Abstract:
An axially symmetric turbojet-engine exhaust nozzle which is directable as a unit. The exhaust nozzle is situated downstream of an exhaust duct ( 1 ) fitted with a spherical wall ( 5 ). A single control ring ( 12 ) driven by linear actuators ( 30 ) allows regulation of the nozzle cross section and direction. Converging flaps ( 7 ) are guided on an upstream side by the spherical wall ( 5 ) and are supported at a downstream side by a control lever ( 13 ) which hinges on the control ring ( 12 ) and rests upstream on an external surface ( 16 ) of the spherical wall ( 5 ). Diverging flaps ( 10 ) hinge on the converging flaps ( 7 ) to form an inner ring of hot flaps. The diverging flaps ( 10 ) are situated downstream in an extension of the converging flaps ( 7 ) and further hinge on an outer ring of cold flaps ( 11 ), which in turn hinge on the control ring ( 12 ). A synchronizing system connects upstream ends of the control levers ( 13 ) to the control ring ( 12 ) and ensures self-centering of the control ring ( 12 ), the outer ring of cold flaps ( 11 ) and the inner ring of hot flaps relative to the spherical wall ( 5 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an axisymmetric, directable and adjustable turbojet-engine exhaust nozzle comprising, downstream of an exhaust duct having an axis X, an outer ring of cold flaps and an inner ring of hot flaps. 
     2. Description of the Related Art 
     Directable nozzles offer additional agility to combat aircraft. Furthermore, directable nozzles offer improved manoeuverability when pitching and yawing. 
     In general, the directable exhaust nozzle is mounted at the end of the exhaust duct using a swivel means having an external component which is pivotable on a sphere affixed to the exhaust duct by a first control means. Converging flaps are supported on the external component to be jointly driven by a second control means, anchored on the external component, to regulate the gas exhaust-cross-section. 
     U.S. Pat. No. 4,984,741 issued to Nightingale shows such a nozzle which has converging flaps that are of arcuate longitudinal cross-section and slide on guides of the external component. When diverging flaps are arranged to hinge on the converging flaps, as indicated in FIG. 11 of Nightingale, a control ring is used which is driven by linear actuators anchored in the external component and connected by rods to the diverging flaps. The cold flaps are driven from the diverging flaps by linkrods. 
     SUMMARY OF THE INVENTION 
     Based on this state of the art, the objective of the present invention is to provide an axisymmetric exhaust nozzle which is directable as a unit wherein a single control mechanism implements nozzle orientation and regulation of nozzle cross-section as a function of flight conditions, thereby allowing design simplification and reduction in weight. 
     The nozzle according to the present invention has the following novel characteristics: 
     the downstream end of the exhaust duct comprises a spherical wall with an axis X, the spherical wall being arranged to support the upstream ends of the converging flaps; 
     a control ring encloses the spherical wall and is displaceable along the X axis and pivotable relative to the X axis by a control mechanism; 
     the cold flaps hinge on one hand on the control ring and on the other hand on the downstream ends of the corresponding diverging flaps; 
     the downstream end of each controlled converging flap is linked to a downstream end of a control lever hinging on the control ring, the upstream end of the control lever resting on an external surface of the spherical wall; and 
     the upstream ends of the control levers are linked to the control ring by a synchronizing system which ensures self-centering of the control ring, the outer ring of cold flaps and the inner ring of hot flaps relative to the spherical wall. 
     Advantageously, the synchronizing system comprises a part hinging on the control ring for each pair of adjacent control levers so as to be pivotable about an axis which is perpendicular to the axis of the control ring. Further, the synchronizing system comprises a pair of linkrods which hinge on one of the parts and on the upstream end of the control lever of each pair of adjacent control levers. 
     In a first embodiment of the invention, the upstream ends of the converging flaps slide by two rollers arranged inside the spherical wall. The downstream end of each control lever hinges on the downstream end of a corresponding one of the converging flaps. The upstream end of each control lever rolls on an external surface of the spherical wall by one roller or caster-skid. 
     In a second embodiment of the invention, the upstream end of each control lever hinges on the upstream end of the corresponding one of the converging flaps. Again, the downstream end of each control lever hinges on the downstream end of the corresponding converging flaps. The upstream end of each converging flap rolls on the external surface of the spherical wall by two rollers or caster-skids. 
     In a variation of the second embodiment, each control lever is replaced by two linkrods which hinge on the control ring. 
     In a third embodiment of the invention, the upstream end of each control lever hinges on the upstream end of the corresponding converging flap. Again, the upstream end each converging flap rolls on the external surface of the spherical wall by two rollers or caster-skids. The downstream end of each control lever is connected to the corresponding converging flap by a first linkrod hinging on a lever. Each lever hinges on the corresponding converging flap and furthermore is connected by a second linkrod to a second ring. The second ring is situated downstream of the control ring and is affixed to the control ring by tierods such that the second ring absorbs at least a portion of pressure stresses exerted by the exhaust gases on the inner ring of flaps. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and features of the invention are elucidated in the following illustrative description of preferred embodiments, with reference to the attached drawings, in which: 
     FIG. 1 is a vertical cross-sectional view taken in a plane through the turbine-engine axis of the rear body of a turbojet fitted with a directable, axisymmetric nozzle according to a first embodiment of the invention; 
     FIG. 2 is a perspective view of the nozzle shown in FIG. 1 with a partial cutaway; 
     FIG. 3 is a half-sectional view showing the ventilation circuit of the nozzle shown in FIG. 1; 
     FIG. 4 is an enlarged, broken-away view of the upstream end of a control lever fitted with a caster-skid; 
     FIG. 5 is a radial or bottom view of the caster-skid shown in FIG. 4; 
     FIGS. 6,  7  view similar to FIGS. 4,  5  of another embodiment of the caster-skid; 
     FIGS. 8-11 are sectional views of the nozzle shown in FIG. 1 in the closed, non-directed configuration, in the open, non-directed configuration, in the closed, downwardly-directed configuration, and in the open, upwardly-directed configuration, respectively; 
     FIG. 12 is a view similar to FIG. 2 showing the nozzle shown in FIG. 1 in an open, downwardly-directed configuration; 
     FIG. 13 is a half-sectional view taken in a plane through the turbine-engine axis of the rear body of a turbojet fitted with a directable, axisymmetric nozzle according to a second embodiment of the invention; 
     FIG. 14 is a geometric development of the configuration of the linear control actuators of the control ring, 
     FIG. 15 shows a dual-chamber linear actuator which allows separation of the functions of adjusting the nozzle cross-section and directing the nozzle; and 
     FIG. 16 is a half-sectional view taken in a plane through the turbine-engine axis of the rear body of a turbojet fitted with a directable, axisymmetric nozzle according to a third embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1,  13  and  18  each show the rear body of an aircraft turbine engine which is fitted downstream of the turbine with a gas exhaust duct  1  which constitutes a surface of revolution about an axis X and which is situated within an external casing  2 . The exhaust duct  1  and the casing  2  bound an annular duct  3  therebetween wherein cooling air for the exhaust duct I circulates. The exhaust duct  1 , for example, may be the external wall of an afterburner chamber. 
     The exhaust duct  1  is fitted at its downstream end with a spherical wall  5  situated within the annular duct  3 . The spherical wall has its origin at O. 
     The upstream ends  6  of the controlled, converging flaps  7  come to rest against a surface of the spherical wall  5 . The upstream ends  9  of the controlled, diverging flaps  10  hinge on the downstream ends  8  of the controlled, converging flaps  7 . 
     In a manner known per se, diverging follower flaps and converging follower flaps are intercalated relative to the controlled, converging flaps  7  and the controlled, diverging flaps  10 , respectively. 
     The converging flaps  7  and the diverging flaps  10  constitute two sets of flaps arranged in the extension of each other which hinge at a common junction to form an inner ring of hot flaps of a converging-diverging nozzle. 
     The converging-diverging nozzle is enclosed by a ring of cold flaps alternatingly consisting of controlled cold flaps and follower flaps. The cold flaps  11  hinge downstream on the controlled, diverging flaps  10  and upstream on a control ring  12  which surrounds the spherical wall  5 . 
     The junction of the diverging flaps  10  and the cold flaps  11  constitutes the nozzle&#39;s exhaust cross section A 9  whereas the junction of the converging flaps  7  and the diverging flaps  10  constitutes the nozzle&#39;s cross section A 8 , the nozzle throat. 
     An external part of the cold flaps  11  forms a continuous downstream contour with a fairing covering the casing  2 . 
     The number of controlled converging flaps  7  is preferably equal to the number of controlled diverging flaps  10  and the number of controlled cold flaps  11 . 
     Each controlled converging flap  7  is supported on the control ring  12  by a control lever  13  hinging at a pivot point  14  on the control ring  12 . The upstream end  15  of each control lever rests in a sliding manner on an external surface  16  of the spherical wall  5 . 
     As regards the embodiments shown in FIGS. 1 and 13, the downstream end  17  of each control lever  13  hinges on a bracket  18  which is rigidly joined to the downstream end  8  of one of the controlled converging flaps  7 . 
     The upstream ends  15  of the control levers  13  furthermore are connected to the control ring  12  by a synchronizing system which ensures self-centering of the control ring  12 , the outer ring of cold flaps and the inner ring of hot flaps relative to the spherical wall  5 . 
     As shown in FIGS. 2 and 12, the synchronizing system comprises, for each pair of adjacent control levers  13 , a part  20  which hinges on the control ring  12  so as to be pivotable about a tangential axis which is perpendicular to an axis Y of the control ring  12 . The synchronizing system furthermore comprises a pair of linkrods  21   a ,  21   b  which hinge on one of the parts  20  and on the upstream end  15  of one of the control levers  13 . 
     The control ring  12  is preferably driven by a set of three linear actuators  30  which are anchored in a stationary structure of the rear body and equidistantly situated in the annular duct  3  about the axis X of the exhaust duct  1 . Identical displacement of the three linear actuators generates translation of the control ring  12  and thereby reliably controls the cross sections A 8  and A 9  of the converging-diverging nozzle. However, a differential displacement of the linear actuators  30  will pivot the control ring  12  about the origin O of the spherical wall  5 . As shown, the axis Y of the control ring  12  intersects the axis X at the origin O of the sphere  5  and may subtend an angle a up to about 20° with the axis X. 
     Because of the synchronizing system described above, the cross sections A 8  and A 9  are perfectly circular regardless of the desired directed position. Therefore, the behavior of the flaps  7 ,  10  and  11  shall be identical with that of an axisymmetric non-directable nozzle. The absence of relative displacement of the controlled flaps in the case of direction alone allows perfect support for the follower flaps and assures good nozzle sealing. 
     In the first embodiment shown in FIGS. 1 through 12, the upstream ends  6  of the converging flaps  7  are fitted with two rollers  40  which roll on an inner surface of the spherical wall  5 . The upstream ends  15  of the control levers  13  are fitted with rollers  41  which roll on the external surface  16  of the spherical wall  5 . A second spherical wall  42  is configured inside the first spherical wall  5  and functions as a heat shield. 
     As shown in FIG. 3, air-tapping orifices  43  are provided to ventilate the space separating the two spherical walls  5  and  42 . Part of this tapped air allows ventilation of the inside of the converging flaps  7  and diverging flaps  10 . A brush seal  45  acts as a seal between the spherical wall  5  and the converging flaps  7 . 
     Pressures applied by the exhaust gases on the inner surface of the converging flaps  7  and diverging flaps  10  bias the converging flaps  7  to pivot outwardly about the axis of the rollers  40 . The resultant of the pressures applies an outward force on the downstream ends  17  of the control levers  13 . To compensate for the outward force, the spherical wall  5  applies a corresponding outward force on the rollers  41  at the upstream end  15  of the levers  13 . 
     To better spread contact pressure on the rollers  41  and to ensure improved sliding of the upstream ends  15  of the control levers  13  on the spherical wall  5 , the rollers  41  may be replaced by caster-skids  44  as shown in FIGS. 4 through 7. 
     It should be kept in mind that the pressure stresses applied to the converging flaps  7  pass through the control levers  13  to the control ring  12  and onto the rollers  41  or the caster skids  44 . The stress-resultant on the control ring  12  at the pivot points  14  being radial and the stresses on the rollers  41  or caster skids  44  being absorbed by the spherical wall  5 , the control ring  12  is subjected only to axial stresses limited to the hinge action of the cold flaps  11 . Therefore, the thrust required from the linear control actuators  30  is relatively small. 
     FIGS. 8 through 11 show various nozzle configurations for the above-described first embodiment. 
     Starting form the non-directed, closed configuration of the nozzle shown in FIG. 8 wherein the three linear actuators  30  are each equally extended, identical retraction of the three linear actuators  30  moves the nozzle into the non-directed, open configuration shown in FIG.  9 . Inversely, identical extension of the linear actuators  30  moves the nozzle from the non-directed, open configuration of FIG. 9 into the non-directed, closed configuration of FIG.  8 . In the course of such identical extensions and retractions of the linear actuators  30 , the follower flaps slide in a known manner relative to the controlled flaps. 
     On the other hand, differential displacements of the linear actuators  30  results in the control ring  12  pivoting about the origin O of the spherical wall  5 , thereby ensuring that all the nozzle flaps shall pivot. In this manner, it is possible to move from the open or closed and non-directed configuration toward the open or closed directed configuration shown in FIGS. 10 and 11 without altering the position of the follower flaps relative to the controlled flaps. 
     Once the nozzle has been directed into a desired position, the cross section A 8  of the nozzle throat may be changed by identically driving the three linear actuators  30 . 
     FIG. 13 shows a second embodiment of the nozzle according to the present invention which differs from the first embodiment described above in that the upstream ends  6  of the controlled converging flaps  7  roll on the external surface  16  of the spherical wall  5  by two rollers  40 . The upstream end  15  of each control lever  13  hinges on the upstream end  6  of the corresponding controlled converging flap  7 . 
     The linkrods  21   a  and  21   b  of the synchronizing system also hinge on the upstream ends  6  of the controlled converging flaps  7 . In this embodiment, the brush seals  45  are situated underneath the converging flaps  7 . 
     The ventilating air circulates underneath the spherical wall  5  to purge the cavity between the spherical wall  5  and the second spherical wall  42  and to ventilate the inside of the converging flaps  7  and the diverging flaps  10  after passing through holes  50  in the spherical wall  5 . The rollers  40  furthermore may be replaced by caster-skids  44  as shown in FIGS. 4 through 7. 
     The operation of the second embodiment of the invention is identical with the operation of the first embodiment. It should be noted, however, that the control levers  13  may be replaced by two linkrods hinging on the control ring  12  and respectively on the upstream and downstream ends of the controlled converging flaps  7 . 
     FIG. 16 shows a third embodiment of the invention which differs from the second embodiment in that a mechanism is employed to decrease the force applied by the rollers  40  on the external surface  16  of the spherical wall  5 . The mechanism is arranged to absorb at least part of the stresses exerted by the exhaust gases on the converging flaps  7 . 
     The mechanism preferably comprises a second ring  60  situated downstream of the control ring  12  and firmly affixed to the control ring  12  by tierods  61 . An L-shaped lever  62  hinges by one end on the downstream part of each controlled convergent flap  7 . The lever  62  is connected in the middle by a first linkrod  63  to the second ring  60  and at a second end by a second linkrod  64  to the downstream end  17  of the corresponding control lever  13 . The pressure stresses applied on the converging flaps  7  thus pass through the lever  62  into the linkrods  63  and  64 . 
     FIG. 14 shows a particular configuration of the linear actuators for the control ring  12 . Each linear actuator  30  is replaced by a pair of triangulated linear actuators. In each pair, there is a master linear actuator  30   a  and a follower linear actuator  30   b . FIG. 14 shows that the master linear actuators  30   a  alternate along the pairs in order to prevent the nozzle from rotating about itself about the axis Y. 
     FIG. 15 shows a dual-chamber linear actuator  30  which allows separation of the control of the cross sections A 8  and A 9  from the control of the nozzle direction.