Abstract:
An actuator operable to drive a thrust reverser in a gas turbine engine, wherein the thrust reverser comprises first and second translatable sleeves. The actuator comprises a first actuating member moveable so as to translate the first sleeve and a second actuating member moveable so as to translate the second sleeve. The actuator further comprises an interlock arrangement operable in a locked mode in which the first actuating member and second actuating member are locked so as to move together and in an unlocked mode in which at least one of the first actuating member and second actuator member is free to move independently of the other. Operation of the actuator to open or close the thrust reverser comprises a first mode wherein the interlock arrangement is in the locked mode and a second mode wherein the interlock arrangement is in the unlocked mode.

Description:
FOREIGN PRIORITY 
       [0001]    This application claims priority to European Patent Application No. 16164568.4 filed Apr. 8, 2016, the entire contents of which is incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to an actuator for driving the components of a thrust reverser in a gas turbine engine, and particularly in a turbofan engine. 
       BACKGROUND 
       [0003]    Gas turbine engines, which are often used to propel aircraft, typically comprise a core engine which is surrounded by a nacelle. A bypass air duct is formed between the core engine and the nacelle. Air which enters the gas turbine engine is driven by a fan assembly along the bypass duct and provides a forward thrust at the rear of the engine. 
         [0004]    In certain situations, such as during landing, it is necessary to slow the speed of the aircraft down significantly. Whilst this can partially be achieved using air brakes which are often present on the wings of an aircraft, it is also necessary to provide a reverse thrust from the gas turbine engines in order to further reduce the speed of the aircraft. In order to divert some of the air which passes through the engine to provide a reverse thrust, a thrust reverser may be arranged in the nacelle surrounding the fan assembly. Electric thrust reverser actuation systems may operate using a clamshell (see e.g. U.S. Pat. No. 5,826,823), blocker door (see e.g. U.S. Pat. No. 9,181,898) or translating cowl arrangement. 
         [0005]    In a translating cowl arrangement, for example as seen in U.S. Pat. No. 8,904,751, the thrust reverser typically comprises a translating cowl mounted to the nacelle, a cascade within the nacelle, and blocker doors. When reverse thrust is required the translating cowl is translated so as to expose the cascade and the blocker doors are moved into the bypass duct so as to direct airflow through the cascade and out of the nacelle. The cascade typically comprises vanes which direct the airflow against the direction of the air which enters the engine and this provides a reverse thrust. 
         [0006]    In typical thrust reverser architectures the cascade is arranged in a fixed position in the nacelle. The translating cowl is often mechanically linked to the blocker doors such that when the translating cowl slides opens it pivots the blocker doors relative to the cascade and radially inward into the bypass duct, resulting in bypassed air within the duct being diverted from the duct through the cascade. 
         [0007]    The applicant has realised that at least some thrust reverser designs can introduce efficiency losses in the turbine engine, especially during the production of forward thrust. When the blocker doors are moved by the motion of a translating cowl, even in a stowed position the blocker doors may partially protrude into the bypass air flow path and causes efficiency losses. The applicant is aware of a thrust reverser comprising a translating cowl and a separate translating cascade linked to the blocker doors, with the blocker doors stowed away and fully hidden from the bypass air flow path so that the bypass ducting becomes more streamlined with less drag losses in flight, thus reducing the efficiency losses of the engine. 
         [0008]    The applicant has now recognised that it may be undesirable to provide separate drives for each of the components in such a thrust reverser to move them into position, i.e. for moving the translating cowl and the cascade separately. 
         [0009]    The present disclosure seeks to provide an improved actuator for a thrust reverser, and a thrust reverser comprising such an actuator. 
       SUMMARY 
       [0010]    According to the present disclosure there is provided an actuator operable to drive a thrust reverser in a gas turbine engine, the thrust reverser comprising a linear translating cowl structure contained within a nacelle surrounding the gas turbine engine, the linear translating cowl structure comprising a first sleeve and a second sleeve; 
         [0011]    wherein the actuator comprises a first actuating member moveable so as to translate the first sleeve, and a second actuating member moveable so as to translate the second sleeve, between positions corresponding to the thrust reverser being open or closed; 
         [0012]    the actuator further comprising an interlock arrangement operable in a locked mode in which the first actuating member and second actuating member are locked so as to move together and in an unlocked mode in which at least one of the first actuating member and second actuator member is free to move independently of the other; 
         [0013]    wherein the first actuating member and second actuating member are further arranged such that operation of the actuator to open or close the thrust reverser comprises: 
         [0014]    a first mode wherein the interlock arrangement is in the locked mode and the first and second actuating members are driven to move together along a first predetermined distance; and 
         [0015]    a second mode wherein the interlock arrangement is in the unlocked mode and either the first actuating member or the second actuating member is driven to move along a second predetermined distance independently of the other actuating member. 
         [0016]    Thus it will be appreciated by those skilled in the art that according to this disclosure two separate sleeve components in a thrust reverser are moved using a single actuator. This actuator is therefore particularly advantageous as it removes the need for a duplex thrust reverser system which would comprise a set of actuators for each sleeve component. A typical nacelle adopting the architecture described in the background above, whereby there is a translating cowl and a translating cascade sleeve, would typically require eight actuators, an isolation control unit and dual direction control units. Whereas a nacelle using the same architecture but using an actuator according to the present disclosure would only require four actuators, an isolation control unit and a single direction control unit. The number of actuators required is therefore significantly reduced. This reduces the space required to house the actuators within the nacelle and has the further advantage that the overall weight of the gas turbine engine is reduced. This helps to further improve the efficiency of the engine. 
         [0017]    In addition by providing two actuating members which are mechanically sequenced together as is the case with the present disclosure, this removes the requirement for inter-sleeve synchronisation as is the case where independent actuator sets are provided for each of the sleeves. Often when independent actuators are provided, if adequate synchronisation cannot be achieved with sufficient robustness an additional and separate mechanical sequencing linkage is provided which adds weight and complexity to the thrust reverser architecture. Using an actuator according to the present disclosure avoids this problem entirely. 
         [0018]    It will be appreciated that an actuator according to the present disclosure can be driven according to standard drive techniques. In a set of examples the actuator is a hydraulic actuator. In such examples a synchronising reduction gearbox may be provided to enable mechanical synchronisation between actuators and further arranged so as to drive an ACME screw which acts to drive the first actuating member and/or the second actuating member. In an alternative set of examples the actuator is an electric actuator. In such examples the actuator may be driven by either an electric motor or a hydraulic motor via a gearbox. In such examples a synchronising reduction gearbox may be provided to enable mechanical synchronisation between actuators and arranged so as to drive a ball screw which acts to drive the first actuating member and/or the second actuating member. 
         [0019]    An actuator according to the present disclosure can provide two coaxial outputs of different strokes with a controlled mechanical sequencing. It will be appreciated by those skilled in the art that the sequence of the modes of operation of the actuator may differ. For example, in a set of examples the actuator is arranged to operate in the first mode and then subsequently in the second mode when opening the thrust reverser. Whereas, in an alternative set of examples, the actuator is arranged to operate in the second mode and then subsequently in the first mode when opening the thrust reverser. In both cases the actuator may operate the modes in reverse order when closing the thrust reverser. It will be appreciated by those skilled in the art that either of the sequences may be preceded or succeeded by a further different mode or one of the same first/second modes as discussed above. For example, the actuator may be arranged to operate in the first mode, then the second mode and then the first mode again or alternatively the second mode, then the first mode and then the second mode again. 
         [0020]    The arrangement of the actuating members in the actuator and the presence of two distinct modes in which the actuating members move together in one mode, and one actuating member moves independently in the other mode, means that one of the actuating members must have a greater range of travel than the other. The actuating member that has the greatest range of travel will be the actuating member which is actuated in both modes. This actuating member therefore is able to move a total distance equal to the sum of the first predetermined distance and the second predetermined distance. The other actuating member, whichever this may be, will have the shortest range of travel; being actuated in only one of the modes. 
         [0021]    As discussed above, one of the significant advantages of the present disclosure is that there is no need for electronic synchronisation between two separate actuating members in order to coordinate their output. In order to ensure accurate mechanical synchronisation the actuator according to the present disclosure may be provided with a drive source that has a single output. It is therefore preferable that the actuator comprises a drive source with a single output arranged to drive either the first actuating member or the second actuating member. This is advantageous as already discussed the actuating members are mechanically coupled to ensure their coupling and decoupling at the relevant positions and thus by providing a drive source with a single output the actuator is more robust. In such a set of examples the drive source may be arranged to drive solely the actuating member which is arranged to travel the greater distance. Furthermore, in such a set of examples the actuating member arranged to travel the greater distance is arranged so as to act upon and drive the other actuating member. As is mentioned above, the drive source may be electric or hydraulic. 
         [0022]    The interlock arrangement which locks the first and second actuating members to enable them to move together in a first mode may be comprised of a host of different components. However, as discussed above it is preferable that the actuator remains relatively simple and requires minimal sequencing and thus in a set of examples the interlock arrangement comprises one or more moveable segments which act between the first actuating member and second actuating member so as to hold them together. Preferably the interlock arrangement comprises one or more moveable segments which act between the first actuating member and the second actuating member so as to mechanically couple the first and second actuating members together. It will be appreciated that such a set of examples is particularly advantageous as the actuating members are coupled together using a simple mechanical arrangement which preferably requires no electronic or hydraulic control logic. 
         [0023]    In a further set of examples the one or more moveable segments are radially moveable. Such examples are beneficially particularly when combined with examples in which the actuating members are coaxial cylindrical members. Thus in at least some examples the first and second actuating members have a coaxial arrangement and the one or more moveable segments are radially moveable so as to act between the first actuating member and the second actuating member. 
         [0024]    In such a set of examples the moveable segments may be provided around the inner circumference of the outer actuating member, preferably evenly distributed around the inner circumference. 
         [0025]    In a further set of examples at least one of the first and second actuating members comprises one or more recesses arranged on an outwardly facing surface to receive the one or more moveable segments in the locked mode. A single recess, e.g. a substantially continuous groove, may be arranged to receive more than one of the moveable segments. This could assist with alignment of the interlock arrangement. For example, one or more recesses are provided on the actuating member which is innermost in such a coaxial arrangement, and arranged so that the moveable segments are able to move into the one or more recesses so as to lock the innermost actuating member and the outermost actuating member together. 
         [0026]    Any number of moveable segments could be provided to lock the actuating members together. For example, the interlock arrangement may comprise between one and nine moveable segments arranged circumferentially around the coaxial arrangement. In at least some examples the interlock arrangement comprises three, six or nine moveable segments arranged circumferentially around the coaxial arrangement. Preferably the moveable segments are evenly distributed around the coaxial arrangement. 
         [0027]    In a set of examples the moveable segments are able to move between two distinct positions, each of which corresponds to the locked mode and the unlocked mode. In the locked mode the moveable segments may be in a position in which each moveable segment spans between both the first actuating member and second actuating member. In the unlocked mode the moveable segments may be positioned such that each moveable segment does not span between the two actuating members. 
         [0028]    The actuator may be arranged to accommodate the moveable segments when they are not received in the recesses in the locked mode. Accordingly the actuator may comprise a main body that surrounds the coaxial arrangement, wherein the main body comprises one or more slots arranged on an inwardly facing surface to receive the one or more moveable segments in the unlocked mode. Such slots provided in the main body of the actuator receive the moveable segments when they move away from coupling together the two actuating members. A single slot, e.g. a substantially continuous groove, may be arranged to receive more than one of the moveable segments. This could assist with alignment of the interlock arrangement. 
         [0029]    In a further set of examples the one or more recesses comprise ramped edges arranged so as to encourage radial movement of the one or more moveable segments towards the one or more slots as the interlock arrangement is switched between the locked and unlocked modes. By providing ramped edges, as the actuating members are driven by the actuator, if significant resistance of motion is experienced by the actuating member with the ramped recesses, the other actuating member will apply a force to the moveable segments which will be encouraged out of the recesses and into the slots provided in the main body. At this point the actuating members will no longer be locked together and will be free to move independently. 
         [0030]    In another set of examples the actuator may be provided with a hardstop. The hardstop may consist of any internal structure that prevents the actuating members from translating any further along the actuator. Preferably the actuator comprises a hardstop arranged to prevent either the first or second actuating member from moving further than the first predetermined distance. The position of the hardstop may, for example, coincide with the position of the slots in the main body and thus may provide a limiting point for one of the actuating members. At this point the moveable segments may be translated into the slots by the motion of the other actuating member. The position of the hardstop may therefore determine when the interlock arrangement is switched between the locked and unlocked modes. 
         [0031]    It will be appreciated that the position of the interlock arrangement may determine the first and/or second predetermined distances. In at least some examples the axial position of the one or more moveable segments along one of the actuating members at least partially determines the first and/or second predetermined distance. In addition, or alternatively, in examples where one or more recesses are provided on one of the actuating members to allow the interlock arrangement to lock the members together, the position of the one or more recesses at least partially determines the first and/or second predetermined distance. 
         [0032]    In some examples the actuator may comprise means for adjusting the position of the interlock arrangement relative to the first and/or second actuating members. In examples where the interlock arrangement comprises one or more moveable segments which act between the first actuating member and the second actuating member, the axial position of the one or more moveable segments along the first and/or second actuating member may be variable. In addition, or alternatively, in examples where the interlock arrangement comprises one or more recesses that receive the one or more moveable segments in the locked mode, the axial position of the one or more recesses along the first and/or second actuating member may be variable. For example, adjusting the position of the segments on the second actuating member and adjusting the position of the corresponding recesses on the first actuating member changes the amount that the first actuating member and second actuating member can be moved relative to one another in the unlocked mode. 
         [0033]    Although the first and second predetermined distances may be approximately equal, preferably the one of the first and second predetermined distances is greater than the other. Accordingly two different stroke lengths may be provided by the actuator. 
         [0034]    It is desirable that the thrust reverser assembly does not inadvertently become active and deploy as this would mean that reverse thrust would be provided during general operation of the gas turbine engine, for example whilst cruising, and this could cause problems for the aircraft. Therefore, in a set of examples the actuator further comprises a primary lock which prevents movement of either actuating member. The primary lock may be operated by a separate control circuit and drive such that it is independent from the main drive of the actuator. It will be appreciated by those skilled in the art that such an example is particularly advantageous as even in the case of a control failure of the main drive of the actuator it can be prevented from inadvertent deployment by the separate control circuit and primary lock. Alternatively the primary lock may also be controlled by the electric or hydraulic control which operates the rest of the actuator. 
         [0035]    In a set of examples the first actuating member and/or the second actuating member are arranged to move linearly. This is advantageous as it can allow for a simple interlock arrangement between the first and second actuating members. Preferably the first actuating member and the second actuating member move linearly in parallel. As is mentioned above, the first and second actuating members may have a coaxial arrangement. In at least some examples the first actuating member comprises a cylindrical member and the second actuating member comprises a hollow cylindrical member which substantially surrounds the first actuating member. Both the first and second actuating members may comprise cylindrical hollow shells, which is beneficial as it means that various other components of the actuator can be accommodated inside one or both of the shells. 
         [0036]    Further according to the present disclosure there is provided a thrust reverser for a gas turbine engine comprising a linear translating cowl structure contained within a nacelle surrounding the gas turbine engine, the linear translating cowl structure comprising a first sleeve and a second sleeve, and an actuator as described hereinabove, wherein the first actuating member moveable is arranged to translate the first sleeve, and the second actuating member is arranged to translate the second sleeve, between positions corresponding to the thrust reverser being open or closed. Preferably such a thrust reverser comprises four actuators arranged to translate the first and second sleeves between positions corresponding to the thrust reverser being open or closed. The gas turbine engine may be a turbofan engine. 
         [0037]    In examples of such a thrust reverser, the first sleeve or the second sleeve may comprise one or more of: a translating cowl, a translating cascade, a blocker door, or any combination thereof. 
         [0038]    It will be appreciated that the thrust reverser may comprise one or more further actuators operable to drive other components. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0039]    One or more non-limiting examples will now be described, with reference to the accompanying drawings, in which: 
           [0040]      FIG. 1  shows a schematic overview of a typical thrust reverser actuation system arranged to drive two independent sleeves; 
           [0041]      FIG. 2  shows a schematic overview of a trust reverser actuation system in accordance with the present disclosure arranged to drive two independent sleeves; 
           [0042]      FIG. 3  shows a first exemplary thrust reverser architecture in a stowed position; 
           [0043]      FIG. 4  shows the thrust reverser architecture of  FIG. 3  in a partially deployed position wherein both the primary sleeve and cascade sleeve are translated; 
           [0044]      FIG. 5  shows the thrust reverser architecture of  FIG. 3  in a further deployed position wherein the primary sleeve has reached its limiting position; 
           [0045]      FIG. 6  shows the thrust reverser architecture of  FIG. 3  wherein the primary sleeve remains stationary and the cascade sleeve is translated; 
           [0046]      FIG. 7  shows the thrust reverser architecture of  FIG. 3  in a fully deployed position wherein translation of the primary and cascade sleeves is arrested; 
           [0047]      FIG. 8  illustrates the head end of an electric actuator in accordance with an example of the present disclosure wherein the actuating members are stowed; 
           [0048]      FIG. 9  illustrates the rod end of the actuator of  FIG. 8  wherein the actuating members are stowed; 
           [0049]      FIG. 10  illustrates the rod end of the actuator of  FIG. 8  wherein the primary actuating member is fully deployed; 
           [0050]      FIG. 11  illustrates the rod end of the actuator of  FIG. 8  wherein the primary actuating member and secondary actuating member are fully deployed; 
           [0051]      FIG. 12  shows the head end of a hydraulic actuator in accordance with an example of the present disclosure wherein the actuating members are stowed; 
           [0052]      FIG. 13  shows the rod end of the hydraulic actuator of  FIG. 12  when in the stowed position; 
           [0053]      FIG. 14  shows the rod end of the hydraulic actuator seen in  FIG. 12  when the primary actuating member is fully deployed; 
           [0054]      FIG. 15  shows the rod end of the hydraulic actuator seen in  FIG. 12  when the primary and secondary actuating members are fully deployed; 
           [0055]      FIG. 16  shows a second exemplary thrust reverser architecture in a stowed position; 
           [0056]      FIG. 17  shows the second thrust reverser architecture in a partially deployed position; 
           [0057]      FIG. 18  shows the second thrust reverser architecture at the point where the primary sleeve has been translated and the secondary sleeve is about to be translated; 
           [0058]      FIG. 19  shows the second thrust reverser architecture when both the primary sleeve and secondary sleeve have been translated together; 
           [0059]      FIG. 20  shows the second thrust reverser architecture in the fully deployed position; 
           [0060]      FIG. 21  shows an electric actuator in accordance with another example of the present disclosure in the stowed position; 
           [0061]      FIG. 22  shows the electric actuator seen in  FIG. 21  when the primary actuating member has been deployed before the secondary actuating member; 
           [0062]      FIG. 23  shows the rod end of the electric actuator seen in  FIG. 21  when the primary actuating member and secondary actuating member are fully deployed together; 
           [0063]      FIG. 24  shows the head end of a hydraulic actuator in accordance with another example of the present disclosure in the stowed position; 
           [0064]      FIG. 25  shows the hydraulic actuator seen in  FIG. 24  when the primary actuating member has been deployed before the secondary actuating member; and 
           [0065]      FIG. 26  shows the hydraulic actuator seen in  FIG. 24  when the primary actuating member and secondary actuating member are fully deployed together. 
       
    
    
     DETAILED DESCRIPTION 
       [0066]      FIG. 1  shows a schematic representation of a thrust reverser actuation system  2  which comprises a first sleeve  4  and a second sleeve  6 . In order to operate each of the sleeves  4 ,  6  a first actuation system  8  and second actuation system  10  are provided. The actuation systems  8 ,  10  are controlled by a common control unit  12 . The actuation systems  8 ,  10  may be electric or hydraulic actuation systems. 
         [0067]      FIG. 2  shows a similar thrust reverser actuation system  2 ′ driven by an actuator which is in accordance with the present disclosure. Instead of an independent actuation system being provided for each of the sleeves  4 ,  6 , a single actuation system  14  is provided which is able to drive both sleeves  4 ,  6 . The single actuation system  14  is controlled by a common control unit  16  which is able to control the way in which the sleeves  4 ,  6  are driven with respect to one another. 
         [0068]    It will be appreciated that there are various architectures of a thrust reverser which comprises two translating sleeves and the specific architecture of the thrust reverser determines the type of action of the actuator which is needed to drive translation of the sleeves. 
         [0069]      FIGS. 3-7  show the kinematics of a first architecture for a thrust reverser as it moves from a first position whereby no reverse thrust is provided to a final position in which reverse thrust is provided. This thrust reverser architecture is compatible with the actuator of the present disclosure. 
         [0070]    The thrust reverser architecture  102  seen in  FIG. 3  comprises a first sleeve  104  (equivalent to a primary sleeve) and a cascade sleeve  106  (equivalent to a secondary sleeve). The cascade sleeve  106  comprises vanes  118  for directing airflow through the cascade sleeve  106  in order to provide reverse thrust. The primary sleeve  104  is operatively connected by a connection rod  120  to a blocker door  122 . The cascade sleeve  106  and the blocker door  122  are contained within the nacelle structure between an outer wall  124  and inner wall  126 . By stowing the cascade sleeve  106  and the blocker door  122  out of the air flow path of the engine, this helps to reduce drag during normal operation and thus improves engine efficiency. 
         [0071]    The cascade sleeve  106  is fixedly connected to an outer shell  128  of the nacelle structure. The blocker door  122  is pivotally connected by an extending arm  130  to a first fixing point  132  on the shell  128  and is directly pivotally connected to a second fixing point  134 . 
         [0072]    In the position seen in  FIG. 3  the thrust reverser is in a stowed configuration in which no reverse thrust is provided. In this configuration air which is propelled by the jet engine is free to flow through the air channel  136  towards the rear of the engine. 
         [0073]      FIG. 4  illustrates a first stage in the transition towards providing reverse thrust. In this thrust reverser architecture  102  the primary sleeve  104  and cascade sleeve  106  initially move together, translating backwards i.e. in an aft direction. The primary sleeve  104  and cascade sleeve  106  continue to move together until they reach a predetermined position as seen in  FIG. 5 . Here it can be seen that the primary sleeve  104  reaches the end of its track  138  at which point it is unable to move any further. At this stage the blocker door  122  has begun to pivot downwards into the air channel  136 . 
         [0074]      FIG. 6  illustrates how the primary sleeve  104  remains stationary and the cascade sleeve  106  continues to translate. It can be seen that the translation of the cascade sleeve  106  causes the outer shell  128  to retract and reveal an opening  140 . This is the opening  140  through which air is able to pass out of the nacelle and provide reverse thrust. It can also be seen in this Figure how the blocker door  122  has begun to move further into the air flow path  136  which is enabled by the extending arm  130  extending to a longer length which allows the blocker door  122  to pivot radially inward.  FIG. 7  shows the thrust reverser  102  in its end point at which full reverse thrust is provided. Here it can be seen that the cascade sleeve  106  has been fully translated such that the blocker door  122  is pivoted fully into the air channel  136  and the cascade sleeve  106  has moved fully out of the cavity in the nacelle provided by the outer wall  124  and inner wall  126 . 
         [0075]    In order to drive the thrust reverser architecture  102  seen in  FIGS. 3-7  there is provided an actuator capable of first driving both the first (primary) sleeve  104  and cascade (secondary) sleeve  106  together and then solely driving the cascade (secondary) sleeve  106 . 
         [0076]    This can be achieved using an electric actuator  214  as seen in  FIG. 8 . This Figure depicts the head end of the electric actuator  214 . The actuator  214  comprises a primary actuating member  242  and a secondary actuating member  244 . The primary actuating member  242  is arranged so as to drive the primary sleeve  104  and the secondary actuating member  244  is arranged to drive the cascade sleeve  106 . During operation of the actuator  214  to open the thrust reverser, the primary actuating member  242  and secondary actuating member  244  move together initially in a first mode. This is achieved by an interlock arrangement that comprises interlock segments  246  which are present in a cavity  250  in the primary actuating member  242  and engage in recesses  252  in the secondary actuating member  244 . The position of the recesses  252  ultimately determines the distance which the second actuating member  244  is able to move independently of the first actuating member  242  in a second mode of operation. 
         [0077]    The secondary actuating member  244  is driven by a ball screw  254  which is driven by a synchronising reduction gearbox  256 , which is driven by either an electric or hydraulic motor (not shown). A primary lock  258  is provided which prevents motion of the secondary actuating member  244  unless the primary lock  258  is released. The primary lock  258  may be driven by an electric motor, an electric solenoid or by hydraulic pressure. The arrow  259  represents the distance which the secondary actuating member  244  can move independently of the first actuating member  242  and is equivalent to the stroke of the secondary actuating member  244  minus the stroke of the primary actuating member  242 . 
         [0078]      FIG. 8  shows the actuator  214  in the stowed position which is equivalent to the thrust reverser being stowed. 
         [0079]      FIG. 9  illustrates the rod end of the actuator  214  also in the stowed position. A slot  260  is provided which allows the interlock segments  246  to be received and thus frees the primary actuating member  242  and secondary actuating member  244  from their interlock arrangement. Also visible is a hardstop  262  which prevents further motion of the primary actuating member  242  and secondary actuating member  244  when they come into contact with the hardstop  262 . 
         [0080]    During operation of the actuator  214  the electric (or hydraulic) motor drives the ball screw  254  which drives the secondary actuating member  244 . Due to the interlock arrangement provided by the interlock segments  246 , both the primary actuating member and secondary actuating member  244  move together in a first mode. They continue to move until the rim  264  of the primary actuating member  242  comes into contact with the hardstop  262 . At this point the primary actuating member  242  can no longer move any further and the interlock segments  246  are free to be received in the slots  260 . This point can be seen in  FIG. 10 . Movement of the interlock segments  246  is encouraged by the ramped e.g. chamfered edges  266  provided in the recesses  252 . As the secondary sleeve  244  is acted on by the ball screw it pushes the interlock segments  246  and the chamfered edges  266  encourage the interlock segments  246  into the slots  260 . Similar chamfered edges  268  are provided on the slots  260  to encourage motion of the interlock segments  246  when the actuating members  242 ,  244  are retracted. 
         [0081]    At this point the primary actuating member  242  is in a locked translational position and the secondary actuating member  244  is freed from interlock with the primary actuating member  242  and is free to continue translational motion. The ball screw  254  continues to drive the secondary actuating member  244  until it abuts against the rim  264  of the primary actuating member  242  which abuts against the hardstop  262 . At this point both the primary actuating member  242  and secondary actuating member  244  are fully deployed and when acting on the primary sleeve and secondary sleeve of the thrust reverser architecture seen in  FIGS. 3-7  the thrust reverser will be fully deployed. 
         [0082]    Of course it will be appreciated that the actuator need not be electric and  FIGS. 12-15  illustrate a hydraulic actuator  314  which is equivalent to the electric actuator  214  seen in  FIGS. 8-11 . The components of the hydraulic actuator  314  are essentially the same and arrangement of the primary actuating member  342 , secondary actuating member  344 , interlock segments  346 , recesses  352 , slots  360  and hardstop  362  is essentially the same which results in the actuator  314  operating in an identical manner to that in  FIGS. 8-11 . The significant difference is that the reduction gearbox  256  is driven by hydraulic fluid and the reduction gearbox drives a synchronising screw  354  which drives the second actuating member  344 . 
         [0083]      FIGS. 13-15  illustrate the same positions of the actuating members  242 ,  244  as seen in  FIGS. 9-11 , the only difference being that a synchronising screw  354  is present. 
         [0084]      FIGS. 16-20  illustrate a second, alternative, thrust reverser architecture  402  in which a single sleeve moves on its own initially and is then joined by a secondary sleeve. The thrust reverser architecture  402  comprises a primary sleeve  404  and a cascade sleeve  406  (equivalent to a secondary sleeve). A blocker door  422  is connected via a linkage  468  to the cascade sleeve  406 . A seal  470  seals the primary sleeve  404  to the inner wall  426  of the nacelle.  FIG. 16  shows the thrust reverser architecture  402  in a stowed position. Here it can be seen that the cascade sleeve  406  along with the blocker door  422  and associated linkage  470  is contained within the walls of the primary sleeve  404  and the outer wall  424  and inner wall  426  of the nacelle. Similarly to the other thrust reverser architecture seem in  FIGS. 3-7 , the cascade sleeve  406  comprises vanes  418  to direct the air flow so as to produce a reverse thrust. The linkage  468  is also connected to the edge of the inner wall  426 . A bumper  472  is fixed against the inner wall of the primary sleeve  404  and rests against the blocker door  422 . When in the stowed position seen in  FIG. 16  air can freely flow through the air channel  436  and provide forward thrust. 
         [0085]      FIG. 17  shows the thrust reverser architecture  402  in a partially deployed position. Here it can be seen that the primary sleeve  404  has been driven backwards i.e. in an aft direction so as to begin to reveal an opening  440  in the outer wall of the nacelle. It can be seen that as the primary sleeve  404  has been brought backwards the bumper  472  is dragged along the length of the blocker door  422  towards its aft end  474 . At this stage the secondary sleeve  406  remains stationary and has not yet been translated. 
         [0086]      FIG. 18  depicts the thrust reverser architecture  402  at a further extended position whereby the primary sleeve  404  has been translated sufficiently that the bumper  472  is no longer in contact with the blocker door  422 . This is also the transition point at which the cascade sleeve  406  begins translating with the primary sleeve  404 . 
         [0087]      FIG. 19  shows how both the primary sleeve  404  and the cascade sleeve  406  are moved together so as to translate backwards. It can be seen that the opening  440  has been further increased, and as the cascade sleeve  406  is translated, due to its connection with the linkage  468  the blocker door  422  begins to pivot radially inward into the air channel  436 . 
         [0088]      FIG. 20  shows the final position of the thrust reverser architecture  402  where full reverse thrust is provided. Here it can be seen that the primary sleeve  404  and secondary sleeve  406  have been fully translated and as a result the blocker door  422  is in its maximum position extending into the air channel  436 . The opening  440  is also at its maximum position. In this configuration a portion of the air passing into the air channel  436  will be diverted by the blocker door  422  towards the cascade sleeve  406  which will direct the air via the vanes  418  out of the opening  440  to provide a reverse thrust. 
         [0089]    In order to drive the second thrust reverser architecture  402  seen in  FIGS. 16-20  using a single actuator there is provided an actuator arranged to first drive the primary sleeve  404  on its own and then drive the primary sleeve  404  and cascade sleeve  406  in unison together. 
         [0090]    This can be achieved using an electric actuator  514  as seen in  FIG. 21 . This Figure depicts the head end of the electric actuator  514 . The actuator  514  comprises a primary actuating member  542  and a secondary actuating member  544 . The primary actuating member  542  is arranged to drive the primary sleeve  404  and the secondary actuating member  544  is arranged to drive the cascade sleeve  406  (equivalent to a secondary sleeve). During operation of the actuator  514  to open the thrust reverser, the primary actuating member  542  is first moved on its own in a first mode. In this mode the secondary actuating member  544  is initially held in position by interlock segments  546  which are present in a cavity  550  in the secondary actuating member  544  and engage in slots  560  which are present in the outer body of the electric actuator  514 . The position of the slots  560  ultimately determines the distance the primary actuating member  542  is able to move independently of the secondary actuating member  544  in the first mode of operation. Also seen in this Figure are recesses  552  provided on the primary actuating member  542 , the recesses  552  are present to allow the interlock segments  546  to release from the slots  560  when the primary actuating member  542  reaches the secondary actuating member  544  at a point at which the recesses  552  align with the interlock segments  546 . 
         [0091]    The primary actuating member  544  is driven by a ball screw  554  which is driven by a synchronising reduction gearbox  556 , which is driven by an electric motor (not shown). A primary lock  558  is provided which prevents motion of the primary actuating member  542  unless the primary lock  558  is released. The primary lock may be driven by an electric motor or an electric solenoid. The arrow  559  represents the distance which the primary actuating member  542  can move independently of the secondary actuating member  544  and is equivalent to the stroke of the primary actuating member  542  minus the stroke of the secondary actuating member  544 . 
         [0092]      FIG. 21  shows the actuator  514  in the stowed position which is equivalent to the thrust reverser being stowed. 
         [0093]      FIG. 22  illustrates the head end of the actuator  514  in a partially deployed position at the stage the primary actuating member  542  has been driven by the ball screw  544  to a point at which the recesses  552  and the interlock segments  546  align. As seen in the Figure, at this point the interlock segments  546  release into the recesses  552  provided in the primary actuating member  542 . The movement of the interlock segments  546  into this position engages the primary actuating member  542  and secondary actuating member  544  in a locked position so that any further movement of the primary actuating member  542  results in combined motion of both actuating members  542 ,  544 . Movement of the interlock segments  546  is encouraged by the ramped e.g. chamfered edges  568  provided in the slots  560 . As the primary actuating member  542  is acted on by the ball screw  554  it pushes the interlock segments  546  and the chamfered edges  568  encourage the interlock segments  546  into the recesses  552 . Similar chamfered edges  566  are provided on the recesses and help to encourage motion of the interlock segments  546  when the actuating members  542 ,  544  are retracted. 
         [0094]      FIG. 23  shows the actuator  514  in a fully deployed position. Here it can be seen that the primary actuating member  542  and secondary actuating member  544  have been driven along a distance at which a rim  564  on the secondary actuating member  544  abuts against a hardstop  562 . At this point the secondary actuating member  544  cannot translate any further. Due to the interlock segments  546  which lock the first actuating member  542  to the second actuating member  544  the first actuating member  542  is also restricted from any further motion. 
         [0095]    Of course it will be appreciated that the actuator need not be electric and  FIGS. 24-26  illustrate a hydraulic actuator  614  which is equivalent to the electric actuator  514  seen in  FIGS. 21-23 . The components of the hydraulic actuator  614  are essentially the same and the arrangement of the primary actuating member  642 , secondary actuating member  644 , interlock segments  646 , recesses  652 , slots  660 , and hardstop  662  is essentially the same which results in the actuator  614  operating in an identical manner to that in  FIGS. 21-23 . The significant difference is that the reduction gearbox drives a synchronising screw  654  which drives the primary actuating member  642 . 
         [0096]    Whilst in the examples shown only a single set of slots and single set of recesses are provided, it will be appreciated by those skilled in the art that further slots and/or recesses may be provided to increase the number of modes of operation of the actuator. For example, in the examples seen in  FIGS. 21-23  a further slot may be provided on the actuator body further towards the rod end of the actuator  514 , specifically proximal to the position of the hardstop  562 . In addition, the recess  552  may be repositioned further along the primary actuating member  542 . This would mean that during operation the primary actuating member  542  would first advance to a point at which the recesses  552  align with the interlock segments  546  at which point the actuating members  542 ,  544  would become locked together. The actuator  514  may then drive both actuating members  542 ,  544  until a point at which the secondary actuating member  544  hits the hardstop  562 . At this point, the interlock segments  546  may move out of the locking arrangement between the actuating members  542 ,  544  and slide into the further slot in the actuator body. This would then allow the primary actuating member  542  to move independently in a third mode. This is just one example of how an actuator with more than two modes of operation may be achieved.