FIELD OF THE INVENTION

The present subject matter relates generally to an aircraft having an aft engine, or more particularly to a fuselage of an aircraft designed to increase the efficiency of the aft engine.

BACKGROUND OF THE INVENTION

A conventional commercial aircraft generally includes 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, such as in a suspended position beneath the wing, separated from the wing and 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.

However, a drag on the aircraft including the turbofan jet engines also affects the net propulsive 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.

Positioning a fan at an aft end of the fuselage of the aircraft may assist with reenergizing a boundary layer airflow over the aft end of the fuselage and improving propulsive efficiency. However, given existing structures at the aft end of the fuselage, such as one or more stabilizers, the airflow ingested by such a fan may not have a uniform velocity or total pressure profile along the circumferential and radial directions of the fan. More specifically, the structures at the aft end of the fuselage may generate a boundary layer or wake resulting in swirl distortion and a distorted velocity or total pressure profile of the airflow ingested by the fan.

Accordingly, an aircraft capable of energizing slow-moving air forming a boundary layer across the fuselage of the aircraft would be useful. Specifically, a fuselage of an aircraft designed to increase the ingestion of relatively low momentum boundary layer airflow into the aft engine and reduce the non-uniformity and distortion of the velocity profile of ingested airflow would be particularly beneficial.

BRIEF DESCRIPTION OF THE 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 defining a longitudinal direction, a vertical direction, and a lateral direction is provided. The aircraft includes a fuselage extending between a forward end and an aft end along the longitudinal direction. The aircraft also includes a boundary layer ingestion fan mounted to the fuselage at the aft end of the fuselage, the boundary layer ingestion fan defining a centerline and including a plurality of fan blades rotatable about the centerline and a nacelle surrounding the plurality of fan blades. The fuselage defines a cross section upstream of the boundary layer ingestion fan, the cross section defining a horizontal reference line extending through the centerline of the boundary layer ingestion fan to define a top half having a top half cross sectional area and a bottom half having a bottom half cross sectional area. The top half cross sectional area of the cross section is greater than the bottom half cross sectional area of the cross section.

In another exemplary embodiment of the present disclosure, an aircraft defining a longitudinal direction, a vertical direction, and a lateral direction is provided. The aircraft includes a fuselage extending between a forward end and an aft end along the longitudinal direction, the fuselage defining a top surface and a bottom surface. The aircraft also includes a boundary layer ingestion fan mounted to the fuselage at the aft end of the fuselage, the boundary layer ingestion fan defining a centerline and including a plurality of fan blades rotatable about the centerline and a nacelle surrounding the plurality of fan blades. The fuselage defines a cross section upstream of the boundary layer ingestion fan, the cross section defining a circumference and a horizontal reference line, wherein the horizontal reference line extends across a widest portion of the cross section along the lateral direction, the fuselage further defining a reference circle at the cross section and having the horizontal reference line as a diameter of the reference circle. At least a portion of the circumference of a top half of the cross section of the fuselage is located outside the reference circle, and wherein at least a portion of the circumference of a bottom half of the cross section of the fuselage is located inside the reference circle.

In yet another exemplary embodiment of the present disclosure, an aircraft defining a longitudinal direction, a vertical direction, and a lateral direction is provided. The aircraft includes a fuselage extending between a forward end and an aft end along the longitudinal direction, the fuselage defining a surface. A boundary layer ingestion fan is mounted to the fuselage at the aft end of the fuselage, the boundary layer ingestion fan defining a centerline and including a plurality of fan blades rotatable about the centerline and a nacelle surrounding the plurality of fan blades. A stabilizer is attached to the fuselage and extending between a leading edge and a trailing edge. The surface of the fuselage defines a first point located in a plane perpendicular to the longitudinal direction and positioned where the leading edge of the stabilizer meets the fuselage, a second point located in a plane perpendicular to the longitudinal direction and positioned where the trailing edge of the stabilizer meets the fuselage, and an inflection point. The surface of the fuselage further defines a first portion of the surface, the first portion extending between the first point and the inflection point, the first portion being convex; and a second portion of the surface, the second portion extending between the inflection point and the second point, the second portion being concave.

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.

