阅读说明：本技术 具有后发动机和辅助动力单元的飞行器 (Aircraft with rear engine and auxiliary power unit ) 是由 亚瑟·威廉·西巴赫 兰迪·M·沃德雷尔 安德鲁·布雷兹·斯特林费洛 于 2020-10-12 设计创作，主要内容包括：提供了一种在前端和后端之间延伸的飞行器。该飞行器包括：定位在飞行器的后端附近的辅助动力单元,辅助动力单元具有辅助动力单元入口管道和辅助动力单元排气管道；以及定位在飞行器的后端附近的边界层摄取风扇,边界层摄取风扇具有支撑轴,其中,辅助动力单元排气管道延伸穿过边界层摄取风扇的支撑轴的一部分。(An aircraft is provided that extends between a forward end and an aft end. The aircraft comprises: an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a boundary layer ingestion fan positioned near the aft end of the aircraft, the boundary layer ingestion fan having a support shaft, wherein the auxiliary power unit exhaust duct extends through a portion of the support shaft of the boundary layer ingestion fan.)

1. An aircraft extending between a forward end and an aft end, the aircraft comprising:

an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and

a boundary layer ingestion fan positioned near the aft end of the aircraft, the boundary layer ingestion fan having a support shaft,

wherein the auxiliary power unit exhaust duct extends through a portion of the support shaft of the boundary layer ingest fan.

2. The aircraft of claim 1, further comprising a mixer in communication with the auxiliary power unit and the boundary layer ingestion fan such that the mixer receives and mixes boundary layer airflow from the boundary layer ingestion fan and auxiliary power unit exhaust flow from the auxiliary power unit exhaust duct.

3. The aircraft of claim 1, further comprising:

an insulation portion between the auxiliary power unit exhaust duct and the support shaft of the boundary layer ingestion fan.

4. The aircraft of claim 1, wherein the boundary layer ingestion fan defines a central axis, and further comprising:

a fan rotatable about the central axis and comprising a plurality of fan blades attached to a fan shaft;

a nacelle surrounding the plurality of fan blades; and

a structural member extending from the support shaft of the boundary layer ingestion fan to the nacelle.

5. The aircraft of claim 4, wherein the auxiliary power unit exhaust duct includes a bypass portion extending through the structural member to the nacelle, wherein an auxiliary power unit exhaust flow through the bypass portion to the nacelle is configured to de-ice the nacelle.

6. The aircraft of claim 4, further comprising:

a motor having a drive shaft offset from the fan shaft; and

a gear in communication with the drive shaft and the fan shaft to drive the boundary layer ingestion fan.

7. The aircraft of claim 1, wherein the auxiliary power unit exhaust duct extends through a center of the support shaft of the boundary layer ingest fan in an axial direction of the boundary layer ingest fan.

8. The aircraft of claim 1, wherein the boundary layer ingestion fan is incorporated into an aft portion of the aircraft at the aft end of the aircraft.

9. The aircraft of claim 1, wherein a portion of the boundary layer ingestion fan constitutes the aft end of the aircraft.

10. An aircraft extending between a forward end and an aft end, the aircraft comprising:

an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and

an aft engine configured to be mounted to the aircraft at the aft end, the aft engine defining a central axis and comprising:

a fan rotatable about the central axis of the aft engine and including a plurality of fan blades attached to a fan shaft;

a nacelle surrounding the plurality of fan blades; and

a structural member extending from a portion of the rear engine to the nacelle;

wherein the auxiliary power unit exhaust duct extends through the structural member to the nacelle.

Technical Field

The present subject matter relates generally to an aircraft propulsion system that includes an engine and an auxiliary power unit located at an aft end of an aircraft.

Background

Conventional commercial aircraft typically include a fuselage, a pair of wings, and a propulsion system that provides thrust. The propulsion system typically includes at least two aircraft engines, such as turbofan jet engines. Each turbofan jet engine is mounted to a respective one of the wings of the aircraft, for example in a suspended position beneath the wing, separately from the wing and the fuselage. Such a configuration allows the turbofan jet engine to interact with independent free air streams that are not affected by the wing and/or fuselage. This configuration may reduce the amount of turbulence in the air entering the inlet of each respective turbofan jet engine, which has a positive effect on the net thrust of the aircraft.

However, drag on aircraft, including turbofan jet engines, also has an effect on the net thrust of the aircraft. The amount of drag (including skin friction, form and induced drag) on an aircraft is generally proportional to the difference between the freestream velocity of the air approaching the aircraft and the average velocity of the wake downstream of the aircraft due to drag on the aircraft.

Systems have been proposed to counteract the effects of drag and/or to improve the efficiency of turbofan jet engines. For example, some propulsion systems incorporate boundary layer ingestion systems to direct relatively slowly moving air that forms part of the boundary layer, e.g., on the fuselage and/or wings, into the turbofan jet engine upstream of its fan section.

Further, in some configurations, a gas turbine engine may be used to drive an electrical generator. For example, the gas turbine engine may be an Auxiliary Power Unit (APU) of an aircraft that includes a generator for generating electrical power for various systems of the aircraft.

Disclosure of Invention

Aspects and advantages of the invention 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 exemplary embodiment of the present disclosure, an aircraft is provided that extends between a forward end and an aft end. The aircraft comprises: an auxiliary power unit positioned near a rear end of the aircraft; the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a boundary layer ingestion fan positioned near the aft end of the aircraft, the boundary layer ingestion fan having a support shaft, wherein the auxiliary power unit exhaust duct extends through a portion of the support shaft of the boundary layer ingestion fan.

In certain exemplary embodiments, the aircraft includes a mixer in communication with the auxiliary power units and the boundary layer ingestion fan such that the mixer receives and mixes the boundary layer airflow from the boundary layer ingestion fan and the auxiliary power unit exhaust flow from the auxiliary power unit exhaust duct.

In certain exemplary embodiments, the aircraft includes an insulated portion between the auxiliary power unit exhaust duct and the support shaft of the boundary layer ingestion fan.

In certain exemplary embodiments, the boundary layer ingestion fan defines a central axis and comprises: a fan rotatable about a central axis and including a plurality of fan blades attached to a fan shaft; a nacelle surrounding a plurality of fan blades; and a structural member extending from the support shaft of the boundary layer ingestion fan to the nacelle.

In certain exemplary embodiments, the auxiliary power unit exhaust duct includes a bypass portion extending through the structural member to the nacelle, wherein an auxiliary power unit exhaust flow through the bypass portion to the nacelle is configured to de-ice the nacelle.

In certain exemplary embodiments, an aircraft, comprises: a motor having a drive shaft offset from the fan shaft; and a gear in communication with the drive shaft and the fan shaft to drive the boundary layer ingestion fan.

In certain exemplary embodiments, the auxiliary power unit exhaust duct extends through a center of a support shaft of the boundary layer ingestion fan in an axial direction of the boundary layer ingestion fan.

In certain exemplary embodiments, the boundary layer ingestion fan is incorporated into the aft portion of the aircraft at the aft end of the aircraft.

In certain exemplary embodiments, a portion of the boundary layer ingestion fan constitutes the aft end of the aircraft.

In another exemplary embodiment of the present disclosure, an aircraft is provided that extends between a forward end and an aft end. The aircraft comprises: an auxiliary power unit positioned near a rear end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a rear engine. An aft engine is configured to be mounted to the aircraft at an aft end, the aft engine defining a central axis and including: a fan rotatable about a central axis of the aft engine and including a plurality of fan blades attached to a fan shaft; a nacelle surrounding a plurality of fan blades; and a structural member extending from a portion of the rear engine to the nacelle, wherein the auxiliary power unit exhaust duct extends through the structural member to the nacelle.

In certain exemplary embodiments, the aft engine includes a power source having a drive shaft and a support shaft extending through the fan shaft, wherein the structural member extends from the support shaft to the nacelle, and wherein the auxiliary power unit exhaust duct extends through the structural member about the drive shaft and the support shaft to the nacelle. In certain exemplary embodiments, the auxiliary power unit exhaust duct includes an outlet portion located at a trailing edge of the nacelle.

In certain exemplary embodiments, the structural member is an inlet guide vane.

In certain exemplary embodiments, the aircraft includes an insulation section between the auxiliary power unit exhaust duct and the inlet guide vanes.

In certain exemplary embodiments, the aft engine is configured as a boundary layer ingestion fan.

In certain exemplary embodiments, an auxiliary power unit exhaust flow through an auxiliary power unit exhaust duct within the nacelle is configured to de-ice the nacelle.

In certain exemplary embodiments, the auxiliary power unit exhaust duct comprises: a first auxiliary power unit exhaust duct portion extending in a first direction around the drive shaft through the first portion of the structural member to the first portion of the nacelle; and a second auxiliary power unit exhaust duct section extending through the second portion of the structural member in the second direction about the drive shaft to the second portion of the nacelle, wherein the first auxiliary power unit exhaust duct section and the second auxiliary power unit exhaust duct section are bifurcated.

In another exemplary embodiment of the present disclosure, an aircraft is provided that extends between a forward end and an aft end. The aircraft comprises: an auxiliary power unit positioned near a rear end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a boundary layer ingestion fan positioned near the aft end of the aircraft between the aft end of the aircraft and the auxiliary power unit, the boundary layer ingestion fan being spaced apart from the auxiliary power unit, wherein the auxiliary power unit exhaust duct extends radially outward to an aft portion of the aircraft.

In certain exemplary embodiments, the auxiliary power unit exhaust duct includes an outlet portion located at a trailing edge of the tail of the aircraft.

In certain exemplary embodiments, the auxiliary power unit exhaust duct extends radially outward to a vertical stabilizer of the aircraft.

In certain exemplary embodiments, the auxiliary power unit exhaust duct extends around the boundary layer ingestion fan, thereby preventing auxiliary power unit exhaust flow through the auxiliary power unit exhaust duct from interfering with the boundary layer ingestion fan.

These and other features, aspects, and advantages of the present invention 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 the principles of the invention.

Drawings

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a top view of an aircraft according to an exemplary embodiment of the present disclosure.

Fig. 2 is a port side view of the exemplary aircraft of fig. 1, according to an exemplary embodiment of the present disclosure.

FIG. 3 is a schematic cross-sectional view of a gas turbine engine mounted to the exemplary aircraft of FIG. 1, according to an exemplary embodiment of the present disclosure.

FIG. 4 is a schematic cross-sectional view of an auxiliary power unit according to an exemplary embodiment of the present disclosure.

FIG. 5 is a schematic cross-sectional view of an auxiliary power unit and a boundary layer ingesting fan, respectively, located near an aft end of an aircraft, according to an exemplary embodiment of the present disclosure.

FIG. 6 is a close-up schematic cross-sectional view of an auxiliary power unit and a boundary layer ingest fan, respectively, located near an aft end of an aircraft, according to an exemplary embodiment of the present disclosure.

FIG. 7 is a schematic cross-sectional view of an auxiliary power unit and a boundary layer ingestion fan, each located near an aft end of an aircraft, with a bypass portion of an auxiliary power unit exhaust duct extending through a structural member to a nacelle, according to an exemplary embodiment of the present disclosure.

FIG. 8 is a schematic cross-sectional view of an auxiliary power unit and a boundary layer ingesting fan, respectively, located near a rear end of an aircraft with a drive shaft of a motor offset from a support shaft, according to an exemplary embodiment of the present disclosure.

FIG. 9 is a schematic cross-sectional view of an auxiliary power unit and a boundary layer ingesting fan, respectively, located near an aft end of an aircraft, according to another exemplary embodiment of the present disclosure.

FIG. 10 is a schematic cross-sectional view of an auxiliary power unit and a boundary layer ingesting fan, respectively, located near an aft end of an aircraft, according to another exemplary embodiment of the present disclosure.

Corresponding reference characters indicate corresponding parts throughout the several views. The examples set forth herein illustrate exemplary embodiments of the disclosure, and these examples should not be construed as limiting the scope of the disclosure in any way.

Detailed Description

Reference will now be made in detail to the present embodiments of the invention, one or more examples of which are illustrated in the accompanying drawings. The detailed description uses numerical and letter designations to refer to features in the drawings. The same or similar reference numbers have been used in the drawings and the description to refer to the same or similar parts of the invention.

The following description is presented to enable any person skilled in the art to make and use the described embodiments, which are intended to be useful in the practice of the invention. Various modifications, equivalents, changes, and substitutions will now occur to those skilled in the art. Any and all such modifications, variations, equivalents, and alternatives are intended to fall within the spirit and scope of the present invention.

For purposes of the following description, the terms "upper", "lower", "right", "left", "vertical", "horizontal", "top", "bottom", "lateral", "longitudinal", and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. It is to be understood, however, that the invention may assume various alternative variations, except where expressly specified to the contrary. It is also to be understood that the specific devices illustrated in the attached drawings, and described in the following specification, are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics relating to the embodiments disclosed herein are not to be considered as limiting.

As used herein, the terms "first," "second," and "third" may be used interchangeably to distinguish one element from another, and are not intended to denote the position or importance of the various elements. The terms "front" and "rear" refer to the relative positions of components based on the actual or expected direction of travel. For example, "forward" may refer to the forward portion of the aircraft based on the expected direction of travel of the aircraft, while "aft" may refer to the aft portion of the aircraft based on the expected direction of travel of the aircraft. The terms "upstream" and "downstream" refer to relative directions with respect to fluid flow in a fluid path. For example, "upstream" refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.

The aircraft of the present disclosure allows for the integration of Auxiliary Power Units (APUs) and Boundary Layer Ingestion (BLI) fans at the aft end of the aircraft. In an exemplary embodiment of the present disclosure, the auxiliary power unit exhaust duct of the APU extends through a portion of the support shaft of the BLI fan to enable the APU to be positioned near the aft end of the aircraft while also adding the BLI fan to a location near the aft end of the aircraft.

In another exemplary embodiment of the present disclosure, an auxiliary power unit exhaust duct of the APU extends through the structural member to the cabin of the aft engine to enable the APU to be positioned near the aft end of the aircraft while also adding a BLI fan to a location near the aft end of the aircraft.

In another exemplary embodiment of the present disclosure, the auxiliary power unit exhaust duct of the APU extends radially outward to the aft of the aircraft to enable the APU to be positioned near the aft end of the aircraft while also adding the BLI fan to a location near the aft end of the aircraft. In this manner, the auxiliary power unit exhaust duct extends around the BLI fan, thereby preventing auxiliary power unit exhaust flow through the auxiliary power unit exhaust duct from interfering with the boundary layer ingestion fan.

Embodiments of the present disclosure reduce the exhaust noise of an aircraft by allowing the integration of APUs and BLI fans at the aft end of the aircraft. Further, embodiments of the present disclosure include a bypass portion of the auxiliary power unit exhaust duct extending through the structural member to the nacelle, wherein an auxiliary power unit exhaust flow through the bypass portion to the nacelle is configured to de-ice the nacelle.

Embodiments of the present disclosure may also include temperature sensors at various locations of the integrated APU and BLI fan systems. For example, in an exemplary embodiment, a temperature sensor may be included at a region of the system to measure the air temperature immediately before the fan blades of the BLI fan, allowing the power to the fan to be increased or decreased based on such temperature readings. This configuration may prevent the BLI fan system from stalling.

Referring now to the drawings, in which like numerals represent like elements throughout the several views, FIG. 1 provides a top view of an exemplary aircraft 10, which aircraft 10 may incorporate various embodiments of the present invention. Fig. 2 provides a port side view of the aircraft 10 shown in fig. 1. As shown collectively in fig. 1 and 2, the aircraft 10 defines a longitudinal centerline 14, a vertical direction V, a lateral direction L, a forward end 16, and an aft end 18 extending therethrough. In addition, the aircraft 10 defines an average line 15 that extends between a forward end 16 and an aft end 18 of the aircraft 10. As used herein, "mean line" refers to a midpoint line extending along the length of the aircraft 10, regardless of the accessories of the aircraft 10 (such as the wings 20 and stabilizers discussed below).

In addition, the aircraft 10 includes a fuselage 12 and a pair of wings 20 that extend longitudinally from a forward end 16 of the aircraft 10 toward an aft end 18 of the aircraft 10. As used herein, the term "fuselage" generally includes the entire body of the aircraft 10, such as the empennage of the aircraft 10. A first such wing 20 extends laterally outward from a port side 22 of the fuselage 12 relative to the longitudinal centerline 14, and a second such wing 20 extends laterally outward from a starboard side 24 of the fuselage 12 relative to the longitudinal centerline 14. Each wing 20 for the exemplary embodiment shown includes one or more leading edge flaps 26 and one or more trailing edge flaps 28. The aircraft 10 also includes a vertical stabilizer 30 having rudder flaps 32 for yaw control and a pair of horizontal stabilizers 34 each having riser flaps 36 for pitch control. The fuselage 12 additionally includes an outer surface or skin 38. However, it should be understood that in other exemplary embodiments of the present disclosure, the aircraft 10 may additionally or alternatively include any other suitable configuration of stabilizers that may or may not extend directly along the vertical direction V or the horizontal/lateral direction L.

The exemplary aircraft 10 of fig. 1 and 2 includes a propulsion system 100, referred to herein as "system 100". The exemplary system 100 includes a pair of aircraft engines, at least one of which is mounted to each of a pair of wings 20, and an aft engine. For the illustrated embodiment, the aircraft engines are configured as turbofan jet engines 102, 104 suspended below the wing 20 in an under-wing configuration. In addition, the rear engine is configured as an engine configured to ingest and consume air that forms a boundary layer on the fuselage 12 of the aircraft 10. Specifically, the aft engines are configured as fans, i.e., Boundary Layer Ingestion (BLI) fans 106, configured to ingest and consume air that forms a boundary layer on the fuselage 12 of the aircraft 10. The BLI fan 106 is mounted to the aircraft 10 at a location aft of the wing 20 and/or jet engines 102, 104 such that the mean line 15 extends therethrough. Specifically, for the illustrated embodiment, the BLI fan 106 is fixedly coupled to the fuselage 12 at the aft end 18 such that the BLI fan 106 is incorporated into or blended with the aft section at the aft end 18. However, it should be understood that in various other embodiments, some of which will be discussed below, the BLI fan 106 may alternatively be positioned at any suitable location at the back end 18.

In various embodiments, the jet engines 102, 104 may be configured to provide power to the generator 108 and/or the energy storage device 110. For example, one or both of the jet engines 102, 104 may be configured to provide mechanical power from a rotating shaft (such as a LP shaft or HP shaft) to the generator 108. Additionally, the generator 108 may be configured to convert mechanical power into electrical power and provide such electrical power to one or both of the energy storage device 110 or the BLI fan 106. Thus, in such embodiments, the propulsion system 100 may be referred to as an electrogas propulsion system. However, it should be understood that the aircraft 10 and the propulsion system 100 depicted in fig. 1 and 2 are provided as examples only, and that in other exemplary embodiments of the present disclosure, any other suitable aircraft 10 having a propulsion system 100 configured in any other suitable manner may be provided.

Further, it will be appreciated that the exemplary aircraft of fig. 1 and 2 may include an auxiliary power unit 150. For the depicted embodiment, the auxiliary power unit 150 is positioned within the fuselage 12 proximate the aft end 18 of the aircraft 10. An auxiliary power unit 150 may be provided to generate electrical power for operating or driving one or more aircraft systems. Additionally or alternatively, the auxiliary power unit 150 may be configured to generate electrical power to, for example, start one or more of the aircraft engines 102, 104.

Referring now to fig. 3, in at least certain embodiments, the jet engines 102, 104 can be configured as high bypass turbofan jet engines. Fig. 3 is a schematic cross-sectional view of an exemplary high bypass turbofan jet engine 200, referred to herein as "turbofan 200". In various embodiments, turbofan 200 may represent jet engines 102, 104. As shown in fig. 3, turbofan 200 defines an axial direction a1 (extending parallel to a longitudinal centerline or axis 201 for reference) and a radial direction R1. Generally, turbofan 200 includes a fan section 202 and a core turbine engine 204 disposed downstream from fan section 202.

The exemplary core turbine engine 204 shown generally includes a substantially tubular casing 206 defining an annular inlet 208. The housing 206 encloses in serial flow relationship: a compressor section including a booster or Low Pressure (LP) compressor 210 and a High Pressure (HP) compressor 212; a combustion section 214; a turbine section including a High Pressure (HP) turbine 216 and a Low Pressure (LP) turbine 218; and an injection exhaust nozzle section 220. A High Pressure (HP) shaft or spool 222 drivingly connects the HP turbine 216 to the HP compressor 212. A Low Pressure (LP) shaft or spool 224 drivingly connects the LP turbine 218 to the LP compressor 210.

For the illustrated embodiment, the fan section 202 includes a variable pitch fan 226, the variable pitch fan 226 having a plurality of fan blades 228 coupled to a disk 230 in a spaced apart manner. As shown, fan blades 228 extend outwardly from disk 230 in a generally radial direction R1. Each fan blade 228 is rotatable relative to the disk 230 about a pitch axis P due to the fan blades 228 being operably coupled to a suitable actuating member 232, the actuating members 232 being configured to collectively change the pitch of the fan blades 228 in unison. The fan blades 228, the discs 230, and the actuating members 232 are rotatable together about the longitudinal axis 201 by the LP shaft 224 across the power gearbox 234. The power gearbox 234 includes a plurality of gears for reducing the rotational speed of the LP shaft 224 to a more efficient fan speed.

Still referring to the exemplary embodiment of FIG. 3, the disk 230 is covered by a rotatable forward hub 236, the rotatable forward hub 236 being aerodynamically shaped to promote airflow through the plurality of fan blades 228. Additionally, exemplary fan section 202 includes an annular fan casing or nacelle 238 that circumferentially surrounds at least a portion of fan 226 and/or core turbine engine 204. It should be appreciated that nacelle 238 may be configured to be supported relative to core turbine engine 204 by a plurality of circumferentially spaced outlet guide vanes 240. Moreover, a downstream section 242 of nacelle 238 may extend over an exterior of core turbine engine 204 to define a bypass airflow passage 244 therebetween.

However, it should be appreciated that the exemplary turbofan engine 200 illustrated in FIG. 3 is intended to be exemplary only, and that in other exemplary embodiments, the turbofan engine 200 may have any other suitable configuration. Further, it should be appreciated that in other exemplary embodiments, the jet engines 102, 104 may alternatively be configured as any other suitable aircraft engines.

Referring now to FIG. 4, a close-up schematic view of the exemplary auxiliary power unit 150 of FIGS. 1 and 2 is shown. It should be appreciated that, in the exemplary embodiment, auxiliary power unit 150 is an engine, and more specifically, a turbine engine that defines an axial direction A, an axis 151 extending along axial direction A, a radial direction R, and a circumferential direction (extending about axis 151), and that also includes a compressor section and a turbine section. More specifically, for the illustrated embodiment, the compressor section includes a compressor 152 and the turbine section includes a turbine 154. Together, the compressor 152 and the turbine 154 at least partially define a core air flow path 156 of the auxiliary power unit 150. Further, the auxiliary power unit 150 includes a drive shaft 158, the drive shaft 158 being coupled to at least one of the compressor 152 or the turbine 154, and more specifically, the drive shaft 158 extends between the compressor 152 and the turbine 154 and couples the compressor 152 and the turbine 154. In this manner, the compressor 152 may rotate with the turbine 154 and be driven by the turbine 154.

The auxiliary power unit 150 also defines an inlet 160, the inlet 160 configured to receive an air flow, which may be an ambient air flow from outside the fuselage 12 of the aircraft 10. During operation of the auxiliary power unit 150, air flows from the inlet 160 to the compressor 152, where an impeller 162 of the compressor 152 (coupled to the drive shaft 158) compresses the air flow. Moreover, the exemplary auxiliary power unit 150 includes a combustion section 164, wherein the exemplary combustion section 164 includes a reverse flow combustor 166. In this manner, compressed air from the compressor section flows around combustor 166 before being mixed with fuel and entering combustion chamber 168 of combustor 166, where the fuel-air mixture is combusted to produce combustion gases. The combustion gases flow through the turbine 154 of the turbine section, and more specifically, drive the wheels 170 of the turbine 154, causing the turbine 154 to rotate. Further, the drive shaft 158 is coupled to the impeller 170 of the turbine 154, and thus rotation of the turbine 154 rotates/drives the drive shaft 158.

Still referring to FIG. 4, the auxiliary power unit 150 includes an auxiliary power unit exhaust duct 163 (see also FIGS. 5-8). Exhaust from the auxiliary power unit 150, such as an auxiliary power unit exhaust flow, flows out of an outlet 161 and through an auxiliary power unit exhaust conduit 163 (see also FIGS. 5-8).

Additionally, in an exemplary embodiment, the engine, or more specifically, the auxiliary power unit 150, includes a stationary member and a rotating member. The rotating member is configured to rotate about a centerline axis 151 of the auxiliary power unit 150 during operation of the auxiliary power unit 150 with one or more of a compressor 152 or a turbine 154. Instead, the stationary member is configured to remain stationary relative to the rotating member during operation of the auxiliary power unit 150. For the illustrated embodiment, the rotating member is the drive shaft 158 of the auxiliary power unit 150 and the stationary member is the stationary support member 172. Notably, the stationary support member 172 is fixedly coupled to an inlet strut 174 located within the core air flow path 156 of the auxiliary power unit 150, upstream of the compressor 152 of the compressor section of the auxiliary power unit 150. The stationary support member 172 (which may also be described as a stator assembly mount) may provide electrical isolation of the electric machine 176. However, in other embodiments, the stationary member may be any other suitable component that remains stationary relative to the rotating member during operation of the auxiliary power unit 150.

In addition, the exemplary auxiliary power unit 150 also includes a motor 176 located at a forward end thereof. The exemplary electric machine 176 generally includes a stator assembly 178 and a rotor assembly 180. Further, as schematically illustrated, the rotor assembly 180 generally includes a rotor 182 and a rotor shaft 184. Similarly, stator assembly 178 generally includes a stator 186 and a stator shaft 188. The motor 176 may be configured as any suitable type of motor 176, such as an ac motor, a dc motor, a permanent magnet motor, an induction motor, a brushed motor, and the like. Thus, it will be appreciated that the stator 186, the rotor 182, or both, may include one or more permanent magnets, electromagnets, coils, or the like.

Further, the illustrated electric machine 176 is electrically coupled to the electrical communication bus 190 by wires 192 of the electrical communication bus 190. More specifically, the stator 186 of the electric machine 176 is electrically coupled to the electrical wires 192 of the electrical communication bus 190. The electrical communication bus may electrically connect the electric machine 176 to a power circuit of the aircraft, propulsion system, or the like. For the illustrated embodiment, electrical communication bus 190 also includes a controller 194. The controller 194 may generally include power electronics, sensors, computers, processors, and the like. In this manner, the controller 194 may regulate and/or direct the power provided to the motor 176, the power drawn from the motor 176, or both.

Further, during operation of the auxiliary power unit 150, the rotor assembly 180 may rotate relative to the stator assembly 178. More specifically, the stator assembly 178 is coupled to a stationary component of the auxiliary power unit 150, and the rotor assembly 180 is coupled to or otherwise rotatable with a rotating component of the auxiliary power unit 150, which for the depicted embodiment is the drive shaft 158. Thus, when operating as a generator, the rotor assembly 180 of the electric machine 176 may be driven by the drive shaft 158 of the auxiliary power unit 150 to generate electrical power, also referred to as extracting power from the auxiliary power unit 150. Conversely, when operating as a motor, the rotor assembly 180 of the electric machine 176 may drive the drive shaft 158 of the auxiliary power unit 150 to, for example, start the auxiliary power unit 150.

Regardless of the mode of operation, the stator assembly 178 of the electric machine 176 may generate or receive electrical power having a relatively high voltage, a high current level, or both. If, for example, insulation within the stator 186 of the stator assembly 178 breaks or is insufficient to contain power, the electricity generated or received by the stator assembly 178 may be connected to one or more conductive components of the electric machine 176 via an arc. In this case, electrical power may be conducted to the drive shaft 158 of the auxiliary power unit 150 through, for example, the rotor assembly 180. Once conducted to the drive shaft 158 of the auxiliary power unit 150, this electricity may flow through one or more relatively sensitive components, thereby damaging those components (e.g., one or more bearings, sensors, etc.).

Thus, for the illustrated embodiment, the auxiliary power unit 150 further includes an electrical breaker 196, and the drive shaft 158 is coupled to the rotor assembly 180 through the electrical breaker 196. Specifically, for the illustrated embodiment, the rotor assembly 180 is coupled to the drive shaft 158 of the auxiliary power unit 150 only through the electrical disconnect 196 such that the electrical disconnect 196 is configured to transmit substantially all of the torque between the drive shaft 158 and the rotor assembly 180 of the electric machine 176. For example, when operating as a motor, substantially all of the torque generated by the electric machine 176 is transferred from the rotor shaft 184 of the rotor assembly 180 of the electric machine 176 to the drive shaft 158 through the electrical disconnect 196. Similarly, when operating as a generator, substantially all of the torque generated by the auxiliary power unit 150 (to be transferred to the electric machine 176) is transferred from the drive shaft 158 to the rotor shaft 184 of the rotor assembly 180 of the electric machine 176 via the electrical disconnect 196.

To prevent the conduction of electricity from the rotor assembly 180 of the motor 176 to the drive shaft 158 of the auxiliary power unit 150, the electrical disconnect 196 is formed substantially entirely of a non-conductive material. For example, in certain exemplary aspects, the non-conductive material can be a plastic material, such as one or more of polyethylene, polypropylene, polyvinyl chloride, acrylonitrile butadiene styrene, phenolic or phenol formaldehyde, polyetheretherketone, polyimide, and the like.

Referring now to fig. 5, a schematic cross-sectional side view of an aft engine is provided, in accordance with various embodiments of the present disclosure. The illustrated aft engine is mounted to the aircraft 10 at an aft end 18 of the aircraft 10. Specifically, for the depicted embodiment, the aft engine is configured as a Boundary Layer Ingestion (BLI) fan 300. As described herein, the aircraft of the present disclosure allows for the integration of Auxiliary Power Units (APUs) and Boundary Layer Ingestion (BLI) fans at the aft end 18 of the aircraft, i.e., a combined APU and BLI system 500. Referring to fig. 5-8, in an exemplary embodiment of the present disclosure, the auxiliary power unit exhaust duct or outlet portion 522 of the APU 510 extends through a portion of the support shaft 315 of the BLI fan 300 to enable the APU 510 to be positioned proximate the aft end 18 of the aircraft 10 while also adding the BLI fan 300 to a location proximate the aft end 18 of the aircraft 10. In this manner, the BLI fan 300, along with the auxiliary power unit 510, form a combined APU and BLI system 500, both of which may be installed near the aft end 18 of the aircraft 10. The BLI fan 300 may be configured in substantially the same manner as the BLI fan 106 described above with reference to FIGS. 1 and 2, and the aircraft 10 may be configured in substantially the same manner as the exemplary aircraft 10 described above with reference to FIGS. 1 and 2. However, in other embodiments, the rear engine may alternatively be configured in any other suitable manner.

As shown in fig. 5, the BLI fan 300 defines an axial direction a2 extending along a longitudinal centerline axis 302 and a radial direction R2 through which the longitudinal centerline axis 302 extends for reference.

Generally, the BLI fan 300 includes a fan 304 rotatable about a centerline axis 302, a nacelle 306 extending about a portion of the fan 304, and a structural support system 308. The fan 304 includes a plurality of fan blades 310 and a fan shaft 312. A plurality of fan blades 310 are attached to a fan shaft 312 and are spaced apart generally in the circumferential direction of the turbofan engine.

In certain exemplary embodiments, the plurality of fan blades 310 may be fixedly attached to the fan shaft 312, or alternatively, the plurality of fan blades 310 may be rotatably attached to the fan shaft 312. For example, the plurality of fan blades 310 may be attached to the fan shaft 312 such that the pitch of each of the plurality of fan blades 310 may be changed in unison, for example, by a pitch change mechanism (not shown). Varying the pitch of the plurality of fan blades 310 may increase the efficiency of the BLI fan 300 and/or may allow the BLI fan 300 to achieve a desired thrust curve. In such an exemplary embodiment, the BLI fan 300 may be referred to as a variable pitch BLI fan.

The fan shaft 312 is mechanically coupled to a power source 314 located at least partially within the fuselage 12 of the aircraft 10. In certain exemplary embodiments, the BLI fan 300 may be configured with an electropneumatic propulsion system, such as the electropneumatic propulsion system 100 described above with reference to FIG. 1. In such embodiments, the power source 314 may be an electric motor that receives electrical power from one or both of an energy storage device or a generator (e.g., such as the auxiliary power unit 150, the energy storage device 110, or the generator 108 of fig. 1 and 2), the generator 108 converting mechanical power received from one or more under-wing mounted aircraft engines into electrical power. It is noted that the motor may be an inward turning motor, or may be an outward turning motor. In either embodiment, the motor may further include a gearbox mechanically coupling the motor to the fan shaft 312. Additionally, in other exemplary embodiments, the power source 314 may alternatively be any other suitable power source. For example, the power source 314 may alternatively be configured as a gas engine, such as a gas turbine engine or an internal combustion engine. Further, in certain exemplary embodiments, the power source 314 may be located at any other suitable location within, for example, the fuselage 12 of the aircraft 10 or the BLI fan 300. For example, in certain exemplary embodiments, the power source 314 may be configured as a gas turbine engine located at least partially within the BLI fan 300.

As described above, the BLI fan 300 additionally includes a structural support system 308 for mounting the BLI fan 300 to the aircraft 10. When the BLI fan 300 is attached to the aircraft 10, the structural support system 308 generally extends from the fuselage 12 of the aircraft 10 through a fan shaft 312 to the nacelle 306 of the BLI fan 300. More specifically, the structural support system 308 generally includes a support shaft 315 extending between a first end 316 and a second end 317. It is worth noting that as used herein, the term "support shaft" generally refers to any structural member, such as a support beam or bar. At a first end 316, a support shaft 315 is attached to the fuselage 12 of the aircraft 10 by a plurality of front attachment arms 318 that support the shaft 315. For example, a plurality of front attachment arms 318 of support shaft 315 at first end 316 of support shaft 315 may be attached to bulkhead 322 of fuselage 12 of aircraft 10.

A support shaft 315 extends from the first end 316 in a rearward direction through at least a portion of the fan shaft 312. For the illustrated embodiment, the support shaft 315 includes a cylindrical body portion 319 that extends through the center of the fan shaft 312, the cylindrical body portion 319 of the support shaft 315 being concentric with the fan shaft 312. In addition, the cylindrical body portion 319 of the support shaft 315 supports the rotation of the fan shaft 312. More particularly, for the illustrated embodiment, a bearing assembly is provided between the main body portion 319 of the support shaft 315 and the fan shaft 312. The exemplary bearing assembly shown generally includes roller bearings 324 located forward of ball bearings 326. However, it should be appreciated that in other embodiments, any other suitable bearing assembly may be provided between the support shaft 315 and the fan shaft 312. Alternatively, the fan shaft 312 may be supported for rotation in any other suitable manner using any other suitable bearing assembly.

Still referring to FIG. 5, the structural support system 308 also includes one or more structural members 328 extending from the structural support shaft 315 to the nacelle 306. Specifically, for the illustrated embodiment, the structure support shaft 315 includes a plurality of rear support arms 320 and a cylindrical support ring 321. A plurality of rear support arms 320 extend from the cylindrical body portion 319 of the support shaft 315 to the cylindrical support ring 321, and one or more structural members 328 are attached to the cylindrical support ring 321. Additionally, for the illustrated embodiment, the one or more structural members 328 include a plurality of circumferentially spaced structural members 328, the structural members 328 being attached to the second end 317 of the support shaft 315, i.e., to the cylindrical support ring 321. The one or more structural members 328 may provide structural support for the nacelle 306 and, for example, the aft cone 330 of the BLI fan 300.

For the embodiment shown in FIG. 5, the plurality of structural members 328 extend substantially in the radial direction R2 to the nacelle 306 to provide structural support for the nacelle 306. Additionally, although not shown, in certain embodiments, the structural members 328 may be evenly spaced apart in the circumferential direction. However, it should be understood that the depicted exemplary structural support system 308 is provided by way of example only, and that in other exemplary embodiments, any other suitable structural support system 308 may be provided. For example, in other exemplary embodiments, the structural members 328 may instead define an angle relative to the radial direction R2, and may also be unevenly spaced along the circumferential direction. Additionally, the support shaft 315 may have any other suitable configuration. For example, in other exemplary embodiments, the support shaft 315 may be formed entirely of a cylindrical body portion such that the cylindrical body portion is mounted directly to the fuselage 12 of the aircraft 10 at the forward end. Similarly, in other embodiments, the support shaft 315 may not include one or both of the rear attachment arms 320 or the cylindrical support ring 321. For example, in certain exemplary embodiments, one or more structural members 328 may be directly attached to the cylindrical body portion 319 of the support shaft 315. Moreover, in other embodiments, support system 308 may include additional support features, such as static support features, located radially inward of fan shaft 312 and within support shaft 315, for example, or elsewhere, for providing a desired amount of support to structural member 328 and nacelle 306.

Notably, still referring to the embodiment of FIG. 5, one or more structural members 328 are attached to the nacelle 306 at locations aft of the plurality of fan blades 310 and extend from the support shaft 315 to the nacelle 306. The one or more structural members 328 may include a plurality of structural members 328 that extend substantially in the radial direction R2, as shown, and are substantially evenly spaced apart in the circumferential direction of the BLI fan 300. For example, the one or more structural members 328 may include three or more structural members 328, five or more structural members 328, eight or more structural members 328, or twelve or more structural members 328. However, in other exemplary embodiments, the one or more structural members 328 may include any other suitable number of structural members 328 and may define any suitable angle with the longitudinal centerline 302. Additionally, in other exemplary embodiments, the one or more structural members 328 may be spaced apart in the circumferential direction in any suitable configuration. It should be understood that, as used herein, approximate terms, such as "approximately," "substantially," or "approximately," mean within ten percent of error.

Further, in at least certain example embodiments, the one or more structural members 328 may each be configured as an outlet guide vane. If configured as outlet guide vanes, the one or more structural members 328 may be configured to direct airflow through the BLI fan 300. Additionally, with this configuration, the one or more structural members 328 may be configured as fixed exit guide vanes or, alternatively, as variable exit guide vanes. For example, each of the one or more structural members 328 may include a flap (not shown) at the aft end that is rotatable about a substantially radial axis to change the direction in which the structural member (configured as an exit guide vane) directs the airflow.

The BLI fan 300 also defines a nozzle 338 between the nacelle 306 and a tail cone 330 aft of the plurality of fan blades 310 and aft of one or more structural members 328 of the structural support system 308. The nozzle 338 may be configured to generate an amount of thrust from air flowing therethrough, and the tail cone 330 may be shaped to minimize the amount of drag on the BLI fan 300. However, in other embodiments, the tailcone 330 may have any other shape and may, for example, terminate forward of the aft end of the nacelle 306 such that the tailcone 330 is surrounded by the nacelle 306 at the aft end. Additionally, in other embodiments, the BLI fan 300 may not be configured to generate any measurable amount of thrust, but may be configured to ingest air from the boundary layer of air of the fuselage 12 of the aircraft 10 and add energy/accelerate such air to reduce the overall drag on the aircraft 10 (thereby increasing the net thrust of the aircraft 10).

Still referring to fig. 5, the BLI fan 300 defines an inlet 334 between the nacelle 306 and the fuselage 12 of the aircraft 10 at a forward end 336 of the BLI fan 300. The nacelle 306 of the BLI fan 300 extends around the mean line 15 of the aircraft 10 and the fuselage 12 of the aircraft 10 at the aft end 18 of the aircraft 10. Specifically, for the depicted embodiment, such as in the depicted embodiment, when the BLI fan 300 is mounted to the aircraft 10, the inlet 334 of the BLI fan 300 extends substantially three hundred sixty degrees in a circumferential direction around the mean line 15 of the aircraft 10 and the fuselage 12 of the aircraft 10.

Referring now to fig. 6, a close-up view of the aft end 18 of the exemplary aircraft 10 described above with reference to fig. 1, 2, and 5 is provided. As described above, the fuselage 12 of the aircraft 10 generally extends from the forward end 16 of the aircraft 10 to the aft end 18 of the aircraft 10, with the aft engine or BLI fan 300 and APU 510 mounted to the fuselage 12 near the aft end 18 of the aircraft 10. Fuselage 12 defines a top side 602 and a bottom side 604 along a vertical direction V. Moreover, the depicted exemplary fuselage 12 defines a frustum 606 located near the aft end 18 of the aircraft 10. Specifically, for the embodiment shown, the frustum 606 is located aft of a pair of wings 20 (fig. 1 and 2) of the aircraft 10. As used herein, the term "frustum" generally refers to a portion of a shape that lies between two parallel planes. Thus, for the depicted embodiment, the frustum 606 is defined between a first or forward plane 608 and a second or aft plane 610, the forward and aft planes 608, 610 being parallel to each other and perpendicular to the longitudinal centerline 14 of the aircraft 10 (fig. 1 and 2). Referring to fig. 6, as described above, the aircraft 10 includes a vertical stabilizer 30 having rudder flaps 32 for yaw control.

Fig. 5-8 illustrate exemplary embodiments of the present disclosure. 5-8, a combined APU and BLI system 500 for the aircraft 10 extending between the front end 16 and the rear end 18 will now be described. As shown in fig. 5-8, the present disclosure allows for the installation of a combined APU and BLI system 500 near the aft end 18 of the aircraft 10.

Referring to fig. 5 and 6, in the exemplary embodiment, APU and BLI system 500 includes an auxiliary power unit 510 located near aft end 18 of aircraft 10, and boundary layer ingestion fan 300 located near aft end 18 of aircraft 10. The auxiliary power unit 510 includes an auxiliary power unit inlet duct or inlet 520 and an auxiliary power unit exhaust duct or outlet section 522. The boundary layer ingestion fan 300 includes a support shaft 315 as described in detail above. As shown in FIGS. 5 and 6, in the exemplary embodiment, auxiliary power unit exhaust duct 522 extends through a portion of support shaft 315 of boundary layer ingest fan 300. In one embodiment, the auxiliary power unit exhaust duct 522 extends through the center of the support shaft 315 of the boundary layer ingestion fan 300 along an axial direction of the boundary layer ingestion fan 300, such as the longitudinal centerline axis 302. In one embodiment, the auxiliary power unit 510 corresponds to the auxiliary power unit 150 described above with respect to FIG. 4. As shown in fig. 5 and 6, the outlet portion 528 of the auxiliary power unit exhaust conduit 522 allows the exhaust gas to be vented or exhausted to the atmosphere.

Referring to FIG. 6, in one embodiment, the inlet duct 520 of the auxiliary power unit 510 is positioned at the top side 602 of the fuselage and extends to the auxiliary power unit 510 toward a central portion of the frustum 606 of the fuselage 12. Further, an exhaust or outlet duct 522 of the auxiliary power unit 510 extends from the auxiliary power unit 510 and through a portion of the support shaft 530 of the boundary layer ingestion fan 512.

In one embodiment, a portion of boundary layer ingestion fan 512 constitutes aft end 18 of aircraft 10, as shown in FIGS. 5 and 6. For example, as shown in fig. 5 and 6, boundary layer ingestion fans 512 are incorporated into the tail or tailcone 330 at the aft end 18 of the aircraft 10.

5-8, in the exemplary embodiment, APU and BLI system 500 includes a mixer 530 in communication with auxiliary power unit 510 and boundary layer ingest fan 300 such that mixer 530 receives and mixes the boundary layer airflow from boundary layer ingest fan 300 and the auxiliary power unit exhaust flow from auxiliary power unit exhaust duct 522. In this manner, the mixer 530 of the present disclosure provides noise reduction for the APU 510 and/or other components of the aircraft 10 by mixing the boundary layer airflow and the auxiliary power unit exhaust flow.

In one embodiment, mixer 530 is formed at the aft-most portion of tail cone 330 and is in communication with an outlet of auxiliary power unit exhaust conduit 522. In one embodiment, mixer 530 comprises a trough mixer. In another embodiment, mixer 530 comprises a chevron mixer. In other embodiments, mixer 530 includes other mixer mechanisms for mixing two separate streams therein.

Referring to FIG. 6, in the exemplary embodiment, APU and BLI system 500 includes an insulation 540 between auxiliary power unit exhaust duct 522 and support shaft 315 of boundary layer ingestion fan 300. In this manner, BLI fan 300 is thermally isolated from the higher temperature of the auxiliary power unit exhaust flow exiting auxiliary power unit exhaust duct 522.

Referring to FIG. 7, in the exemplary embodiment, APU and BLI system 500 includes a mechanism for de-icing nacelle 306 of boundary layer ingestion fan 300. For example, the auxiliary power unit exhaust duct 522 includes a bypass portion 524 that extends through the structural member 328 to the nacelle 306. In this manner, the higher temperature of the auxiliary power unit exhaust flow traveling through bypass portion 524 to nacelle 306 is configured to de-ice nacelle 306. In essence, bypass portion 524 allows some auxiliary power unit exhaust flow to be directed from auxiliary power unit exhaust duct 522 to a portion of nacelle 306, thereby providing de-icing capability using this configuration of bypass portion 524. As shown in FIG. 7, bypass portion 524 may extend to a forward edge of nacelle 306. Other configurations of the bypass portion 524 through all areas of the nacelle 306 are contemplated, such as extending from a forward edge to an aft edge of the nacelle 306.

Referring to FIG. 8, in an exemplary embodiment, the APU and BLI system 500 includes a BLI fan 300 having a motor or power source 314, the motor or power source 314 having a drive shaft 341 offset from a fan shaft 312. In this configuration, the BLI fan 300 further includes a gear 344 in communication with the drive shaft 341 and the fan shaft 312 to drive the BLI fan 300. In one embodiment, the gear 344 includes a ring gear, single helix, double helix, spur gear or other gear mechanism to allow the offset drive shaft 341 to drive the fan shaft 312 of the BLI fan 300. It is contemplated that in some embodiments, power source or motor 314 drives gear 344 and that in some embodiments, power source or motor 314 is an annular motor.

Fig. 9 illustrates another exemplary embodiment of the present disclosure. Referring to FIG. 9, a combined APU and BLI system 700 for the aircraft 10 extending between the front end 16 and the rear end 18 will now be described. As shown in fig. 9, the present disclosure allows for the installation of a combined APU and BLI system 700 near the aft end 18 of the aircraft 10.

Referring to FIG. 9, in the exemplary embodiment, APU and BLI system 700 includes an auxiliary power unit 710 located proximate aft end 18 of aircraft 10, and an aft engine or boundary layer ingestion fan 712 located proximate aft end 18 of aircraft 10. The auxiliary power unit 710 includes an auxiliary power unit inlet duct or inlet 720 and an auxiliary power unit exhaust duct or outlet portion 722.

In one embodiment, aft engine or boundary layer ingest fan 712 corresponds to aft engine or boundary layer ingest fan 300 described above with respect to FIG. 5. As described herein, the aft engine is configured as a boundary layer ingestion fan 300, 712.

Referring to FIG. 9, in an exemplary embodiment of the present disclosure, an auxiliary power unit exhaust duct 722 of the APU 710 extends through the structural member 328 to the nacelle 306 of the aft engine or BLI fan 712 to enable positioning of the APU near the aft end 18 of the aircraft 10 while also adding the BLI fan 712 to a location proximate the aft end 18 of the aircraft 10. Referring to FIG. 9, in one embodiment, an auxiliary power unit exhaust duct 722 extends through structural member 328 to nacelle 306 about drive shaft 341 and support shaft 315.

Referring to FIG. 9, in the exemplary embodiment, an auxiliary power unit exhaust duct 722 of APU 710 includes a first auxiliary power unit exhaust duct section 724 and a second auxiliary power unit exhaust duct section 726. In one embodiment, first auxiliary power unit exhaust duct portion 724 extends through first portion 742 of structural member 328 to first portion 744 of nacelle 306 about drive shaft 341 in first direction 740. Furthermore, a second auxiliary power unit exhaust duct portion 726 extends in a second direction 746 around the drive shaft 341 through a second portion 748 of the structural member 328 to a second portion 750 of the nacelle 306. As shown in FIG. 9, the first auxiliary power unit exhaust conduit section 724 and the second auxiliary power unit exhaust conduit section 726 are bifurcated. In this manner, auxiliary power unit exhaust duct 722 extends around BLI fan 712, thereby preventing auxiliary power unit exhaust flow through auxiliary power unit exhaust duct 722 from interfering with boundary layer ingestion fan 712.

In this manner, and with reference to FIG. 9, in the exemplary embodiment, APU and BLI system 700 provides a mechanism for de-icing nacelle 306 of boundary layer ingestion fan 712 by including a first auxiliary power unit exhaust duct section 724 and a second auxiliary power unit exhaust duct section 726 that extend through structural member 328 to nacelle 306. In this manner, the higher temperature of the auxiliary power unit exhaust flow traveling through the first and second auxiliary power unit exhaust duct sections 724 and 726 to different portions of the nacelle 306 is configured to de-ice the nacelle 306. In essence, first and second auxiliary power unit exhaust duct portions 724 and 726 allow some auxiliary power unit exhaust flow to pass from auxiliary power unit exhaust duct 722 to portions of nacelle 306, thereby providing deicing capabilities using this configuration of auxiliary power unit exhaust duct 722. As shown in FIG. 9, the first and second auxiliary power unit exhaust duct sections 724 and 726 may extend to all portions of the nacelle 306.

In one embodiment, the auxiliary power unit exhaust duct 722 includes an outlet portion 728 located at a trailing edge 730 of the nacelle 306. In one embodiment, the first and second auxiliary power unit exhaust duct sections 724 and 726 provide two separate outlet sections 728 located at a trailing edge 730 of the nacelle 306.

In the exemplary embodiment, structural member 328 through which auxiliary power unit exhaust duct 722 of APU 710 extends is a BLI fan or guide vane of rear engine 712. The combined APU and BLI system 700 provides a radially uniform temperature profile for the fan blades 310 by exhausting air through the guide vanes or structural members 328 (e.g., inlet guide vanes) of the BLI fan 712. It is contemplated that the auxiliary power unit exhaust duct 722 of the APU 710 may extend through any component of the BLI fan or rear engine 712, such as, for example, inlet guide vanes, outlet guide vanes, or other components of the BLI fan or rear engine 712.

Referring to FIG. 9, in the exemplary embodiment, APU and BLI system 700 includes an insulation portion 760 between auxiliary power unit exhaust duct 722 and a structural member 328 (e.g., a rear engine or guide vanes of BLI fan 712). In this manner, the BLI fan 712 is thermally isolated from the higher temperature of the auxiliary power unit exhaust flow exiting the auxiliary power unit exhaust duct 722.

In one embodiment, the auxiliary power unit 710 corresponds to the auxiliary power unit 150 as described above with respect to FIG. 4. As shown in FIG. 9, the outlet portion of the auxiliary power unit exhaust conduit 722 allows exhaust gas to be vented or exhausted to the atmosphere.

Fig. 10 illustrates another exemplary embodiment of the present disclosure. Referring to FIG. 10, a combined APU and BLI system 800 for the aircraft 10 extending between the front end 16 and the rear end 18 will now be described. As shown in fig. 10, the present disclosure allows for the installation of a combined APU and BLI system 800 near the aft end 18 of the aircraft 10.

Referring to FIG. 10, in the exemplary embodiment, APU and BLI system 800 includes an auxiliary power unit 810 that is positioned proximate aft end 18 of aircraft 10, and an aft engine or boundary layer ingestion fan 812 that is positioned proximate aft end 18 of aircraft 10. The auxiliary power unit 810 includes an auxiliary power unit inlet duct or inlet 820 and an auxiliary power unit exhaust duct or outlet portion 822.

In one embodiment, the aft engine or boundary layer ingest fan 812 corresponds to the aft engine or boundary layer ingest fan 300 described above with reference to FIG. 5. As described herein, the aft engine is configured as a boundary layer ingestion fan 300, 812.

Referring to FIG. 10, in the exemplary embodiment, boundary layer ingestion fans 812 are spaced apart from auxiliary power units 810, each of which is positioned near aft end 18 of aircraft 10. The auxiliary power unit exhaust duct 822 extends radially outward to the aft of the aircraft 10, for example, the auxiliary power unit exhaust duct 822 extends radially outward to the vertical stabilizer 30 of the aircraft 10, as shown in FIG. 10. In one embodiment, the auxiliary power unit exhaust duct 822 includes an outlet portion 828 that is located at a trailing edge of an aft portion of the aircraft 10, for example, at a trailing edge of the rudder flap 32, as shown in FIG. 10.

Referring to FIG. 10, in an exemplary embodiment of the present disclosure, an auxiliary power unit exhaust duct 822 of the APU 810 extending radially outward to the aft portion of the aircraft 10 (e.g., to the vertical stabilizer 30) enables the APU 810 to be positioned near the aft end 18 of the aircraft 10 while adding the BLI fan 812 to a location near the aft end 18 of the aircraft 10. In this manner, the auxiliary power unit exhaust duct 822 extends around the BLI fan 812, thereby preventing auxiliary power unit exhaust flow through the auxiliary power unit exhaust duct 822 from interfering with the operation of the boundary layer ingestion fan 812.

The aircraft of the present disclosure allows for integration of an Auxiliary Power Unit (APU) and Boundary Layer Ingestion (BLI) fans at the aft end of the aircraft. Embodiments of the present disclosure reduce exhaust noise of an aircraft by allowing integration of APUs and BLI fans at the aft end of the aircraft. Further, embodiments of the present disclosure include a bypass portion of the auxiliary power unit exhaust duct extending through the structural member to the nacelle, wherein an auxiliary power unit exhaust flow through the bypass portion to the nacelle is configured to de-ice the nacelle.

Embodiments of the present disclosure may also include temperature sensors at various locations of the integrated APU and BLI fan systems. For example, in an exemplary embodiment, a temperature sensor may be included at a region of the system to measure the air temperature immediately before the fan blades of the BLI fan, allowing the power to the fan to be increased or decreased based on such temperature readings. This configuration may prevent the BLI fan system from stalling.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

While this disclosure has been described as having an exemplary design, the present disclosure may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Further aspects of the invention are provided by the subject matter of the following clauses:

1. an aircraft extending between a forward end and an aft end, the aircraft comprising: an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a boundary layer ingestion fan positioned proximate the aft end of the aircraft, the boundary layer ingestion fan having a support shaft, wherein the auxiliary power unit exhaust duct extends through a portion of the support shaft of the boundary layer ingestion fan.

2. The aircraft of any preceding item, further comprising a mixer in communication with the auxiliary power unit and the boundary layer ingestion fan such that the mixer receives and mixes boundary layer airflow from the boundary layer ingestion fan and auxiliary power unit exhaust flow from the auxiliary power unit exhaust duct.

3. The aircraft of any preceding claim, further comprising: an insulation portion between the auxiliary power unit exhaust duct and the support shaft of the boundary layer ingestion fan.

4. The aircraft of any preceding item, wherein the boundary layer ingestion fan defines a central axis, and further comprising: a fan rotatable about the central axis and comprising a plurality of fan blades attached to a fan shaft; a nacelle surrounding the plurality of fan blades; and a structural member extending from the support shaft of the boundary layer ingestion fan to the nacelle.

5. The aircraft of any preceding claim, wherein the auxiliary power unit exhaust duct includes a bypass portion extending through the structural member to the nacelle, wherein an auxiliary power unit exhaust flow through the bypass portion to the nacelle is configured to de-ice the nacelle.

6. The aircraft of any preceding claim, further comprising: a motor having a drive shaft offset from the fan shaft; and a gear in communication with the drive shaft and the fan shaft to drive the boundary layer ingestion fan.

7. The aircraft of any preceding item, wherein the auxiliary power unit exhaust duct extends through a center of the support shaft of the boundary layer ingestion fan in an axial direction of the boundary layer ingestion fan.

8. The aircraft of any preceding item, wherein the boundary layer ingestion fan is incorporated into a tail of the aircraft at the aft end of the aircraft.

9. The aircraft of any preceding item, wherein a portion of the boundary layer ingestion fan constitutes the aft end of the aircraft.

10. An aircraft extending between a forward end and an aft end, the aircraft comprising: an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and an aft engine configured to be mounted to the aircraft at the aft end, the aft engine defining a central axis and comprising: a fan rotatable about the central axis of the aft engine and including a plurality of fan blades attached to a fan shaft; a nacelle surrounding the plurality of fan blades; and a structural member extending from a portion of the rear engine to the nacelle; wherein the auxiliary power unit exhaust duct extends through the structural member to the nacelle.

11. The aircraft of any preceding claim, wherein the aft engine further comprises: a power source having a drive shaft; and a support shaft extending through the fan shaft, wherein the structural member extends from the support shaft to the nacelle, and wherein the auxiliary power unit exhaust duct extends through the structural member around the drive shaft and the support shaft to the nacelle.

12. The aircraft of any preceding claim, wherein the auxiliary power unit exhaust duct comprises an outlet portion at a trailing edge of the nacelle.

13. The aircraft of any preceding item, wherein the structural member is an inlet guide vane.

14. The aircraft of any preceding claim, further comprising: an insulating portion between the auxiliary power unit exhaust duct and the inlet guide vane.

15. The aircraft of any preceding item, wherein the aft engine is configured as a boundary layer ingestion fan.

16. The aircraft of any preceding item, wherein an auxiliary power unit exhaust flow through the auxiliary power unit exhaust duct within the nacelle is configured to de-ice the nacelle.

17. The aircraft of any preceding item, wherein the auxiliary power unit exhaust duct comprises: a first auxiliary power unit exhaust duct portion extending in a first direction about the drive shaft through a first portion of the structural member to a first portion of the nacelle; and a second auxiliary power unit exhaust duct portion extending through the second portion of the structural member in a second direction about the drive shaft to a second portion of the nacelle, wherein the first and second auxiliary power unit exhaust duct portions are bifurcated.

18. An aircraft extending between a forward end and an aft end, the aircraft comprising: an auxiliary power unit positioned near the aft end of the aircraft, the auxiliary power unit having an auxiliary power unit inlet duct and an auxiliary power unit exhaust duct; and a boundary layer ingestion fan positioned near the aft end of the aircraft between the aft end of the aircraft and the auxiliary power unit, the boundary layer ingestion fan being spaced apart from the auxiliary power unit, wherein the auxiliary power unit exhaust duct extends radially outward to an aft portion of the aircraft.

19. The aircraft of any preceding claim, wherein the auxiliary power unit exhaust duct includes an outlet portion located at a trailing edge of the tail of the aircraft.

20. The aircraft of any preceding item, wherein the auxiliary power unit exhaust duct extends radially outward to a vertical stabilizer of the aircraft.