Abstract:
A fan ramp aerodynamically guides bypass duct air from the aft end of the fan case to the forward end of the cascades. To improve packaging of the thrust reverser assembly, the fan ramp begins on the interior of the fan case n continues onto the structure surrounding the cascade.

Description:
FIELD 
       [0001]    The present disclosure relates to nacelles for turbofan aircraft propulsion systems, and more particularly to thrust reverser assemblies for the same. 
       BACKGROUND 
       [0002]    Nacelles for turbofan aircraft propulsion systems (such as those that power modern commercial airliners) typically include thrust reversing assemblies. Thrust reversers typically include one or more cascades which guide fan air out of the thrust reverser in an outward and forward direction to generate reverse thrust. The fan air flows within a duct formed by the nacelle and surrounding the engine. During thrust reverser deployment, the fan air is blocked within the duct and turned toward the cascades with the help of blocker doors. 
       SUMMARY 
       [0003]    An aircraft propulsion system is disclosed. The aircraft propulsion system may comprise an annular fan case that houses a fan, the fan case comprising a radially interior surface and a radially exterior surface, the radially interior surface of the fan case deviating radially outward from an ideal loft surface that begins forward of an aft end of the fan case such that the fan case comprises a portion of a fan ramp. The fan ramp may aerodynamically guide air in a bypass air duct to a forward portion of a cascade. The ideal loft surface may be defined as a line extending between a portion of the fan case that is forward of an axial end of the fan case and a forward portion of a blocker door. The radially interior surface of the fan case may be curved. The radially interior surface of the fan case may curve radially outward to form a portion of the fan ramp. The aircraft propulsion system may further comprise a thrust reverser assembly that includes the cascade and a torque box at least partially surrounding the cascade and supporting the cascade. The aircraft propulsion system may further comprise a gas turbine engine. The bypass duct may be formed around a gas turbine engine. The aircraft propulsion system may further comprise a fan that drives air through the bypass duct. The aircraft propulsion system may further comprise a translating sleeve comprising a portion of a thrust reversing assembly that may be shifted aft to expose the fan ramp to a bypass air duct. 
         [0004]    An aircraft propulsion system is disclosed. The aircraft propulsion system may comprise a gas turbine engine, a bypass air duct formed around the engine, a fan coupled to the engine that drives bypass air through the bypass air duct, an annular fan case located radially external of the fan with a radially interior surface defining at least in part the bypass duct, a thrust reverser assembly including a cascade and torque box at least partially surrounding the cascade and supporting it, and/or a fan ramp including a continuously curved aerodynamic surface extending from a point forward of an aft end of the interior surface of the fan case to the forward portion of the cascade and which aerodynamically guides air in the bypass duct from the fan case to the cascade forward portion, and, wherein the fan ramp is formed at least in part on the fan case. The radially interior surface of the fan case may deviate radially outward from an ideal loft surface that begins forward of an aft end of the fan case such that the fan case comprises a portion of the fan ramp. The ideal loft surface may be defined, in cross-section, as a line extending between a portion of the fan case that is forward of an axial end of the fan case and a forward portion of a blocker door. The radially interior surface of the km case may be curved. The radially interior surface of the fan case may curve radially outward to form a portion of the fan ramp. The aircraft propulsion system may further comprise an inner fixed structure formed about the gas turbine engine and defining at least in part the bypass duct. The aircraft propulsion system may further comprise a translating sleeve comprising a portion of a thrust reversing assembly that may be shifted aft to expose the fan ramp to the bypass air duct. The translating sleeve may he shifted forward to cover the fan ramp. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present disclosure, however, may best be obtained by referring to the detailed description and claims when considered in connection with the drawing figures, wherein like numerals denote like elements. 
           [0006]      FIG. 1A  illustrates a schematic cross-sectional view of a prior art aircraft propulsion system having a thrust reversing assembly in a stowed position; 
           [0007]      FIG. 1B  illustrates a schematic cross-sectional view of a prior art aircraft propulsion system having a thrust reversing assembly in a deployed position; 
           [0008]      FIG. 2  illustrates a schematic cross-sectional view of a prior art aircraft propulsion system fan ramp; 
           [0009]      FIG. 3  illustrates, in accordance with various embodiments, a perspective cutaway view of an aircraft propulsion system having a fan ramp partially formed on an aft end of a fan case; 
           [0010]      FIG. 4  illustrates, in accordance with various embodiments, a schematic cross-sectional view of an aircraft propulsion system having a fan ramp partially formed on an aft end of a fan case, wherein the thrust reversing assembly is stowed; and 
           [0011]      FIG. 5  illustrates, in accordance with various embodiments, a schematic cross-sectional view of an aircraft propulsion system having a fan ramp partially formed on an aft end of a fan case, wherein the thrust reversing assembly is deployed. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    The detailed description of exemplary embodiments herein makes reference to the accompanying drawings, which show exemplary embodiments by way of illustration. While these exemplary embodiments are described in sufficient detail to enable those skilled in the art to practice the inventions, it should be understood that other embodiments may be realized and that logical., chemical and mechanical changes may be made without departing from the spirit and scope of the inventions. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component or step may include a singular embodiment or step. Also, any reference to attached, fixed, connected or the like may include permanent, removable, temporary, partial, full and/or any other possible attachment option. Additionally, any reference to without contact (or similar phrases) may also include reduced con tact or minimal contact. 
         [0013]    As used herein, “aft” refers to the direction associated with the tail (e.g., the back end) of an aircraft, or generally, to the direction of exhaust of the gas turbine. As used herein, “forward” refers to the directed associated with the nose (e.g., the front end) of an aircraft, or generally, to the direction of flight or motion. For example, with reference to  FIG. 1 , point A is forward of point A′ along axis A-A′. 
         [0014]    With reference now to  FIG. 1A , a partial cross-section of a jet aircraft propulsion system nacelle  100  is shown. The nacelle  100  may extend from forward to aft along the axis A-A′. In flight, air from point A may now around and/or through the propulsion system in the direction from point A to point A′. 
         [0015]    The nacelle  100  may generally function to package a gas turbine engine and a fan or turbofan  102 , and may guide air around the external portion of the nacelle  100  and internally through the nacelle  100  to define the bypass duct  104 . 
         [0016]    The nacelle  100  may include an air inlet  106  through which air may enter the nacelle  100 . Some portion of airflow may enter the gas turbine engine, and some portion of airflow may flow through the bypass air duct  104 . An inner fixed structure (“IFS”)  108  may define an inner airflow surface of the bypass air duct  104  and may be disposed coaxially about the gas turbine engine. The gas turbine engine may burn a hydrocarbon fuel in the presence of compressed air to generate exhaust gas. The exhaust gas may drive a turbine, which may, through a shaft, drive the turbofan  102  at the forward portion of the nacelle  100 . The turbofan  102  may rotate to generate bypass fan airflow in a bypass air duct  104 . 
         [0017]    The nacelle  100  may further comprise a thrust reversing assembly or a thrust reverser. The thrust reversing assembly may comprise a plurality of thrust reversing components, including, for example, a translating sleeve  110 , a cascade  112 , one or more blocker doors  116 , and/or one or more drag links  118 . The blocker door  116  may be coupled to the IFS  108  by the drag link  118 . 
         [0018]    Generally, with reference to  FIG. 1B , during a thrust reversing operation, the blocker door  116  may deploy from a stowed position to block bypass air flowing through the bypass air duct  104 , In particular, the translating sleeve  110  may translate aft. As the translating sleeve  110  moves aft, the blocker door  116 , which is coupled to the translating sleeve  110 , may translate aft as well. The drag link  118  may, however, remain fixed to the IFS  108 . 
         [0019]    Thus, as the blocker door  116  translates aft with the translating sleeve  110 , the drag link  118  may pull the blocker door  116  radially inward into a deployed position. As shown, in a deployed position, the blocker door  116  may project radially within the bypass duct  104  to block at least a portion of the fan air flow in the bypass air duct  104 . 
         [0020]    As air enters the bypass air duct  104 , a curved structure or “fan ramp”  105  may channel air into the cascade  112 . The blocker door  116  may, in addition, redirect fan air into the cascade  112 . The cascade  112  may therefore channel fan air out of the nacelle  100  in a forward direction to generate reverse thrust. 
         [0021]    With reference to  FIG. 2 , a portion of a prior art nacelle  100  is shown in greater detail. Specifically, a prior art fan case  202 , fan ramp  105 , and blocker door  116  are shown. In general, the fan case  202  may compose art annular or cylindrical structure that surrounds the fan  102  and functions, in part, as a structural containment to protect the aircraft in the unlikely event of a fan blade failure. The fan case  202  may therefore comprise an inner surface and an outer surface. The inner surface may comprise a constant. (or substantially constant) radius. The inner surface of the fan case  202  normally does not include any curvature and is substantially flat. 
         [0022]    The ideal air flow through the fan duct  104  defines loft surfaces or loft lines when viewed as two dimensional representations of the fan duct geometry and air flow) and is a product of the fan duct geometry including all the protrusions into the air flow and steps and gaps between surfaces.  FIG. 2  illustrates how the air ideally flows between the hen case  202  and the blocker doors  116  when the blocker doors are stowed through the depiction of loft line  204 . Ideally the air flows smoothly and in a straight line over the gap beginning at the aft end of the fan case  204  until the forward edge of the blocker door  116 , as illustrated. Note that the fan case  202  interior surface defines the loft line as the radially exterior boundary of the bypass air duct  104 , as does the blocker door bottom surface. In the event of thrust reverser deployment, the loft lines change as now the air flow in the bypass air duct is redirected radially outward through the cascades  112 . During this reverse thrust operation, the fan ramp  105  now helps define the loft line as air flows adjacent to it in order to make the curve towards the cascades  112 . However, in normal thrust operation, when the thrust reverser is stowed, the fan ramp  105  is by definition not part of the loft lines. Thus, the beginning of the fan ramp  105  surface can be defined as the point where the loft lines during reverse thruster deployment begin to depart from the loft lines during normal forward thrust operation in order for the air flow to turn towards the cascades  112 . 
         [0023]    Now, as shown with reference to  FIGS. 3-5 , a perspective view of a partially cutaway nacelle  300  is shown. The nacelle  300  may include a cascade  412 , a blocker door  416 , a drag link  418 , an IFS  108 , and a translating sleeve  411 . In addition, unlike the nacelle  100  described above, the nacelle  300  may comprise a fan case  410  having a curvature. The fan case  302  may comprise a radially interior surface  410   b  and a radially exterior surface  410   a.  The radially interior surface  410   b  of the fan case  302  may deviate from the loft line  406  for normal forward thrust operation illustrated in  FIG. 4 , the deviation commencing forward of an aft end  408  of the fan case  302 . This (levitation of the aft end of fan case  302  from the loft line  406  is a curve which will help define the air flow in the bypass duct durying reverse thrust operation and help to turn the air flow towards the cascades  412 . In this manner, the curvature on the aft end of fan case  302  may constitute part of fan ramp  502 . Stated another way, in various embodiments, a fan ramp&#39;s forward most point is the forward most point where its loft line deviates from the ideal loft surface  406 . As shown in  FIG. 4 , radially interior surface  410   b  of fan case  302  deviates from the loft line  406  and, accordingly, radially interior surface  410   b  of fan case  302  comprises a portion of the fan ramp  502 . 
         [0024]    Again, as shown in greater detail with respect to  FIGS. 4 and 5  (showing a thrust reversing assembly  400  in a stowed and deployed configuration, respectively), the fan case  302  may terminate at an aft end  408  that is aft of a deviation of the radially interior surface  410   b  of the fan case  302  from the loft line  406 . Thus, the fan can case  302  may contribute to the curvature of the fan ramp  502 . In other words, the fan ramp  502  may be formed in part on the fan case  302 . 
         [0025]    As a result of the fan ramp sharing described above, a variety of system components (e.g., a torque box, the cascade  412 , and the like) may be allowed to occupy a more forward portion of the nacelle  300  (in comparison to the nacelle  100 ). In addition, as the fan ramp  502  occupies a more forward position than is conventional, a torque box may also occupy a more forward position than is conventional and/or its dimensions (in particular its width) reduced during construction. The aerodynamic geometry of the nacelle  300  may be improved over that associated with the nacelle  100  as well. For example, the nacelle  300  may sweep more steeply aft than the nacelle  100 . 
         [0026]    Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. Furthermore, the connecting lines shown in the various figures contained herein are intended to represent exemplary functional relationships and/or physical couplings between the various elements. It should be noted that many alternative or additional functional relationships or physical connections may be present in a practical system. However, the benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of the inventions. The scope of the inventions is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” Different cross-hatching is used throughout the figures to denote different parts but not necessarily to denote the same or different materials. Systems, methods and apparatus are provided herein. In the detailed description herein, references to “one embodiment”, “an embodiment”, “various embodiments”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. After reading the description, it will be apparent to one skilled in the relevant art(s) how to implement the disclosure in alternative embodiments. 
         [0027]    Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112(f) unless the element is expressly recited using the phrase “means for.” As used herein, the terms “comprises,” “comprising,” any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.