Patent ID: 12187453

DETAILED DESCRIPTION

FIG.1shows a rear fuselage section of a fuselage14of the prior art is represented. It comprises a skin15defining the envelope of the fuselage. The rear fuselage section extends between a rear end17and a front end18at which it is attached with another section of the fuselage14. The rear fuselage section hosts a combustion engine10. The combustion engine is in an auxiliary power unit (APU). The combustion engine may be a gas turbine engine driving a power output shaft that provides mechanical rotational power to drive an electric generator or mechanically driven systems in the aircraft.

The rear fuselage section may include, at its rearward end, a tail cone and mounts, or at least portions of a mount, for a vertical tail plane and horizontal tail planes. The front end of the rear fuselage section may be defined by a frame (former) and forward of the compartment within the fuselage for the APU. The rear end17may be a rear of a tail cone of the fuselage.

The APU engine10produces exhaust gases that are discharged through an exhaust opening16forming in the skin15at the rear end of the fuselage14. The exhaust outlet16is connected to the engine through an exhaust duct11. The exhaust16is situated at the rear end17of the rear fuselage section and forms the rear end of the aircraft. One may note that the shape of the rear end17is mainly determined to host the exhaust16. The shape of the rear end17is not optimal in terms of aerodynamics.

The APU engine10ingests atmospheric air entering the aircraft through an air intake opening13forming an opening in the skin15of the fuselage14. The air intake opening13is connected to the engine via an intake duct12. The air intake opening is located on a lower side of the aircraft fuselage14, towards the front of the rear fuselage section. The air intake opening13is far ahead of the exhaust opening16to avoid exhaust gases being ingested by the engine10through the air intake opening13. Nonetheless, as it will be shown in connection withFIG.2, the dynamic air pressure profile around the rear fuselage section when the aircraft is in flight may provoke exhaust gases to flow along the skin and into the air intake opening13.

FIG.2shows an exemplary pressure profile of air in flight conditions around the skin of a rear fuselage section. The rear section includes a horizontal tail plane26and vertical tail plane25. Each line delimits two areas of the skin with different pressure levels. A first area20has a lower dynamic air pressure than the areas22, which themselves have a lower dynamic air pressure than the area23. The skin of area23has a lower dynamic air pressure than the areas24.

The areas24are situated at the rear of the vertical tail plane25and of at the rear end of the fuselage14. The dynamic pressure at the location of the air intake opening13is lower than the pressure at the exhaust opening16. Due to the lower dynamic pressure in area24that includes the exhaust opening, air and exhaust gases will flow along the skin of the rear fuselage section towards the air intake opening, in the arrangement shown inFIG.1of the exhaust opening and the air intake opening. Because exhaust gases flow to the air intake opening13, the APU engine10will ingest exhaust gases which reduces the fuel efficiency of the engine causing the engine to burn additional fuel to compensate for the reduced efficiency.

FIGS.3Aand B show an embodiment of the invention.FIGS.4and5show other embodiments of the invention.

In the embodiment shown inFIGS.3A and4, an engine30, e.g., an APU engine, is installed in a rear fuselage section of an aircraft's fuselage14.

The engine30comprises an air intake opening31in the skin on a port side of the rear fuselage section. The air intake opening31intersects with a horizontal plane that includes the longitudinal axis39of the aircraft. The air intake opening31directs atmospheric air into an air intake duct33which directs the air into the engine air intake30.1of engine30.

InFIGS.3A and4, the engine30is forward, along the length of the rear fuselage section, of both the air intake opening31and the exhaust outlet32. Moreover, the air exhaust outlet32is forward, along the length of the rear fuselage section, of the air intake opening31.

The air intake duct33directs air entering the air intake opening to the engine30. The air intake duct33may be curved, as shown inFIG.3A. In particular, the air intake duct, shown inFIG.3A, a U-shaped section downstream of the opening31and upstream of a generally straight section of the duct that is directly connected to an air inlet of the engine. A first portion of the intake conduct33extends rearward in the fuselage from the air intake31opening to the U-shaped section. The U-shaped portion is a second portion of the intake duct and is curved to redirect air towards the front of the aircraft and towards the engine30. A third portion of the intake duct33is immediately downstream in the duct from the second portion and extends towards the front of the fuselage to the engine.

The first portion may be arranged to minimize the angle formed by an axis of the first portion of the intake duct33with the natural air flow direction along the fuselage just before air enters the air intake opening31. Minimizing this angle reduces the pressure loss of the air in the first portion due to the air turning from flowing over the skin to enter the intake opening31and flow into the first portion. Reducing the pressure loss through the air intake duct ensures that the dynamic pressure of the air reaching the engine is at the same pressure or only slightly less than the dynamic pressure of the atmospheric air at the skin of the fuselage. This ensures that the air flowing through the duct33into the engine has a relatively high energy which improves the fuel efficiency of the engine.

The engine30generates exhaust gases that are discharged from the aircraft through the exhaust opening32. This opening may be on an upper side of the fuselage14, as is shown inFIG.4, on a lower side as shown inFIGS.3A,3B and5, or at the rear end17of the tail cone of the rear fuselage assembly.

The exhaust opening32may intersect a vertical plane that includes the longitudinal axis39of the aircraft. The exhaust opening32forms the outlet of the exhaust duct34. The exhaust from the engine exhaust outlet30.2flows into the inlet of the exhaust duct34.

In the embodiments shown inFIGS.3A,3B,4and5, the center of the air intake opening31is offset by about 90 degrees, such as within 10 degrees of 90 degrees, to the center of the exhaust outlet32. This offset is with respect to a plane perpendicular to the longitudinal axis39of the aircraft.

The exhaust opening32is forward of the air intake opening31, such that is the exhaust opening32is closer to the front of the aircraft than the air intake31. The distance that the exhaust opening32is forward of the intake opening31may be in a range of five percent to 25%, or 12% to 20% of the length of the rear fuselage section. The length of the rear fuselage section is between the front end18and the rear end17of the rear fuselage section. Moreover, the exhaust opening32may be a distance from the rear end17in a range of 50% to 15%, or 40% to 20%, or 35% to 25% of the length of the rear fuselage section. Similarly, the air intake opening31may be a distance from the rear end17in a range of 20% to zero, or 5% to 20% or 10% to 15%.

The air intake opening31is located at an area of high dynamic pressure, as shown inFIG.2in areas24and23. The air intake opening is at an area of higher dynamic pressure than is the exhaust opening. Exhaust gases passing through the exhaust opening do not flow to areas having higher pressure such as the area having the air intake opening.

Guide vanes40may be in the exhaust opening32, as shown inFIGS.4and5. The guide vanes40are adapted to guide the exhaust gases out through the exhaust opening. The guide vanes40in the exhaust opening may be used if the air intake opening31is sufficiently close to the exhaust opening that there is a significant risk of exhaust gases entering the intake opening. The guide vanes40may be configured to direct the exhaust gases to flow longitudinally and/or angularly with respect to the longitudinal axis39in a direction away from the air intake opening. Indeed the exhaust gases may be directed by the guide vanes40in a direction opposite to the direction of the air intake opening31. The guide vanes40may also enhance laminar flow of the exhaust gases as the gases exit the opening and enter the atmosphere.

The exhaust duct34may be short and straight to allow the exhaust gases to flow through the duct, out the exhaust opening32and into the atmosphere. A short and straight exhaust duct minimizes pressure losses in the duct and thereby enhances the discharge of exhaust gases. Similarly, the guide vanes40promoting laminar flow also minimize pressure losses. Minimizing pressure losses in the exhaust duct improves the performance of the engine by minimizing backpressure on the engine exhaust.

In some embodiments of the invention, the exhaust duct34may be inclined at positive or negative angles with respect to a horizontal plane that includes the longitudinal axis39of the fuselage. Moreover, the engine30may be similarly inclined as shown inFIGS.4and5. A longitudinal axis38of the engine may be inclined with respect to the horizontal plane by at least 10 degrees, at least 13 degrees and, for example, as much as 20 or 25 degrees. In contrast, an APU engine is conventionally inclined by only 6 to 8 degrees.

An aerodynamic tail cone37is shown inFIGS.3A,3B,4and5, and forms the end of the rear fuselage section. The tail cone37is shaped to provide good aerodynamic performance at the rear of the fuselage. In some embodiments of the invention, the tail cone does not have an exhaust or air intake opening at the rearmost portion of the tail cone. Thus, the rearmost portion of the tail cone may be shaped to enhance aerodynamic performance and need not be configured to support an opening.

The embodiment shown inFIG.3Aincludes a scoop35that extends at least partially over the air intake opening31and diverts air flowing over the skin of the fuselage into the opening. The scoop35may include a panel, e.g. door, having a rear edge attached to the fuselage rearward of the air intake opening and a leading edge extending forward and over the air intake opening. The scoop35may pivot to a close position flush with and closing the air intake opening while the engine is not operating.

The embodiment shown inFIG.3B, shows a flap door36associated with the air intake opening31. The flap door has a closed position shown inFIG.3Bthat closes the opening, and an open position in which the door is pivoted to open the opening. The door may be hinged to a forward end of the air intake opening and pivot inward into the air intake duct. The flap door36does not protrude beyond the skin surrounding the air intake opening and thus does not contribute drag to the air flowing over the skin.

The scoop35and the flap door36may be actuated between an open position (respectively outward and inward) in which they allow air to be drawn from the atmosphere by the engine30, and a closed position in which they close the opening formed by the air intake31in the fuselage's skin15. The closed position is used when the engine is off. In the closed position, the scoop and flap door do not contribute drag to the airflow over the skin surrounding the air intake opening.

FIG.5illustrates another embodiment of the invention. This embodiment is similar to that ofFIGS.3aand4, with an air intake on the port side of the rear fuselage section and a tail cone37. However it differs in that the exhaust32is placed on a lower side of the rear fuselage section. In order to facilitate the gas exhaust through the exhaust32, and to minimize the energy consumption of the engine30, the engine is tilted with its front end higher than its rear end. The tilting angle between a longitudinal axis38of the engine30and a longitudinal axis39of the aircraft is of opposite sign compared to the tilting angle formed between the same axes in the embodiment ofFIGS.3aand4.

FIG.6represents angular segregation between the air intake opening31and the exhaust opening32the embodiment of the invention shown inFIG.4.FIG.6shows a schematic cross section of the rear fuselage section that represents the skin15as a circle. The air intake opening31is shown at about 8:30, if the circle representing the skin is treated as the face of a clock facing rearward of the aircraft. The exhaust opening32is at 12:30.FIG.6is an applicable representation regardless whether the air intake opening rearward, forward or at the same lateral location along the fuselage length as the exhaust opening.

The longitudinal axis39is at the center of the circle shown inFIG.6. An exhaust vector43is from the longitudinal axis39to the center of the exhaust opening32. An air intake vector44is from the longitudinal axis39to a center of the air intake opening31.

The angular segregation between the air intake opening31and the exhaust opening32is represented by angle42between the exhaust vector43and the air intake vector44. The angular segregating angle42is of more than 85 degrees on this example, for example of about 95 degrees, such as within a range of 70 degrees to 100 degrees, or 80 degrees to 90 degrees.

Rather than vectors, the angular segregation may be defined by a an intake plane46which includes the longitudinal axis39and a center of the air intake31opening, and an exhaust plane45which includes the longitudinal axis and a center of the exhaust opening32.

In addition to the angular segregation, the air intake opening and the exhaust opening may be separated by a physical separator47protruding outward from the skin of the fuselage14. Examples of a physical separator47are the vertical tail plane, either of the horizontal tail planes or a fin parallel to the longitudinal axis39. The physical separator physically separates the exhaust gases from the air intake opening31.

FIG.7shows an aircraft41according to the invention is represented with the rear fuselage section shown in cross-section. The rear fuselage section of this aircraft corresponds to the embodiment shown inFIG.4. The air intake opening31is aft of the exhaust opening32. Both openings are in the tail cone and aft of the vertical and horizontal tail planes. Also, neither opening is at the rear end17of the tail cone.

In alternative embodiments not shown in the figures, the intake conduct may have a straight shape, with no curve section, from the air intake to the engine. In such embodiments, in order to minimize the length and weight of the intake conduct, this intake conduct brings air on the same side of the engine as the side of the air intake on the fuselage: for example if the air intake is on a port side, the air conduct brings the air to the port side of the engine.

In alternative embodiments not shown in the figures, the air intake and the exhaust may be on opposite sides, for example: respectively on the port side and on the starboard side of the fuselage, or on the lower side and the upper side of the fuselage.

While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both, unless the this application states otherwise. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority.