Abstract:
Brush seals formed in hemispherical rings are supported to the end of the convergent nozzle of the each of the clam shells of a multi-axis vector thrust nozzle of a gas turbine engine powering aircraft. The brush seal may be arced or straight and bear against the spherical surface of the collar formed on the end of the tail pipe and is mounted so that high pressure forces the bristles against the backing plate of the seals.

Description:
TECHNICAL FIELD 
     This invention relates to seals and more particularly to seals for an exhaust nozzle with vectoring capabilities that is movable about multiple axes for a gas turbine engine. 
     BACKGROUND ART 
     This invention constitutes an improvement over the multi-axis thrust vectoring nozzle described and claimed in U.S. Pat. No. 4,836,451 granted to Herrick et al on Jun. 6, 1989 entitled “Yaw and Pitch Convergent-Divergent Thrust Vectoring Nozzle” assigned to United Technologies Corporation, the assignee common to this patent application which discloses a yaw and pitch convergent-divergent exhaust nozzle for a gas turbine engine. As disclosed in this patent a pair of cooperating clam shells hinged to a gimbal ring and pivotal about an axis perpendicular to the clam shell hinge axis surrounds the engine&#39;s tail pipe. The clam shells define a variable area nozzle throat which can be selectively directed vertically by rotation of the clam shells about its hinged axis or horizontally by rotation of the clam shells and gimbal ring about the gimbal axis for effectively varying the area of the exhaust nozzle to change or divert the exhaust flow and biasing the exhaust flow for vectoring the aircraft. 
     As is known in the aircraft engine technology, the prevention of hot mainstream gas or coolant leakage between mating components in multi-function exhaust systems is extremely important. It is of paramount importance that the hot gasses in the exhaust of the engine do not migrate into regions of low allowable temperature substructure and of like importance the compressor air utilized for cooling should not be diverted and prevented from reaching the destination to accomplish the necessary cooling. By preventing the hot gas ingestion, additional low weight, low allowable temperature structures can be utilized with a consequential improvement to the thrust-to-weight ratio. By preventing cooling system leakage, the nozzle performance is enhanced. Therefore, improving sealing technology enhances both aerodynamic and structural efficiency. 
     As noted in the U.S. Pat. No. 4,836,451 patent supra, arcuate seals disposed between the clamshell spherical surfaces and the collar spherical surface for preventing the flow of exhaust gas therebetween. The type of seals disclosed in this patent are seals, such as piston rings or spring seals. 
     As one skilled in the seal technology appreciates, seals are generally applied to parts which have relative motion only along a single axis, i.e. rotation or translation. Also, sealing between rotating, pivoting or translating members has been accomplished by techniques that include, for example, labyrinth, finger, piston rings and sheet metal seals. These types of seals have proven to be unsatisfactory for use in an application where the moving components move along multi-axes relative to each other. 
     We can obviate the problems enumerated in the above by providing a brush seal formed in hemis-spherical portions of a ring that is judiciously located in the convergent flap of a multi-axis vector nozzle. The brush seal comprises an arced or straight brush pieces of a plurality of high compliance high temper wire bristles. It has been found on an experimental rig tests that the seal made in accordance with this invention reduced leakage on the spherical section of the spherical convergent flap nozzle by as much as 44% and 72% when compared to conventional sheet metal and piston ring seals. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide improved sealing means for a multi-axis vector exhaust nozzle for a gas turbine engine of the type that powers aircraft. 
     A feature of this invention is a brush seal formed in a ring that is judiciously located in the convergent flap of the multi-axis nozzle. 
     A still further feature of this invention is the utilization of high compliant, high temper, small diameter wire bristles formed in either an arc or straight configuration. 
     The foregoing and other features of the present invention will become more apparent from the following description and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic in cross section illustrating the prior art multi-axis vector nozzle; 
     FIG. 2 is a view in section taken through the vertical plane illustrating this invention; 
     FIG. 3 is a partial view in section illustrating the details of this invention; and 
     FIG. 4 is a partial view in section taken along lines  4 — 4  of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The prior art nozzle depicted in FIG. 1 shows a schematic cross section taken in the vertical plane of a nozzle  10  where the nozzle receives pressurized exhaust gas  6  from a gas turbine engine (not shown) through a conduit  12 . The conduit  12  terminates in a collar portion  14  having a generally spherical external surface  16 . The collar  14  includes a rearwardly facing opening  18  for discharging the exhaust gas into the nozzle outlet  20 . The nozzle  10  further includes a gimbal ring  22  disposed about the collar  14  and including two opposed gimbal pivots  24 ,  26  for supporting the gimbal ring  22  relative to the nozzle static structure  28 . 
     The gimbal pivots  24 ,  26  lie along a gimbal axis  30  shown in the vertical plane of FIG.  1  and which passes through a center point  32  defined by the collar spherical surface.  16 . The gimbal ring  22  supports upper and lower clamshells  34 ,  36  which are independently pivotable about a common axis  38  oriented both perpendicular to the gimbal axis  30  and transverse to the nozzle center line  40 . The common axis  38  passes through the collar spherical surface center point  32  and is shown coincident therewith in the vertical cross section of the FIG.  1 . 
     Clamshells  34 ,  36  are independently pivotable to achieve a varying nozzle throat dimension  42  in order to provide the optimum nozzle outlet area for efficient thrust production. Thrust vectoring in the vertical plane may be achieved by orienting the clamshells  34 ,  36  asymmetrically with respect to the nozzle center line  40  so as to bias the flow of discharged gas  8  relative thereto. 
     The embodiment of FIG. 1 also includes upper and lower divergent flaps  44 ,  46  for providing a properly divergent gas flow path downstream of the nozzle throat  42 . The divergent flaps  44 ,  46  are pivotably secured by linear hinges  48 ,  50  of the respective upper and lower clamshells  34 ,  36 . The divergent flaps  44 ,  46  in cooperation with a pair of spaced apart fixed side walls  59  (only one being shown) define a divergent gas flow path aftward of the nozzle throat  42  for ensuring efficient expansion of the exhaust gas  8 , especially for supersonic flow nozzles  10 . 
     The divergent flaps  44 ,  46  are independently movable relative to the associated clamshell components  34 ,  36  and may thus be positioned to vary the divergent angle as well as the pitch thrust angle of the discharged gases  8 . Outer fairing flaps  56 ,  58  provide a smooth exterior surface for airflow about the aircraft, and are hinged adjacent the upper and lower gimbal pivots  26 ,  24  as shown. 
     As noted the upper and lower clamshells  34 ,  36  have generally spherical interior surfaces  68 ,  70  that maintain a uniform spacing with regard to the spherical surface  16  of the collar  14 . The nozzle  10  provides seals  72 ,  74  which will be described in greater detail hereinbelow disposed between the clamshell spherical surfaces  68 ,  70  and the collar spherical surface  16  for preventing the flow of exhaust gas  6  therebetween or the loss of coolant for cooling the components of nozzle  10 . While the clamshells  34 ,  36  slide relative to the collar spherical surface along the vertical and horizontal axes, they attempt to maintain a uniform spacing over the entire range of motion but because of the hostile environment in which these components operate, it is difficult to keep this uniform spacing. 
     In accordance with this invention and as best seen in FIGS. 3 and 4, the seals  72  and  74  are fabricated in hemispherical rings that include a semi circular front ring  76  and a complementary shaped backing plate  78 . A plurality of small diameter high temper wire bristles  80 , say 0.003 inch diameter, Haynes 25, are sandwiched between the front ring  76  and backing plate  78  and the rear end extends substantially to the outer diameter thereof. The bristles at point  81  are bonded in a suitable manner, say by brazing, to the front ring  76  and backing plate  78  to form an integral seal member  72  and  74 . Each of the seal members  72  and  74  are clamped in the annular recess  77  formed between the end of the convergent flap  35 , adjacent to the downward extending flange portion  82  axially spaced from the end of clamp member  84 . The ends of front ring  76  and backing plate  78  remote from the working ends of the bristles extend to the back wall of recess  77 . Clamp member  84  may be attached to the outer surface of the convergent flap  35  by the machine bolt  86  that threadably engages internal threads formed in the convergent flap. This allows the easy removal of the seal for maintenance purposes. An O-seal  88  may be inserted in the end of the convergent flap  35  to further reduce leakage. 
     As noted from FIG. 3 the seal is oriented relative to the gas stream in the nozzle such that the high pressure faces the bristles and forces the bristles against the backing plate. This assures that the bristles will be in sliding relation and hence in sealing relation with the spherical surface of the collar for every condition over the entire operating envelope of the nozzle  10 . 
     Although this invention has been shown and described with respect to detailed embodiments thereof, it will be appreciated and understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and scope of the claimed invention.