Abstract:
A method for adjusting a throat area of a jet aircraft exhaust nozzle assembly includes positioning a lower structure within a substantially rectangular nozzle assembly, coupling a ramp flap to the lower structure, and coupling an outer flap to the nozzle assembly such that movement of at least one of the ramp flap and the outer flap adjusts the throat area of the nozzle assembly.

Description:
GOVERNMENT RIGHTS STATEMENT 
   The United States Government may have rights in this invention pursuant to Contract No. MDA972-01-3-002. 

   BACKGROUND OF THE INVENTION 
   This invention relates generally to jet aircraft exhaust nozzles and more particularly, to methods and apparatus for adjusting a nozzle throat within a jet aircraft exhaust nozzle. 
   At least some known engines include either a fixed exhaust nozzle system, such as is typical of commercial subsonic engines, or a variable exhaust nozzle system, such as is typical of supersonic military aircraft. The geometry of fixed nozzle systems are not kinematically changed or variable and as such may not operate as efficiently as variable exhaust nozzle systems. 
   More specifically, variable geometry systems are configured to operate over a wide range of pressure ratios (P8/Pamb) by adjusting a nozzle throat (A 8 ) based on the demands of the engine cycle, and adjusting a nozzle area ratio (A 9 /A 8 ) to facilitate achieving a desired engine performance at various operating points. 
   In at least some known variable exhaust nozzle systems, A 8  and A 9 /A 8  control is established by “linking” A 9 /A 8  to A 8 , i.e. establishing a kinematically-linked area ratio schedule. For example, at least one known engine includes a variable exhaust nozzle system that includes a circumferential series of overlapping flaps and seals that define a convergent flowpath that establishes a desired nozzle throat A 8 . A similar set of overlapping flaps and seals is connected to an aft end of the convergent flaps and seals and establishes a divergent portion, or an exit area (A 9 ) of the nozzle. The divergent flaps are also kinematically-linked using a separate kinematic member, such as a compression link that is coupled to a relatively stationary part of the exhaust system, such as a duct. The resulting four bar linkage, duct, convergent flap, divergent flap, and compression link, define the kinematic relationship of the exit area A 9  to the nozzle throat area A 8 , and thus also defines the A 9 /A 8  schedule as a function of A 8 . Such an arrangement typically results in an A 9 /A 8  schedule which increases as A 8  increases. 
   However, the use of an overlapping flap and seal structure in the nozzle design may result in numerous leakage paths which may cause a corresponding decrease in engine operating efficiency. Additionally, the relatively large quantity of parts used to fabricate the nozzle may increase the cost, weight, and maintenance of such engines. 
   BRIEF SUMMARY OF THE INVENTION 
   In one aspect, a method for assembling an exhaust nozzle assembly is provided. The method includes positioning a lower structure within a substantially rectangular nozzle assembly, coupling a ramp flap to the lower structure, and coupling an outer flap to the nozzle assembly such that movement of at least one of the ramp flap and the outer flap adjusts the throat area of the nozzle assembly. 
   In another aspect, an exhaust nozzle assembly is provided. The nozzle assembly includes a lower structure positioned within a substantially rectangular nozzle assembly, a ramp flap coupled to the lower structure, and an outer flap coupled to the nozzle assembly, at least one of the ramp flap and the outer flap configured to adjust a throat area of the nozzle assembly. 
   In a further aspect, a gas turbine engine is provided. The gas turbine engine includes a flade rotor producing a flade discharge airflow, and a substantially rectangular flade nozzle assembly configured to receive the flade discharge airflow. The flade nozzle includes a lower structure positioned within the flade nozzle assembly, a ramp flap coupled to the lower structure, and an outer flap coupled to the nozzle assembly, at least one of the ramp flap and the outer flap configured to adjust a throat area of the flade nozzle assembly. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an end view of an aircraft including an exemplary engine. 
       FIG. 2  is a schematic illustration of an exemplary FLADE engine that may be used with the jet aircraft shown in  FIG. 1 . 
       FIG. 3  is an enlarged schematic view of an exemplary nozzle system that may be used with the jet aircraft  10  shown in  FIG. 1 . 
       FIG. 4  is a side view of the nozzle system shown in  FIG. 3  positioned for a different engine operational setting. 
       FIG. 5  is a side view of the nozzle system shown in  FIG. 3  positioned for yet another engine operational setting. 
       FIG. 6  is an end view of an alternative exemplary nozzle system that may be used with the jet aircraft shown in  FIG. 1 . 
       FIG. 7  is another exemplary embodiment of a nozzle system that may be used with the jet aircraft shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  is a schematic illustration of a portion of a jet aircraft  10  including a plurality of engines (not shown) and a plurality of nozzle assemblies  12 . Each nozzle assembly  12  includes an upper portion  13 , a lower portion  14 , and a plurality of sidewalls  15  that are coupled together. In the exemplary embodiment, each nozzle assembly  12  has a substantially rectangular cross-sectional profile. 
     FIG. 2  is a schematic illustration of an exemplary “fan-on-blade” or FLADE engine  16  that may be used with jet aircraft  10  (shown in  FIG. 1 ). Engine  16  includes a flade inlet  20  through which a relatively large percentage of an engine inlet airflow  22  enters during predetermined engine operations, such as during an aircraft takeoff. Airflow  22  enters flade inlet  20  and passes between an array of variable area inlet guide vanes  24 . As illustrated in  FIG. 2 , inlet guide vanes  24  are actuated to their open position to direct large amounts of airflow toward a flade rotor  26 . 
   Inlet guide vanes  24  control the volume of airflow entering a flade flowpath  28  and direct the airflow at a proper angle onto flade rotor  26  wherein the airflow is compressed and accelerated. Airflow discharged from flade rotor  26  passes through a plurality of outlet guide vanes  30  which straighten the airflow and reduce its rotary velocity component. Flade discharge airflow  32  flows through a scroll duct  34  toward a convergent/divergent flade exhaust nozzle  90 . 
     FIG. 3  is an enlarged schematic view of an exemplary nozzle system  90  that may be used with jet aircraft  10  (shown in  FIG. 1 ).  FIG. 4  is a side view of nozzle system  90  positioned for a different engine operational setting.  FIG. 5  is a side view of nozzle system  90  positioned for yet another engine operational setting. In the exemplary embodiment, nozzle  90  includes an upper portion  92 , a lower portion  94 , and a plurality of sidewalls (not shown) that are coupled together to form a substantially rectangular nozzle area. Nozzle  90  also includes a relatively large lower structure  102  that is coupled to nozzle lower portion. Lower structure  102  includes an internally-formed forward portion  104 , a center recessed portion  106 , and a stationary aft portion  108 . Nozzle  90  also includes an outer flap  110 , a ramp flap  112 , and a flade flap  114 . 
   In one embodiment, ramp flap  112  and flade flap  114  are mechanically coupled with a hinge  118 , such that ramp flap  112  and flade flap  114  are rotatable about a central axis  120  of hinge  118 . Outer flap  110  includes a hinge  122  that is coupled between a first end  124  of flap  110  and a portion of nozzle assembly  90  such as, but not limited to, upper portion  92  and the sidewalls. 
   In one embodiment, actuation of various flaps, i.e. outer flap  110 , a ramp flap  112 , and a flade flap  114 , is accomplished using various mechanical devices. For example, outer flap  110  may be actuated using hinge  122 , while ramp flap  112  and flade flap  114  may be actuated through hinge  118 . In one embodiment, outer flap  110 , ramp flap  112 , and flade flap  114  are each coupled to an actuator  130 . In another embodiment, outer flap  110 , ramp flap  112 , and flade flap  114  are each coupled to each respective actuator  130  through a respective mechanical linkage  132 . Because the flade stream flowing through a flade passage  134  is relatively cool, actuators  130  and actuation linkages  132  for ramp flap  112  and flade flap  114  can be located within flade passage  134 , i.e. within a cavity defined between ramp flap  112 , flade flap  114  and lower structure  102 . 
   In use, flade flap  114  controls a flade throat area  140 , also referred to herein as A 98 , to substantially match engine  16  cycle demands. Ramp flap  112 , positioned upstream of flade-flap  114 , is movable to variably adjust a throat area  142 , also referred to herein as A 8 , of the engine mixed core/fan stream. Outer flap  110 , located on an upper surface of nozzle  90 , is rotably pivotable about hinge  122  to adjust a nozzle exit area  144 , also referred to herein as A 9 i, of nozzle  90 . Accordingly, nozzle  90  includes three independently controlled nozzle surfaces, outer flap  110 , ramp flap  112 , and flade flap  114 , which are adjusted to enable engine  16  to operate within a wide range of cycle-demanded operating conditions A 8  and A 98 , and to generate A 9 i to facilitate optimizing nozzle performance. 
   In  FIG. 3 , outer flap  110 , ramp flap  112 , and flade flap  114  are positioned in a “takeoff” position. Specifically, ramp flap  112  has been rotated around central axis  120  to increase throat area  142 , and flade flap  114  has been rotated around central axis  120  to increase flade throat area  140 . As a result, a first sized throat area  142  is defined to approximately match a fan backpressure requirement during takeoff. 
   In  FIG. 4 , outer flap  110 , ramp flap  112 , and flade flap  114  are positioned for “transonic climb” engine operation. Specifically, ramp flap  112  has been rotated around central axis  120  to decrease throat area  142 , flade flap  114  has been rotated around central axis  120  to decrease flade throat area  140 . As a result, a second sized throat area  146  is defined that is smaller than first defined throat area  142 . As a result, second sized throat area  146  is defined to approximately match the fan backpressure requirement during transonic climb. Additionally, outer flap  110  is positioned such that nozzle exit area  144  is sized to optimize nozzle performance, i.e. sizing A 9 /A 8  such that nozzle performance is maximized. 
   In  FIG. 5 , outer flap  110 , ramp flap  112 , and flade flap  114  are positioned for a “supersonic cruise” engine operation. Specifically, ramp flap  112  has been rotated around central axis  120  to substantially decrease throat area  142 , and flade flap  114  has been rotated around central axis  120  to substantially decrease flade throat area  140 . As a result, a third sized throat area  148  is defined that is smaller than first sized throat area  142  to approximately match the fan backpressure requirement during supersonic cruise. Additionally, outer flap  110  is positioned such that nozzle exit area  144  is sized to optimize nozzle performance, i.e. sizing A 9 /A 8  such that nozzle performance is maximized. 
     FIG. 6  is an end view of an alternative exemplary nozzle system  90  that may be used with jet aircraft  10  (shown in  FIG. 1 ). Within nozzle system  90 , instead of being hinged, outer flap  110  is coupled within a plurality of tracks  150  and translated in a forward and aft direction  152 . Guide tracks  150  are mechanically coupled to at least one sidewall  154 . In use, outer flap  110  is translated in the forward and aft direction using an actuation system such as, but not limited to actuator  130  and linkage  132  (shown in  FIG. 3 ). 
     FIG. 7  is another exemplary embodiment of a nozzle system  200  that can be used with jet aircraft  10 , (shown in  FIG. 1 ). Nozzle system  200  includes a lower structure  202  including a forward portion  204 , a middle recessed portion  206 , and a stationary aft portion  208 . Nozzle  200  also includes an outer flap  210  and a ramp flap  212 . Ramp flap  212  includes a flade flap  214  formed unitarily with ramp flap  212 . Lower structure  202  also includes a hinge  216  mechanically coupled to ramp flap  212  such that ramp flap  212  rotably pivots about hinge  216 . 
   In another exemplary embodiment, sidewalls  154 , in a region where ramp flap  112 ,  212  and flade flaps  114 ,  214  contact them, are configured to approximate a surface of revolution described by rotating the edge of ramp flap  112 ,  212  and flade flaps  114 ,  214  about their respective hinge axis. For example, the portion of sidewalls  154  that interface with outer flap  110 ,  210 , in the case of the pivoting outer flap embodiment approximate the surface of revolution described by rotating the edge of outer flap  110  about its hinge axis. In the case of translating outer flap  210 , there is less restriction on sidewall shaping, therefore sidewall  154  is configured to maintain a good seal as outer flap  210  translates through its range of motion. Otherwise, the only restriction on shaping the areas of sidewalls  154  which do not interface with ramp-flap  112 , outer-flap  110 , or flade-flap  114  is it should be done in a way that does not adversely impact aerodynamic or low observable (LO) performance. 
   In another exemplary embodiment, engine  16  (shown in  FIG. 2 ) does not include a flade stream, therefore a portion of the fan air is directed into what is currently shown as the flade stream, thus providing cooling air for lower structure  102  and  202  respectively. In an alternative embodiment, if no ramp cooling is desired, flade flap  114 ,  214  can be eliminated and stationary lower structure  208  begins at ramp-flap  112 ,  212  hinge joint. 
   Although the embodiments described herein describe a nozzle assembly having a simple rectangular cross section, it should be realized that lower structure  102 ,  202 , ramp-flap  112 ,  212 , flade-flap  114 ,  214 , and outer-flap  110 ,  210  can be contoured across the span to create various cross sections which may have structural or other aircraft installation benefits. 
   The above-described nozzle systems are cost-effective and highly reliable. Nozzle system  90  includes three independently controlled nozzle surfaces, outer flap  110 , ramp flap  112 , and flade flap  114 , which are adjusted to match the cycle-demanded A 8  and A 98  and generate the A 9 i which produces the optimal nozzle performance. As a result, the relatively small quantity of parts used to fabricate the nozzle can result in a decrease in the cost, weight, and maintenance of the engine. 
   Exemplary embodiments of nozzle systems are described above in detail. The nozzle systems are not limited to the specific embodiments described herein, but rather, components of each assembly may be utilized independently and separately from other components described herein. For example, each flade flap, ramp flap, and outer flap can also be used in combination with other nozzle assembly components described herein. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.