Abstract:
A blocker door for a gas turbine engine thrust reverser having a tray with a base and sidewalk extending about the base to define a volume, the volume being dosed by a cover that extends beyond the periphery of the tray. The extension of the cover beyond the periphery provides a sealing feature.

Description:
TECHNICAL FIELD OF INVENTION 
       [0001]    The invention relates to thrust reverser arrangements for a gas turbine engine and in particular a cascade thrust reverser. 
       BACKGROUND OF INVENTION 
       [0002]    Thrust reversers are provided on a gas turbine engine to selectively alter the direction of the fan flow from the engine. The thrust reversers are typically deployed on landing to decelerate an aircraft. 
         [0003]    One type of thrust reverser is known as a cascade thrust reverser that has an array of cascade boxes downstream of a fan casing that are deployed by an axial rearward translation of a cowl that causes blocker doors to rotate from a stowed position to their deployed position and direct the engine air through the cascade. 
         [0004]    Engine efficiency is driven partly by the amount of air loss that could otherwise be used to generate thrust and it is an object of the invention to seek to provide an improved thrust reverser arrangement that limits these losses when the thrust reverser is not deployed. 
       STATEMENTS OF INVENTION 
       [0005]    According to a first aspect of the invention there is provided a blocker door for a gas turbine engine thrust reverser having a tray with a base and sidewalls extending about the base to define a volume, the volume being closed by a cover that extends beyond the periphery of the tray, wherein the extension of the cover beyond the periphery provides a sealing feature. 
         [0006]    The tray may be rectangular, trapezoidal or combination with chamfered sides, in plan and is preferably formed of a metal or more preferably a composite, made up of a plurality of resin impregnated plies of carbon or glass fibres. 
         [0007]    Preferably the tray further comprises a flange extending from the sidewalls to which the cover is joined, the cover extending beyond the periphery of the flange. The flange may extend outwardly or inwardly from the sidewalk. Preferably the flange is integral with the sidewalls. 
         [0008]    The cover which faces the bypass duct is preferably a moulded rubber directly bonded or mechanically fastened to the flange or sidewalk. The rubber offers the advantage that it can have a flexibility that can be used to seal with another part of the engine when the blocker door is stowed or deployed. 
         [0009]    The cover may be perforated for acoustic lining purpose. Preferably the volume contains an acoustic liner. Preferably the acoustic liner is a honeycomb. 
         [0010]    Preferably the sealing feature is a flat (“lip”) seal, or a P or omega seal. 
         [0011]    According to a second aspect of the invention there is provided a thrust reverser unit for a gas turbine comprising a cowl having an inner surface and a blocker door according to any of the preceding seven paragraphs, wherein the sealing feature seals against the inner surface of the cowl when the blocker door is in a stowed position. 
         [0012]    Preferably the inner surface has a land and a depression, the tray being located in the depression and the sealing feature sealing against the land. 
         [0013]    The inner wall may have a plurality of depressions, each depression locating a respective tray. The inner wall may have a land between adjacent depressions. 
         [0014]    Preferably the cowl is translatable from an axially forward stowed position to an axially rearward deployed position. 
         [0015]    The thrust reverser may further comprising a linkage connecting the blocker door with the cowl, the linkage arranged such that translation of the cowl from the stowed position to the deployed position effects employment of the blocker door from a stowed position against the inner surface of the cowl to a deployed position across a gas turbine bypass duct. 
         [0016]    In a deployed position the sealing feature of a first blocker door may abut a sealing feature of a second blocker door. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0017]    The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
           [0018]      FIG. 1  depicts an exemplary ducted gas turbine having a thrust reverser cascade; 
           [0019]      FIG. 2  shows a isometric (perspective) view of the ducted gas turbine with the cowl open for inspection or maintenance of the engine core; 
           [0020]      FIG. 3  depicts the nacelle with the cowl in its stowed position; 
           [0021]      FIG. 4  depicts the nacelle with the cowl in its deployed position; 
           [0022]      FIG. 5  is a partial cross-section through the centre of the blocker door showing the engine including the thrust reverser cascades with the cowl in the stowed position 
           [0023]      FIG. 6  is as partial cross-section through the centre of the blocker door showing the engine including the thrust reverser cascades with the cowl in the deployed position 
           [0024]      FIG. 7  is a perspective (isometric) view of blocker doors in their stowed position; 
           [0025]      FIG. 8  is a perspective (isometric) view of the blocker doors in their deployed position; 
           [0026]      FIG. 9  is a partial cross sectional view (local ZX plane) of stowed blocker doors showing the circumferential arrangement. 
           [0027]      FIG. 10  is a view of a stowed blocker door with an alternative (integrated) seal. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0028]    Referring to  FIG. 1 , a ducted fan gas turbine engine generally indicated at  10  has a principal and rotational axis  11 . The engine  10  comprises a propulsive fan  13  and a core engine  9  having, in axial flow series, an air intake  12 , an intermediate pressure compressor  14 , a high-pressure compressor  15 , combustion equipment  16 , a high-pressure turbine, an intermediate-pressure turbine  18 , a low-pressure turbine  19  and terminating with a core exhaust nozzle  20 . A nacelle  21  generally surrounds the engine  10  and defines the intake  12 , a bypass duct  22  and an exhaust nozzle  23 . 
         [0029]    The gas turbine engine  10  works in the conventional manner so that air entering the intake  11  is accelerated by the fan  13  to produce two air flows: a first airflow A into the intermediate pressure compressor  14  and a second airflow B which passes through a bypass duct  22  to provide propulsive thrust. The intermediate pressure compressor  14  compresses the airflow A directed into it before delivering that air to the high pressure compressor  15  where further compression takes place. 
         [0030]    The compressed air exhausted from the high pressure compressor  15  is directed into the combustor  16  where it is mixed with fuel and combusted. The resultant hot combustion products then expand through, and thereby drive, the high, intermediate and low-pressure turbines  17 ,  18 ,  19  before being exhausted through the nozzles  20  to provide additional propulsive thrust. The high, intermediate and low pressure turbines  17 ,  18 ,  19  respectively drive the high, intermediate pressure compressors  15 , 14  and the fan  13  by suitable interconnecting shafts. 
         [0031]    A centre plug  29  is positioned within the core exhaust nozzle  20  to provide a form for the core gas flow A to expand against and to smooth its flow from the core engine. The centre plug  29  extends rearward of the cone nozzle&#39;s exit plane  27 . 
         [0032]    The fan is circumferentially surrounded by a structural member in the form of a fan casing  24  which is supported by an annular array of outlet guide vanes  28 . The fan casing  24  comprises a rigid containment casing  25  and attached rearwardly thereto is a rear fan casing  26 . 
         [0033]    The gas turbine engine  10  is installed under an aircraft wing  7  via a pylon  8 . The nacelle  21  comprises an axially forward cover  35  (fan cowl) and a translatable cowl  37 . Both the cover and the cowl are provided by C-shaped openable doors with each door being separately hinged to the aircraft pylon  8 . The nacelle has a thrust reverser unit  31  which is formed from a number of cascade panels arranged sequentially around the circumference of the engine  10 . The hinged doors permit access to the engine core for maintenance or inspection purposes. 
         [0034]      FIG. 2  depicts the open nacelle  21  has hinges positioned at the top of the engine or on the pylon and which permits each part of the C duct defined by the cover  35 , the translating cowl  37  and inner fixed structure  40  to rotate away from the engine to permit access thereto. Both the cowl and the cover  35  can pivot away from the engine. The thrust reverser unit  31  is mounted to the cover and can pivot away from the engine with the cover. 
         [0035]    The cowl  37  is provided with an axially forward tongue  60  which is formed of two parts  60   a  and  60   b  extending from each of the two doors forming the translatable cowl. The cover  35  has a recess which engages the tongue when the cowl and cover are dosed to provide a streamlined external surface for the nacelle. 
         [0036]    This is shown in  FIG. 3  where the nacelle is closed in an in-flight position. The translatable cowl is in its stowed position such that the cowl abuts the axially forward cover. translatable thrust reverser unit is in an axial forward position in contrast to  FIG. 4 , where the unit has been deployed rearwardly to open the cascades  41 . As shown in  FIG. 4  the tongue  60  in the deployed position of the cowl is aligned with the axial position of the cascade. Advantageously, this negates the need for a blanking cascade panel to be provided in the cascade in order to inhibit the flow of thrust reverser air radially towards the ground. However, it is possible to provide an appropriate cascade panel with or without the use a cowl that does not have a tongue arrangement. Where a tongue is used it can be provided with a radially inner form that turns the air towards the front of the engine. In both these figures the tongue  60  is located 180 degrees from the pylon (not shown) and is located on the underside of the engine. 
         [0037]      FIG. 5  is a partial cross section through the cascade and cowl arrangement of  FIG. 3 . The cowl  37  has a bifurcated fairing that has a radially outer wall  62  that forms an airwashed surface for the external surface of the nacelle and a radially inner wall  64  that forms an airwashed surface for the bypass duct  22 . A blocker door  39  is located against the radially inner surface of the radially inner wall  64  in the stowed position with the inner wail of the fairing providing additional support for the blocker door against the pressures of the flow through the bypass. The inner wall is stepped  66  to enable the blocker door to be recessed in the stowed position in order to provide a streamlined surface. A frame  68  joins the radially inner and outer walls ( 64 , 62 ). 
         [0038]    Between the inner and outer walls there is a cavity  70  within which the cascade  41  is located. When the cowl is in the stowed position of  FIGS. 3 and 5  the cascade is isolated from the main flow through the bypass duct by the blocker door  39  and the radially inner wall  64  of the fairing. In addition, any leakage flow through either of these parts is inhibited from leaving the engine by the radially outer wall  62  of the cowl which seals against the cover  35 . Any parasitic air flows inside the cavity  70  reduces the performance of the powerplant and therefore it is imperative to reduce them to minimum. 
         [0039]    The cascade  41  comprises an arrangement of vanes that are designed to turn a flow of air from the bypass duct when the cowl is translated to its open position towards the front of the engine to provide the reverse thrust relative to the normal direction of thrust generated by the engine. The cascade is assembled as a series of panels each of which provides a segment of the circumference of the thrust reverser. 
         [0040]    In  FIG. 6  the cowl  37  is shown in its deployed position which is axially rearward of the stowed position. The blocker doors  39  are connected to the trans cowl via hinges (for axial translation of the blocker doors) and by linkages to the inner fixed structure (for rotation of the blocker doors) to direct the bypass flow through the cascades where the flow is turned in a forward direction and through a passage opened in the outer wall of the nacelle by the axially rearward movement of the outer wall. The flow of air through the cascade is shown by the arrows B and C. 
         [0041]      FIG. 7  is a perspective view of the blocker doors  39  arranged in their stowed position. Each door has a generally trapezoidal form which is mounted within a correspondingly shaped depression in the inner wall  64  of the translatable cowl. By locating the blocker doors in respective depressions it is possible to the blocker doors and inner wall to together provide a streamlined outer wall for the bypass duct  22 . 
         [0042]    In  FIG. 8  the blocker doors are deployed following translation of the cowl. The axially rearward and narrower end of the door rotates inwards till the edges abut the edges of the adjacent and neighbouring doors to provide the barrier that deflects the air flow from the bypass duct through the thrust reverser cascade. 
         [0043]    The leakage, parasitic flow in cavity  70 , past the stowed blocker panels can reduce the overall efficiency of the engine and it is desirable to minimise this leakage. The blocker panels are formed as an assembly including a backskin  100 , an internal support material  102  (honeycomb) and an air-washed facing sheet  104 . 
         [0044]    As shown in  FIG. 9 , the backskin is moulded or otherwise formed into a tray having a base  106 , side walls  108 , and a flange  110  which protrudes from the side walls. The backskin is formed of metal or, more preferably, a composite material which may be formed of a laminate of individual plies of carbon or glass fibres held within a resin matrix. The flange extends around the periphery of the tray and provides a surface to which the facing sheet can be joined. 
         [0045]    The tray is filled with the internal support material that provides rigidity to the blocker doors so that on deployment into the gas flow when reverse thrust is required the doors can withstand the high force of the flow. The support material is preferably in the form of a honeycomb, which, when combined with perforated facing sheet  104 , contributes to a noise insulation lining as well as providing the required strength. 
         [0046]    The tray is closed with a facing sheet  104 , bonded or otherwise secured to the flange  110 . The facing sheet has some flexibility and is preferably formed of a rubber or other elastomeric material that can be perforated to allow a small flow of air into and out of the tray that assists with the acoustic damping. 
         [0047]    By making the facing sheet  104  from elastomeric material or rubber and making the rubber sheet protrude beyond the periphery of the flange to provide a “lip” seal portion  112  and in the stowed position seals against the inner wall  64  of the translatable cowl and against the cascade support structure  43  along its and beneficially all edges. The pressure of the air in the bypass duct forces the seal against a land on the inner wall of the cowl. 
         [0048]    In the deployed position the flexible rubber sheet seals against the core engine fairing  40  at its radially inner edge, against abutting blocker doors along its side edges. 
         [0049]    The seal is enhanced by the pressure in the bypass duct which presses the seal against the inner wall of the cowl in use to further limit the parasitic flow of air past the seal. 
         [0050]    Although the seals have been depicted and described here as flat (“flip”) seals it will be appreciated that other forms of seals e.g. P or Omega seals that have a shaped end may also be used.  FIG. 10  depicts an alternative arrangement, where the inner wall  64  has a step to provide a ledge  114  that supports the seal. The “omega” seal  116  has an elongate portion  117  and as bulbous portion  118  integrally moulded together. Advantageously, sealing is improved by providing two seal locations: the first against the ledge on the land, the second against the side of the depression  120  in the inner wall  64 . The choice of material, material thickness and/or shape  112  &amp;  118  and its programmed hardness for the facing sheet can also be selected to achieve the desired functionality for the seal. Additionally, because the cover is formed of a thermoplastic or thermosetting resin or rubber material it is possible to provide this as a moulded construction with graded material and/or functional properties. Advantageously, the periphery of the cover that seals against the outer wall of the bypass duct may therefore be formed to be more rigid or more flexible than the inner section of the cover which secures the cover to the tray. 
         [0051]    If the facing sheet is formed of a fire resistant material the use of the blocker doors as a fire barrier is enhanced. 
         [0052]    Access to the core engine and associated accessories is achieved by deploying the thrust reverser unit and/or rotating open the translating cowls. The core fairing  40 , which is hinged independently, is then rotated open. Alternatively, individual panels may be provided and readily removed.