Patent Description:
During transition between forward flight and hovering the cover must turn the flow of air over the wing into the duct. This sharp turn may result in flow separation and turbulence, as well as significant loading on the system used to actuate movement of the cover. Thrust may be reduced, drag increased, and vibration transmitted to the aircraft wing. Therefore, an aerodynamically and mechanically efficient cover for a wing-embedded lift fan is desirable.

<CIT>, in accordance with its abstract, states a vertical and short take-off and landing aircraft comprising a fuselage, a set canard wings, a set of lift fan wings, air deflectors, lift wings, and a pusher propeller. The canard wings are attached forward of the center of gravity to the fuselage. The lift fan wings are attached about the fuselage generally about the center of gravity of the aircraft. The lift fan wings comprise a generally circular duct extending vertically through the wing, a multi-bladed fan mounted for free rotation axially in the duct, and a prime mover connected to the fan for selectively applying rotational torque to the fan. The air deflectors are arranged about the lift fan wing in a louver-type of system for directing even flow of air to the fan. The lift wings are attached to the fuselage aft of the center of gravity of the aircraft and generally at a location vertically higher than the lift fan wings. The pusher propeller is connected to the prime mover and attached to the fuselage aft of the lift Jan wings.

<CIT>, in accordance with its abstract, states a louver system for vectoring the flow through aircraft lift fans. It uses swept louvers as opposed to straight and this permits a constant flow area over a large vectoring operating range and is intended to replace vectoring cascades of vanes that are rotated below lift fans. <CIT>, in accordance with its abstract, states a louvre offtake arrangement for a gas turbine engine includes a first duct, where a primary flow flows; a second duct, defining an offtake, connected to the first duct at an inlet; and a plurality of louvres arranged at the inlet. At least one louvre protrudes from the second duct into the first duct to divert part of the primary flow towards the second duct.

In <CIT> there is described, a thrust vectoring louver cascade provided for a lift fan employed in the propulsion of V/STOL Aircraft. The V-shaped louvers of the cascade are pivoted about their apexes to provide increased mass flow of the propulsive gas stream, particularly when it is vectored to angle its output thrust from the vertical.

<CIT>, in accordance with its abstract, states an apparatus and method are disclosed for a gas turbine engine including an offtake located within the air flow of the engine. The offtake has an inlet and a louver covering the inlet. The louver has multiple airfoils arranged to direct the air flow into the inlet of the offtake.

In <CIT> there is described a VTO inlet designed for both vertical and horizontal flight, and more particularly, to an inlet for the left fan for such an aircraft wherein optimum performance of the inlet is made possible in the vertical, hover, and transition portions of the flight.

The present disclosure provides systems, apparatuses, and methods relating to a fan apparatus.

According to a first aspect there is provided a fan apparatus as defined in claim <NUM>.

According to a second aspect there is provided an aircraft as defined in claim <NUM>.

According to a third aspect there is provided a method of controlling airflow as defined in claim <NUM>. Preferred embodiments are provided in the dependent claims.

Features, functions, and advantages may be achieved independently in various examples of the present disclosure, or may be combined in yet other examples, insofar as they fall within the scope of the appended claims.

Various aspects and examples of a fan apparatus, an airfoil structure, an aircraft, a louvered cover for a lift fan, a louver actuation assembly, and a sealing assembly for a cover, as well as related methods, are described below and illustrated in the associated drawings. Unless otherwise specified, a fan apparatus, an airfoil structure, an aircraft, a louvered cover for a lift fan, a louver actuation assembly, and a sealing assembly for a cover, in accordance with the present teachings, and/or its various components may, but are not required to, contain at least one of the structures, components, functionalities, and/or variations described, illustrated, and/or incorporated herein. Furthermore, unless specifically excluded, the process steps, structures, components, functionalities, and/or variations described, illustrated, and/or incorporated herein in connection with the present teachings may be included in other similar devices and methods, including being interchangeable between disclosed examples. The following description of various examples is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. Additionally, the advantages provided by the examples described below are illustrative in nature and not all examples provide the same advantages or the same degree of advantages.

This Detailed Description includes the following sections, which follow immediately below: (<NUM>) Overview; (<NUM>) Examples, Components, and Alternatives; (<NUM>) Illustrative Combinations and Additional Examples; (<NUM>) Advantages, Features, and Benefits; and (<NUM>) Conclusion. The Examples, Components, and Alternatives section is further divided into subsections A through F, each of which is labeled accordingly.

The present disclosure provides systems, apparatuses, and methods relating to a fan apparatus including a lift fan mounted in a duct and a cover for the lift fan. In some examples, a fan apparatus has a louvered cover including louvers having different chord lengths and/or different projection distances relative to one another when the louvers are in an intermediate (transitional) position. In some examples, a fan apparatus includes a louver actuation assembly configured to move louvers of the fan apparatus rotationally and translationally between open and closed positions. In some examples, a fan apparatus includes a fluid-actuated sealing assembly configured to form a seal between a sealing member and a cover, such as a louvered cover.

In some examples, a fan apparatus comprises a duct having an opening. The fan apparatus also comprises a lift fan mounted in the duct and a series of louvers positioned at the opening and each configured to move between an open position and a closed position. The louvers are offset from one another along a fore-to-aft axis. The series of louvers include a fore louver and an aft louver. A chord length of the aft louver is greater than a chord length of the fore louver.

In some examples, an aircraft comprises an airfoil structure including a duct having an opening. The aircraft also comprises a lift fan mounted in the duct and a series of louvers positioned at the opening and each configured to move between an open position and a closed position via an intermediate position when the aircraft transitions between a horizontal flight mode and a vertical flight mode. The louvers are offset from one another along a fore-to-aft axis of the aircraft. The series of louvers include a fore louver and an aft louver. The aft louver has a greater chord length and/or, in the intermediate position, projects farther out of the duct than the fore louver.

In some examples, a method of controlling airflow is performed with respect to an airfoil structure containing a lift fan mounted in a duct, during a transition phase between horizontal and vertical flight modes of an aircraft. In the method, a series of louvers located at an opening of the duct each is moved between an open or closed position and an intermediate position. An aft louver of the series has a greater chord length and/or, in the intermediate position, projects farther out of the duct than a fore louver of the series.

In some examples, a fan apparatus includes a duct having a duct opening. The fan apparatus also comprises a lift fan mounted in the duct and a plurality of louvers positioned at the duct opening. Each louver is configured to move between an open position and a closed position. The closed position is rotationally offset and translationally offset from the open position.

In some examples, an aircraft comprises an airfoil structure including a duct having a duct opening. The aircraft also comprises a lift fan mounted in the duct, a beam fixed to and spanning the duct, and a linkage bar substantially enclosed by the beam. A plurality of louvers are positioned at the duct opening and each is coupled to the linkage bar. An actuator is configured to drive longitudinal travel of the linkage bar in the beam, such that the plurality of louvers each move between an open position and a closed position when the aircraft transitions from a vertical flight mode to a horizontal flight mode.

In some examples, a method of controlling airflow is performed with respect to an airfoil structure containing a lift fan mounted in a duct. In the method, each louver of a plurality of louvers located at an opening of the duct is moved between an open position and a closed position. The closed position is rotationally offset and translationally offset from the open position.

In some examples, a fan apparatus comprises a duct having a duct opening, a fan mounted in the duct, and a plurality of louvers positioned at the duct opening. Each louver has an open position and a closed position. A sealing member is attached to the duct at the duct opening and forms a wall of a plenum. A pressure source is configured to pressurize the plenum such that the sealing member is urged against an edge of one or more of the louvers in the closed position.

In some examples, an aircraft comprises an airfoil structure including a duct or chamber having an opening. The aircraft also comprises a cover positioned at the opening and having an open position and a closed position, and a sealing member located at a lip of the opening and forming a wall of a plenum. A pressure source is configured to pressurize the plenum such that the sealing member is urged against an edge of the cover in the closed position.

In some examples, an aircraft comprises an airfoil structure including a duct having a duct opening. A sealing member is located at a lip of the duct opening and forms a wall of a plenum. A lift fan is mounted in the duct. A plurality of louvers are positioned at the duct opening and each is configured to move between an open position and a closed position when the aircraft transitions between a vertical flight mode and a horizontal flight mode. A sealing member is located at a lip of the duct opening and forms a wall of a plenum. A pressure source is configured to pressurize the plenum such that the sealing member is urged against an edge of one or more of the louvers in the closed position.

In some examples, a method of creating a seal in an aircraft is provided. In the method, a cover at an opening of a duct or chamber of the aircraft is closed to position an edge of the cover adjacent a sealing member forming a wall of a plenum. The plenum is pressurized to urge the sealing member against the edge of the cover.

The following subsections describe selected aspects of illustrative VTOL aircraft, lift fan apparatuses for VTOL aircraft, louvered covers for lift fan apparatuses, louver actuation assemblies for louvered covers, and fluid-actuated sealing assemblies for covers, such as louvered covers, as well as related systems and/or methods. The examples in these subsections are intended for illustration and should not be interpreted as limiting the entire scope of the present disclosure. Each section may include one or more distinct examples, and/or contextual or related information, function, and/or structure.

This subsection describes an illustrative aircraft <NUM> including fan apparatuses <NUM>. Each fan apparatus includes a lift fan <NUM> and louvered covers <NUM>; see <FIG>. Aircraft <NUM> may have any suitable combination of components and features, and may be used in any processes, described for the aircraft of subsections B-F.

<FIG> shows aircraft <NUM> in horizontal wing-supported flight, with forward flight <NUM> corresponding to a fore-to-aft axis <NUM> (or longitudinal axis) defined by the aircraft. The aircraft includes two fixed wings <NUM> extending from a fuselage <NUM>. Each wing <NUM> contains three fan apparatuses <NUM>, each including a lift fan <NUM> mounted in a duct <NUM> extending vertically through the wing. In general, aircraft <NUM> may include any effective number of lift fans, mounted in any effective position in an airfoil structure <NUM> of the aircraft, such as wings <NUM>, fuselage <NUM>, a tail, or the like. The number and positions of the lift fans may vary depending on aircraft configuration and phases of flights the aircraft is required to perform, for example take-off, climb, hover, outboard transition, cruise, forward-flight, descent, inboard transition, and landing.

<FIG> shows one of wings <NUM> in schematic cross-section through one of the fan apparatuses <NUM> during horizontal flight <NUM> of aircraft <NUM>. Wing <NUM> is an airfoil structure <NUM> having a leading edge <NUM> opposite a trailing edge <NUM>, with the leading and trailing edges separated along fore-to-aft axis <NUM> from one another. Leading edge <NUM> is more rounded than trailing edge <NUM>, and trailing edge <NUM> is more tapered than leading edge <NUM>. The wing has an upper surface <NUM> and a lower surface <NUM>. The upper and lower surfaces may be symmetrical to one another, as shown, or these surfaces may have different contours to give the wing camber.

Duct <NUM> extends vertically through wing <NUM> from upper surface <NUM> to lower surface <NUM>. The duct forms an approximately circular aperture through the wing, defined by a duct wall <NUM> of the duct. Duct <NUM> has an inlet opening <NUM> at upper surface <NUM> of the wing, and an outlet opening <NUM> at lower surface <NUM> of the wing. The wing or duct may be described as having a fore-to-aft axis or longitudinal axis, which is parallel to fore-to-aft axis <NUM> of aircraft <NUM>. When the aircraft is in horizontal flight, the fore-to-aft or longitudinal axis of the aircraft and/or wing may coincide with a relative wind direction, where relative wind is defined as the direction of movement of the surrounding atmosphere relative to the aircraft.

A lift fan <NUM> is mounted in duct <NUM>. The lift fan includes a fan blade assembly <NUM> (also called a fan rotor) and a stator <NUM>. The stator is rigidly fixed to duct <NUM>. The fan blade assembly is mounted above, and supported on stator <NUM>, and driven by a fan motor <NUM> about a rotational axis <NUM>, which is aligned with a central axis of duct <NUM>. Lift fan <NUM> and duct <NUM> may be referred to as contained in wing <NUM>.

A pair of louvered covers <NUM> are movably coupled to duct <NUM>. An upper cover <NUM> is located at inlet opening <NUM>, and a lower cover <NUM> is located at outlet opening <NUM>. Lift fan <NUM> is situated between upper cover <NUM> and lower cover <NUM>. Each louvered cover <NUM> includes a plurality of louvers <NUM> arranged as a series along the fore-to-aft axis of duct <NUM>. Each louver <NUM> has an airfoil shape configured to direct airflow into or out of duct <NUM>.

<FIG> show louvered covers <NUM> of lift fan <NUM> in three different positions, namely, a closed position, an intermediate position (interchangeably called a transitional position), and an open position. The closed position of <FIG> substantially excludes airflow into and/or through duct <NUM> during horizontal flight. The intermediate position of <FIG>, also called a partially open and/or partially closed position, deflects inlet airflow <NUM> into duct <NUM> at inlet opening <NUM>. The intermediate position is used when aircraft <NUM> is transitioning from horizontal to vertical flight, or vice versa, indicated by transition arrows <NUM>. Louvers <NUM> of upper cover <NUM> are angled forward. Louvers <NUM> of lower cover <NUM> are angled rearward, as shown, or may be angled forward or fully open, among others. In any event, louvers <NUM> of lower cover <NUM> guide outlet airflow <NUM> out of duct <NUM>. The open position of <FIG> is used during vertical flight <NUM> (e.g., take off, vertical ascent, hovering, vertical descent, and landing). Airflow <NUM>, <NUM> is more vertical than during the transition phase. The closed, intermediate, or open position of a louvered cover is produced collectively by the closed, intermediate, or open positions of the individual louvers <NUM> of the cover, and vice versa. For example, in a closed position of a louvered cover, each louver is arranged in a closed position.

<FIG> shows upper cover <NUM> in a closed position. Each louver <NUM> of the cover has a lateral extent or span, between opposite ends of the louver, which is generally perpendicular to fore-to-aft axis <NUM> of the aircraft. Each louver is shaped to conform to the shape of duct <NUM>, for example a circular shape. Accordingly, the louvers of the cover may have different lengths and each may be rounded at its opposite ends and/or along a leading/trailing edge, to match the adjacent horizontal curvature of the duct wall.

The louvers of the cover are configured for installation at different fore-to-aft positions of the duct. For example, in <FIG>, first, second, third, and fourth louvers <NUM> are arranged in order from fore to aft. The first and fourth louvers have shorter lateral extents than the second and third louvers. The first and fourth louvers are symmetrical to one another in plan, with the first louver have an arcuate leading edge and a linear trailing edge, and the fourth louver having an arcuate trailing edge and a linear leading edge. The second and third louvers are symmetrical to one another in plan, with each having leading and trailing edges that are linear and arcuate ends opposite one another.

<FIG> shows a schematic diagram of actuation assemblies of the aircraft of <FIG> for one of fan apparatuses <NUM>. Each actuation assembly may be operatively associated with a lift fan <NUM> mounted in a duct <NUM>, a louvered cover <NUM> at an opening of the duct, and/or a sealing member <NUM> at the duct wall of duct <NUM>. A fan actuation assembly <NUM> is operatively coupled to fan blade assembly <NUM> ("fan rotor") and includes fan motor <NUM> and a linkage, such as a driveshaft, that is firmly attached to the fan blade assembly and rotated by operation of the fan motor. A louver actuation assembly <NUM> is operatively coupled to louvered cover <NUM> and drives movement of louvers <NUM> of the cover between open, intermediate (transitional), and closed positions. The louver actuation assembly includes an actuator <NUM> (such as a motor) and a linkage assembly <NUM> that transmits motive force from the actuator to each louver <NUM> of the cover. A sealing actuation assembly <NUM> is operatively coupled to sealing member <NUM>. The sealing actuation assembly includes a pressure/vacuum source <NUM> to push sealing member <NUM> inward toward a central axis defined by duct <NUM> or pull sealing member <NUM> outward away from the central axis. The pressure/vacuum source may include only a pressure source, only a vacuum source, or both types of sources.

A controller <NUM> is configured to control and coordinate operation of the actuation assemblies. The controller controls operation of fan motor <NUM>, such as its activation state and speed. The controller also controls operation of louver actuator <NUM>, to move louvers <NUM> between open, intermediate, and closed positions. The controller further controls operation of pressure/vacuum source <NUM>, to seal the louvered cover when in a closed position.

Further aspects of illustrative actuation assemblies are described elsewhere in the present disclosure. For example, subsection C describes an illustrative louver actuation assembly, and subsection D describes an illustrative fluid-actuated sealing assembly for use with a cover of an aircraft.

This subsection describes VTOL aircraft <NUM>, <NUM>, and <NUM> having illustrative fan apparatuses <NUM>, <NUM>, and <NUM>, each including a louvered cover configured to further reduce the height of the boundary layer over a ducted lift fan relative to aircraft <NUM> of subsection A, when transitioning between vertical and horizontal flight modes (i.e., vertical to horizontal or horizontal to vertical); see <FIG>. This further reduction of the boundary layer provides aerodynamic and mechanical advantages during transition, such as less drag, reduced turbulence and vibration, improved flight control, a lower load on louvers of the louvered covers (and on a corresponding louver actuation assembly), and/or the like.

<FIG> shows a more schematic representation of an upper portion of wing <NUM> of aircraft <NUM> taken around fan apparatus <NUM> (compare with <FIG>). The fan apparatus includes lift fan <NUM>, duct <NUM>, and louvers <NUM> of upper cover <NUM>. A boundary layer <NUM> of slower moving air is produced by airflow over louvers <NUM> at inlet opening <NUM> of duct <NUM>, with upper cover <NUM> in a closed position. A closed-position height <NUM> of the boundary layer near a trailing edge of duct <NUM> is indicated.

<FIG> shows fan apparatus <NUM> as in <FIG>, except with louvers <NUM> of upper cover <NUM> in an intermediate position as in <FIG>, during transition between horizontal and vertical flight. Boundary layer <NUM> now has a reduced height <NUM>. However, further reduction of the boundary layer height for the intermediate position of the louvers would be aerodynamically and mechanically advantageous.

<FIG> illustrate three cover configurations for further reduction of the boundary layer height during transition between flight modes. The features of these three cover configurations may be used alone or in any suitable combination in an upper cover and/or a lower cover for a lift fan.

<FIG> show a fan apparatus <NUM> including a lift fan <NUM>, a duct <NUM>, and a fore-to-aft series of louvers 238a-238d of an upper cover <NUM> from a wing <NUM> of a VTOL aircraft <NUM>. Upper cover <NUM> is in a closed position in <FIG> and an intermediate position in <FIG> (compare with <FIG>). In contrast to louvers <NUM>, louvers 238a-238d have varying chord lengths <NUM> relative to one another, which further reduces a closed-position height <NUM> of a boundary layer <NUM> over duct <NUM> (<FIG>) to a further reduced height <NUM> (<FIG>).

Chord length <NUM> for each louver 238a-238d is defined as the maximum chord length for the louver, measured between a leading edge and a trailing edge of the louver. The chord length increases successively and progressively from fore to aft along the series of louvers 238a-238d (and along fore-to-aft axis <NUM>). More specifically, chord length <NUM> of louver 238a is less than louver 238b, which is less than louver 238c, which is less than louver 238d. Due at least in part to this difference in chord length, louvers that are located more aft along fore-to-aft series of louvers 238a-238d project farther out of duct <NUM> than louvers located closer to the fore (upstream) edge of upper cover <NUM>. A projection distance <NUM> (interchangeably called an extension length) of fore-most louver 238a out of duct <NUM> is compared with that of aft-most louver 238d in <FIG>. The greater projection distance <NUM> of aft-most louver 238d during transition allows it to reach farther out of the duct, to channel less-affected air into duct <NUM> from farther above the duct, thereby further reducing the boundary layer height. The projection distance is measured orthogonally from an upper edge or boundary of the duct, as shown in <FIG>.

The chord lengths and projection distances of the louvers may have any suitable relationships to further reduce the height of the boundary layer during transition between flight modes. One or more aft louvers of a louvered cover may have a greater chord length and/or projection distance than one or more fore louvers of the cover. The terms "fore louver" and "aft louver" are defined relative to one another, where a fore louver(s) of a cover is located upstream of each aft louver of the cover. For example, in <FIG>, louver 238b is a fore louver relative to louvers 238c and 238d, which are aft louvers relative to louver 238b, and louver 238b is an aft louver relative to louver 238a. The chord length and/or projection distance in the intermediate positions of the louvers may vary among the louvers of the cover by any amount effective to further reduce the boundary layer of a duct, such as an increase of at least <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> percent, among others, between a fore louver and an aft louver of the cover. The chord lengths and/or projection distances may or may not increase successively along the fore-to-aft series of louvers of the cover. The increase may be a linear increase <NUM>, as shown in <FIG>, or a nonlinear increase. If nonlinear, the increase may be logarithmic or exponential. A linear increase may be desirable to balance the contribution of louvers for further reduction in boundary layer height among the louvers. A logarithmic increase may be desirable to weight the further reduction toward an upstream portion of the cover. An exponential increase may be desirable to weight the further reduction toward a downstream portion of the cover.

<FIG> shows show a fan apparatus <NUM> including a lift fan <NUM>, a duct <NUM>, and a fore-to-aft series (along axis <NUM>) of louvers 338a-338d of an upper cover <NUM> from a wing <NUM> of a VTOL aircraft <NUM>. Louvers 338a-338d are in intermediate positions during transition between flight modes. A boundary layer <NUM> having a further reduced height <NUM> is present over duct <NUM>. Louvers 338a-338d have respective projection distances <NUM> exhibiting a linear increase <NUM> from fore to aft. However, in contrast to louvers 238a-238d of <FIG>, louvers 338a-338d each have the same chord length. Instead, the fore-to-aft increase in projection distances <NUM> is created by varying the position of a pivot axis <NUM> of the louvers, namely, situating each successive pivot axis progressively farther from the leading edge of the louver along the series of louvers.

<FIG> shows show a fan apparatus <NUM> including a lift fan <NUM>, a duct <NUM>, and a fore-to-aft series (along axis <NUM>) of louvers 438a-438d of an upper cover <NUM> from a wing <NUM> of a VTOL aircraft <NUM>. Louvers 438a-438d are in intermediate positions during transition between flight modes. A boundary layer <NUM> having a further reduced height <NUM> is present over duct <NUM>. Louvers 438a-438d have respective projection distances <NUM> exhibiting a linear increase <NUM> from fore to aft. However, as in <FIG> and in contrast to louvers 238a-238d of <FIG>, louvers 438a-438d each have the same chord length. Instead, the fore-to-aft increase in projection distances <NUM> is created by varying an angle <NUM> each louver 438a-438d forms with the top of duct <NUM>. Different angles <NUM> may be achieved by rotating louvers 438a-438d through different angular ranges and/or at different angular rotation rates between an open or closed position and the intermediate position. An illustrative louver actuation assembly for achieving different angular ranges and different angular rotation rates for a series of louvers is described below in subsection C.

A previously-proposed louver actuation mechanism has louvers of a louvered cover articulated on fixed hinges. A common pushrod is pivotably coupled to an arm of each of the louvers at a position spaced from the hinge axis of the corresponding fixed hinge. The pushrod is driven longitudinally to rotate each of the louvers via the fixed hinges, without any translational offset of the louvers. However, this actuation mechanism has some drawbacks. For example, because there is no translation of the louvers, the louvers are not positioned optimally throughout their rotational ranges. This is especially true for the forward-most louver and the aft-most louver of the cover. The forward-most louver remains too far from the forward edge (the forward inlet lip) of the duct at transition, where flow tends to separate when the aircraft is hovering with some forward speed. Also, the aft-most louver may remain too close to the aft edge (the aft inlet lip) of the duct, where the aft-most louver may act as a barrier for airflow into an aftwardly-adjacent louvered cover when the aircraft is hovering.

This subsection describes a VTOL aircraft <NUM> having an illustrative louver actuation assembly <NUM> for a fan apparatus <NUM> contained in an airfoil structure <NUM>; see <FIG>. The louver actuation assembly utilizes louvers on movable hinges instead of fixed hinges, such that the actuation assembly both rotates and translates louvers 538a-538f of a louvered cover <NUM> for a lift fan <NUM> of the fan apparatus.

Louver actuation assembly <NUM> offers various advantages, as described further below, including any combination of the following. The louver actuation assembly has a greater mechanical advantage because effective angles of the lever arms for the louvers never get too shallow. The louver actuation assembly provides more optimal translational and rotational positioning of individual louvers for open and intermediate positions of a louvered cover. Less flow separation occurs between the leading edge of the duct and the forward-most louver. Less interference is produced between louvers of adjacent louvered covers in the open position. Actuation components are protected inside a fixed beam of the fan apparatus. A common linkage bar of the louver actuation assembly slides in the beam along a travel path predefined by one or more guide channels, which reduces play and produces a stiffer actuation.

<FIG> shows a fragmentary portion of an airfoil structure <NUM> (such as a wing) of aircraft <NUM> taken around fan apparatus <NUM> and viewed from above louvered cover <NUM>, which is an upper cover <NUM>. In other examples, the louvered cover described in this subsection may be situated as a lower cover for a fan apparatus, at an outlet opening of a duct. Cover <NUM> includes a frame <NUM> and six louvers 538a-538f movably coupled to the frame, although any suitable number of louvers may be used in the cover. (The cover/louvers are shown dashed in <FIG>. ) Aircraft has a fore-to-aft axis <NUM> and louvers 538a-538f are arranged as a series along the axis, with each louver being elongated orthogonal to axis <NUM>. Six louvers are shown here for illustration, but any suitable number of louvers may be utilized for the louvered covers, such as <NUM>, <NUM>, <NUM>, or more louvers.

Frame <NUM> has a pair of beams 567a, 567b spanning duct <NUM> under louvers 538a-538f. Each beam 567a, 567b is firmly attached to (i.e., fixed to) duct <NUM> at opposite ends of the beam and remains fixed with respect to duct <NUM> while louvers 538a-538f are actuated. Each beam 567a, 567b spans duct <NUM> parallel to fore-to-aft axis <NUM> and has an airfoil shape (e.g., generally as shown for wing <NUM> in <FIG>, except with leading edge <NUM> located at the top of the beam). The beam houses and substantially encloses a portion of actuation assembly <NUM>, as described further below. In other examples, the frame may have only one beam or three or more beams. Each beam interchangeably is called a spine or a strut.

<FIG> shows only an upper portion of fan apparatus <NUM>, with lift fan <NUM> mounted in duct <NUM> and depicted in dashed lines. Louvered cover <NUM> is located at an inlet opening <NUM> of the duct. Louvers 538a-538f are arranged in open positions. Duct <NUM>, louvered cover <NUM>, and frame <NUM> have been sectioned as indicated in <FIG> through beam 567b.

Each of louvers 538a-538f includes a vane <NUM> (interchangeably called a flap) and a pair of carriers 569a, 569b firmly attached to the vane (see louver 538c in <FIG>). The vane spans duct <NUM> in the closed position of the louver, has an airfoil shape, and forms the body of the louver. Each vane <NUM> may remain completely outside beams 567a, 567b. Carriers 569a, 569b connect vane <NUM> to louver actuation assembly <NUM> and extend into respective beams 567a, 567b. In other examples, more for fewer carriers may be present in each louver, in correspondence with the number of fixed beams located adjacent the louvered cover in the duct.

Louver actuation assembly <NUM> includes an actuator <NUM> and a pair of matching linkage assemblies 550a, 550b substantially housed in respective beams 567a, 567b of frame <NUM>. The linkage assemblies are coupled to one another and to actuator <NUM> via a rotatable coupling <NUM>. The rotatable coupling is drivable in opposite rotational directions by actuator <NUM>. A gearbox may mechanically connect actuator <NUM> and rotatable coupling <NUM> to one another.

Each linkage assembly 550a, 550b includes a crank <NUM>, a crank link <NUM>, a linkage bar <NUM> (interchangeably called a pushrod), and six louver links <NUM> (one for each louver); see <FIG>. Pivot joints <NUM> pivotably couple crank <NUM> to a first end of crank link <NUM>, a second end of crank link <NUM> to linkage bar <NUM>, linkage bar <NUM> to a carrier 569a or 569b of each louver, a first end of each louver link <NUM> to beam 567a or 567b, and a second end of each louver link <NUM> to the corresponding carrier 569a or 569b for the louver. Pivot joints <NUM>, any or all of which may be hinge joints, are indicated by small circles/ovals in <FIG>, but only a fraction of the pivot joints are expressly labeled with a reference number, to improve clarity.

Rotation of rotatable coupling <NUM> by actuator <NUM> drives rotation <NUM> of both cranks <NUM> (see <FIG> and <FIG>). This rotation transmits force from each crank <NUM> to the corresponding linkage bar <NUM> via crank link <NUM> (see <FIG>). The force drives longitudinal travel <NUM> of each linkage bar <NUM> inside the corresponding beam 567a, 567b, which in turn produces both rotation and translation of each louver 538a-538f (compare <FIG>). Each crank <NUM> and adjacent crank link <NUM> form a respective cam to drive the longitudinal travel of linkage bar <NUM>. The cam has a large arc to increase mechanical advantage. In other examples, the cams may be replaced by, or supplemented with, a different mechanism, such as a jack screw, timing belt, etc..

<FIG> shows louvers 538a-538f in a closed position of louvered cover <NUM>. Adjacent pairs of louvers are in contact with one another along the leading/trailing edges of their vanes to form a seal that prevents airflow through the cover at positions between the louvers. For example, the vane of louver 538b has a leading edge that forms a seal with the trailing edge of the vane of louver 538a, and has a trailing edge that forms a seal with the leading edge of the vane of louver 538c.

Each linkage assembly 550a, 550b has an over-center configuration of crank <NUM> in the closed position of louvered cover <NUM>. The over-center configuration maintains the louvered cover in the closed position without active assistance from actuator <NUM> (also see <FIG>). The over-center configuration in <FIG> can be reached by rotating crank <NUM> clockwise, that is, opposite to (counter-clockwise) rotation <NUM> indicated in <FIG>. Once louvers 538a-538f are in their closed positions, the arm of the crank, and especially a pivot joint <NUM> connecting crank <NUM> to crank link <NUM>, has passed a center point. Any opening force applied directly to the vanes of louvers 538a-538f, such as by airflow, now urges further clockwise rotation of crank <NUM>. However, this clockwise rotation is blocked mechanically, which passively holds louvered cover <NUM> in the closed position until actuator <NUM> actively drives counter-clockwise rotation of crank <NUM>. In other examples, the cam has more complex geometry such that the open position of the louvered cover also is maintained passively without active assistance from the actuator.

The rate of rotation of each louver 538a-538f is determined by the length and orientation of the corresponding louver links <NUM> (one in each linkage assembly 550a, 550b) for that louver. In the depicted embodiment, louvers 538a-538f are configured to rotate at different angular rates, with the rate of rotation progressively increasing from fore to aft along the series of louvers 538a-538f. This configuration is achieved by using louver links <NUM> of different lengths and/or different orientations. The configuration allows the louvers to have different orientations from one another in an intermediate (transitional) position (see <FIG>; also see <FIG> and subsection B), and/or to fan out in the open position (see <FIG>), for more efficiently guiding air into the duct during vertical flight.

<FIG> shows a more detailed sectional side view of beam 567b taken in isolation, and <FIG> shows a cross-sectional view of beam 567b substantially housing linkage assembly 550b (also see <FIG>). Each beam 567a, 567b defines a slot 578a or 578b that is elongated substantially parallel to a longitudinal axis <NUM> of the beam (also see <FIG>). The slot is sized to permit linkage assembly 550a or 550b to be housed inside and substantially enclosed by the corresponding beam 567a or 567b. For example, crank <NUM>, crank link <NUM>, linkage bar <NUM>, and louver links <NUM> of each linkage assembly 550a or 550b are each substantially housed inside the corresponding beam. Each linkage bar <NUM> travels along slot 578a or 578b (and longitudinal axis <NUM>) inside the corresponding beam when louvers 538a-538f are actuated.

Each slot 578a, 578b is open on top (see <FIG>, <FIG>, and <FIG>). Louvers 538a-538f are separately coupled to beams 567a, 567b, and to linkage bars <NUM> housed in the beams, using louvers links <NUM> and carriers 569a, 569b, each of which extends out of beam 567a or 567b through the open top of slot 578a or 578b (also see <FIG>).

Each slot 578a, 578b includes a pair of forward guide channels <NUM> and a pair of aft guide channels <NUM> defined by opposite lateral walls of the slot (see <FIG>; only one aft guide channel <NUM> is visible). Linkage bar <NUM> includes and/or is attached to low-friction forward and aft slider elements <NUM>, <NUM> that slide longitudinally in forward and aft guide channels <NUM>, <NUM>. This configuration provides smooth, mechanically efficient travel of linkage bar <NUM> along a predefined travel path in the beam. Forward and aft guide channels <NUM>, <NUM> are elongated along nonparallel axes, which makes the predefined travel path curved instead of linear. A curved travel path can be beneficial to allow the linkage bar to follow a curved contour of the top of the duct. In other examples, fewer guide channels may be present, such as formed in only one lateral wall of each slot, and/or replacing each corresponding forward and aft pair of guide channels with a (longer) single guide channel, among others. Accordingly, each guide channel may be linear, as depicted in <FIG>, or may be curved along its long axis.

An effective seal is needed for the peripheral edge of movable covers on aircraft, such as a louvered cover of a ducted lift fan. (Sealing between louvers is much less problematic and can be realized with a flexible flange extending along a leading or trailing edge of the louvers. ) Without such a peripheral seal, there can be leakage airflow at the periphery of the cover during forward flight with the cover closed. For example, with a wing-embedded lift fan, this leakage airflow is through the duct, from the higher pressure bottom side to the lower pressure top side of the wing, resulting in aerodynamic losses. A louvered cover for a duct, when placed in a closed position, contacts an aerodynamically critical, convex surface at an opening of the duct. Any step or deviation in the smooth contour of the convex surface, to enable better sealing of the cover, could lead to detached airflow and therefore losses in performance when the cover is opened during transitional flight and/or hovering. When hovering, very high airflow occurs over the convex surface, resulting in low pressure (suction) on the convex surface. This suction could degrade the aerodynamic performance of the convex surface if part of the convex surface is made deformable to improve sealing. If a standard rubber gasket is used instead, the gasket requires a high amount of physical pressure to compress the gasket and ensure a tight seal. Accordingly, an actuation mechanism for a standard rubber gasket is too heavy to be practical for a VTOL aircraft. A new sealing system is needed for the louvered covers of VTOL aircraft.

This subsection describes aircraft <NUM> and <NUM> each having an illustrative fluid-actuated sealing system for a cover positioned at an opening of a duct or chamber, and an illustrative method <NUM> of forming a seal in an aircraft; see <FIG>. The sealing system enables efficient and lightweight sealing for a louvered cover at the circumference of the inlet lip of the duct.

<FIG> shows an airfoil structure <NUM> of aircraft <NUM>. The airfoil structure includes a chamber <NUM> having an opening <NUM>. A pivotable cover <NUM> is located at the opening and movable between a closed position, which is depicted with solid lines, and an open position, which is shown in phantom.

A sealing member <NUM> is attached to chamber <NUM> at a chamber wall <NUM> and at opening <NUM>. Sealing member <NUM> is actuated as described below for aircraft <NUM>, to form a seal, optionally a circumferential seal, with an edge of cover <NUM>.

<FIG> shows an airfoil structure <NUM> of an aircraft <NUM>. The airfoil structure contains a fan apparatus <NUM>. The fan apparatus includes a duct <NUM> containing a lift fan <NUM> and defining an inlet opening <NUM>. A louvered cover <NUM> including louvers <NUM> is located at the opening and movable between an open position and a closed position.

A sealing member <NUM> is attached to duct <NUM> at a duct wall <NUM> thereof. The sealing member may be a thin rubber membrane that is embedded in an area of the duct wall where the louvers in closed positions would otherwise make contact with the duct wall itself. Sealing member <NUM> is actuated as described below to form a seal with an edge of one or more louvers <NUM> of louvered cover <NUM>. The sealing member is formed of a flexible/deformable material, such as an elastically deformable material (e.g., rubber that is natural, synthetic (including an elastomer), or a combination thereof). The sealing member forms a seal and part of the aerodynamic surface at an opening of the duct.

<FIG> shows a top view of fan apparatus <NUM> with louvered cover <NUM> in a closed position, and <FIG> shows the same view with the louvered cover and lift fan <NUM> removed. Sealing member <NUM> is positioned at a lip <NUM> of inlet opening <NUM> and defines at least part of the inlet opening. The sealing member may extend more than halfway or substantially completely, among others, around a central axis <NUM> defined by duct <NUM>.

<FIG> shows a fragmentary sectional view of fan apparatus <NUM> taken through duct <NUM> with the louvered cover in an open position (e.g., when the aircraft is hovering), and thus not visible here (also see <FIG>). The lift fan is driving airflow <NUM> through the duct. A sealing actuation assembly <NUM> including a pressure/vacuum source <NUM> is applying suction <NUM> to sealing member <NUM> via a plenum <NUM>, to counteract suction created by airflow <NUM>, which would otherwise deform sealing member <NUM> into a less aerodynamic shape. Suction <NUM> on sealing member <NUM> may be greater than the suction created by airflow <NUM>. The pressure/vacuum source is operatively connected to a controller <NUM> and is in fluid communication with plenum <NUM> via piping <NUM> and a pneumatic fitting <NUM>. Pressure/vacuum source <NUM> may have a single pump for fluid (e.g., an air pump) that is reversible to apply suction or (positive) pressure, or separate pumps for applying suction and pressure. In other examples, the pressure/vacuum source may be a pneumatic cylinder that is mechanically actuated, or a valve connected to another pressure/vacuum source(s) of the aircraft, such as a turbine.

Plenum <NUM> is formed collectively by duct <NUM> and sealing member <NUM>. The duct defines a recess <NUM>, such as an annular recess, in duct wall <NUM>, and sealing member <NUM> is attached to the duct over the recess. The sealing member is bonded to duct wall <NUM> at a pair of indentations 705a, 705b formed by the duct wall along opposite edges of recess <NUM>, such that the sealing member covers an open side of recess <NUM> to complete the plenum. Sealing member <NUM> is structured as a membrane having an outer surface <NUM> and an inner surface <NUM> opposite one another, with the outer surface being closer to central axis <NUM> of the duct (also see <FIG>). The outer surface is flush with duct wall <NUM> to avoid any offset that would alter airflow along the duct wall. The inner surface provides a wall <NUM> of plenum <NUM>. A portion of the inner surface may be bonded to a shoulder <NUM> formed by each indentation 705a, 705b, and an edge of sealing member <NUM> may be bonded to a wall <NUM> of each indentation 705a, 705b. The depth of each indentation 705a, 705b matches the thickness of sealing member <NUM>.

Plenum <NUM> contains a porous material <NUM>, interchangeably called a porous insert. The porous insert may be a single piece, a series of pieces arranged along the plenum and each having a cross-sectional shape matching that of the plenum, or pellets/particles, among others.

Porous material <NUM> is sufficiently permeable to permit fluid to flow through the porous material between a port <NUM> of the plenum and wall <NUM> of sealing member <NUM>, to push the sealing member with fluid pressure or pull the sealing member with fluid suction. Plenum <NUM> is substantially filled with porous material <NUM>, which advantageously limits movement of sealing member <NUM> toward the plenum when suction is applied to the plenum. Sealing member <NUM> is urged against the porous material under suction during hovering of the aircraft, which holds sealing member <NUM> in an aerodynamic shape relative to adjacent duct wall <NUM>. The porous material also ensures that suction is applied to sealing member <NUM> uniformly along its length.

Any suitable fluid may be used to apply pressure and suction with pressure/vacuum source <NUM>. The fluid may be gaseous (e.g., air, nitrogen, carbon dioxide, or the like) or liquid (e.g., oil or water). Accordingly, sealing actuation assembly <NUM> may be pneumatic or hydraulic.

<FIG> shows another fragmentary sectional view of fan apparatus <NUM>, as in <FIG>, except with the louvered cover <NUM> in a closed position, taken during forward flight of aircraft <NUM>. Sealing actuation assembly <NUM> is pressurizing plenum <NUM>, by applying fluid pressure <NUM> to the plenum and sealing member <NUM>. The fluid pressure urges sealing member <NUM> away from recess <NUM> and against an edge <NUM> of one or more louvers <NUM> of louvered cover <NUM>. The deformability of sealing member <NUM> allows it to conform to the local contours of louvers <NUM>, thereby creating a fluid tight seal at the interface. A gap <NUM> may be formed between porous material <NUM> and sealing member <NUM> in some examples when the plenum is pressurized.

<FIG> is a flowchart depicting steps of an illustrative method <NUM> of forming a seal in an aircraft, and may not recite all steps of the method. The steps listed in the flowchart may be performed in any suitable order and combination (including simultaneously) using any of the aircraft, systems, apparatus, and devices of the present disclosure. Any of the steps may be omitted from the method.

At step <NUM>, a cover of a duct (or chamber) is opened. The duct (or chamber) may be included in an airfoil structure, such as a wing, of an aircraft, and may be situated at an opening (an inlet opening or outlet opening) of the duct (or chamber). The cover may or may not be a louvered cover including a plurality of louvers. The cover may be opened partially to an intermediate (transitional) position and/or fully to an open position, to permit airflow into the duct (or chamber).

At step <NUM>, a lift fan mounted in the duct is operated. The lift fan may be operated during a vertical flight mode of the aircraft. The lift fan may be activated before or after step <NUM>, depending on the phase of flight.

At step <NUM>, the cover is closed (i.e., moved to a closed position). The cover may be closed using any suitable actuation assembly. For example, the cover may be closed by moving each louver of a plurality of louvers of the cover to a closed position, to substantially exclude airflow into or out of the duct or chamber via the opening.

At step <NUM>, a plenum is pressurized to urge a sealing member against an edge of the cover. The plenum may be formed collectively by a wall(s) of the duct (or chamber) and the sealing member. Step <NUM> may form a substantially circumferential seal between the cover and the sealing member, to more completely exclude airflow into or out of the opening of the duct or chamber. In some examples, a seal may be formed between the sealing member and an edge of each louver of a plurality of louvers of the cover.

At step <NUM>, the aircraft flies forward (in a horizontal flight mode). The aircraft may fly forward with the cover closed and sealed, while airflow into or out of the duct (or chamber) is restricted or prevented by the seal between the sealing member and the cover.

At step <NUM>, suction is applied to the plenum. With suction applied, the sealing member maintains its aerodynamic shape and position when the cover is opened, such as at step <NUM>. Step <NUM> may be performed before, during, or after step <NUM>.

This section describes steps of an illustrative method <NUM> of controlling airflow into a lift fan; see <FIG>. Aspects of aircraft, fans, and/or fan covers described above may be utilized in the method steps described below. Where appropriate, reference may be made to components and systems that may be used in carrying out each step. These references are for illustration, and are not intended to limit the possible ways of carrying out any particular step of the method.

<FIG> is a flowchart illustrating steps performed in an illustrative method, and may not recite the complete process or all steps of the method. Although various steps of method <NUM> are described below and depicted in <FIG>, the steps need not necessarily all be performed, and in some cases may be performed simultaneously or in a different order than the order shown.

At step <NUM>, the method includes using a plurality of louvers extending over the lift fan. The lift fan may be mounted in a duct in an airfoil, such as the wing of a VTOL aircraft. Together the louvers may comprise a fan cover, and may be operatively linked by an actuation system. The louvers may be positioned at an inlet opening of the duct. Each louver may span the inlet opening, and may have an airfoil shape configured to direct airflow alternately over or into the inlet opening.

The louvers may be actuated to alter the volume of air that enters the fan duct. The louvers may be controlled by a flight control system of the aircraft as part of flight phases such as takeoff and landing, climbing and descent, and/or cruising and maneuvering. Steps <NUM>-<NUM> of method <NUM> may each be performed according to and/or as part of a phase of flight, as indicated in <FIG>.

Step <NUM> may be performed during takeoff and/or hover, and includes maintaining the louvers in open positions. In the open positions, the louvers may be configured to direct air from above the duct through the inlet opening into the duct. Distal portions of the louvers may extend above the duct and surrounding airfoil surface, and each louver may extend at a different angle in order to entrain air from a wide range of angles. Angles of the louver may vary from a forward (fore) end of the duct to a rear (aft) end of the duct, and in some examples may vary linearly by approximately thirty degrees or more. A longitudinally central louver may be approximately vertical, while fore louvers rotate open to less than a vertical position and aft louvers rotate past the vertical position.

Step <NUM> may be performed during transition from hover to horizontal flight, and includes moving the louvers from open to closed positions. As the aircraft transitions between vertical (hovering) and horizontal flight, incoming airflow may be generated by horizontal acceleration as well as vertical suction of the fan, and the angle of incoming airflow at the duct may change. The louvers may be rotated to match the changing angle of incoming airflow and effectively turn the air in order to maintain airflow into the lift fan.

The louvers may be rotated such that each remains at approximately a zero angle of attack to the incoming airflow as the incoming airflow changes, or at least such that an angle of attack between positive and negative <NUM> degrees is maintained.

The louvers may be rotated through a limited angular range, from an orientation selected to maximize air entrainment in the open position to a near-horizontal orientation in the closed position. Each louver may rotate through a different angular range, and may rotate at a different angular rate. In the present example the angular ranges may be between approximately <NUM> and <NUM> degrees. In some examples, the angular ranges may be between approximately <NUM> and <NUM> degrees.

The louvers may be rotated at a constant rate from the open position to the closed position, may be rotated in stages, and/or may be rotated in any manner consistent with desired flight control. For example, the aircraft may transition directly from vertical to horizontal flight modes, or the aircraft may operate for an extended period in the transitional mode.

Step <NUM> may be performed during horizontal or wing-borne flight, and includes maintaining the louvers in the closed positions. In flight, the lift fan may be off and incoming airflow may result only from horizontal acceleration. In the closed positions, the louvers may be configured to direct the incoming airflow over the airfoil surface and exclude the incoming airflow from the inlet opening of the duct. The louvers may lie approximately flush with the airfoil surface, and substantially cover the inlet opening of the duct.

Step <NUM> may be performed during transition from horizontal flight to hover, and includes moving the louvers from the closed positions to the open positions. As the aircraft transitions between horizontal flight and hover, incoming airflow may be generated by vertical suction of the fan as well as by horizontal acceleration, and the angle of incoming airflow at the duct may change. The orientations of the louvers may be changed to allow air into the inlet opening to supply the lift fan, and to match the changing angle of the incoming airflow.

Step <NUM> may be performed during hover and/or landing, and includes maintaining the louvers in the open positions. The open positions of the louvers may be the same as maintained in step <NUM> during takeoff. Method <NUM> may be repeated, and/or any of steps <NUM>-<NUM> performed as needed during operation of the aircraft to effectively control airflow into the lift fan.

Examples disclosed herein may be described in the context of an illustrative aircraft <NUM> (see <FIG>), such as any of the VTOL aircraft disclosed herein, and an illustrative aircraft manufacturing and service method <NUM> (see <FIG>). Method <NUM> includes a plurality of processes, stages, or phases. During pre-production, method <NUM> may include a specification and design phase <NUM> of aircraft <NUM> and a material procurement phase <NUM>. During production, a component and subassembly manufacturing phase <NUM> and a system integration phase <NUM> of aircraft <NUM> may take place. Thereafter, aircraft <NUM> may go through a certification and delivery phase <NUM> to be placed into in-service phase <NUM>. While in service (e.g., by an operator), aircraft <NUM> may be scheduled for routine maintenance and service phase <NUM> (which may also include modification, reconfiguration, refurbishment, and so on of one or more systems of aircraft <NUM>). While the examples described herein relate generally to operational use during in-service phase <NUM> of aircraft <NUM>, they may be practiced at other stages of method <NUM>.

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

As shown in <FIG>, aircraft <NUM> produced by illustrative method <NUM> may include a frame <NUM> with a plurality of systems <NUM> and an interior <NUM>. Examples of plurality of systems <NUM> include one or more of a propulsion system <NUM>, an electrical system <NUM>, a hydraulic system <NUM>, an environmental system <NUM>, and a flight control system <NUM>. Each system may comprise various subsystems, such as controllers, processors, actuators, effectors, motors, generators, etc., depending on the functionality involved. Any number of other systems may be included. Although an aerospace example is shown, the principles disclosed herein may be applied to other industries, such as the automotive industry, rail transport industry, and nautical engineering industry. Accordingly, in addition to aircraft <NUM>, the principles disclosed herein may apply to other vehicles, e.g., land vehicles, marine vehicles, etc..

Apparatuses and methods shown or described herein may be employed during any one or more of the stages of the aircraft manufacturing and service method <NUM>. For example, components or subassemblies corresponding to component and subassembly manufacturing phase <NUM> may be fabricated or manufactured in a manner similar to components or subassemblies produced while aircraft <NUM> is operating during in-service phase <NUM>. Also, one or more examples of the apparatuses, methods, or combinations thereof may be utilized during manufacturing phase <NUM> and system integration phase <NUM>, for example, by substantially expediting assembly of or reducing the cost of aircraft <NUM>. Similarly, one or more examples of the apparatus or method realizations, or a combination thereof, may be utilized, for example and without limitation, while aircraft <NUM> is in in-service phase <NUM> and/or during maintenance and service phase <NUM>.

The different examples of a fan apparatus, a louvered cover with varying chord lengths and/or projection distances, an actuation assembly for a louvered cover, a sealable cover for a duct/chamber, and corresponding aircraft and associated methods described herein, provide several advantages over known solutions. For example, illustrative examples described herein of louvered covers including louvers with different chord lengths and/or different projection distances in an intermediate position reduce the height of a boundary layer over an airfoil structure when transitioning between horizontal and vertical flight modes, for a smoother and more efficient transition. Illustrative examples described herein of louver actuation assemblies move louvers of a louvered cover with improved mechanical advantage and more optimal positioning, by rotation and translation of the louvers. Illustrative examples described herein of sealing assemblies provide sealing of covers, such as louvered covers of fan apparatuses, by fluid-driven actuation of a sealing member, which provides a lighter actuation mechanism with fewer moving parts and/or more reliable sealing.

Additionally, and among other benefits, illustrative examples described herein provide low-turbulence airflow to a lift fan of a fan apparatus.

Additionally, and among other benefits, illustrative examples described herein improve lift and reduce drag and vibration during transition between flight modes in a VTOL aircraft.

Additionally, and among other benefits, illustrative examples described herein house a linkage assembly for louver actuation inside a fixed beam of a fan apparatus, which protects the linkage assembly and makes the fan apparatus more aerodynamic.

No known system or apparatus can perform these functions, particularly under flight conditions. Thus, the illustrative examples described herein are particularly useful for airfoil-embedded lift fans of VTOL aircraft. However, not all examples described herein provide the same advantages or the same degree of advantage.

Claim 1:
A fan apparatus (<NUM>), comprising:
a duct (<NUM>) having an opening (<NUM>, <NUM>);
a lift fan (<NUM>) mounted in the duct (<NUM>);
a series of louvers (238a-238d) positioned at the opening (<NUM>, <NUM>) and each configured to move between an open position, an intermediate position, and a closed position, the louvers (238a-238d) being offset from one another along a fore-to-aft axis (<NUM>); and
wherein the series of louvers (238a-238d) includes a fore louver and an aft louver, and wherein a chord length (<NUM>) of the aft louver is greater than a chord length (<NUM>) of the fore louver, and
wherein, in the intermediate position, the aft louver of the series projects farther out of the duct (<NUM>) than the fore louver of the series.