At least a portion of the upper skin panel may be core stiffened.

At least a portion of the lower skin panel may be core stiffened.

The upper skin panel may comprise fiberglass or carbon fiber.

The lower skin panel may comprise fiberglass or carbon fiber.

The structural composite airfoil may have a length, and wherein a position along the length may be defined by a percentage of the distance along the length from the leading edge.

The front C-channel spar may be positioned between <NUM>% and <NUM>% of the length away from the leading edge.

The front C-channel spar may be positioned at <NUM>% or at about <NUM>% of the length away from the leading edge.

A/the middle C-channel spar may be positioned between <NUM>% and <NUM>% of the length away from the leading edge.

A/the middle C-channel spar may be positioned at <NUM>% or at about <NUM>% of the length away from the leading edge.

A/the rear C-channel spar may be positioned between <NUM>% and <NUM>% of the length away from the leading edge, and/or between <NUM>% and <NUM>% of the length away from the leading edge.

A/the rear C-channel spar may be positioned at <NUM>% or at about <NUM>% of the length away from the leading edge.

The secondary structural element may comprise a duckbill closeout.

The secondary structural element may comprise a bonded closeout.

The secondary structural element may comprise a riveted closeout.

The lower skin panel may comprise a lower leading edge end and a lower trailing edge end, wherein the lower trailing edge end is opposite the lower leading edge end.

The lower trailing edge end may form an integral Z-spar.

The primary structural element may comprise an/the integral Z-spar.

The integral Z-spar may be formed by the lower skin panel within the trailing edge region of the primary structural element.

The integral Z-spar may comprise a joggle configured to receive a portion of a trailing edge closeout cover.

The integral Z-spar may comprise a first bend, a second bend, and a first Z-spar segment extending between the first bend and the second bend.

The first Z-spar segment may be perpendicular (or substantially perpendicular) to the lower skin panel and/or perpendicular (or substantially perpendicular) to the upper skin panel.

The integral Z-spar may further comprise a second Z-spar segment extending aft of the second bend, wherein the second Z-spar segment is coupled to the upper skin panel.

The second Z-spar segment may be adjacent an interior surface of the upper skin panel.

The second Z-spar segment may be coupled to the upper skin panel via a Z-spar fastener, wherein the Z-spar fastener is recessed into the upper skin panel, and wherein the Z-spar fastener extends through the second Z-spar segment.

A/the joggle of the integral Z-spar may be forward of the first bend.

There is also disclosed herein an aircraft comprising the structural composite airfoil as described above.

There is also disclosed herein a trailing edge flap for an aircraft comprising the structural composite airfoil as described above.

There is also disclosed herein a method of assembling a structural composite airfoil, the method comprising: coupling an upper skin panel to a front C-channel spar, wherein the structural composite airfoil extends from a leading edge to a trailing edge, wherein a first channel of the front C-channel spar faces the leading edge of the structural composite airfoil, wherein the front C-channel spar comprises an upper flange, a lower flange, and an elongated span extending between the upper flange and the lower flange, wherein the coupling the upper skin panel to the front C-channel spar comprises coupling the upper skin panel to the upper flange of the front C-channel spar , and wherein the upper flange forms an acute angle with the elongated span; coupling a lower skin panel to the front C-channel spar such that an internal volume is defined between the upper skin panel and the lower skin panel, wherein the upper skin panel, the lower skin panel, and the front C-channel spar together form at least a portion of a primary structural element of the structural composite airfoil; coupling a leading edge skin panel to the front C-channel spar, wherein the leading edge skin panel defines the leading edge of the structural composite airfoil, wherein the coupling the leading edge skin panel comprises coupling a first end region of the leading edge skin panel to the upper flange of the front C-channel spar, wherein the coupling the leading edge skin panel further comprises coupling a second end region of the leading edge skin panel to the lower flange of the front C-channel spar, wherein the leading edge skin panel has a bullnose shape; and coupling a trailing edge closeout cover to the lower skin panel, wherein a first cover end region of the trailing edge closeout cover is bonded to the lower skin panel, the first cover end region of the trailing edge closeout cover is recessed into the lower skin panel; and a second cover end region of the trailing edge closeout cover comprises an integral wedge coupled to the upper skin panel.

With reference to <FIG>, one or more structural composite airfoils <NUM> may be included in an apparatus <NUM>. Structural composite airfoils <NUM> may be utilized in many different industries and applications, such as the aerospace, automotive, architecture, marine, wind power generation, remote control aircraft, military, recreation, and/or motorsport industries. In <FIG>, an example of apparatus <NUM> that may include one or more structural composite airfoils <NUM> generally is illustrated in the form of an aircraft <NUM>. Aircraft <NUM> may take any suitable form, including commercial aircraft, military aircraft, or any other suitable aircraft. While <FIG> illustrates aircraft <NUM> in the form of a fixed-wing aircraft, other types and configurations of aircraft are within the scope of aircraft <NUM> according to the present disclosure, including (but not limited to) rotorcraft and helicopters.

Apparatus <NUM> (e.g., aircraft <NUM>) may include one or more structural composite airfoils <NUM>. As illustrative, non-exclusive examples, structural composite airfoils <NUM> may be utilized in wings <NUM> (e.g., flaps <NUM>, which may be inboard or outboard flaps), though other components of aircraft <NUM>, such as horizontal stabilizers <NUM>, vertical stabilizers <NUM>, and other components additionally or alternatively may include one or more structural composite airfoils <NUM>. Other applications in aircraft <NUM> (or other apparatus <NUM>) for structural composite airfoils <NUM> may include other wing control surfaces, ailerons, flaperons, air brakes, elevators, slats, spoilers, rudders, canards, and/or winglets. In other industries, examples of apparatus <NUM> including one or more structural composite airfoils <NUM> may include or be a portion of space satellites, transit vehicles, shipping containers, rapid transit vehicles, automobile bodies, propeller blades, turbine blades, and/or marine vehicles (e.g., sailboats), among others.

<FIG> provides illustrative, non-exclusive examples of structural composite airfoils <NUM> according to the present disclosure. In general, elements that are likely to be included are illustrated in solid lines, while elements that are optional are illustrated in dashed lines. However, elements that are shown in solid lines are not essential to all examples, and an element shown in solid lines may be omitted from a particular example without departing from the scope of the present disclosure.

Structural composite airfoil <NUM> has a leading edge <NUM> and a trailing edge <NUM>, and generally includes a primary structural element <NUM> and a secondary structural element <NUM>. As used herein, a "primary structural element" is an element or structure which carries flight, ground, or pressurization loads, and whose failure would reduce the structural integrity of the apparatus or assembly of which structural composite airfoil <NUM> is a part. As used herein, a "secondary structural element" is an element or structure whose failure does not affect the safety of the apparatus or assembly of which structural composite airfoil <NUM> is a part.

Primary structural element <NUM> extends from a leading edge region <NUM> to a trailing edge region <NUM>. As shown in <FIG>, leading edge region <NUM> is adjacent leading edge <NUM> of structural composite airfoil <NUM>, but leading edge region <NUM> may not actually define leading edge <NUM>. Leading edge region <NUM> may be said to be the region of primary structural element <NUM> that is closest to leading edge <NUM>. Similarly, trailing edge region <NUM> may be said to be the region of primary structural element <NUM> that is closest to trailing edge <NUM>, though trailing edge region <NUM> of primary structural element <NUM> does not define trailing edge <NUM> of structural composite airfoil <NUM>. As used herein, a first element or structure is said to be "aft" of another element or structure if the first element or structure is positioned closer to trailing edge <NUM> than is the other element or structure. Similarly, as used herein, a first element or structure is said to be "forward" of another element or structure if the first element or structure is positioned closer to leading edge <NUM> than is the other element or structure.

Primary structural element <NUM> includes at least an upper skin panel <NUM>, a lower skin panel <NUM>, and a front C-channel spar <NUM>. An internal volume <NUM> is defined between upper skin panel <NUM> and lower skin panel <NUM>. Front C-channel spar <NUM> includes an upper flange <NUM> and a lower flange <NUM>, with upper flange <NUM> being coupled to upper skin panel <NUM>, and lower flange <NUM> being coupled to lower skin panel <NUM>. A first channel <NUM> of front C-channel spar <NUM> faces leading edge <NUM> of structural composite airfoil <NUM>. This arrangement of front C-channel spar <NUM> with respect to leading edge <NUM> may permit effective coupling of a leading edge skin panel <NUM> to upper skin panel <NUM> and lower skin panel <NUM> (via front C-channel spar <NUM>) without forming any joggles in upper skin panel <NUM> or lower skin panel <NUM>, thereby potentially reducing complexities in manufacturing upper skin panel <NUM> and lower skin panel <NUM>.

Upper flange <NUM> forms a first angle <NUM> with an elongated span <NUM> of front C-channel spar, and lower flange <NUM> forms a second angle <NUM> with elongated span <NUM>, with first channel <NUM> being defined by upper flange <NUM>, lower flange <NUM>, and elongated span <NUM>. First angle <NUM> and/or second angle <NUM> may be acute angles in some examples of structural composite airfoil <NUM>. Typical conventional airfoil constructions would involve such angles being greater than ninety degrees to facilitate removal of the part from the tool, and/or the channel of the front spar would be arranged facing the trailing edge of the airfoil. Examples of presently disclosed structural composite airfoils <NUM> may advantageously provide for interfacing between components or elements (e.g., interfacing leading edge skin panel <NUM> and upper flange <NUM>) without forming joggles in upper skin panel <NUM> or lower skin panel <NUM> or utilizing splice straps, and/or may allow for a part count reduction by reducing or eliminating the number of splice straps, nutplates, and/or other fasteners used in assembling structural composite airfoils <NUM>. Additionally or alternatively, upper flange <NUM> may be angled with respect to elongated span <NUM> so as to be complementary to a first end region <NUM> of leading edge skin panel <NUM>. Similarly, lower flange <NUM> may be angled with respect to elongated span <NUM> so as to be complementary to a second end region <NUM> of leading edge skin panel <NUM>.

Leading edge <NUM> of structural composite airfoil <NUM> is defined by leading edge skin panel <NUM>, which is generally shaped to have a bullnose shape. Leading edge skin panel <NUM> may be positioned adjacent leading edge region <NUM> of primary structural element <NUM>, though leading edge skin panel <NUM> may be a discrete part outside of, or distinct from, primary structural element <NUM>. In other examples, leading edge skin panel <NUM> may be within leading edge region <NUM> of primary structural element <NUM> and/or define leading edge region <NUM> of primary structural element <NUM>, such as in examples where primary structural element <NUM> extends to leading edge <NUM>. Leading edge skin panel <NUM> is coupled to upper skin panel <NUM> and lower skin panel <NUM> via front C-channel spar <NUM>. Specifically, first end region <NUM> of leading edge skin panel <NUM> is coupled to upper flange <NUM> of front C-channel spar <NUM>, and second end region <NUM> of leading edge skin panel <NUM> is coupled to lower flange <NUM> of front C-channel spar <NUM>. Because upper flange <NUM> of front C-channel spar <NUM> is coupled to leading edge skin panel <NUM> and to upper skin panel <NUM>, front C-channel spar <NUM> effectively couples leading edge skin panel <NUM> to upper skin panel <NUM>. In some examples, leading edge skin panel <NUM> does not overlap upper skin panel <NUM> (e.g., does not overlap an upper leading edge end <NUM> of upper skin panel <NUM>) on upper flange <NUM>. In a specific example, upper leading edge end <NUM> of upper skin panel <NUM> may be abutted to leading edge skin panel <NUM> (e.g., to first end region <NUM> of leading edge skin panel <NUM>). In other examples, upper skin panel <NUM> may be coupled to upper flange <NUM> without contacting leading edge skin panel <NUM>. Similarly, because lower flange <NUM> of front C-channel spar <NUM> is coupled to leading edge skin panel <NUM> and to lower skin panel <NUM>, front C-channel spar <NUM> effectively couples leading edge skin panel <NUM> to lower skin panel <NUM>. In some examples, leading edge skin panel <NUM> does not overlap lower skin panel <NUM> (e.g., does not overlap a lower leading edge end <NUM> of lower skin panel <NUM>) on lower flange <NUM>. In some examples, lower leading edge end <NUM> of lower skin panel <NUM> may be abutted to leading edge skin panel <NUM> (e.g., to second end region <NUM>). In other examples, lower skin panel <NUM> may be coupled to lower flange <NUM> without contacting leading edge skin panel <NUM>.

Trailing edge <NUM> of structural composite airfoil <NUM> is defined by secondary structural element <NUM>. In various examples of structural composite airfoil <NUM>, secondary structural element <NUM> may include a wedge closeout, a duckbill closeout, a bonded closeout, and/or a riveted closeout. Examples of suitable trailing edge closeouts are also disclosed in <CIT>, and titled AERODYNAMIC CONTROL SURFACE AND ASSOCIATED TRAILING EDGE CLOSE-OUT METHOD.

Upper skin panel <NUM> generally extends from upper leading edge end <NUM> to an upper trailing edge end <NUM>. Upper leading edge end <NUM> corresponds to the end of upper skin panel <NUM> that is closest to leading edge <NUM> of structural composite airfoil <NUM>, and upper trailing edge end <NUM> corresponds to the end of upper skin panel <NUM> that is closest to trailing edge <NUM> of structural composite airfoil <NUM>. Similarly, lower skin panel <NUM> generally extends from lower leading edge end <NUM> to a lower trailing edge end <NUM>. Lower leading edge end <NUM> corresponds to the end of lower skin panel <NUM> that is closest to leading edge <NUM>, and lower trailing edge end <NUM> corresponds to the end of lower skin panel <NUM> that is closest to trailing edge <NUM>. As described above, upper leading edge end <NUM> and lower leading edge end <NUM> may be coupled to front C-channel spar <NUM>. In some examples, upper trailing edge end <NUM> may be coupled to lower trailing edge end <NUM>. Additionally or alternatively, upper trailing edge end <NUM> and/or lower trailing edge end <NUM> may form or define trailing edge <NUM> of structural composite airfoil <NUM>.

Structural composite airfoil <NUM> may include one or more fasteners securing various components to each other. For example, a first fastener <NUM> may couple leading edge skin panel <NUM> (e.g., first end region <NUM> of leading edge skin panel <NUM>) to upper flange <NUM> of front C-channel spar <NUM>. In some examples, first fastener <NUM> is a plurality of first fasteners <NUM> spaced apart along the width of structural composite airfoil <NUM> (the width of the airfoil extending into/out of the page) to secure leading edge skin panel <NUM> to front C-channel spar <NUM> along first end region <NUM>. Leading edge skin panel <NUM> may be configured to interface with upper skin panel <NUM> without any joggle formed in either panel, via coupling of both leading edge skin panel <NUM> and upper skin panel <NUM> to upper flange <NUM>. Additionally or alternatively, structural composite airfoils <NUM> may be formed without a discrete splice strap joining leading edge skin panel <NUM> and upper skin panel <NUM>, because upper flange <NUM> may be configured to effectively splice leading edge skin panel <NUM> and upper skin panel <NUM>.

Similarly, a second fastener <NUM> may couple leading edge skin panel <NUM> (e.g., second end region <NUM> of leading edge skin panel <NUM>) to lower flange <NUM> of front C-channel spar <NUM>. In some examples, second fastener <NUM> is a plurality of second fasteners <NUM> spaced apart along the width of structural composite airfoil <NUM> (the width of the airfoil extending into/out of the page) to secure leading edge skin panel <NUM> to front C-channel spar <NUM> along second end region <NUM>. Leading edge skin panel <NUM> may be configured to interface with lower skin panel <NUM> without any joggle formed in either panel, via coupling of both leading edge skin panel <NUM> and lower skin panel <NUM> to lower flange <NUM>. Additionally or alternatively, structural composite airfoils <NUM> may be formed without a discrete splice strap joining leading edge skin panel <NUM> and lower skin panel <NUM>, because lower flange <NUM> may be configured to effectively splice leading edge skin panel <NUM> and lower skin panel <NUM>. First fastener <NUM> and second fastener <NUM> may be configured such that leading edge skin panel <NUM> may be selectively removable from primary structural element <NUM> by removing first fastener <NUM> and second fastener <NUM>.

A third fastener <NUM> (or a plurality of third fasteners <NUM> spaced apart along the width of structural composite airfoil <NUM>) may be positioned to couple upper skin panel <NUM> to upper flange <NUM> of front C-channel spar <NUM>. Third fastener <NUM> generally couples upper leading edge end <NUM> of upper skin panel <NUM> to upper flange <NUM>. A fourth fastener <NUM> (or plurality of fourth fasteners <NUM> spaced apart along the width of structural composite airfoil <NUM>) may be positioned to couple lower skin panel <NUM> to lower flange <NUM> of front C-channel spar <NUM>. Fourth fastener <NUM> generally couples lower leading edge end <NUM> of lower skin panel <NUM> to lower flange <NUM>. Third fastener <NUM> and/or fourth fastener <NUM> may be accessible (e.g., not blind) even after primary structural element <NUM> is assembled. Additionally or alternatively, third fastener <NUM> and/or fourth fastener <NUM> may be permanent fasteners (e.g., hex drive bolts) that are secured without nutplates.

Structural composite airfoil <NUM> may further include a middle C-channel spar <NUM> and/or a rear C-channel spar <NUM>, one or both of which may form part of primary structural element <NUM>. In the example shown in <FIG>, primary structural element <NUM> is defined by front C-channel spar <NUM>, middle C-channel spar <NUM>, rear C-channel spar <NUM>, and the respective portions of upper skin panel <NUM> and lower skin panel <NUM> extending between front C-channel spar <NUM> and rear C-channel spar <NUM>. In other examples of structural composite airfoil <NUM>, primary structural element <NUM> may extend further towards leading edge <NUM> than illustrated in <FIG>. For example, while primary structural element <NUM> may extend only between front C-channel spar <NUM> and rear C-channel spar <NUM> as noted above, in other examples, primary structural element <NUM> optionally may extend further forward such that primary structural element <NUM> also extends to and includes leading edge <NUM>. Additionally or alternatively, primary structural element <NUM> may extend further towards trailing edge <NUM> than illustrated in <FIG>. For example, primary structural element <NUM> may include at least a portion of structural composite airfoil <NUM> aft of rear C-channel spar <NUM>.

In examples including middle C-channel spar <NUM>, said middle C-channel spar <NUM> may include a second channel <NUM> facing leading edge <NUM>. Middle C-channel spar <NUM> may be coupled to upper skin panel <NUM> and lower skin panel <NUM>. For example, middle C-channel spar <NUM> may include a middle upper flange <NUM> coupled to upper skin panel <NUM>. Additionally or alternatively, middle C-channel spar <NUM> may include a middle lower flange <NUM> coupled to lower skin panel <NUM>. Middle C-channel spar <NUM> is positioned aft of front C-channel spar <NUM>.

In examples including rear C-channel spar <NUM>, said rear C-channel spar <NUM> may include a third channel <NUM> facing leading edge <NUM>. Rear C-channel spar <NUM> may be coupled to upper skin panel <NUM> and lower skin panel <NUM>. For example, rear C-channel spar <NUM> may include a rear upper flange <NUM> coupled to upper skin panel <NUM>. Additionally or alternatively, rear C-channel spar <NUM> may include a rear lower flange <NUM> coupled to lower skin panel <NUM>. Rear C-channel spar <NUM> is positioned aft of front C-channel spar <NUM>. In examples of structural composite airfoil <NUM> including middle C-channel spar <NUM> and rear C-channel spar <NUM>, rear C-channel spar <NUM> is positioned aft of middle C-channel spar <NUM>.

A plurality of other fasteners <NUM> may be utilized to couple upper skin panel <NUM> to middle C-channel spar <NUM> (e.g., middle upper flange <NUM>) and/or to rear C-channel spar <NUM> (e.g., rear upper flange <NUM>). Similarly, one or more fasteners <NUM> may be used to couple lower skin panel <NUM> to middle C-channel spar <NUM> (e.g., middle lower flange <NUM>) and/or to rear C-channel spar <NUM> (e.g., rear lower flange <NUM>). Additionally or alternatively, one or more fasteners <NUM> may be used to couple upper trailing edge end <NUM> to lower trailing edge end <NUM>.

Each of upper skin panel <NUM> and lower skin panel <NUM> may be a composite panel formed of a plurality of layers (plies) of a fiber-reinforced polymer that are laminated together. For example, upper skin panel <NUM> and lower skin panel <NUM> may be formed of carbon fiber reinforced polymer material or fiberglass reinforced polymer material. In other examples, upper skin panel <NUM> and/or lower skin panel <NUM> may be a metallic material, a polymer, or other suitable material.

In some examples, at least a portion of upper skin panel <NUM> may be core stiffened. As used herein, "core stiffened" refers to skin panels having at least a first skin and a low-density core material coupled to the skin. Core stiffened materials optionally include a second skin, with the core material sandwiched between the first and second skins to form a sandwich panel. Suitable materials for forming core stiffened portions are well known in the art, and include honeycomb core materials and metallic core materials, though other core materials are within the scope of the present disclosure. For example, upper skin panel <NUM> may include a first upper core stiffened portion <NUM>, a second upper core stiffened portion <NUM>, and a third upper core stiffened portion <NUM>. First upper core stiffened portion <NUM> may be positioned between front C-channel spar <NUM> and middle C-channel spar <NUM>, second upper core stiffened portion <NUM> may be positioned between middle C-channel spar <NUM> and rear C-channel spar <NUM>, and/or third upper core stiffened portion <NUM> may be positioned between rear C-channel spar <NUM> and upper trailing edge end <NUM>. One or more of upper core stiffened portions <NUM>, <NUM>, <NUM> may be tapered, such as in areas of the respective section near C-channel spar <NUM>, <NUM>, and/or <NUM>. For example, upper core stiffened portion <NUM>, <NUM>, and/or <NUM> may have a height or thickness extending downward from upper skin panel <NUM> towards lower skin panel <NUM>, with said height or thickness decreasing in the vicinity of one or more of the C-channel spars <NUM>, <NUM>, and/or <NUM>, thereby forming the taper. In the example of <FIG>, the thickness of first upper core stiffened portion <NUM> is tapered adjacent front C-channel spar <NUM> and adjacent middle C-channel spar <NUM>, the thickness of second upper core stiffened portion <NUM> is tapered adjacent middle C-channel spar <NUM> and rear C-channel spar <NUM>, and the thickness of third upper core stiffened portion <NUM> is tapered adjacent rear C-channel spar <NUM> and adjacent trailing edge <NUM>. In other examples, the height or thickness of one or more upper core stiffened portions <NUM>, <NUM>, and/or <NUM> may be constant or substantially constant, rather than tapering where the respective upper core stiffened portion <NUM>, <NUM>, and/or <NUM> meets the respective C-channel spar <NUM>, <NUM>, <NUM>. In some examples, one or more of upper core stiffened portions <NUM>, <NUM>, and/or <NUM> may abut a respective C-channel spar <NUM>, <NUM>, and/or <NUM>. While upper skin panel <NUM> as shown in <FIG> includes three distinct upper core stiffened portions <NUM>, <NUM>, <NUM>, in other examples, upper skin panel <NUM> may be core stiffened along its entire length, along a greater or lesser portion of its length, and/or may include more or fewer discrete upper core stiffened sections than is shown in <FIG>.

Additionally or alternatively, at least a portion of lower skin panel <NUM> may be core stiffened. For example, lower skin panel <NUM> includes a first lower core stiffened portion <NUM>, a second lower core stiffened portion <NUM>, and a third lower core stiffened portion <NUM>. First lower core stiffened portion <NUM> may be positioned between front C-channel spar <NUM> and middle C-channel spar <NUM>, second lower core stiffened portion <NUM> may be positioned between middle C-channel spar <NUM> and rear C-channel spar <NUM>, and/or third lower core stiffened portion <NUM> may be positioned between rear C-channel spar <NUM> and lower trailing edge end <NUM>. One or more of lower core stiffened portions <NUM>, <NUM>, <NUM> may be tapered, such as in areas of the respective section near C-channel spar <NUM>, <NUM>, and/or <NUM>. For example, lower core stiffened portion <NUM>, <NUM>, and/or <NUM> may have a height or thickness extending upward from lower skin panel <NUM> towards upper skin panel <NUM>, with said height or thickness decreasing in the vicinity of one or more of the C-channel spars <NUM>, <NUM>, and/or <NUM>, thereby forming the taper. In the example of <FIG>, the thickness of first lower core stiffened portion <NUM> is tapered adjacent front C-channel spar <NUM> and adjacent middle C-channel spar <NUM>, the thickness of second lower core stiffened portion <NUM> is tapered adjacent middle C-channel spar <NUM> and rear C-channel spar <NUM>, and the thickness of third lower core stiffened portion <NUM> is tapered adjacent rear C-channel spar <NUM> and adjacent trailing edge <NUM>. In other examples, the height or thickness of one or more lower core stiffened portions <NUM>, <NUM>, and/or <NUM> may be constant or substantially constant, rather than tapering where the respective lower core stiffened portion <NUM>, <NUM>, and/or <NUM> meets the respective C-channel spar <NUM>, <NUM>, <NUM>. In some examples, one or more of lower core stiffened portions <NUM>, <NUM>, and/or <NUM> may abut a respective C-channel spar <NUM>, <NUM>, and/or <NUM>. While lower skin panel <NUM> as shown in <FIG> includes three distinct lower core stiffened portions <NUM>, <NUM>, <NUM>, in other examples, lower skin panel <NUM> may be core stiffened along its entire length, may be core stiffened along a greater or lesser portion of its length, and/or may include more or fewer discrete lower core stiffened sections than is shown in <FIG>.

Structural composite airfoil <NUM> has a length <NUM>, which may also be referred to herein as a chord length <NUM>, and a position along length <NUM> may be defined in terms of a percentage of the distance along length <NUM> from leading edge <NUM>. In these terms, front C-channel spar <NUM> may be positioned between <NUM>% and <NUM>% of length <NUM> away from leading edge <NUM>. In some examples, front C-channel spar <NUM> is positioned at <NUM>% of length <NUM> away from leading edge <NUM> (or at about <NUM>% of length <NUM> away from leading edge <NUM>). Front C-channel spar <NUM> may be positioned as far forward as practical for integration in some examples. Additionally or alternatively, middle C-channel spar <NUM> may be positioned between <NUM>% and <NUM>% of length <NUM> away from leading edge <NUM>, such as at <NUM>% of length <NUM> away from leading edge <NUM> (or about <NUM>% of length <NUM> away from leading edge <NUM>). In some examples, middle C-channel spar <NUM> may be positioned for balancing torsional capability within primary structural element <NUM> on either side of middle C-channel spar <NUM>. Additionally or alternatively, rear C-channel spar <NUM> may be positioned between <NUM>% and <NUM>% of length <NUM> away from leading edge <NUM>, and/or between <NUM>% and <NUM>% of length <NUM> away from leading edge <NUM>. In some examples, rear C-channel spar <NUM> may be positioned at <NUM>% of length <NUM> away from leading edge <NUM> (or about <NUM>% of length <NUM> away from leading edge <NUM>). In some examples, rear C-channel spar <NUM> may be positioned as far aft as practical for integration.

Some examples of structural composite airfoil <NUM> may include an integral Z-spar <NUM>, which may be a part of primary structural element <NUM>, with elements aft of integral Z-spar <NUM> being part of secondary structural element <NUM> in some examples. Thus, positioning integral Z-spar <NUM> aft of middle C-channel spar <NUM> and/or rear C-channel spar <NUM> (or in lieu of one or both of these spars) may lengthen, or extend, the length of primary structural element <NUM>, and/or may increase the percentage of length <NUM> of structural composite airfoil <NUM> that corresponds to primary structural element <NUM>. In some examples, integral Z-spar <NUM> may be formed within trailing edge region <NUM> of primary structural element <NUM>. <FIG> illustrate examples of such integral Z-spars <NUM>, with <FIG> illustrating an example of integral Z-spar <NUM> formed in lower skin panel <NUM>, and <FIG> illustrating an example of integral Z-spar <NUM> formed in upper skin panel <NUM>. Integral Z-spar <NUM> is generally positioned adjacent trailing edge <NUM> of structural composite airfoil <NUM>, such as by being positioned at least <NUM>% of length <NUM> away from leading edge <NUM>. In some examples, integral Z-spar <NUM> may be positioned between <NUM>-<NUM>% of length <NUM> away from leading edge <NUM>.

With reference to <FIG>, integral Z-spar <NUM> may be formed in lower trailing edge end <NUM> of lower skin panel <NUM>. Integral Z-spar <NUM> may include a first bend <NUM>, a second bend <NUM>, and a first Z-spar segment <NUM> extending between first bend <NUM> and second bend <NUM>. In some examples, first Z-spar segment <NUM> may be at least perpendicular or at least substantially perpendicular to lower skin panel <NUM> and/or upper skin panel <NUM>. In some examples, first Z-spar segment <NUM> may form an angle with lower skin panel <NUM> that is greater than <NUM> degrees, and/or greater than <NUM> degrees. Additionally or alternatively, first Z-spar segment <NUM> may form an angle with upper skin panel <NUM> that is greater than <NUM> degrees, and/or greater than <NUM> degrees. Integral Z-spar <NUM> may further include a second Z-spar segment <NUM> extending aft of second bend <NUM>. Second Z-spar segment <NUM> may be coupled to upper skin panel <NUM>, as shown in <FIG>. In the example shown in <FIG>, second Z-spar segment <NUM> is positioned adjacent an interior surface <NUM> of upper skin panel <NUM>. A Z-spar fastener <NUM> may couple integral Z-spar <NUM> to upper skin panel <NUM>. In some examples, Z-spar fastener <NUM> is recessed into upper skin panel <NUM> (e.g., such that Z-spar fastener <NUM> is at least substantially flush or sub flush with an upper panel surface <NUM> of upper skin panel <NUM>) and extends through upper skin panel <NUM> and second Z-spar segment <NUM> to couple integral Z-spar <NUM> to upper skin panel <NUM>.

Integral Z-spar <NUM> may include a Z-spar joggle <NUM> in lower skin panel <NUM> that may be configured to receive a portion of a trailing edge closeout cover <NUM>, which may at least partially define secondary structural element <NUM> and/or trailing edge <NUM> of structural composite airfoil <NUM>. Z-spar joggle <NUM> is effectively a small shift in lower skin panel <NUM> upwards toward upper skin panel <NUM>, and generally is positioned forward of first bend <NUM>. A first cover end region <NUM> of trailing edge closeout cover <NUM> may be bonded to lower skin panel <NUM>, as shown in <FIG>. Additionally or alternatively, first cover end region <NUM> may be riveted or otherwise fastened or coupled to lower skin panel <NUM>. To create a smooth surface at the interface and improve aerodynamic performance, first cover end region <NUM> may be slightly recessed into lower skin panel <NUM>, such as via Z-spar joggle <NUM>, as shown in <FIG>. Z-spar joggle <NUM> may be tailored to create a greater or smaller recess in lower skin panel <NUM>, depending on the thickness of first cover end region <NUM>, such that a lower panel surface <NUM> of lower skin panel <NUM> is flush or substantially flush with a lower cover surface <NUM> of trailing edge closeout cover <NUM> within first cover end region <NUM>. In other words, Z-spar joggle <NUM> may be larger to create a bigger recess to receive and engage with a given trailing edge closeout cover <NUM> having a thicker first cover end region <NUM>, whereas Z-spar joggle <NUM> may be smaller to create a smaller recess to receive and engage with a different given trailing edge closeout cover <NUM> having a thinner first cover end region <NUM>. Any gaps remaining at the interface of Z-spar joggle <NUM> and first cover end region <NUM> (or elsewhere on structural composite airfoil <NUM>) may be filled with a sealant, a filler material, and/or a resin, and then smoothed.

A second cover end region <NUM> of trailing edge closeout cover <NUM> may include an integral wedge <NUM> that may be coupled (e.g., bonded and/or coupled via one or more fasteners) to upper skin panel <NUM>, as shown in <FIG>. Alternatively, integral wedge <NUM> may be integrally formed with upper skin panel <NUM>. In still other examples, integral wedge <NUM> may be a discrete component separate from trailing edge closeout cover <NUM> and separate from upper skin panel <NUM>, and which may be bonded or otherwise coupled to upper skin panel <NUM> and/or trailing edge closeout cover <NUM>. For example, integral wedge <NUM> may be formed by building up plies of material, molding, and/or by machining a mating face profile to mate with upper skin panel <NUM>.

With reference to <FIG>, integral Z-spar <NUM> may be formed in upper trailing edge end <NUM> of upper skin panel <NUM>. In the example shown in <FIG>, second Z-spar segment <NUM> is coupled to lower skin panel <NUM>, and is positioned adjacent an interior surface <NUM> of lower skin panel <NUM>. Z-spar fastener <NUM> couples integral Z-spar <NUM> to lower skin panel <NUM>, with Z-spar fastener <NUM> being recessed into lower skin panel <NUM> (e.g., such that Z-spar fastener <NUM> is at least flush or at least substantially flush or sub flush with lower panel surface <NUM> of lower skin panel <NUM>) and extending through lower skin panel <NUM> and second Z-spar segment <NUM> to couple integral Z-spar <NUM> to lower skin panel <NUM>.

In <FIG>, integral Z-spar <NUM> includes Z-spar joggle <NUM> in upper skin panel <NUM> that is configured to receive a portion of trailing edge closeout cover <NUM>, with Z-spar joggle <NUM> being positioned forward of first bend <NUM>. Z-spar joggle <NUM> is effectively a small shift in upper skin panel <NUM> toward lower skin panel <NUM>. First cover end region <NUM> of trailing edge closeout over <NUM> is bonded to upper skin panel <NUM> instead of lower skin panel <NUM> in this example. Additionally or alternatively, first cover end region <NUM> may be riveted or otherwise fastened or coupled to upper skin panel <NUM>. To create a smooth surface at the interface and improve aerodynamic performance, first cover end region <NUM> may be slightly recessed into upper skin panel <NUM>, such as via Z-spar joggle <NUM>, as shown in <FIG>. Z-spar joggle <NUM> may be tailored to create a greater or smaller recess in upper skin panel <NUM>, depending on the thickness of first cover end region <NUM>, such that an upper panel surface <NUM> of upper skin panel <NUM> is flush or substantially flush with an upper cover surface <NUM> of trailing edge closeout cover <NUM> within first cover end region <NUM>. In other words, Z-spar joggle <NUM> may be larger to create a bigger recess to receive and engage with a given trailing edge closeout cover <NUM> having a thicker first cover end region <NUM>, whereas Z-spar joggle <NUM> may be smaller to create a smaller recess to receive and engage with a different given trailing edge closeout cover <NUM> having a thinner first cover end region <NUM>.

Second cover end region <NUM> of trailing edge closeout cover <NUM> may include integral wedge <NUM> that may be coupled (e.g., bonded and/or coupled via one or more fasteners) to lower skin panel <NUM>. Alternatively, and as shown in <FIG>, integral wedge <NUM> may be integrally formed with lower skin panel <NUM>. In still other examples, integral wedge <NUM> may be a discrete component separate from trailing edge closeout cover <NUM> and separate from lower skin panel <NUM>, and which may be bonded or otherwise coupled to lower skin panel <NUM> and/or trailing edge closeout cover <NUM>. Integral wedge <NUM> may be formed, for example, by building up plies of material, molding, and/or by machining a mating face profile to mate with lower skin panel <NUM>.

<FIG> schematically provides a flowchart that represents illustrative, non-exclusive examples of methods <NUM> according to the present disclosure. In <FIG>, some steps are illustrated in dashed boxes indicating that such steps may be optional or may correspond to an optional version of a method according to the present disclosure. That said, not all methods <NUM> according to the present disclosure are required to include the steps illustrated in solid boxes. The methods <NUM> and steps illustrated in <FIG> are not limiting and other methods and steps are within the scope of the present disclosure, including methods having greater than or fewer than the number of steps illustrated, as understood from the discussions herein.

Methods <NUM> generally include coupling an upper skin panel (e.g., upper skin panel <NUM>) to a front C-channel spar (e.g., front C-channel spar <NUM>), at <NUM>, and coupling a lower skin panel (e.g., lower skin panel <NUM>) to the front C-channel spar, at <NUM>. Coupling the upper skin panel to the front C-channel spar at <NUM> generally includes coupling the upper skin panel to an upper flange (e.g., upper flange <NUM>) of the front C-channel spar. Similarly, coupling the lower skin panel to the front C-channel spar at <NUM> generally includes coupling the lower skin panel to a lower flange (e.g., lower flange <NUM>) of the front C-channel spar. As compared to conventional techniques, coupling the upper skin panel at <NUM> and/or coupling the lower skin panel at <NUM> may be performed with a reduced number of nutplates or other fastening components. Additionally or alternatively, coupling the upper skin panel at <NUM> and/or coupling the lower skin panel at <NUM> may be performed without the use of splice straps. Reducing the number of fasteners or fastening components may reduce the weight of the resulting structural composite airfoil, reduce manufacturing costs, and/or reduce manufacturing processing time.

Methods <NUM> also include coupling a leading edge skin panel (e.g., leading edge skin panel <NUM>) to the front C-channel spar, at <NUM>. Coupling the leading edge skin panel at <NUM> generally includes coupling a first end region of the leading edge skin panel (e.g., first end region <NUM>) to the upper flange of the front C-channel spar, and coupling a second end region of the leading edge skin panel (e.g., second end region <NUM>) to the lower flange of the front C-channel spar. Coupling the leading edge skin panel at <NUM> may be performed without overlapping the upper skin panel and the leading edge skin panel on the upper flange of the front C-channel spar. Similarly, coupling the leading edge skin panel at <NUM> may be performed without overlapping the lower skin panel and the leading edge skin panel on the lower flange of the front C-channel spar. Coupling the leading edge skin panel at <NUM> may include coupling the leading edge skin panel without the use of splice straps, such that the leading edge skin panel may be directly coupled to the front C-channel spar. In some methods <NUM>, coupling the leading edge skin panel at <NUM> includes abutting the first end region of the leading edge skin panel and the upper skin panel (e.g., upper leading edge end <NUM> of upper skin panel <NUM>), which may include forming a lap joint or splice joint between the two. Additionally or alternatively, coupling the leading edge skin panel at <NUM> may include abutting the second end region of the leading edge skin panel and the lower skin panel (e.g., lower leading edge end <NUM> of lower skin panel <NUM>) and/or forming a lap joint or splice joint therebetween.

In some examples, method <NUM> includes coupling the upper skin panel to a middle C-channel spar (e.g., middle C-channel spar <NUM>) at <NUM>, coupling the upper skin panel to a rear C-channel spar (e.g., rear C-channel spar <NUM>) at <NUM>, coupling the lower skin panel to the middle C-channel spar at <NUM>, and/or coupling the lower skin panel to the rear C-Channel spar at <NUM>. Additionally or alternatively, methods <NUM> may include coupling a secondary structural element (e.g., secondary structural element <NUM>), such as a closeout, to the upper skin panel (e.g., upper trailing edge end <NUM>) and/or to the lower skin panel (e.g., lower trailing edge end <NUM>), at <NUM>. Additionally or alternatively, methods <NUM> may include forming an integral Z-spar (e.g., integral Z-spar <NUM>) in the lower skin panel or upper skin panel, at <NUM>.

As used herein, the terms "selective" and "selectively," when modifying an action, movement, configuration, or other activity of one or more components or characteristics of an apparatus, mean that the specific action, movement, configuration, or other activity is a direct or indirect result of user manipulation of an aspect of, or one or more components of, the apparatus.

As used herein, the phrase "at least one," in reference to a list of one or more entities should be understood to mean at least one entity selected from any one or more of the entities in the list of entities, but not necessarily including at least one of each and every entity specifically listed within the list of entities and not excluding any combinations of entities in the list of entities. This definition also allows that entities may optionally be present other than the entities specifically identified within the list of entities to which the phrase "at least one" refers, whether related or unrelated to those entities specifically identified. Thus, as a non-limiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and/or B") may refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including entities other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including entities other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other entities). In other words, the phrases "at least one," "one or more," and "and/or" are open-ended expressions that are both conjunctive and disjunctive in operation. For example, each of the expressions "at least one of A, B, and C," "at least one of A, B, or C," "one or more of A, B, and C," "one or more of A, B, or C," and "A, B, and/or C" may mean A alone, B alone, C alone, A and B together, A and C together, B and C together, or A, B, and C together, and optionally any of the above in combination with at least one other entity.

The various disclosed elements of apparatuses and steps of methods disclosed herein are not required to all apparatuses and methods according to the present disclosure, and the present disclosure includes all novel and non-obvious combinations and subcombinations of the various elements and steps disclosed herein. Moreover, one or more of the various elements and steps disclosed herein may define independent inventive subject matter that is separate and apart from the whole of a disclosed apparatus or method. Accordingly, such inventive subject matter is not required to be associated with the specific apparatuses and methods that are expressly disclosed herein, and such inventive subject matter may find utility in apparatuses and/or methods that are not expressly disclosed herein.

Claim 1:
A structural composite airfoil (<NUM>) having a leading edge (<NUM>) and a trailing edge (<NUM>), the structural composite airfoil comprising:
a primary structural element (<NUM>) extending from a leading edge region (<NUM>) to a trailing edge region (<NUM>), wherein the leading edge region is adjacent the leading edge of the structural composite airfoil, wherein the primary structural element comprises:
an upper skin panel (<NUM>);
a lower skin panel (<NUM>);
an internal volume (<NUM>) defined between the upper skin panel and the lower skin panel; and
a front C-channel spar (<NUM>) comprising an upper flange (<NUM>) coupled to the upper skin panel, wherein the front C-channel spar further comprises a lower flange (<NUM>) coupled to the lower skin panel, wherein a first channel (<NUM>) of the front C-channel spar faces the leading edge of the structural composite airfoil, wherein the upper flange forms a first angle (<NUM>) with an elongated span (<NUM>) of the front C-channel spar, wherein the lower flange forms a second angle (<NUM>) with the elongated span, and wherein the first angle is acute;
a secondary structural element (<NUM>) defining the trailing edge of the structural composite airfoil;
a leading edge skin panel (<NUM>) defining the leading edge of the structural composite airfoil and positioned adjacent the leading edge region of the primary structural element, wherein a first end region (<NUM>) of the leading edge skin panel is coupled to the upper flange of the front C-channel spar, wherein a second end region (<NUM>) of the leading edge skin panel is coupled to the lower flange of the front C-channel spar, and wherein the leading edge skin panel has a bullnose shape; and
a trailing edge closeout cover (<NUM>), wherein:
a first cover end region (<NUM>) of the trailing edge closeout cover is bonded to the lower skin panel, and the first cover end region of the trailing edge closeout cover is recessed into the lower skin panel; and
a second cover end region (<NUM>) of the trailing edge closeout cover comprises an integral wedge (<NUM>) coupled to the upper skin panel.