Abstract:
A system for pneumatically actuating a split flap hingedly mounted near or at a trailing edge of an airfoil. The system includes a bladder system disposed between the split flap and the upper surface of the airfoil. The split flap is a small-chord (usually 1-3% of total wing chord) long-span lower panel which separates from the airfoil trailing edge by means of a hinge or a flexible lower skin. Deployment of the split flap is actuated pneumatically by the inflatable bladder system. The split flap may exist at a fixed wing trailing edge, a moving flap trailing edge, or an empennage trailing edge. The pneumatic bladder provides distributed force to extend and retract the split flap. This pneumatic approach eliminates extra drag, reduces cost and weight, and lessens flutter concerns.

Description:
BACKGROUND 
       [0001]    The embodiments disclosed hereinafter generally relate to hinged surfaces on the trailing edge of airfoils of a fixed-wing aircraft, such as wings, flight control surfaces (e.g., flaps), and horizontal stabilizers. In particular, the embodiments disclosed herein relate to methods for actuating split flaps hingedly mounted to such airfoils. 
         [0002]    A split flap is a hinged plate which forms a portion of an airfoil. A split flap provides aerodynamic advantages to an aircraft, but its small scale (typically 1-3% of chord) and location at the extreme trailing edge create difficulties. 
         [0003]    It is known to actuate a split flap by means of a complicated mechanical linkage, typically with some form of external hinge or actuation. External hinges or actuation produce extra drag. Complex mechanical linkages involve high part counts, leading to additional cost and weight. The discrete mechanical supports may be more subject to flutter, and a linkage will be susceptible to jamming. Furthermore, actuation of the split flap at discrete points (such as a typical mechanical linkage) is difficult due to the very low stiffness of the small thin split flap, which may increase the risk of the split flap buzzing or fluttering. This forces actuation at many points. 
         [0004]    There is a need for systems and methods for actuating split flaps which eliminate extra drag, reduce cost and weight, and lessen flutter and jamming concerns. 
       SUMMARY 
       [0005]    The embodiments disclosed hereinafter relate to a system for pneumatically actuating a split flap hingedly mounted near or at a trailing edge of an airfoil. The system includes a bladder system disposed between the split flap and the upper surface of the airfoil. The split flap is a small-chord (usually 1-3% of total wing chord) long-span lower panel which separates from the airfoil trailing edge by means of a hinge or a flexible lower skin. Deployment of the split flap is actuated pneumatically by the inflatable bladder system. The split flap may exist at a fixed wing trailing edge, a moving flap trailing edge, or an empennage trailing edge. The pneumatic bladder provides distributed force to extend and retract the split flap. 
         [0006]    The pneumatic actuation provides many features and advantages. The bladder system will have few moving parts, thereby reducing cost and weight, as well as reducing jam risk. The bladder system provides continuous support to the split flap along its length, which allows for a thinner split flap (no actuation hard points or severe stiffness requirements) and reduces the risk of flutter by eliminating unsupported span (combined with a piano hinge or a continuous flexing skin). The configuration of the bladder system can be tailored to create spanwise variation in the deployment angle of the split flap to best meet aerodynamic demands. The bladder can have internal spanwise-oriented septa which allow for multiple deployed positions for the split flap. Chordwise-oriented septa can reduce the spanwise extent of split flap retraction due to a ruptured bladder. Load alleviation for the flap under high loads can be achieved by deflating the bays of the bladder system, which can be done quickly by means of pressure release valves (possibly redundant). Applying suction to the bladder system keeps the flap fully retracted under load. Torsional springs can be added if additional flap closing force is required. 
         [0007]    The apparatus in accordance with various embodiments disclosed hereinafter comprises: an airfoil having upper and lower surfaces; a split flap coupled to the lower surface; and an array of inflatable bays disposed between the split flap and the upper surface of the airfoil. In one implementation, the inflatable bays are arranged in columns and rows, adjacent bays in each column being separated by a spanwise septum, while adjacent bays in each row are separated by a chordwise septum. The inflatable bays in any particular column can be inflated in sequence, thereby deploying the split flap in stages. The inflatable bays in alternating columns can be inflated using independent sources of pressurized air, thereby mitigating the effects of rupture of any one bay by maintaining pressure across the other half of the flap. In addition, the bays in different columns may be constructed to have differing shapes when fully inflated, resulting in varying degrees of flap deflection in a spanwise direction. 
         [0008]    In accordance with the broad scope of the invention, the array has at least two inflatable bays arranged in any number of columns and any number of rows. In the case where the array includes only two inflatable bays, in one embodiment they can be arranged in one row and in another embodiment they can be arranged in one column. Although in the embodiments disclosed herein the array of inflatable bays has two rows and more than two columns, the following aspects are indicative of the broad scope of various aspects of the invention. 
         [0009]    One aspect of the invention is an apparatus comprising: an airfoil having upper and lower surfaces; a deployable flap having a forward edge supported by the lower surface and extending in a spanwise direction; and a bladder system comprising first and second bays which are individually inflatable and adjacent to each other. The first and second bays are disposed between a portion of the flap and the upper surface. That portion of the flap has a first configuration when the first bay is inflated and the second bay is deflated, and has a second configuration different than the first configuration when the first and second bays are both inflated. The flap portion is deployed at a greater angle relative to the lower surface when the flap portion is in the second configuration than when the flap portion is in the first configuration. 
         [0010]    Another aspect of the invention is a method for deploying a hinged flap that is supported by a lower surface of an airfoil near the airfoil&#39;s trailing edge, comprising supplying pressurized air to mutually adjacent first and second bays of a bladder system, the first and second bays being disposed between an upper surface of the airfoil and at least a spanwise section of the hinged flap, the first spanwise section of the hinged flap being deflected to a first deployed position when the first bay is inflated and the second bay is deflated and being deflected to a second deployed position beyond the first deployed position when the first and second bays are both inflated. 
         [0011]    A further aspect of the invention is an apparatus comprising: an airfoil having upper and lower surfaces and a trailing edge; a deployable flap having a forward edge supported by the lower surface near the trailing edge of the airfoil and extending in a spanwise direction; and at least one bladder disposed between the upper surface and the flap, the at least one bladder being segmented in a spanwise direction to form spanwise segments, wherein the spanwise segments of the at least one bladder are inflatable to cause the flap to move from a stored position to a deployed position. 
         [0012]    Other aspects of the invention are disclosed and claimed below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1 through 3  are diagrams showing a cross-sectional view of a portion of an airfoil having a trailing edge equipped with a pneumatically actuatable split flap in accordance with various embodiments.  FIGS. 1-3  show the respective position of the split flap before actuation, after a first actuation stage and after a second actuation stage. 
           [0014]      FIG. 4  is a diagram showing components of a system for pneumatically actuating deflection of the portion of a split flap depicted in  FIGS. 1-3 . The boldface arrows indicate airflow through pneumatic connections, while the lines intersecting the controller indicate electrical connections. 
           [0015]      FIG. 5  is a diagram showing a plan view of a system for supplying pressurized air to actuate a split flap in accordance with one embodiment. 
           [0016]      FIG. 6  is a diagram showing a plan view of a system for supplying pressurized air to actuate a split flap in accordance with another embodiment. 
           [0017]      FIG. 7  is a diagram showing a sectional view of a portion (i.e., the airfoil trailing edge with split flap) of the system depicted in  FIG. 6 , the section being taken along line  7 - 7  indicated in  FIG. 6 . 
           [0018]      FIGS. 8 and 9  are diagrams showing components of a system for pneumatically actuating deflection and retraction, respectively, of the portion of a split flap depicted in  FIGS. 1-3 . The boldface arrows indicate airflow through pneumatic connections, while the lines intersecting the controller indicate electrical connections. 
           [0019]      FIG. 10  is a diagram showing some components of a pneumatic bladder actuation system having means for leak mitigation in accordance with a further embodiment. The boldface arrows indicate airflow through pneumatic connections, while the lines intersecting the controller indicate electrical connections. 
       
    
    
       [0020]    Reference will hereinafter be made to the drawings in which similar elements in different drawings bear the same reference numerals. 
       DETAILED DESCRIPTION 
       [0021]      FIG. 1  shows a cross-sectional view of a trailing edge portion of an airfoil  10  equipped with a pneumatic actuator for deploying a split flap  14  in accordance with various embodiments. The airfoil  10  comprises a lower aerodynamic surface  12 , an upper aerodynamic surface  18  and a solid tip  20  at the extreme trailing edge. The airfoil may be made of carbon fiber-reinforced polymer, metal or other suitable material. The deployable flap  14  has a forward edge supported by the lower surface  14  and extends in a spanwise direction (i.e., a direction parallel to the span of the airfoil). The split flap  14  may also be made of carbon fiber-reinforced polymer, metal (e.g., aluminum) or other suitable material. 
         [0022]      FIG. 1  shows the split flap  14  in an unactuated state. In the unactuated state, the flap  14  is generally aligned with the lower surface  12  and covers an opening in the lower surface. The solid tip  20  has a recess for receiving the rear edge of the flap  14 . The flap  14  is supported by the lower surface  12  via a mounting plate  42  having a hinge  16  at its rear edge. Hinge  16  may be constructed in the manner of a piano hinge. The flap  14  is pivotable relative to the lower surface about an axis of hinge  16 . Alternatively, the flap could be connected to the lower surface by means of a continuous flexing skin, thereby eliminating the hinge. 
         [0023]    The pneumatic actuator shown in  FIG. 1  comprises a bladder system disposed between the upper surface  18  of airfoil  10  and the split flap  14 . The only components of the bladder system which are visible in  FIG. 1  are a collapsible bladder  22  having an internal septum  24  that partitions the bladder  22  to form a first-stage bay  26  and a second-stage bay  28  which share a common wall (i.e., septum  24 ). The septum  24  forms respective interior surfaces of bays  26  and  28 . Bays  26  and  28  are stacked between the upper surface  18  of airfoil  10  and the split flap  14 . One portion of bay  26  is attached (e.g., by adhesive) to the airfoil upper surface  18 , while one portion of bay  28  is similarly attached to the flap  14 . Both bays are shown in a collapsed (i.e., non-inflated) state. 
         [0024]    In accordance with different embodiments, the stacked bays  26  and  28  shown in  FIG.1  may form one column in a bladder system comprising a multi-column array of inflatable bays (not visible in  FIG. 1 , but see  FIGS. 5 and 6 , to be described in detail later), each column comprising a pair of similarly stacked inflatable bays disposed between the upper surface  18  of airfoil  10  and respective spanwise sections of the split flap  14 . In the case of a two-row multi-column array of inflatable bays, the internal septum  24  seen in  FIG. 1  may extend in a spanwise direction for the entire length of the array, with adjacent bays in each row sharing a common chordwise septum. 
         [0025]    In the alternative to adjacent bays which share a common septum, two adjacent bays (whether in a row or a column) may be formed as separate receptacles or bags which are then attached by adhesive or heat bonding or other suitable means, depending on the material used to construct the receptacles. 
         [0026]    In accordance with further alternatives, a multiplicity of pairs of stacked bays may be installed separately without attachment of successive pairs of stacked bays to each other. Furthermore, the respective pairs of stacked bays may be separated by gaps and need not be adjacent to each other. 
         [0027]    In accordance with some embodiments, the bladder system can be made of a collapsible fiber-reinforced material, the matrix material being nylon or rubber. The use of fiber-reinforced material has the advantage that a bay will cease to expand in response to internal air pressure above a designed level when a predetermined configuration is attained, i.e., when the walls of the bay are fully expanded to the point where the reinforcing fibers become fully extended and resist further expansion of the bay. 
         [0028]    Referring again to  FIG. 1 , bays  26  and  28  are individually inflatable via respective air inlet tubes  32  and  34  which are coupled to respective ports of those bays. Although  FIG. 1  does not indicate the hardware for coupling an air inlet tube to a bladder port, such hardware is well known to persons skilled in the inflatable bladder art. (For example, each bay of the bladder system could be provided with a mouth which is clamped to the end of a pipe or tube.) Respective portions of air inlet tubes  32  and  34  are embedded in and thereby supported by a block  40  of polymeric material, e.g., phenolic resin. In the particular configuration of the air supply system partly shown in  FIG. 1 , the air inlet tube  32  is in fluid communication with an air distribution pipe  30 , while the air inlet tube  34  is in fluid communication with the air distribution pipe  30  via a valve  36 . The air distribution pipe  30 , in turn, communicates with a source of pressurized air, e.g., an air pump (not shown in  FIG. 1 ). 
         [0029]    Optionally, a valve could be installed between air inlet tube  32  and air distribution pipe  30 . Alternatively, valve  36  could be omitted and a valve could be placed between the pressurized air source and the air inlet tube  32 , which arrangement would enable the inflation of bay  28  before the inflation of bay  26 . 
         [0030]    More specifically, the air distribution pipe  30  can be part of an air distribution system which is coupled to the source that provides the high-pressure input for operating the system. For example, the source can be connected to a main distribution valve via a main duct (not shown in  FIG. 1 ). A controller (not shown) electrically activates the main distribution valve via an electrical line when deployment of the split flap has been commanded. The controller can be activated by the pilot or it can be preprogrammed according to flight conditions. When the main distribution valve is open, it distributes pressurized air to a set of valves (e.g., valve  36  shown in  FIG. 1 ) via a manifold. The open valves in turn supply pressurized air to respective air inlet tubes. 
         [0031]    In cases where the source of pressurized air is an electronically controlled air pump, the controller also activates the air pump when deployment of the split flap has been commanded.  FIGS. 2 and 3  show the flap position and state of the inflatable bays upon completion of first and second stages of actuation, respectively. In the first stage, partial deployment of flap  14  is actuated by inflation of bay  26 .  FIG. 2  shows a state wherein, when bay  26  is fully inflated, flap  14  is deflected at a first angle relative to lower surface  12  of airfoil  10 . In the second stage, full deployment of flap  14  is actuated by inflation of bay  28 .  FIG. 3  shows a state wherein, when bays  26  and  28  are both fully inflated, flap  14  is deflected at a second angle greater than the first angle. Alternatively, bays  26  and  28  can be inflated concurrently. 
         [0032]    However, in view of the fact that the flap  14  is not a rigid structure and is susceptible to twisting, all spanwise sections of the split flap will not be deflected at precisely the same angle during either partial or full deployment. In the example depicted in  FIGS. 2 and 3 , the depicted portion of flap  14  has a first configuration when bay  26  is inflated and bay  28  is deflated (as seen in  FIG. 2 ), and has a second configuration different than the first configuration when bays  26  and  28  are both inflated (as seen in  FIG. 3 ). Other portions of the flap not depicted in  FIGS. 2 and 3  may be deflected at angles different than those depicted in  FIGS. 2 and 3 . 
         [0033]    Moreover, in the case where an array of inflatable bays having multiple columns (each column consisting of a pair of stacked bays of the type depicted in  FIGS. 1-3 ) is installed between the flap and the upper surface of the airfoil, the pair of bays may be constructed such that respective columns have different configurations when the bays in those columns are fully inflated. This allows the designer to tailor the deflection of the flap such that the amount of deflection varies in a spanwise direction. 
         [0034]    It should also be appreciated that the number of inflatable bays in a column can be greater than two. For example, if each stack had three bays, then upon inflation of the first bay only, the flap would be deployed to a first partially deployed position; then upon inflation of the second bay while the first bay remains inflated, the flap would be deployed to a second partially deployed position intermediate the first partially deployed position and a fully deployed position; and finally, upon inflation of the third bay in the stack while the first and second bays remain inflated, the flap would be deployed to the fully deployed position. 
         [0035]      FIG. 4  shows components of a system for pneumatically actuating deflection of the portion of a split flap depicted in  FIGS. 1-3 . In the first stage of actuation, bay  26  is inflated when a controller  8  activates an air pump  44 . The boldface arrows in  FIG. 4  indicate airflow through pneumatic connections, while the lines intersecting the controller indicate electrical connections. In the second stage of actuation (subsequent to the first stage), bay  28  is inflated when a controller  8  opens valve  36  (while air pump  44  is still activated), thereby placing bay  28  in fluid communication with air pump  44 . In a configuration where an intervening valve is installed between air pump  44  and bay  26  (not shown in  FIG. 4 ), that intervening valve would be opened by the controller during the first stage of actuation, thereby placing bay  28  in fluid communication with air pump  44 . 
         [0036]    The controller  8  can be programmed to activate the air pump and not open valve  36  upon receipt of a command which indicates that the split flap should be deflected by the angle depicted in  FIG. 2 . Furthermore, controller  8  can be programmed to activate the air pump and then open valve  36  upon receipt of a command indicating that the split flap should be deflected by the angle depicted in  FIG. 3 , which is greater than the angle depicted in  FIG. 2 . 
         [0037]      FIG. 5  shows a system for supplying pressurized air to actuate a split flap in accordance with one embodiment. The view in  FIG. 5  is looking up at an airfoil  10  with a split flap  14  seated in an opening in a lower surface  12  of airfoil  10 . In this example, the airfoil  10  is a trailing edge flap and the split flap  14  is a tip flap that is deflectable (in a direction out of the paper) relative to the trailing edge flap. The system shown in  FIG. 5  includes an array of inflatable bays (located behind flap  14  and not visible from the vantage of  FIG. 5 . In the example seen in  FIG. 5 , the array of inflatable bays has two rows and eleven columns, each column of bays being arrange in a stack as previously described with reference to  FIGS. 1-3 . Each pair of stacked bays can be inflated by supplying pressurized air from an air pump  44 . Optionally, the air pump  44  could be remotely located (off the flap) if desired. 
         [0038]    The pressurized air from pump  44  is distributed by a air feed line  46  to a multiplicity of air distribution pipes  30 . Consistent with the description of the air distribution pipe  30  shown in  FIGS. 1-3 , each air distribution pipe  30  seen in  FIG. 5  can supply air to a respective pair of stacked bays via respective valves and air inlet tubes (not shown in  FIG. 5 ). Additional valves can be installed (for example, in the respective air distribution pipes  30 ) as needed to avoid loss of pressure in the feed line  46  in the event of a rupture somewhere in the bladder system. Also, if the flap is made of solid laminate composite or sheet metal, it will tend to twist if some, but not all bays deflate. However, other bays which remain inflated would still hold the flap in a deflected position, even as the flap twist angle varies. 
         [0039]    In the implementation shown in  FIG. 5 , a single air pump drives the entire flap using a single feed line. The air pump is reversible so that the flap can be retracted by sucking air out of the feed line  46 , thereby sucking air out of the collapsible bays. Redundant air release valves (not shown in  FIG. 5 ) can be placed on the inflatable bays to facilitate flap retraction if needed. The state of each air release valve can be controlled by the same controller which controls the states of the air distribution valves. Each air release valve opens the bay on which the valve is installed. Then the external pressure applied by the airstream on flap  14  collapses the bay and forces air out the open air release valve. If more closing force is needed, torsional springs can be installed at the hinge line  16  to urge the flap to close more rapidly. 
         [0040]      FIG. 6  shows a system for supplying pressurized air to actuate a split flap in accordance with another embodiment. Again, the view in  FIG. 6  is looking up at an airfoil  10  with a split flap  14  seated in an opening in a lower surface  12  of airfoil  10 . The system shown in  FIG. 6  includes an array of inflatable bays located behind flap  14 , but for purposes of illustration, fours adjoining pairs of stacked inflatable bays are identified by reference numerals  56 ,  58 ,  60  and  62  in  FIG. 6 . These bays share common boundaries, which take the form of chordwise septa  50 ,  52  and  54 , which partition a bladder into four spanwise sections. 
         [0041]      FIG. 7  is a diagram showing a sectional view of a portion (i.e., the airfoil trailing edge with split flap) of the system depicted in  FIG. 6 , the section being taken along line  7 - 7  indicated in  FIG. 6 . As seen in  FIG. 7 , each spanwise section is in turn partitioned by a spanwise septum  24  to form inflatable bays  26  and  28  of a type previously described. 
         [0042]    Thus, viewed in conjunction,  FIGS. 6 and 7  show an exemplary bladder system consisting of an array having two rows and four columns of inflatable bays, the stacked bays in each column sharing a respective spanwise septum  24 , and the bays in adjacent columns sharing a respective chordwise septum  50 ,  52  or  54 . The designations  1 / 2  in  FIG. 6  indicate two columns (each being a pair of stacked bays), the inflatable bays of which are selectively placed in fluid communication with a pressure source A (not shown) stacks. Similarly, the designations  3 / 4  in  FIG. 6  indicate two columns (each being a pair of stacked bays), the inflatable bays of which are selectively placed in fluid communication with a pressure source B (not shown). As seen in  FIG. 6 , the bay pairs  1 / 2  are arranged in alternating sequence with the bay pairs  3 / 4 . Bay No.  1  of each bay pair  1 / 2  can be inflated by pressure source A using air distribution subsystem  64 , whereas Bay No.  2  of each bay pair  1 / 2  can be inflated by pressure source A using air distribution subsystem  66 . As previously described, Bays Nos.  1  and  2 , corresponding to bays  28  and  26  shown in  FIG. 7 , can be inflated in sequence or concurrently. Similarly Bay No.  3  of each bay pair  3 / 4  can be inflated by pressure source B using air distribution subsystem  68 , whereas Bay No.  4  of each bay pair  3 / 4  can be inflated by pressure source B using air distribution subsystem  70 . Bays Nos.  3  and  4 , which again correspond to bays  28  and  26  shown in  FIG. 7 , can be inflated in sequence or concurrently. Although not shown in  FIG. 6 , valves may be installed at appropriate locations to enable the inflation of Bays Nos.  1  and  2  or  3  and  4  in sequence. 
         [0043]    The arrangement shown in  FIG. 6  enables the inflatable bays in alternating columns (i.e., spanwise segments) to be inflated using independent sources of pressurized air, thereby mitigating the effects of rupture of any one bay by maintaining pressure across the other half of the flap. The use of two separate pressure sources mitigates the effect of a failure of a pressure source. 
         [0044]    In accordance with another embodiment, the configuration of the bladder system can be tailored to create spanwise variation in the deployment angle of the split flap to best meet aerodynamic demands. An exemplary apparatus comprises an airfoil having upper and lower surfaces; a deployable flap having a forward edge supported by the lower surface and extending in a spanwise direction; and a bladder system comprising a first inflatable spanwise section disposed between the upper surface and a first spanwise section of the flap, and a second inflatable spanwise section disposed between the upper surface and a second spanwise section of the flap. Such an embodiment has been previously described with reference to  FIGS. 6 and 7 . A spanwise variation in flap deflection can be provided configuring one inflatable spanwise section of the bladder system (e.g., section  60  in  FIG. 6 ) to be sufficiently different from another inflatable spanwise section (e.g., section  62  in  FIG. 6 ) that the amounts of deflection of these spanwise sections of the flap are substantially different. For example, the bladder system could be configured such that one end of the split flap deflected by 30° while the other end deflected by 60°, as a result of which the split flap would be twisted along its length. 
         [0045]    In accordance with a further embodiment, one or more venturis can be utilized to evacuate the bladder system when flap retraction is commanded. The venturi draws the air back out of the same tubing that was used to inflate the bladder system, thereby deflating a bay or multiple bays of the device. Other tubing could be dedicated for the evacuation, but a preferred solution is to utilize the inflation ports. 
         [0046]      FIGS. 8 and 9  show components of a system for pneumatically actuating either deflection or retraction of the portion of a split flap depicted in  FIGS. 1-3 . Again the boldface arrows indicate airflow through pneumatic connections (e.g., tubing), while the lines intersecting the controller indicate electrical connections. Air pump  44  is connected to a directional valve  4  by way of tube  72 . Activation of air pump  44  and the directional state of valve  4  are electronically controlled by a controller  8 . In the inflation mode depicted in  FIG. 8 , valve  4  directs air flow from pump  44  to a tube  74  that bypasses a venturi  6 . The flow through tube  74  is directed to a port of the first-stage bay  26  by tubes  76  and  78 , which are connected in series. The controller  8  also controls the state of a valve  36  which, in an open state, couples pressurized air in tube  80  into tube  82 . Tube  82  is in turn connected to a port of the second-stage bay  28 . The controller can be programmed to open valve  36  after switching the state of valve  4  so that it directs pressurized air into bypass tube  74 , in which case bay  28  will be inflated after bay  26  has been inflated. 
         [0047]    The venturi  6  has a first port connected to valve  4  via a tube  84 , a second port connected to tube  76  and a third port connected to a tube  86 . Tube  86  is connected to a vent (not shown). In the inflation mode depicted in  FIG. 8 , the venturi  6  does not interfere with the air flow from pump  44  to bays  26  and  28 , and pressurized air produced by pump  44  does not escape via tube  86 . 
         [0048]    In contrast,  FIG. 9  depicts the system in a deflation mode. The controller  8  is programmed to maintain valve  36  open and switch directional valve  4  so that the latter now directs the pressurized air from pump  44  into tube  84  instead of bypass tube  74 . The result of this mode change is that the pressure in tube  76  on one side of venturi  6  becomes lower than the pressure in tube  84  on the other side of venturi  6 , causing pressurized air produced by pump  44  to escape from venturi  6  via its third port, flowing into outlet tube  86 . The air escaping through the venturi  6  produces a vacuum due to the Bernoulli principle, the vacuum being produced and held as long as the air flow is directed across the venturi, thereby evacuating bays  26  and  28 . The resulting reverse air flow through tubes  76 ,  78 ,  80  and  82 , which causes bays  26  and  28  to deflate, is indicated by arrowheads in  FIG. 9 . 
         [0049]      FIG. 10  shows components of a pneumatic bladder actuation system having means for leak mitigation in accordance with a further embodiment. This embodiment differs from the embodiment depicted in  FIG. 8  in that a valve  38  is disposed between tubes  76  and  78 , and the first- and second-stage bays  26  and  28  are provided with respective pressure transducers  86  and  88  which are connected to the controller  8 .  FIG. 10  shows the system in an inflation mode, with valves  36  and  38  in an open state. Bay  26  (if intact) will inflate as it receives pressurized air from an air pump (not shown) via tube  76 , open valve  38  and tube  78 , while bay  28  (if intact) will inflate as it receives pressurized air from the same pump via tubes  76  and  80 , open valve  36  and tube  82 . 
         [0050]    In accordance with this embodiment, means are provided for detecting and mitigating a leak in any of the bladder sections. The controller receives signals representing the internal pressure of bay  26  from pressure transducer  86  via electrical connection  90 , while it also receives signals representing the internal pressure of bay  28  from pressure transducer  88  via electrical connection  92 . The controller  8  is programmed to monitor the pressure increase of each bay. Should one fail to inflate, the controller would send a signal to the corresponding valve for that bladder and close it off. For example, if the controller were to determine that the pressure signal from pressure transducer  26  indicated that bay  26  was not inflating, then controller  8  would send a control signal (via electrical connection  96 ) to valve  38 , changing the latter&#39;s state from open to closed. This would prevent the pressurized air from leaking out any rupture in bay  26 , which would have the effect of preventing the inflation of bay  28  also. Similarly, in response to pressure signals from pressure transducer  88  indicating that bay  28  was not inflating, controller  8  would send a control signal (via electrical connection  94 ) to valve  36 , changing the latter&#39;s state from open to closed. 
         [0051]    This solution provides a means to remain redundant in the event of a leak. Other sections of the flap would still inflate since they have been sized to operate without all bladder sections inflating. Evacuation of the functioning bladder sections would still fully close the flap to restore normal flight configuration. 
         [0052]    In the embodiments depicted in  FIGS. 1-7  (none of which are to scale), the split flap aft edge appears to be some distance from the true trailing edge of the airfoil. In accordance with other embodiments, however, the split flap aft edge can extend to the true aft edge of the flap/wing/horizontal stabilizer. This results in a more effective split flap from the aerodynamic perspective, but because the volume of a collapsed bladder is difficult to manage in a tiny wedge, this may require a thicker trailing edge tip, resulting in greater drag when the flap is retracted. 
         [0053]    While the invention has been described with reference to various embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. For example, two spanwise-segmented (by chordwise septa) bladders attached to each other may be substituted for a single spanwise-segmented (by chordwise septa) bladder in which each spanwise segment comprises a pair of bays formed by a spanwise septum. Alternatively, a spanwise array of bladders attached in series, in which each bladder comprises a pair of bays formed by a spanwise septum, may be substituted for a single spanwise-segmented (by chordwise septa) bladder in which each spanwise segment comprises a pair of bays formed by a spanwise septum. In addition, many modifications may be made to adapt a particular situation to the teachings of the invention without departing from the essential scope thereof. Therefore it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention. 
         [0054]    As used in the claims, the term “hinge” should not be construed to encompass only a hinge made with movable components (such as a piano hinge), but rather should be given a meaning that further encompasses other types of hinges, such as a hinge made of flexible material (e.g., a flexible connection or living hinge).