Patent Description:
A conventional commercial aircraft generally includes a fuselage, a pair of wings, and a propulsion system that provides thrust to the aircraft. The propulsion system typically includes at least two aircraft engines, such as turbofan jet engines. Each turbofan jet engine is mounted to a respective wing of the aircraft, such as in a suspended position beneath the wing, separated from the wing and the fuselage. Such a configuration allows for the turbofan jet engines to interact with separate, freestream airflows that are not impacted by the wings and/or fuselage. This configuration can reduce an amount of turbulence within the air entering an inlet of each respective turbofan jet engine, which has a positive effect on a net propulsive thrust of the aircraft.

Drag on the aircraft, including the turbofan jet engines, has an effect on the net propulsion thrust of the aircraft. A total amount of drag on the aircraft, including skin friction and form drag, is generally proportional to a difference between a freestream velocity of air approaching the aircraft and an average velocity of a wake downstream from the aircraft that is produced due to the drag on the aircraft. Systems have been proposed to counter the effects of drag and/or to improve an efficiency of the turbofan jet engines. For example, certain propulsion systems include boundary layer ingestion systems to route a portion of relatively slow-moving air forming a boundary layer across the fuselage and/or the wings, into the turbofan jet engines upstream from a fan section of the turbofan jet engines. This configuration may reenergize the boundary layer airflow downstream from the aircraft that has a nonuniform or distorted velocity profile.

One issue with known aircraft propulsion systems is generating and providing reverse thrust to the aircraft in order to reduce the speed of movement of the aircraft. For example, when the aircraft is landing, the aircraft is moving at high speeds which puts strain on the braking system of the aircraft. Conventional thrust reverser systems that assist the braking system in slowing or stopping the aircraft include heavy equipment thereby adding weight to the aircraft and reducing the fuel efficiency of the system. Therefore, an improved system may provide improved fuel efficiency, improve propulsive efficiency, thereby reducing operating and maintenance costs, and improve the life of the aircraft.

<CIT>) discloses an aircraft comprising trailing edge flaps, a wing mounted propulsor positioned such that the flaps are located in a slipstream of the first propulsor in use when deployed. The aircraft further comprises a thrust vectorable propulsor configured to selectively vary the exhaust efflux vector of the propulsor in at least one plane.

<CIT>) a method and apparatus for controlling power distribution in an electrical aircraft propulsive system having at least one electrical propulsion unit which includes a plurality of rotatable blades, each blade having an adjustable pitch; a pitch adjusting mechanism for adjusting the pitch of the blades; at least one electrical machine electrically connected to the electrical propulsion unit so as to provide electrical power when in use; and, a control system.

<CIT>) a propulsion system for an aircraft having an aft engine configured to be mounted to the aircraft at an aft end of the aircraft.

An aircraft propulsion system according to claim <NUM> is provided.

Further, a method according to claim <NUM> is provided.

The present inventive subject matter will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below:.

One or more embodiments of the inventive subject matter described herein relates to systems and methods that effectively provide thrust to an aircraft propulsion system. The systems and methods change a direction of rotation of a fan of a boundary layer ingestion (BLI) fan system. The systems and methods change a position of blades of the fan with an electric motor. By changing the direction of the rotation of the fan of the BLI fan system, and changing the position of the blades of the BLI fan system, the systems and methods change a direction of airflow through the BLI fan system. The change in the direction of airflow of the BLI fan system enables the BLI fan system to provide forward thrust as well as reverse thrust to the aircraft propulsion system. One technical effect of the subject matter described herein is managing the desired amount and direction of thrust that may be provided by the BLI fan system to the aircraft system. One technical effect of the subject matter described herein is improved reduction of speed of the aircraft system (e.g., slows more quickly) when the aircraft system is landing, decelerating, or the like, thereby extending part life of a braking system of the aircraft.

As used herein, the terms "first", "second", or "third" may be used interchangeably to distinguish one component from another and are not intended to signify location or importance of the individual components. The terms "forward" and "aft" refer to the relative positions of a component based on an actual or anticipated direction of travel. For example, "forward" may refer to a front of an aircraft based on an anticipated direction of travel of the aircraft, and "aft" may refer to a back of the aircraft based on an anticipated direction of travel of the aircraft. Additionally, the terms "upstream" and "downstream" refer to the relative direction with respect to fluid flow in a fluid pathway. For example, "upstream refers to the direction from which the fluid flows, and "downstream" refers to the direction to which the fluid flows.

<FIG> illustrates a top view of an aircraft system <NUM> in accordance with one embodiment. <FIG> illustrates a side view of the aircraft system <NUM> in accordance with one embodiment. <FIG> and <FIG> will be discussed together in detail herein.

The aircraft system <NUM> includes an aircraft <NUM> having a fuselage <NUM> that extends between a forward end <NUM> and an aft end <NUM> of the aircraft <NUM> along a longitudinal direction of the aircraft <NUM>. The aircraft <NUM> defines a longitudinal centerline <NUM> that extends therethrough a vertical direction V and a lateral direction L. The aircraft <NUM> defines a mean line <NUM> that extends between the forward end <NUM> and the aft end <NUM> of the fuselage <NUM>. As used herein, the term "fuselage" generally includes all of the body of the aircraft <NUM>, such as an empennage of the aircraft <NUM>. Additionally, as used herein, the "mean line" refers to a midpoint line extending along a length of the aircraft <NUM>, not taking into account the appendages of the aircraft system <NUM> (e.g., wings <NUM> and stabilizers that will be discussed in more detail below).

The aircraft <NUM> includes a pair of wings <NUM>. A first wing extends laterally from a port side <NUM> of the fuselage <NUM> in the lateral direction L, and a second wing extends laterally from a starboard side <NUM> of the fuselage <NUM>. Each of the wings <NUM> includes one or more leading edge flaps <NUM> and one or more trailing edge flaps <NUM>. Optionally, the wings <NUM> may not include the leading edge flaps <NUM> and/or the trailing edge flaps <NUM>. The aircraft <NUM> includes a vertical stabilizer <NUM> and a pair of horizontal stabilizers <NUM> at the aft end <NUM> of the aircraft <NUM>. The vertical stabilizer <NUM> has a rudder flap <NUM> for yaw control, and each of horizontal stabilizers <NUM> has an elevator flap <NUM> for pitch control of the aircraft system <NUM>. The fuselage <NUM> includes an outer surface or skin <NUM>. <FIG> and <FIG> illustrate one embodiment of the aircraft system <NUM>. Optionally, the aircraft system <NUM> may include any alternative configuration of stabilizers, wings, or the like, that may extend from the aircraft <NUM> along the vertical direction V, the horizontal or lateral direction L, or in any alternative direction away from the centerline <NUM> and/or the mean line <NUM>.

The aircraft system <NUM> includes an aircraft propulsion system <NUM>. The aircraft propulsion system <NUM> includes a pair of aircraft engines, at least one mounted to each of the pair of wings <NUM>, and an aft engine. In the illustrated embodiment, the aircraft propulsion system <NUM> engines maybe configured as turbofan jet engines <NUM>, <NUM> that are suspended beneath the wings <NUM> in an under-wing configuration. Additionally or alternatively, the jet engines <NUM>, <NUM> may be positioned at a different location between the forward and aft ends <NUM>, <NUM> of the aircraft <NUM>, may be positioned above the wings <NUM>, or at any alternative location. Optionally, the aircraft propulsion system <NUM> may include any number and/or configuration of jet engines including non-limiting examples of turbofans, turboprops, turbojets, or the like. For example, the aircraft propulsion system <NUM> may not include underwing mounted jet engines <NUM>, <NUM>, and may include any alternative power source (e.g., an electric power source) for powering the aircraft system <NUM>.

The aft engine is a fan that is configured to ingest and consume air forming a boundary layer over the fuselage <NUM> of the aircraft <NUM>. The aft engine may be referred to herein as a boundary layer ingestion (BLI) fan system <NUM>. The BLI fan system <NUM> is mounted to the fuselage <NUM> at a location aft of the wings <NUM> and/or the jet engines <NUM>, <NUM>, such that the mean line <NUM> extends through the BLI fan system <NUM>. For example, such a configuration positions a center axis of the BLI fan system <NUM> above the centerline <NUM> in the vertical direction V. Additionally, the BLI fan system <NUM> maybe mounted parallel to the centerline <NUM> in the lateral direction L, or at an angle to the centerline <NUM>. For example, the center axis of the BLI fan system <NUM> may define an angle with the centerline <NUM>. The BLI fan system <NUM> is fixedly connected to the fuselage <NUM> at the aft end <NUM> such that the BLI fan system <NUM> is incorporated into or blended with a tail section of the aircraft system <NUM> at the aft end <NUM>. Optionally, the BLI fan system <NUM> may be positioned in any alternative locations near the aft end <NUM> of the aircraft <NUM>.

The jet engines <NUM>, <NUM> are configured to provide power to an electric generator <NUM> and/or an energy storage device <NUM> of the aircraft propulsion system <NUM>. For example, one or more of the jet engines <NUM>, <NUM> may be configured to provide mechanical power from a rotating shaft (e.g., a low-pressure shaft or high-pressure shaft) to the electric generator <NUM>. In the illustrated embodiment, the jet engines <NUM>, <NUM> are operably coupled with a single electric generator <NUM>. Optionally, the jet engines <NUM>, <NUM> may be operably coupled with two or more electric generators. The electric generator <NUM> may convert the rotational energy generated by the jet engines <NUM>, <NUM> into electrical energy. Additionally or alternatively, the electric generator <NUM> may convert the mechanical power to electrical power and provide the converted electrical power to the energy storage device <NUM>.

The aircraft propulsion system <NUM> includes an electric motor <NUM> operably coupled with the BLI fan system <NUM>. For example, the electric motor <NUM> may electrically control one or more operation of the BLI fan system <NUM>. Optionally, the electric motor <NUM> may be operably coupled with one or more components of the BLI fan system <NUM>. Additionally, the electric generator <NUM> and/or the energy storage device <NUM> are electrically coupled with the electric motor <NUM>. For example, the electric generator <NUM> may provide converted electrical power to the electric motor <NUM>. The electric motor <NUM> may control operation of the BLI fan system <NUM> using the electrical power generated by the electric generator <NUM> and supplied to the electric motor <NUM>.

In the illustrated embodiment, the electric generator <NUM>, the energy storage device <NUM>, and the electric motor <NUM> are separated from the jet engines <NUM>, <NUM>. Additionally or alternatively, one or more of the electric generator <NUM>, energy storage device <NUM>, or the electric motor <NUM> may be configured with the jet engines <NUM>, <NUM>. Optionally, the aircraft propulsion system <NUM> may include plural electric generators <NUM>. Each electric generator <NUM> may be operably coupled with each of the jet engines <NUM>, <NUM>. Optionally, one or more of the jet engines <NUM>, <NUM> may be a high bypass, turbofan jet engine with an electric generator driven by one or more shafts of the turbofan jet engine.

<FIG> illustrates a cross-sectional perspective view of the BLI fan system <NUM>.

The BLI fan system <NUM> is mounted to the aircraft <NUM> near the aft end <NUM> of the aircraft system <NUM>. The BLI fan system <NUM> defines a radial direction R and an axial direction A. The axial direction A extends along a longitudinal, axial centerline <NUM> that extends through a center of the BLI fan system <NUM> between a forward end <NUM> and a rear end <NUM> of an outer nacelle <NUM>. The outer nacelle <NUM> includes an inlet <NUM> at the forward end <NUM> and an outlet <NUM> at the rear end <NUM>. For example, during cruising operation of the aircraft system <NUM>, boundary layer air may flow into the inlet <NUM> at the forward end <NUM> and exit the BLI fan system <NUM> from the outlet <NUM> at the rear end <NUM> of the outer nacelle <NUM>. For example, the outer nacelle <NUM> defines a passageway through which air is configured to flow.

The aircraft propulsion system <NUM> (of <FIG> and <FIG>) also includes an actuator <NUM> operably coupled with the BLI fan system <NUM>. The actuator <NUM> may be a motor, a mechanical actuator, a hydraulic actuator, a hydraulic pump, or the like. In the illustrated embodiment, a single actuator <NUM> is operably coupled with the BLI fan system <NUM>. Additionally or alternatively, the propulsion system <NUM> may have one or more actuators <NUM> that are operably coupled with the BLI fan system <NUM>. The actuator <NUM> is disposed within the fuselage <NUM> at the aft end <NUM> of the aircraft system <NUM>. Alternatively, the actuator <NUM> may be disposed at an alternative location within the aircraft system <NUM>.

The actuator <NUM> electrically and/or mechanically controls operations of the BLI fan system <NUM>. Additionally, the electric generator <NUM> and/or the energy storage device <NUM> are electrically coupled with the actuator <NUM>. For example, the electric generator <NUM> may provide converted electrical power to the actuator <NUM>. The actuator <NUM> may control one or more operations of the BLI fan system <NUM> using the electrical power generated by the electric generator <NUM> and supplied to the actuator <NUM>.

The BLI fan system <NUM> includes inlet guide vanes <NUM> and outlet guide vanes <NUM>. Optionally, in one or more embodiments, the BLI fan system <NUM> may be devoid of the inlet guide vanes <NUM> and/or devoid of the outlet guide vanes <NUM>. Additionally or alternatively, the inlet guide vanes <NUM> may be referred to as inlet guide blades <NUM>, and the outlet guide vanes <NUM> may be referred to as outlet guide blades <NUM>. For example, the inlet and outlet guide blades <NUM>, <NUM> may be shaped and sized similar to or unique to the fan blades <NUM>. The inlet guide vanes <NUM> are fixedly coupled to the outer nacelle <NUM> and disposed near the forward end <NUM> of the outer nacelle <NUM> along the axial centerline <NUM>. The outlet guide vanes <NUM> are fixedly coupled to the outer nacelle <NUM> and disposed near the rear end <NUM> of the outer nacelle <NUM> along the axial centerline <NUM>. For example, the fan <NUM> is disposed between the inlet guide vanes <NUM> and the outlet guide vanes <NUM>. Additionally or alternatively, the inlet and/or outlet guide vanes <NUM>, <NUM> may be variable guide vanes. One or more of the inlet guide vanes <NUM> and/or one or more of the outlet guide vanes <NUM> may be rotatable about a guide vane axis (not shown) corresponding to each inlet guide vanes <NUM> and/or each outlet guide vanes <NUM>. For example, the actuator <NUM> may be operably coupled with the inlet and/or outlet guide vanes <NUM>, <NUM> and may provide electrical or mechanical power in order to rotate the inlet and/or outlet guide vanes <NUM>, <NUM> from a first pitch angle to a different, second pitch angle. Optionally, a first actuator may be operably coupled with and control the position of the inlet guide vanes <NUM> and a different, second actuator may be operably coupled with and control the position of the outlet guide vanes <NUM>.

The inlet and outlet guide vanes <NUM>, <NUM> are shaped, sized, and oriented within the outer nacelle <NUM> in order to direct and/or condition a flow of air that flows through the BLI fan system <NUM>. For example, the inlet and outlet guide vanes <NUM>, <NUM> may increase an efficiency of the BLI fan system <NUM>, may reduce distortion of air flowing into the BLI fan system <NUM>, add strength and/or rigidity to the BLI fan system <NUM>, or the like, relative to a BLI fan system <NUM> that is devoid inlet and/or outlet guide vanes <NUM>, <NUM>.

The BLI fan system <NUM> includes a fan <NUM> that includes a rotating fan shaft <NUM> that is rotatable about the axial centerline <NUM> within the outer nacelle <NUM>. The BLI fan system <NUM> includes plural fan blades <NUM> that are spaced substantially uniform with respect to each other fan blade <NUM> about the axial centerline <NUM>. In one or more embodiments, the fan blades <NUM> may be fixedly attached to the fan shaft <NUM> or may be rotatably attached to the fan shaft <NUM>. For example, the fan blades <NUM> may be attached to the fan shaft <NUM> such that a pitch angle of each of the blades <NUM> may be changed (e.g., in unison or not in unison) by the actuator <NUM> directing the blades <NUM> to rotate around or about a blade axis of each of the fan blades <NUM>. In one or more embodiments, the pitch angle of the fan blades <NUM> may be changed by the actuator <NUM>, by a hydraulic pump (not shown), or an alternative mechanism. Changing the pitch of the plurality of fan blades <NUM> may increase an efficiency of the BLI fan system <NUM>, may allow the BLI fan system <NUM> to achieve a desired thrust, or the like, relative to a BLI fan system <NUM> that does not change the pitch of the fan blades <NUM>. For example, the BLI fan system <NUM> may be referred to as a variable pitch fan. The pitch angle of the fan blades <NUM> will be discussed in more detail below.

The fan shaft <NUM> of the BLI fan system <NUM> is operably coupled with the electric motor <NUM> (of <FIG> and <FIG>). The electric motor <NUM> may change one or more of the speed of rotation of the fan shaft <NUM>, a direction of rotation of the fan shaft <NUM> of the fan <NUM>, or the like. Changing a direction and/or speed of rotation of the fan <NUM> may increase an efficiency of the aircraft propulsion system <NUM>, may increase an efficiency of the BLI fan system <NUM>, may allow the BLI fan system <NUM> to achieve a desired direction and/or amount of thrust, or the like, relative to a BLI fan system <NUM> that does not change the speed and/or direction of rotation of the fan <NUM>. The direction of rotation of the fan <NUM> will be discussed in more detail below.

The BLI fan system <NUM> includes a tail cone <NUM> and a nozzle <NUM>. The nozzle <NUM> is disposed between the outer nacelle <NUM> and the tail cone <NUM> at the rear end <NUM> of the nacelle <NUM>. The tail cone <NUM> is shaped and sized to direct the flow of air that is flowing through the outlet <NUM> of the BLI fan system <NUM>. The nozzle <NUM> generates an amount of thrust from the air that is flowing through the BLI fan system <NUM>, and the tail cone <NUM> is shaped in order to minimize an amount of drag on the BLI fan system <NUM>. Additionally or alternatively, the tail cone <NUM> may have any alternative shape and/or size, may be disposed at an alternative position within the BLI fan system <NUM> (e.g., between the inlet <NUM> and the outlet <NUM>), or the like.

<FIG> illustrates a partial perspective view of the BLI fan system <NUM> having the fan blades <NUM> positioned at a first pitch angle in accordance with one embodiment. <FIG> illustrates a partial front view of the BLI fan system <NUM> having the blades <NUM> positioned at the first pitch angle in accordance with one embodiment. <FIG> illustrates a side view of the BLI fan system <NUM>. <FIG>, <FIG> and <FIG> will be discussed in detail together.

The fan <NUM> and the plural fan blades <NUM> rotate in a first direction of rotation <NUM> about the axial centerline <NUM> of the BLI fan system <NUM>. Each of the fan blades <NUM> has a pressure side <NUM> and a suction side <NUM> that is opposite the pressure side <NUM>. The pressure side <NUM> and the suction side <NUM> are interconnected by a leading edge <NUM> and a trailing edge <NUM> that is opposite the leading edge <NUM>. The pressure side <NUM> is generally concave in shape, and the suction side <NUM> is generally convex in shape between the leading and trailing edges <NUM>, <NUM>. For example, the generally concave pressure side <NUM> and the generally convex suction side <NUM> provides an aerodynamic surface over which fluid flows through the BLI fan system <NUM>.

The blades <NUM> in the embodiment of <FIG> and <FIG> are positioned at a first pitch angle <NUM> with respect to a blade axis <NUM> corresponding to each blade <NUM>. For example, the first pitch angle <NUM> may be less than <NUM> degrees from a horizontal axis as illustrated in <FIG>. For example, the first pitch angle <NUM> may be defined as the angle between the horizontal axis and a blade chord line.

Air is flowing through the BLI fan system <NUM> in a first direction of airflow <NUM> when the blades <NUM> are positioned in the first pitch angle <NUM> and when the fan <NUM> is rotating in a first direction of rotation <NUM> (e.g., in a clockwise direction illustrated in <FIG>) around the axial centerline <NUM> of the BLI fan system <NUM>. The flow of air in the first direction of airflow <NUM> flows into the inlet <NUM> at the forward end <NUM> of the outer nacelle <NUM> and exits the BLI fan system <NUM> through the outlet <NUM> at the rear end <NUM> of the outer nacelle <NUM>. Additionally, the inlet guide vanes <NUM> and the outlet guide vanes <NUM> (illustrated in <FIG>) may be positioned at, respectively, a first inlet pitch angle and a first outlet pitch angle (not shown) when the flow of air is flowing in the first direction of airflow <NUM> through the BLI fan system <NUM>.

The air flowing in the first direction of airflow <NUM> flows in a direction from the leading edge <NUM> of the blade <NUM> to the trailing edge <NUM> of each blade <NUM>. For example, a first relative velocity <NUM> of the airflow that is moving in the first direction of airflow <NUM> is configured to be directed towards the leading edge <NUM> of each blade <NUM>.

The fan blades <NUM> positioned at the first pitch angle <NUM> and the fan <NUM> rotating in the first direction of rotation <NUM> generates forward thrust <NUM> that propels the aircraft system <NUM> in the forward direction of movement <NUM> of the aircraft system <NUM>. For example, during operation of the aircraft system <NUM> when the aircraft system <NUM> is cruising and/or accelerating (e.g., during take-off), the BLI fan system <NUM> provides forward thrust <NUM> to the aircraft system <NUM>. The BLI fan system <NUM> assists the jet engines <NUM>, <NUM> in moving the aircraft system <NUM> in the direction of travel in the forward direction of movement <NUM>.

<FIG>, <FIG>, and <FIG>, illustrated a change to the position of the blades <NUM> and change in the direction of rotation of the fan <NUM>. <FIG> illustrates a partial perspective view of the BLI fan system <NUM> having the blades <NUM> positioned at a different, second pitch angle in accordance with one embodiment. <FIG> illustrates a partial front view of the BLI fan system <NUM> having the blades <NUM> positioned at the second pitch angle in accordance with one embodiment. <FIG> illustrates a side view of the BLI fan system <NUM>. <FIG>, <FIG> and <FIG> will be discussed in detail together.

The blades <NUM> in the embodiment of <FIG> and <FIG> are positioned at a different, second pitch angle <NUM> with respect to the blade axis <NUM> corresponding to each blade <NUM>. The actuator <NUM> of the aircraft propulsion system <NUM> may operably control the blades <NUM> in order to change the position of the pitch angle of the blades <NUM> from the first pitch angle <NUM> to the second pitch angle <NUM>. For example, the actuator <NUM> may include a switch (not shown) or an alternative electrical or mechanical component that electrically or mechanically controls the position of the blades <NUM>. The switch may be manually controlled by an operator onboard the aircraft system <NUM>, by an operator off-board the aircraft system <NUM>, or may be autonomously controlled by one or more systems of the aircraft system <NUM>. Each blade <NUM> rotates (e.g., a clockwise direction of rotation <NUM> illustrated in <FIG>) from the position of the first pitch angle <NUM> to the position of the second pitch angle <NUM> about each corresponding blade axis <NUM>. For example, the electric generator <NUM> (of <FIG>) may convert the mechanical energy from the jet engines <NUM>, <NUM> to electric energy that is used by the actuator <NUM> to change the position of the blades <NUM>. Optionally, a hydraulic pump or an alternative mechanism may change the position of the blades <NUM>. Optionally, each blade <NUM> may rotate in a direction opposite the direction of rotation <NUM> illustrated in <FIG> from the position of the first pitch angle <NUM> to the position of the second pitch angle <NUM>. For example, the blades <NUM> may rotate in a counter-clockwise direction of rotation.

The electric motor <NUM> changes the direction of rotation of the fan <NUM> from the first direction of rotation <NUM> (e.g., clockwise in <FIG>) to a different, second direction of rotation <NUM> (e.g., illustrated as counter-clockwise in <FIG>) about the axial centerline <NUM> of the BLI fan system <NUM>. For example, the electric motor <NUM> may include one or more phase switches (not shown), or alternative electrical components, that may electrically change the direction of rotation of the fan. The phase switch may be manually controlled by an operator onboard the aircraft system <NUM>, by an operator off-board the aircraft system <NUM>, or may be autonomously controlled by one or more systems of the aircraft system <NUM>. Optionally, the electric motor <NUM> may change the direction of rotation of the fan <NUM> to the second direction of rotation <NUM>, and may increase and/or decrease a speed of rotation of the fan <NUM>. For example, the electric motor <NUM> may direct the speed of the fan to decrease (e.g., to a predetermined lower fan speed limit threshold, to a stop, or the like), then change the direction of rotation of the fan to the second direction of rotation <NUM>. Optionally, the direction of rotation of the fan may remain unchanged when the blades <NUM> are configured to rotate in the counter-clockwise direction (e.g., a direction opposite the direction of rotation <NUM>).

Optionally, in one or more embodiments, the actuator <NUM> may operably control the inlet guide vanes <NUM> and/or the outlet guide vanes <NUM> in order to change the position of the pitch angle of the inlet and/or outlet guide vanes <NUM>, <NUM> to a different, second pitch angle. For example, the actuator <NUM> may include one or more switches (not shown) or an alternative electrical component that electrically controls the position of the inlet and/or outlet guide vanes <NUM>, <NUM>. The actuator <NUM> may change the position of the inlet and outlet guide vanes <NUM>, <NUM> from a first inlet pitch angle to a different, second inlet pitch angle, and from a first outlet pitch angle to a different, second outlet pitch angle, respectively. For example, the inlet guide vanes <NUM> may have a first inlet pitch angle that is unique to the first outlet pitch angle of the outlet guide vanes <NUM> and that is unique to the first pitch angle <NUM> of the fan blades <NUM>. Additionally, the actuator <NUM> may change the position of the inlet guide vanes <NUM> to a second inlet pitch angle that is unique to the second outlet pitch angle of the outlet guide vanes <NUM> and that is unique to the second pitch angle <NUM> of the fan blades <NUM>. For example, the actuator <NUM> may change the position of the inlet guide vanes <NUM>, the outlet guide vanes <NUM>, and the fan blades <NUM> to unique and/or common positions. Optionally, the propulsion system <NUM> may include three actuators <NUM> that operably control the position of the inlet guide vanes <NUM>, the fan blades <NUM>, and the outlet guide vanes <NUM>. For example, a first actuator may be operably coupled with the fan blades <NUM> in order to change the position of the pitch angle of the fan blades <NUM>, a second actuator may be operably coupled with the inlet guide vanes <NUM> in order to change the position of the pitch angle of the inlet guide vanes <NUM>, and a third actuator may be operably coupled with the outlet guide vanes <NUM> in order to change the position of the pitch angle of the outlet guide vanes <NUM>. Additionally or alternatively, the actuator <NUM> may include three switches. For example, a first switch may be operably coupled with the with the fan blades <NUM> in order to change the position of the pitch angle of the fan blades <NUM>, a second switch may be operably coupled with the inlet guide vanes <NUM> in order to change the position of the pitch angle of the inlet guide vanes <NUM>, and a third switch may be operably coupled with the outlet guide vanes <NUM> in order to change the position of the pitch angle of the outlet guide vanes <NUM>.

Changing the position of the blades <NUM> of the BLI fan system <NUM> from the first pitch angle <NUM> to the second pitch angle <NUM>, and changing the direction of rotation of the fan <NUM> from the first direction of rotation <NUM> to the second direction of rotation <NUM> changes a direction of flow of air through the BLI fan system <NUM> from the first direction of airflow <NUM> to a different, second direction of airflow <NUM>. The flow of air in the second direction of airflow <NUM> flows into the outlet <NUM> at the rear end <NUM> of the outer nacelle <NUM> and exits the BLI fan system <NUM> through the inlet <NUM> at the forward end <NUM> of the outer nacelle <NUM>.

The air flowing in the second direction of airflow <NUM> flows in a direction from the leading edge <NUM> of the blade <NUM> to the trailing edge <NUM> of each blade <NUM>. For example, a second relative velocity <NUM> of the airflow that is moving in the second direction of airflow <NUM> is configured to be directed towards the leading edge <NUM> of each blade <NUM>.

The fan blades <NUM> positioned at the second pitch angle <NUM> and the fan <NUM> rotating in the second direction of rotation <NUM> generates reverse thrust <NUM> that counteracts the propulsion of the aircraft system <NUM> in the forward direction of movement <NUM> of the aircraft system <NUM>. For example, during operation of the aircraft system <NUM> when the aircraft system <NUM> is landing, the BLI fan system <NUM> provides reverse thrust <NUM> to the aircraft system <NUM>. The BLI fan system <NUM> assists a braking system (not shown) of the aircraft system <NUM> by slowing, reducing, or stopping the forward direction of movement <NUM> of the aircraft system <NUM>.

As illustrated in <FIG>, when the fan <NUM> is rotating in the first direction of rotation <NUM>, the blades are positioned at the first pitch angle <NUM>, and air is flowing through the BLI fan system <NUM> in the first direction of airflow <NUM>, the first direction of airflow <NUM> through the BLI fan system <NUM> is in an opposite direction as the direction of movement <NUM> of the aircraft system <NUM>. Alternatively, as illustrated in <FIG>, when the fan <NUM> is rotating in the second direction of rotation <NUM>, the blades are positioned at the second pitch angle <NUM>, and air is flowing through the BLI fan system <NUM> in the second direction of airflow <NUM>, the second direction of airflow <NUM> through the BLI fan system <NUM> is in the same direction as the direction of movement <NUM> of the aircraft system <NUM>. Optionally, the inlet guide vanes <NUM> and the outlet guide vanes <NUM> may be positioned at, respectively, a first inlet pitch angle and a first outlet pitch angle (e.g., a first inlet pitch angle that may be the same or different than the first pitch angle <NUM>, and a first outlet pitch angle that may be the same or different than the first pitch angle <NUM>) when the flow of air is flowing in the first direction of airflow <NUM> through the BLI fan system <NUM>, and the inlet and outlet guide vanes <NUM>, <NUM> may be positioned at, respectively, a different, second inlet pitch angle and different, second outlet pitch angle (e.g., a second inlet pitch angle that may be the same or different than the second pitch angle <NUM>, and a second outlet pitch angle that may be the same or different than the second pitch angle <NUM>) when the flow of air is flowing in the second direction of airflow <NUM> through the BLI fan system <NUM>.

The BLI fan system <NUM> includes a flare <NUM> that is disposed at the rear end <NUM> of the outer nacelle <NUM>. The flare <NUM> extends around a perimeter of the outer nacelle <NUM>. The flare <NUM> is shaped and sized in order to direct the flow of air flowing in the second direction of airflow <NUM> into the outlet <NUM> of the BLI fan system <NUM>. For example, the flare <NUM> includes an inner flare surface <NUM> that is disposed near the outlet <NUM> of the outer nacelle <NUM>, and an outer flare surface <NUM> that is disposed distal to the outer nacelle <NUM> relative to the inner flare surface <NUM>. The outer flare surface <NUM> has a diameter that is larger than a diameter of the inner flare surface <NUM>. For example, the flare <NUM> may direct non-boundary layer air into the outlet <NUM> of the BLI fan system <NUM> when the BLI fan system <NUM> is providing reverse thrust (e.g., reverse thrust <NUM>) to the aircraft system <NUM>.

<FIG> illustrates a flowchart of a method <NUM> for providing a propulsion system of an aircraft. At <NUM>, a boundary layer ingestion (BLI) fan system (e.g., BLI fan system <NUM>) is disposed at an aft end of an aircraft system. The BLI fan system includes a fan <NUM> that includes plural blades <NUM>. The fan <NUM> with blades <NUM> rotate about an axial centerline <NUM> of the BLI fan system <NUM>. The BLI fan system <NUM> consumes or ingests boundary layer air of the aircraft system <NUM>. Additionally or alternatively, the BLI fan system <NUM> may be disposed at an alternative location of an aircraft system and may consume or ingest freestream air or air that has not been distorted by a fuselage, wings, or the like, of the aircraft system. The BLI fan system <NUM> provides forward and reverse thrust to the aircraft system <NUM>. For example, the BLI fan system <NUM> may provide forward thrust (e.g., forward thrust <NUM> of <FIG>) to the aircraft system <NUM> when the aircraft system <NUM> is taking off, cruising, or accelerating, or the like, and the BLI fan system <NUM> may provide reverse thrust (e.g., reverse thrust <NUM> of <FIG>) to the aircraft system <NUM> when the aircraft system <NUM> is landing, decelerating, or the like.

At <NUM>, an electric motor <NUM> is operably coupled with the BLI fan system <NUM>. For example, the electric motor <NUM> may be disposed at a position within the fuselage <NUM> of the aircraft system <NUM>, and may be electrically coupled with the BLI fan system <NUM>. Additionally, an actuator <NUM> is operably coupled with the BLI fan system <NUM>. For example, the actuator <NUM> may be disposed at a position within the fuselage <NUM> of the aircraft system <NUM>, and may be electrically coupled with the BLI fan system <NUM>. In one or more embodiments, the electric motor <NUM> and the actuator <NUM> may receive electrical energy from an electric generator <NUM>, from an energy storage device <NUM>, or the like. For example, the electric generator <NUM> may convert mechanical energy from the jet engines <NUM>, <NUM> into electrical energy that may be utilized by the electric motor <NUM> and/or the actuator <NUM>. Optionally, the electric motor <NUM> and/or the actuator <NUM> may receive electrical energy from any alternative power source such as an electric battery or the like. Additionally or alternatively, an electric battery may provide power to the aircraft during take-off, may provide power to the electric motor, or the like. In one or more embodiments, the propulsion system <NUM> may include numerous electric motors <NUM>, actuators <NUM>, hydraulic pumps, or any alternative power source, operably coupled with the BLI fan system <NUM>.

At <NUM>, the electric motor <NUM> changes a direction of rotation of the fan <NUM> from the first direction of rotation <NUM> to the different, second direction of rotation <NUM>. For example, the electric motor <NUM> may include a phase switch, or any alternative component that may change the direction of rotation of the fan <NUM>. The electric motor <NUM> controls the direction of rotation of the fan <NUM>. For example, the electric motor <NUM> may reduce the speed of the rotation of the fan <NUM> as the fan <NUM> rotates in the first direction of rotation <NUM> until the speed of the rotation of the fan <NUM> has reached a predetermined threshold, has come to a stop, or the like. The phase switch changes a phase of the electric motor <NUM> in order to change the direction of rotation of the fan <NUM> to the second direction of rotation <NUM>. The electric motor <NUM> may increase or decrease the speed of the rotation of the fan <NUM> rotating in the first direction or rotation <NUM> or the second direction of rotation <NUM> until the speed of the rotation of the fan <NUM> has reached a desired operating speed. The fan <NUM> rotating in the first direction of rotation <NUM> provides forward thrust <NUM> to the aircraft system <NUM>. The fan <NUM> rotating in the second direction of rotation <NUM> provides reverse thrust <NUM> to the aircraft system <NUM>.

At <NUM>, the actuator <NUM> changes a position of the blades <NUM> of the BLI fan system <NUM> from the first pitch angle <NUM> to the different, second pitch angle <NUM>. For example, the actuator <NUM> directs the blades <NUM> to rotate to the second pitch angle <NUM> position about the corresponding blade axis <NUM> of each blade <NUM>. Optionally, the position of the blades <NUM> of the BLI fan system <NUM> may change from the first pitch angle <NUM> to and/or from the second pitch angle <NUM> by mechanical actuators, hydraulic actuators, or the like. The blades <NUM> positioned in the first pitch angle <NUM> provides forward thrust <NUM> to the aircraft system <NUM>. The blades <NUM> positioned in the second pitch angle <NUM> provides reverse thrust <NUM> to the aircraft system <NUM>.

Optionally, the actuator <NUM> may change a position of the inlet guide vanes <NUM> and/or the outlet guide vanes <NUM>. For example, the actuator <NUM> may change a position of the inlet guide vanes <NUM> from a first inlet pitch angle to the different, second inlet pitch angle by directing the inlet guide vanes <NUM> to rotate to the second inlet pitch angle about a corresponding vane axis (not shown) of each inlet guide vane <NUM>. Additionally, the actuator <NUM> may change a position of the outlet guide from a first outlet pitch angle to the different, second outlet pitch angle by directing the outlet guide vanes <NUM> to rotate to the second outlet pitch angle about a corresponding vane axis (not shown) of each outlet guide vane <NUM>.

In one or more embodiments, the electric motor <NUM> may change one or more of the direction or speed of rotation of the fan <NUM> from the first direction of rotation <NUM> to the second direction of rotation <NUM>, but the actuator <NUM> may not change the position of the blades <NUM>. Additionally or alternatively, the actuator <NUM> may change the position of the blades <NUM> from the first pitch angle <NUM> to the second pitch angle <NUM>, but the electric motor <NUM> may not change the direction and/or speed of rotation of the fan <NUM>. Optionally, in one or more embodiments, the pitch angle of the outlet guide vanes and/or the inlet guide vanes may be changed to/from a forward thrust mode of operation to a reverse thrust mode of operation. Optionally, the propulsion system <NUM> may include multiple BLI fan systems <NUM>. For example, the multiple BLI fan systems <NUM> may control different components or systems in order to work together to provide forward thrust or reverse thrust for the aircraft system <NUM>. One or more of the multiple BLI fan systems <NUM> may change one or more of the direction of rotation of the fan <NUM> or the position of the blades <NUM>. For example, a first BLI fan system <NUM> may change only the direction of rotation and the speed of rotation of the fan <NUM>, and a second BLI fan system <NUM> may change the position of the blades <NUM>. Optionally, the one or more BLI fan system <NUM> may have any uniform or unique combination of changes to the rotation of the fan <NUM> and/or the position of the blades <NUM>.

In the illustrated embodiments, the propulsion system <NUM> is used to provide propulsion to an aircraft system. Additionally or alternatively, the propulsion system <NUM> may be used to provide propulsion to any alternative system, non-limiting examples include water systems, vehicle systems, clean energy systems, or the like.

Furthermore, references to "one embodiment" of the presently described subject matter are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising" or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property.

It is to be understood that the above description is intended to be illustrative, and not restrictive. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the subject matter set forth herein.

While the dimensions and types of materials described herein are intended to define the parameters of the disclosed subject matter, they are by no means limiting and are exemplary embodiments. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the subject matter described herein should, therefore, be determined with reference to the appended claims.

In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein. " Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

Claim 1:
An aircraft propulsion system (<NUM>) comprising:
a boundary layer ingestion, BLI, fan system (<NUM>) configured to be disposed at an aft end (<NUM>) of an aircraft (<NUM>), the BLI fan system (<NUM>) comprising a fan (<NUM>) within an outer nacelle (<NUM>), the fan (<NUM>) configured to rotate about an axial centerline (<NUM>) of the BLI fan system (<NUM>) in a first direction of rotation (<NUM>), the BLI fan system (<NUM>) comprising blades (<NUM>) positioned at a first pitch angle (<NUM>) configured to rotate with the fan (<NUM>);
an electric motor (<NUM>) operably coupled with the BLI fan system (<NUM>) and configured to change a direction of rotation of the fan (<NUM>) to a different, second direction of rotation (<NUM>); and
an actuator (<NUM>) operably coupled with the BLI fan system (<NUM>) and configured to change a position of the blades (<NUM>) of the fan (<NUM>) to be positioned at a different, second pitch angle (<NUM>);
characterised by a flare (<NUM>) disposed at a rear end (<NUM>) of the BLI fan system (<NUM>) and extending around a perimeter of the outer nacelle, wherein the flare (<NUM>) is configured to direct airflow into the BLI fan system (<NUM>).