VTOL vehicle with fan blades outside of exhaust flowpath

An aircraft defining a vertical direction and a transverse direction. The aircraft may include a fuselage, a wing extending from the fuselage, and a hybrid-electric propulsion system. The hybrid-electric propulsion system may include a power source, a plurality of vertical thrust electric fans arranged along the wing and driven by the power source, and a forward thrust propulsor. The power source may include a combustion engine and an electric generator. The combustion engine may also define a flowpath for exhausting combustion gases. The forward thrust propulsor may be selectively or permanently mechanically coupled to the combustion engine. The forward thrust propulsor may include a propulsor fan having a plurality of fan blades arranged outside of the flowpath of the combustion engine for exhausting combustion gases.

FIELD

The present subject matter relates generally to a propulsion system for an aircraft having vertical takeoff and landing capabilities.

BACKGROUND

Aircraft have been developed with a capability for performing vertical takeoff and landings. Such a capability may allow for the aircraft to reach relatively rugged terrains and remote locations, where it may be impractical or infeasible to construct a runway large enough to allow for a traditional aircraft (lacking vertical takeoff capability) to takeoff or land.

Typically these aircraft capable of performing vertical takeoff and landings have engines and propulsors that are vectored to generate both vertical thrust and forward thrust. However, the design characteristics that make a propulsor efficient for vertical takeoff and landing may not result in efficient forward flight. Accordingly, existing aircraft capable of performing vertical takeoff and landing include propulsors that may be well suited for generating vertical thrust, but that may not be very well suited for efficient forward flight. This discrepancy between vertical takeoff and landing and cruise efficiency is exaggerated as cruise speed increases. An aircraft capable of more efficiently performing a vertical takeoff and landing combined with high speed cruise would therefore be useful.

BRIEF DESCRIPTION

Aspects and advantages will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

In one aspect, the present disclosure is directed to an aircraft defining a vertical direction and a transverse direction. The aircraft includes a fuselage, a wing extending from the fuselage, and a hybrid-electric propulsion system. The hybrid electric propulsion system includes a power source, a plurality of vertical thrust electric fans arranged along the wing and driven by the power source, and a forward thrust propulsor. The power source includes a combustion engine and an electric generator. The combustion engine also defines a flowpath for exhausting combustion gases. The forward thrust propulsor is selectively or permanently mechanically coupled to the combustion engine. The forward thrust propulsor includes a propulsor fan having a plurality of fan blades arranged outside of the flowpath of the combustion engine for exhausting combustion gases.

In one embodiment, the combustion engine may include a casing defining an exterior surface. Further, the plurality of fan blades of the propulsor fan may be arranged outside the exterior surface of the casing of the combustion engine. In another embodiment, the forward thrust propulsor may be configured as a variable pitch propulsor. In such an embodiment, the forward thrust propulsor may include an outer nacelle at least partially defining a fan air flowpath and further including a pitch change mechanism. The pitch change mechanism may be positioned inward of the fan air flowpath and outward of the flowpath of the combustion engine. In a further embodiment, the combustion engine may define an outlet positioned inward of the fan blades in a substantially radial direction and downstream, aft, or both of the fan blades in a substantially axial direction. In another embodiment, the fan blades may be positioned aft, downstream, or both of a turbine section of the combustion engine along an axial direction.

In another embodiment, the variable pitch propulsor may define a pitch range enabling the forward thrust propulsor to generate forward thrust, reverse thrust, and substantially no thrust during operation. In one exemplary embodiment, the combustion engine may be a turboshaft engine. In such an embodiment, the turboshaft engine may include an output shaft. Further, the forward thrust propulsor may include a fan shaft selectively or permanently mechanically coupled to the output shaft. In one embodiment, the forward thrust propulsor may be mounted to the fuselage of the aircraft at an aft end of the aircraft. In another embodiment, the hybrid-electric propulsion system may further include a coupling unit. Further, the combustion engine may be selectively mechanically coupled to the forward thrust propulsor through the coupling unit.

In another embodiment, the hybrid-electric propulsion system may further include a speed change mechanism. As such, the combustion engine may be mechanically coupled to the forward thrust propulsor through the speed change mechanism. In additional embodiments, the power source may further include an electric energy storage unit. In such embodiments, each of the plurality of vertical thrust electric fans may be electrically coupled to and driven by at least one of the electric generator or the electric energy storage unit. In one exemplary embodiment, the power source may further include an electric motor electrically coupled to and driven by the electric energy storage unit. Further, the electric motor may be coupled to and configured to drive the forward thrust propulsor.

In additional embodiments, the plurality of vertical thrust electric fans may be integrated into the wing and fixed in orientation to generate thrust along the vertical direction. In one particular embodiment, the wing may be a first wing. Further, the plurality of vertical thrust electric fans may be a first plurality of vertical thrust electric fans. In such embodiments, the aircraft may further include a second wing coupled to and extending from the fuselage. The hybrid-electric propulsion system may further include a second plurality of vertical thrust electric fans integrated into the second wing and oriented to generate thrust along the vertical direction. As such, the second plurality of vertical thrust electric fans may be arranged along a length of the second wing.

In another embodiment, the wing may be a first wing, and the plurality of vertical thrust electric fans of the hybrid electric propulsion system may be a first plurality of vertical thrust electric fans. In such an embodiment, the aircraft may further include a second wing, a third wing, and a fourth wing. Further, the hybrid electric propulsion system may further include a second plurality of vertical thrust electric fans integrated into the second wing and arranged along a length of the second wing, a third plurality of vertical thrust electric fans integrated into the third wing and arranged along a length of the third wing, and a fourth plurality of vertical thrust electric fans integrated into the fourth wing and arranged along a length of the fourth wing. As such, each of the second plurality of vertical thrust electric fans, the third plurality of vertical thrust electric fans, and fourth plurality of vertical thrust electric fans may be oriented to generate thrust along the vertical direction. It should be further understood that the aircraft may further include any of the additional features as described herein.

In another aspect, the present disclosure is directed to a hybrid-electric propulsion system for an aircraft including a power source, a plurality of vertical thrust electric fans, and a forward thrust propulsor. The power source includes a combustion engine and an electric generator. The power source includes a combustion engine defining a flowpath for exhausting combustion gases. The plurality of vertical thrust electric fans are driven by the power source. The forward thrust propulsor is selectively or permanently mechanically coupled to the combustion engine and includes a propulsor fan having a plurality of fan blades. Further, the plurality of fan blades of the propulsor fan are arranged outside of the flowpath of the combustion engine for exhausting combustion gases.

In one embodiment, the combustion engine may include a casing defining an exterior surface. Further, the plurality of fan blades of the propulsor fan may be arranged outside the exterior surface of the casing of the forward thrust propulsor. In another embodiment, the forward thrust propulsor may be configured as a variable pitch propulsor including at least one pitch change mechanism. As such, the variable pitch propulsor may define a pitch range enabling the forward thrust propulsor to generate forward thrust, reverse thrust, and substantially no thrust during operation.

These and other features, aspects, and advantages will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain certain principles of the invention. It should be further understood that the hybrid-electric propulsion system may further include any of the additional features as described herein.

DETAILED DESCRIPTION

An aircraft is generally provided capable of performing vertical takeoff and landing. The aircraft defines a vertical direction and a transverse direction. More specifically, the aircraft includes a fuselage, a wing coupled to and extending from the fuselage, and a hybrid-electric propulsion system. As such, the hybrid-electric propulsion system includes a power source, a plurality of vertical thrust electric fans, and a forward thrust propulsor. The power source includes a combustion engine and an electric generator. The combustion engine defines a flowpath for exhausting combustion gases. Further, the plurality of vertical thrust electric fans are arranged along a length of the wing and driven by the power source. The forward thrust propulsor is selectively or permanently mechanically coupled to the combustion engine. Furthermore, the forward thrust propulsor includes a propulsor fan having a plurality of fan blades. More specifically, the plurality of fan blades is arranged outside of the flowpath of the combustion engine for exhausting combustion gases.

A vertical takeoff and landing aircraft having a forward thrust propulsor mechanically coupled to a combustion engine in accordance with one or more embodiments of the present disclosure may allow for a more robust and efficient coupling of the forward thrust propulsor to the combustion engine, while still allowing for desired amount of control of the amount of forward thrust generated by the forward thrust propulsor. Arranging the propulsor fan blades outside of the flowpath of the engine exhaust may ensure the operation of the forward thrust propulsor is not negatively affected by the engine exhaust. Furthermore, such a placement of the forward thrust propulsor may allow for smoother flow to the propulsor fan blades and may therefore lead to a more efficient aircraft.

Referring now to the drawings, wherein identical numerals indicate the same elements throughout the Figures (“Figs.”),FIGS. 1 through 3depict an aircraft10in accordance with various embodiments of the present disclosure. More specifically,FIG. 1provides a perspective view of the exemplary aircraft10;FIG. 2provides a top, schematic view of the exemplary aircraft10ofFIG. 1in a vertical thrust configuration; andFIG. 3provides a top, schematic view of the exemplary aircraft10ofFIG. 1in a forward thrust configuration. As shown inFIGS. 1 through 3collectively, the aircraft10defines a longitudinal direction L (and a longitudinal centerline12that extends therethrough), a vertical direction V, and a transverse direction T. Additionally, the aircraft10defines a port side14and an opposite starboard side16.

The aircraft10includes a fuselage18extending between a forward end20and an aft end22generally along the longitudinal centerline12of the aircraft10. The aircraft10additionally includes a four wings, each attached to or formed integrally with the fuselage18. Specifically, for the embodiment depicted, the aircraft10includes a first wing, a second wing, a third wing, and a fourth wing, or more particularly an aft starboard wing24, an aft port wing26, a forward starboard wing28, and a forward port wing30. Each of these wings24,26,28,30is attached to, or formed integrally with, the fuselage18and extends from the fuselage18outwardly generally along the transverse direction T (i.e., outwardly relative to the fuselage18). It will be appreciated that although the forward port wing30and forward starboard wing28are depicted as being separate wings, in other embodiments, the forward port wing30and forward starboard wing28may be formed integrally, and together attached to the fuselage18. Similarly, although the aft port wing26and aft starboard wing24are depicted as being separate wings, in other embodiments, the aft port wing26and aft starboard wing24may be formed integrally, and together attached the fuselage18.

Although not depicted, in other embodiments, the aircraft10may additionally include one or more stabilizers, such as one or more vertical stabilizers, horizontal stabilizers, etc. Moreover, although not depicted, in certain embodiments, one or more of the wings may additionally include flaps, such as leading-edge flaps or trailing edge flaps, for assisting with controlling the aircraft10during flight.

Referring still toFIGS. 1 through 3, the exemplary aircraft10further includes a hybrid-electric propulsion system32for providing the aircraft10with a desired amount of thrust during operation. Broadly speaking, the exemplary hybrid-electric propulsion system32includes a plurality of vertical thrust electric fans (or “VTE fans”) for generating vertical thrust during operation, a forward thrust propulsor34, and a power source36for driving the plurality of VTE fans and the forward thrust propulsor34. Additionally, for the embodiment depicted, the hybrid-electric propulsion system32includes an electric communication bus38for, e.g., providing electrical power from the power source36to the plurality of VTE fans.

More specifically, for the embodiment depicted, the power source36includes a combustion engine40, an electric machine42, and an electric energy storage unit44. As will be described in greater detail below with reference toFIG. 6, the combustion engine40is configured to mechanically drive the forward thrust propulsor34. More specifically, the forward thrust propulsor34is selectively or permanently mechanically coupled to the combustion engine40. Additionally, the combustion engine40is coupled to the electric machine42. Accordingly, in at least certain embodiments, the combustion engine40may drive the electric machine42such that the electric machine42may generate electrical power. In such a manner, the electric machine42may be configured as an electric generator. Further, in such an exemplary embodiment, the electric machine42may provide the electrical power to, e.g., the plurality of VTE fans during at least certain operations of the aircraft10, to the electric energy storage unit44, or both. In such a manner, the plurality of VTE fans may be driven by the power source36, and, more particularly, may be driven at least in part by the electric machine42.

Referring particularly toFIGS. 2 and 3, the electric energy storage unit44may be a battery or other suitable component for storing electrical power. The electric energy storage unit44may receive electrical power from, e.g., the electric machine42(operating as an electric generator), and store electrical power for use during operation of the aircraft10. For example, the electric energy storage unit44may receive and store electrical power from the electric machine42(operating as an electric generator) during certain operations and subsequently provide electrical power to the plurality of VTE fans during other operations. Additionally, in still other operations, the electric energy storage unit44may provide electrical power back to the electric machine42to, e.g., power the aft fan for short durations, power the combustion engine40during emergency operations, or add power to the forward thrust propulsor34and/or to the combustion engine40during high power demand operations. Accordingly, with such exemplary embodiments, the electric machine42may further be configured as an electric motor.

Referring to a first of the plurality of wings of the aircraft10, and more particularly to the aft starboard wing24depicted inFIG. 2, the hybrid-electric propulsion system32includes a first plurality of VTE fans46integrated into the aft starboard wing24and oriented to generate thrust along the vertical direction V. In such a manner, each of the first plurality of VTE fans46are vertical lift fans and, as will be discussed in more detail below, are fixed in position such that they are only capable of generating thrust substantially along the vertical direction V of the aircraft10. As will be discussed in greater detail below, each of the first plurality of VTE fans46is electrically coupled to the power source36to receive electrical power from, e.g., the electric machine42or the electric energy storage unit44.

It will be appreciated, that as used herein, the term “along the vertical direction V of the aircraft10” refers to a vertical direction defined by a normal orientation of the aircraft10. For example, if the aircraft10is, e.g., tilted forward during certain operations, the first plurality of VTE fans46may provide thrust in a direction that is still along the vertical direction of the aircraft10, but tilted relative to absolute vertical direction. Additionally, in this context, the term “substantially” refers to being within about thirty degrees of the vertical direction V of the aircraft10.

Additionally, the first plurality of VTE fans46are arranged along a length of the aft starboard wing24generally along the transverse direction T. Additionally, the first plurality of VTE fans46includes an outermost VTE fan48along the transverse direction T relative to the fuselage18of the aircraft10and at least one interior VTE fan50. More particularly, for the embodiment ofFIG. 2, the first plurality of VTE fans46includes three interior VTE fans50. However, in other embodiments, the first plurality of VTE fans46may have any other suitable number of interior fans, as will be discussed in more detail below. It will be appreciated that the outermost VTE fan48is at least one of a variable pitch fan or a variable speed fan to provide increased stability to the aircraft10. For example, in certain embodiments, the outermost VTE fan48may be a variable pitch and variable speed fan. As will be appreciated, by changing a pitch of a plurality of fan blades of the outermost VTE fan48, an amount of thrust generated by the outermost VTE fan48may be modified without requiring any change to a rotational speed of the outermost VTE fan48.

It will further be appreciated that the hybrid-electric propulsion system32includes a similar plurality of vertical thrust electric fans integrated into the other wings26,28,30of the aircraft10. Each of these electric fans are similarly oriented to generate thrust substantially along the vertical direction V of the aircraft10, and in such a manner may therefore also be configured as VTE fans. More specifically, the hybrid-electric propulsion system32further includes a second plurality of VTE fans52integrated into the aft port wing26and arranged along a length of the aft port wing26, a third plurality of VTE fans54integrated into the forward starboard wing28and arranged along a length of the forward starboard wing28, and a fourth plurality of VTE fans56integrated into the forward port wing30and arranged along a length of the forward port wing30.

As with the first plurality of VTE fans46, the second plurality of VTE fans52includes an outermost VTE fan58along the transverse direction T. Additionally, the third plurality of VTE fans54also includes an outermost VTE fan60along the transverse direction T, and the fourth plurality of VTE fans56includes an outermost VTE fan62along the transverse direction T. The outermost VTE fans58,60,62of the second plurality of VTE fans52, of the third plurality of VTE fans54, and of the fourth plurality of VTE fans56, respectively, are similarly configured as one of a variable pitch fan or a variable speed fan. More particularly, for the embodiment ofFIG. 2, each of such outermost VTE fans58,60,62are configured as variable pitch fans. Accordingly, each of such outermost VTE fans58,60,62may be configured in substantially the same manner as the outermost VTE fan48of the first plurality of VTE fans46(see, e.g.,FIGS. 4 and 5).

With reference back to the first plurality of VTE fans46, for the embodiment ofFIG. 2, at least one of the interior VTE fans50of the first plurality of VTE fans46is configured differently than the outermost VTE fan48. More specifically, for the embodiment depicted, the interior VTE fans50of the first plurality of VTE fans46are each configured as fixed pitch fans, while the outermost VTE fan48is configured as a variable pitch fan (discussed above). Such a configuration may allow at least some of the first plurality of VTE fans46to have a simpler configuration, while the first plurality of VTE fans46may still provide a desired amount of stability for the aircraft10due to the inclusion of a variable pitch outermost VTE fan48.

Similarly, the second plurality of VTE fans52includes at least one interior VTE fan64, the third plurality of VTE fans54includes at least one interior VTE fan66, and the fourth plurality of VTE fans56includes at least one interior VTE fan68. More specifically, the second plurality of VTE fans52includes three interior VTE fans64, the third plurality of VTE fans54includes one interior VTE fan66, and the fourth plurality of VTE fans56also includes one interior VTE fan68. For the embodiment depicted, each of the at least one interior VTE fans64,66,68of the respective pluralities of VTE fans52,54,56is configured differently than the outermost VTE fan58,60,62of the respective pluralities of VTE fans52,54,56.

It will be appreciated, however, that in other exemplary embodiments, each of the respective pluralities of VTE fans46,52,54,56may have any other suitable number of interior VTE fans50,64,66,68. Further, in certain exemplary embodiments, the at least one interior VTE fan50,64,66,68of each plurality of VTE fans46,52,54,56may be configured in the same manner as the outermost VTE fans48,58,60,62of the respective plurality of VTE fans52,54,56. For example, in other exemplary embodiments, each of the first plurality of VTE fans46, second plurality of VTE fans52, third plurality of VTE fans54, and fourth plurality of VTE fans56may be configured as variable speed, fixed pitch fans, or alternatively, may each be configured as variable speed, variable pitch fans (the “variable speed” functionality described below).

Moreover, as is depicted inFIG. 2, the electric communication bus38electrically connects the power source36, e.g., the electric machine42and/or the electric energy storage unit44, to each of the pluralities of VTE fans46,52,54,56. Notably, for the embodiment depicted, the electric communication bus38includes a main controller80and a plurality of electric power controllers82. The main controller80is electrically connected to both the electric machine42and the electric energy storage unit44and is configured to, e.g., direct electrical power from one or both of the electric machine42and electric energy storage unit44to each of the pluralities of VTE fans46,52,54,56. For example, in certain operations, the main controller80may direct electrical power from the electric machine42to each of the pluralities of VTE fans46,52,54,56, may direct electrical power from the electric energy storage unit44to each of the pluralities of VTE fans46,52,54,56, may direct electrical power from the electric machine42to the electric energy storage unit44(e.g., during forward flight), or may direct electrical power from the electric energy storage unit44to the electric machine42(e.g., during emergency operations or high power demand operations). Other operations are contemplated as well.

In the exemplary embodiment ofFIG. 2, the electric communication bus38includes an electric power controller82for each VTE fan (i.e., each VTE fan of the first plurality of VTE fans46, of the second plurality of VTE fans52, of the third plurality of VTE fans54, and of the fourth plurality of VTE fans56). Additionally, each of the plurality of electric power controllers82is associated with one VTE fan of the pluralities of VTE fans46,52,54,56. More specifically, still, the power source36is electrically coupled to each VTE fan of the pluralities of VTE fans46,52,54,56through the respective electric power controller82. In such a manner, the electric power controller82may modify the electric power provided from the power source36to each respective VTE fan. Accordingly, for the embodiment shown, the hybrid-electric propulsion system32includes twelve electric power controllers82, one for each of the twelve VTE fans included within the hybrid-electric propulsion system32.

In certain exemplary embodiments, each of the electric power controllers82may be one or more of a power converter, a power inverter, or a power transformer. Accordingly, in certain exemplary embodiments, the electric power controllers82may be configured to convert electrical power received through the electric communication bus38from alternating current (“AC”) electrical power to direct current (“DC”) electrical power, or vice versa. Further, the electric power controllers82may be configured in at least certain embodiments to modify an amount of the electrical power (e.g., a voltage or a current) received through the electric communication bus38from the power source36before transferring such electrical power to a respective VTE fan.

Accordingly, in at least certain embodiments, each of the electric power controllers82may modify an amount of electrical power provided to a respective VTE fan, which may allow for the aircraft10, and more specifically, may allow for the main controller80, to modify a rotational speed of each VTE fan of the pluralities of VTE fans46,52,54,56. For example, each of the electric power controllers82may be operably coupled to the main controller80through, e.g., a wired or wireless communication bus (not shown), such that the main controller80may control the electrical power provided to each of the individual VTE fans.

Accordingly, it will be appreciated that in at least certain embodiments each VTE fan of the pluralities of VTE fans46,52,54,56may be variable speed fans. Accordingly, by modifying an amount of electrical power provided to each VTE fan through a respective electric power controller82, the aircraft10may modify a rotational speed of the respective VTE fan, and therefore an amount of vertical thrust provided by the respective VTE fan. In such a manner, the aircraft10may allow for more dynamic control during vertical takeoff and landing, or other vertical thrust operations.

It should be appreciated, however, that in other exemplary embodiments, the aircraft10, or rather, the electric communication bus38may not include an electric power controller82for each of the individual VTE fans. Instead, for example, in other embodiments, the electric communication bus38may include a single electric power controller82for each of the individual pluralities of VTE fans46,52,54,56. In still other embodiments, however, any other suitable configuration may be provided.

Moreover, as briefly stated above, and as is shown inFIGS. 2 and 3, each of the wings24,26,28,30are fixed wings including a variable control portion that is generally movable between a vertical thrust position (FIG. 2) and a forward thrust position (FIG. 3). More specifically, referring now also toFIGS. 4 and 5, providing a side, cross-sectional view of the aft starboard wing24and an interior VTE fan50of the first plurality of VTE fans46, the aft starboard wing24(as well as the other wings26,28,30, discussed in more detail below) generally includes a variable geometry portion84. The variable geometry portion84is movable between a forward thrust position (FIG. 4), one or more transitional positions (not shown), and a vertical thrust position (FIG. 5), and further is generally formed of a surface portion of the respective wings24,26,28,30. As will be appreciated, however, a main body or frame portion of the wings24,26,28,30remain stationary during this movement.

When the variable geometry portion84is moved from the forward thrust position to the vertical thrust position, the first plurality of VTE fans46are exposed. By contrast, when the variable geometry portion84is moved from the vertical thrust position to the forward thrust position, the first plurality of VTE fans46are substantially completely covered. For the embodiment depicted, the variable geometry portion84forms a lift fan exhaust arrangement for the first plurality of VTE fans46when moved to the vertical thrust position. It will be appreciated, that as used herein, the term “exhaust arrangement” refers generally to any structure located downstream of the respective fan configured to channel at least a portion of an airflow from the respective fan to increase a power loading (i.e., a ratio of thrust produced to an amount of power received) of such fan. For example, the exhaust arrangement may be configured generally as a nozzle or diffuser for the respective fans.

More specifically, for the embodiment depicted, the aft starboard wing24, or rather, the variable geometry portion84of the aft starboard wing24, generally includes a forward section86and an aft section88. Referring back briefly toFIGS. 2 and 3, it will be appreciated that for the embodiment shown, the forward section86and the aft section88of the variable geometry portion84each extend from the innermost VTE fan of the first plurality of VTE fans46to the outermost VTE fan48of the first plurality of VTE fans46. In such a manner, when the variable geometry portion84is moved to the vertical thrust position, the exhaust arrangement formed by the variable geometry portion84also extends from the innermost VTE fan of the first plurality of VTE fans46to the outermost VTE fan48of the first plurality of VTE fans46.

Referring particularly toFIG. 4, when the variable geometry portion84of the aft starboard wing24is in the forward thrust position, the forward section86and the aft section88together define at least in part an airfoil cross-sectional shape. Such may allow for relatively efficient forward flight for the aircraft10. By contrast, however, as is depicted inFIG. 5, when the variable geometry portion84of the aft starboard wing24is moved to the vertical thrust position, the forward section86and the aft section88of the variable geometry portion84together form the exhaust arrangement. For example, in certain exemplary embodiments, the forward section86may be mounted on a forward track92within the aft starboard wing24such that when it is moved from the forward thrust position to the vertical thrust position it translates forward along the lateral direction and pivots downward along the vertical direction V to the position shown inFIG. 5. Similarly, the aft section88may be mounted on an aft track95within the aft starboard wing24such that when it is moved from the forward thrust position to the vertical thrust position it translates aft along the lateral direction and pivots downward along the vertical direction V to the position shown inFIG. 5.

It will be appreciated that each of the first plurality of VTE fans46define a fan diameter94, and for the embodiment depicted (seeFIG. 2), the fan diameter94of each of the plurality of VTE fans is substantially the same. Further, the exhaust arrangement formed by the variable geometry portion84of the aft starboard wing24defines a length96along the vertical direction V. For the embodiment depicted, the length96is equal to, or greater than the fan diameter94of each VTE fan of the first plurality of VTE fans46. More specifically, for the embodiment depicted, the length96is at least about ten percent greater the fan diameter94of each VTE fan of the first plurality of VTE fans46. For example, in at least certain embodiments, the length96may be at least about fifteen percent greater, such as at least about twenty-five percent greater, such as at least about fifty percent greater than the fan diameter94of each VTE fan of the first plurality of VTE fans46, and may be less than or equal to ten times the fan diameter94of each VTE fan.

It will additionally be appreciated that each of the remaining wings26,28,30may similarly include a variable geometry portion84movable between a forward thrust position and a vertical thrust position, wherein such variable geometry portion84forms an exhaust arrangement when in the vertical thrust position. It will be appreciated, however, that in other exemplary embodiments, the variable geometry portion84of each wings24,26,28,30may have any other suitable configuration for forming an exhaust arrangement for each respective plurality of VTE fans46,52,54,56integrated therein.

It will further be appreciated that inclusion of wings24,26,28,30having a variable geometry portion84for forming an exhaust arrangement for each of the pluralities of VTE fans46,52,54,56may allow for higher efficiency VTE fans at a given fan diameter. Or, alternatively, each of the pluralities of VTE fans46,52,54,56may be smaller than would otherwise be required to generate a necessary amount of vertical thrust for the aircraft10to perform vertical takeoffs, vertical landings, and general hover maneuvers.

Further, with the inclusion of the distributed VTE fans along the length of the respective wings24,26,28,30in the manner described herein, combined with the increased efficiency allowed by the exhaust arrangements formed by the respective wings24,26,28,30, each of the wings24,26,28,30may define a higher aspect ratio than conventionally possible for a fan-in-wing configuration, providing for relatively efficient forward flight. It will be appreciated, that as used herein, the term “aspect ratio,” with reference to one or more of the wings24,26,28,30, generally refers to a ratio of the wing's span to its mean chord. Inclusion of wings configured in such a manner may allow for an overall more efficient aircraft10.

Moreover, as briefly noted above, the hybrid-electric propulsion system32is configured as a hybrid-electric propulsion system including the power source36(the power source36having the combustion engine40and the electric machine42) and the forward thrust propulsor34, with the forward thrust propulsor34selectively or permanently mechanically coupled to the combustion engine40of the power source36. More specifically, referring now toFIG. 6, a simplified view is provided of the exemplary combustion engine40of the power source36of the hybrid-electric propulsion system32described above with reference toFIGS. 1 through 3. For the embodiment depicted, the combustion engine40is a turboshaft engine. The turboshaft engine includes in serial flow order, a compressor section including a low pressure compressor98and a high pressure compressor100, a combustion section102, and a turbine section including a high pressure turbine104and a low pressure turbine106. During operation, a flow of air74is received within the compressor section and is progressively compressed as it flows therethrough, i.e., as it flows from the low pressure compressor98to the high pressure compressor100. The compressed air is then provided to the combustion section102where it is mixed with fuel and burned to generate hot combustion gas76. The aircraft10further includes a fuel tank108for providing the fuel to the combustion section102(seeFIGS. 2 and 3).

The hot combustion gas76is expanded through the turbine section where rotational energy is extracted therefrom. Specifically, the hot combustion gas rotates the high pressure turbine104and the low pressure turbine106as the gas flows therethrough and is expanded. These components may be enclosed within a casing, e.g., the fuselage18of the aircraft10or a casing19of the combustion engine40. The hot combustion gas76may be exhausted, e.g., to atmosphere, from the low pressure turbine106, as will be discussed in more detail below. Notably, the compressor sections98,100; combustion section102; and turbine sections104,106together define a core air flowpath75through the combustion engine40.

Also for the embodiment depicted, the high pressure turbine104is connected to the high pressure compressor100through a high pressure shaft or spool112, such that a rotation of the high pressure turbine104additionally rotates the high pressure compressor100. Similarly, the low pressure turbine106is connected to the low pressure compressor98through a low pressure shaft or spool114, such that rotation of the low pressure turbine106additionally rotates the low pressure compressor98.

It will be appreciated, however, that the exemplary turboshaft engine depicted inFIG. 6is provided by way of example only. In other exemplary embodiments, the turboshaft engine may have any other suitable configuration. For example, in other embodiments, the turboshaft engine may include any other suitable number of compressors and/or any other suitable number of turbines. Further, in still other embodiments, the combustion engine may be any other suitable combustion engine, such as a rotary or internal combustion engine.

Referring still toFIG. 6, the low pressure shaft114additionally drives an output shaft. More specifically, for the embodiment ofFIG. 6, the low pressure shaft114additionally drives a first output shaft, or a forward output shaft116, of the turboshaft engine and further drives a second output shaft, or an aft output shaft118of the turboshaft engine. The forward output shaft116extends to the electric machine42. Accordingly, rotation of the turboshaft engine provides, at least during certain operations, rotational energy to the electric machine42via the forward output shaft116. The electric machine42, in turn, is configured to convert the rotational energy to generate electrical power. More specifically, it will be appreciated that at least certain embodiments of the electric machine42, such as the embodiment shown, may generally include a rotor120and a stator122. The rotational energy of the turboshaft engine is provided via the forward output shaft116and configured to rotate the rotor120of the electric machine42relative to the stator122. Such relative movement may generate electrical power.

Inclusion of a turboshaft engine and electric machine42in accordance with such an exemplary embodiment may allow for the electric power source36to generate a relatively high amount of electric power and to provide such electric power to the plurality of VTE fans of the hybrid-electric propulsion system32.

Referring now toFIGS. 6 through 8,FIG. 7shows a simplified view of a ducted forward propulsor34, andFIG. 8shows a simplified view of non-ducted forward propulsor34. As shown and previously discussed, the combustion engine40further drives the forward thrust propulsor34of the hybrid-electric propulsion system32. For the embodiments depicted, the forward thrust propulsor34includes a propulsor fan124coupled to a fan shaft126. The aft output shaft118of the turboshaft engine is selectively mechanically coupled to, or permanently mechanically coupled to, the fan shaft126to allow the turboshaft engine to drive the propulsor fan124. More specifically, during operation, the aft output shaft118of the turboshaft engine may drive the fan shaft126to rotate the propulsor fan124about a fan axis128. Referring particularly toFIGS. 6 and 7, the forward thrust propulsor34may further include an outer casing or outer nacelle130surrounding at least a portion of the fan124. In such a manner, the forward thrust propulsor34may be referred to as a ducted fan. Contrarily, the forward thrust propulsor34may not include the outer nacelle130, as seen inFIG. 8, and may be referred to as a non-ducted fan.

It will be appreciated, that as used herein, the term “permanently mechanically coupled to,” with reference to the fan shaft126and output shaft118refers to a coupling that does not allow for the output shaft118to be decoupled from, or otherwise freely rotatable relative to, the fan shaft126during operation, such as flight operations, of the aircraft10.

Still referring toFIG. 6 through 8, it will be appreciated that the exemplary hybrid-electric propulsion system32depicted further includes a coupling unit148, with the turboshaft engine selectively mechanically coupled to the forward thrust propulsor34through the coupling unit148. The coupling unit148may be at least one of a clutch or a torque converter. More specifically, for the embodiment depicted, the coupling unit148includes a clutch, and more specifically, includes a one-way clutch. For example, in certain embodiments, the one-way clutch may be a sprag clutch.

Further, in certain exemplary embodiments, as is depicted in phantom, the forward thrust propulsor34may additionally include a drive electric machine144, or rather, a drive motor, coupled to the fan shaft126. The drive electric machine144may be electrically coupled to the power source36, such as to one or more of the electric machine42or electric energy storage unit44, through the electric communication bus38(seeFIG. 2). The drive electric machine144may receive electrical power to drive the propulsor fan124of the forward thrust propulsor34during, e.g., emergency operations, or in a noise and/or emission sensitive environment. Inclusion of a one-way clutch in the coupling unit148, such as a sprag clutch, may allow for the drive electric machine144to rotate the propulsor fan124without having to correspondingly rotate the combustion engine40(i.e., turboshaft for the embodiment depicted).

It should be recognized that, in other embodiments, the hybrid-electric propulsion system32may not include a direct mechanical coupling between the combustion engine40and the propulsor fan124. For example, at least the propulsor fan124by itself or the compulsory fan and a combination of the all or some of the VTE fans may be entirely electrically driven. For instance, the electric machine144may drive the propulsor fan124via power supplied by the electric energy storage unit44precharged before flight and/or powered via the combustion engine40.

It will be appreciated, however, that in other exemplary embodiments, the clutch of the coupling unit148may instead be a two-way clutch actuatable between an engaged position and a disengaged position. When in the engaged position, the fan shaft126may rotate with the aft output shaft118of the turboshaft engine (via an intermediate shaft150). By contrast, when in the disengaged position, the aft output shaft118of the turboshaft engine may rotate independently of the fan shaft126. For example, in certain embodiments, the aircraft10may move the clutch to the disengaged position during, e.g., vertical takeoff, vertical landing, or hover operations wherein forward thrust is not required from the forward thrust propulsor34. However, when the aircraft10transitions to forward thrust operations, such as cruise operations, the clutch may be moved to the engaged position to allow the forward thrust propulsor34to generate forward thrust for the aircraft10.

Further still, the aircraft10additionally includes a speed change mechanism152, with turboshaft engine being mechanically coupled to the forward thrust propulsor34through the speed change mechanism152. More specifically, for the embodiments ofFIGS. 6 through 8, the speed change mechanism152is configured as a gearbox. More specifically, the speed change mechanism152may be configured as a planetary gear box. Further, in still other embodiments, any other suitable speed change mechanism152may be utilized. For example, in other exemplary embodiments, speed change mechanism152may be a transmission, such that the combustion engine40is mechanically coupled to the forward thrust propulsor34through the transmission. More specifically, in certain embodiments, the transmission may be one of a continuously variable transmission or a hydraulic transmission.

It will be appreciated that although for the embodiments depicted the aircraft10includes the speed change mechanism152located forward of the coupling unit148, in other embodiments, the relative location of these components may be reversed (which, e.g., may reduce a wear on the speed change mechanism152when, e.g., the coupling unit148decouples the two shafts118,126). Further, although the exemplary aircraft10depicted includes a speed change mechanism152, a coupling unit148, and a forward thrust propulsor34having a variable pitch fan, in other exemplary embodiments, the aircraft10may not include each or any of these components/features.

In other embodiments, the aircraft10may rely on a variability of a pitch of the fan124of the forward thrust propulsor34for neutralizing any forward thrust from the forward thrust propulsor34during, e.g., vertical takeoff and vertical landing operations (discussed in more detail below). Additionally, or alternatively, in other embodiments, the aircraft10may rely on the coupling unit148to neutralize a forward thrust from the forward thrust propulsor34during vertical takeoff and vertical landing operations (e.g., by including an actuatable clutch/two-way clutch). With such an embodiment, the aircraft10may therefore include a fixed pitch fan with the forward thrust propulsor34. Additionally, or alternatively, still, in other embodiments, the aircraft10may rely on the speed change mechanism152, such as a continuously variable transmission (such as an infinitely variable transmission), to substantially neutralize a forward thrust from the forward thrust propulsor34during vertical takeoff and landing operations. With such an embodiment, the aircraft10may therefore omit the coupling unit148and further may include a fixed pitch fan with the forward thrust propulsor34. Further, in still other embodiments, any other suitable combination of these three components/features may be utilized. Still other embodiments and combinations are contemplated as well.

Still referring toFIGS. 6 through 8, it will further be appreciated that for the embodiment depicted, the forward thrust propulsor34may be mounted to the aircraft10, such as to the fuselage18of the aircraft10or the casing19of the combustion engine40, at an aft end22of the aircraft10. The forward thrust propulsor34defines an axial direction A extending along the length of the combustion engine40and a radial direction R extending out relative to the axial direction A. As seen particularly inFIGS. 6 and 7, the forward thrust propulsor34may be a ducted fan including the outer nacelle130and one or more struts159, or other structural members, extending between the outer nacelle130and the fuselage18of the aircraft10and/or the casing19of the combustion engine40. In other embodiments, however, as seen inFIG. 8, the forward thrust propulsor may be a non-ducted fan without the outer nacelle130. Moreover, the forward thrust propulsor34may be configured as a boundary layer ingestion fan defining an inlet132extending substantially 360 degrees around the fuselage18or the casing19. In such a manner, the forward thrust propulsor34may ingest a boundary layer airflow over the fuselage18or the casing19, and may re-energize such airflow to create a forward thrust for the aircraft10. More specifically, the combination of the outer nacelle130, the fuselage18, and/or the casing19may at least partially define a fan air flowpath77, with the fan124of the forward thrust propulsor34positioned at least partially within the fan air flowpath77.

Further, the propulsor fan124of the forward thrust propulsor34includes a plurality of fan blades134coupled to a disk136, with the disk136coupled to the fan shaft126via rotating fan frame157. The fan blades134are arranged outside the core air flowpath75of the combustion gasses76exhausted from the combustion engine40. In the illustrated embodiments, the combustion engine may be enclosed by the fuselage18and/or the casing19. As such, the fuselage18or casing19may define an exterior surface21, which for the embodiment shown defines in part the fan air flowpath77. The plurality of fan blades134are arranged outside the exterior surface21of the casing19of the combustion engine40and/or the fuselage18. For example, the fan blades134may be arranged in the fan air flowpath77and outside of the core air flowpath75, and more particularly, the exhaust path for the combustion gases76substantially along the radial direction R of the forward thrust propulsor34. The combustion engine40may include an outlet79at the end of the core air flowpath75for exhausting the combustion gases76. The outlet79may be positioned inward of the fan blades134in the radial direction R and downstream, aft, or both of the fan blades134in the axial direction A. As such, the fan blades134are arranged outside of the combustion gases76exiting the outlet79. Additionally, the fan blades134may be position aft, downstream, or both of the turbine section of the combustion engine40in the axial direction A. More specifically, as seen inFIG. 6, the fan blades134are located aft of both the high pressure turbine104and the lower pressure turbine106.

As seen particularly inFIGS. 7 and 8, the rotating fan frame157may include rotors78along a length of the rotating fan frame157extending through the core air flowpath75. More specifically, the rotors78are arranged in the exhaust stream of the combustion gasses76. As such, the rotors78may extract additional energy from the exhausted combustion gasses76to drive the forward thrust propulsor34.

Further still, in the embodiments shown, the aircraft10may include a tail cone23at an aft end of the combustion engine40defining an aft end of the core air flowpath75. More specifically, the tail cone23may be coupled to the fan shaft126, the coupling unit148or both in order to allow the tail cone23to rotate about the fan axis128. As such, the tail cone may rotate with the propulsor fan124at the same rotational rate. In another embodiment, the tail cone23may be coupled to the intermediary shaft150, the speed change mechanism152, or both in order to allow the tail cone23to rotate about fan axis123at the same rotational rate as the intermediary shaft150.

For the embodiments depicted, the forward thrust propulsor34is configured as a variable pitch propulsor. More specifically, each of the plurality of fan blades134are rotatably coupled to the disk136about a respective pitch axis138. The forward thrust propulsor34further includes a pitch change mechanism140operable with each of the plurality of fan blades134to rotate each of the plurality of fan blades134about their respective pitch axes138, e.g., in unison. The pitch change mechanism140may be located anywhere between the fan shaft126and the fan blades134. For example, as seen inFIG. 6, the pitch change mechanism140may be located at the fan shaft126. In another embodiment, as seen inFIG. 7, the pitch change mechanism140may be located inward of the fuselage18and/or the casing19along the radial direction R. More specifically, for the embodiment ofFIG. 7, the pitch change mechanism140is located inward of the fan air flowpath77along the radial direction R and outward of the core air flowpath75along the radial direction R. Still in a further embodiment, as seen inFIG. 8, the pitch change mechanism140may be located outside the fuselage18and/or casing19along the radial direction R. More specifically, the pitch change mechanism140may be located in the fan air flowpath77.

As will be appreciated, changing a pitch of the plurality of fan blades134may allow for a modification of an amount of thrust generated by the forward thrust propulsor34during operation without requiring a change in a rotational speed of the fan124. For example, referring generally toFIGS. 9 through 11, three views of a fan blade134of the plurality of fan blades134of the forward thrust propulsor34are provided, each along the pitch axis138of the fan blade134. For the embodiment ofFIG. 9, the fan is in a first position defining a first pitch angle142relative to a first circumferential direction C1. The first pitch angle142may be a positive angle relative to the first circumferential direction C1. When the plurality of fan blades134of the propulsor fan124are rotated in a first circumferential direction C1(with the plurality of fan blades134of the propulsor fan124defining the first pitch angle142), the fan124generates a forward thrust. By contrast,FIG. 10depicts the propulsor fan124in a second position wherein the fan blades134define a second pitch angle (not labeled) relative to the first circumferential direction C1. The second pitch angle may be substantially equal to 0. When the plurality of fan blades134of the propulsor fan124are rotated in the first circumferential direction C1(with the plurality of fan blades134defining the second pitch angle), the propulsor fan124generates substantially no thrust. Further,FIG. 11depicts the propulsor fan124in a third position defining a third pitch angle146relative to the first circumferential direction C1. The third pitch angle146may be a negative pitch angle relative to the circumferential direction C1. When the plurality of fan blades134of the propulsor fan124are rotated in the first circumferential direction C1(with the plurality of fan blades134of the propulsor fan124defining the third pitch angle146), the propulsor fan124generates a reverse thrust.

In such a manner, it will be appreciated that for the embodiment depicted, the propulsor fan124defines a pitch range (i.e., a range of pitch angles) enabling the variable pitch fan124to generate a forward thrust, a reverse thrust, and substantially no thrust during operation. Accordingly, such may allow for greater control of the aircraft10in, e.g., a hover mode or other vertical flight mode, and may also allow for electric power generation through the aft fan in forward flight by operating it in a wind turbining mode.