Patent Publication Number: US-2007120009-A1

Title: Aircraft ram air inlet with multi-member closure flap

Description:
PRIORITY CLAIM  
      This application is based on and claims the priority under 35 U.S.C. §119 of German Patent Application 103 35 482.4, filed on Aug. 2, 2003, the entire disclosure of which is incorporated herein by reference.  
     FIELD OF THE INVENTION  
      The invention relates to a ram air inlet or intake arrangement of an aircraft, including a ram air channel with an intake opening, and a flap arrangement to selectively open or close the air intake opening.  
     BACKGROUND INFORMATION  
      Conventional passenger transport aircraft typically include an air conditioning system including one or more air conditioning plants or packs, commonly based on an air cycle process, in which highly compressed process air, namely bleed air from a propulsion engine or an auxiliary power unit (APU) engine, is compressed and expanded, while being cooled by heat exchange at one or more stages. Through this air cycle, the process air is cooled and dehumidified. The cooling of the process air through a heat exchanger during the air cycle may, among other things, be carried out in a main or primary heat exchanger operating as a ram air heat exchanger. In this regard, cooler ambient air from the outside environment surrounding the aircraft flows through one set of passages of this heat exchanger, while removing heat from the hot process air that flows through the other set of passages of this heat exchanger. This cool ambient air is typically ram air entering a ram air intake and flowing through a ram air channel to the main or primary heat exchanger. The ram air intake is typically arranged on the outside fuselage at a location exhibiting an increased ram or stagnation air pressure due to the apparent incident wind of the oncoming air during flight of the aircraft. After passing through the heat exchanger, the ram air is then exhausted through an outlet channel that exits the aircraft fuselage at an area of relatively lower pressure in comparison to the stagnation or ram pressure existing at the ram air intake.  
      In many conventional aircraft types, the air conditioning packs are installed in the lower portion of the aircraft fuselage, or particularly in the area of the so called “belly fairing”, such as in the Airbus A319, A320, A321, A330 and A340 aircraft. To provide the cooling ram air to the air conditioning packs located in the belly fairing, these aircraft typically include ram air inlets or intake openings in the lower belly area of the aircraft fuselage.  
      In the planning and construction of aircraft, it is desired or intended to move the air conditioning packs from the location in the belly fairing to a location at the sides of the interior of the fuselage, near the wing roots. Especially with such a location of the air conditioning packs, the previously existing location of ram air inlets is not optimal, for example due to long ram air channels that would be required. There is thus a need to provide an arrangement of ram air inlets at exterior locations of the aircraft subjected to the highest stagnation or ram air pressure of the outside ambient air during flight of the aircraft, while also achieving the shortest and most direct configuration of the ram air channels leading to the air conditioning pack heat exchangers, in order to reduce the overall weight, while increasing the cooling efficiency and the maximum cooling capacity of the air conditioning system. However, on the other hand, a location and configuration of the ram air inlets must ensure that the overall aerodynamic resistance, e.g. the total coefficient of drag, of the aircraft is not significantly increased by these ram air inlets.  
      It is further known to provide inlet closure flaps for selectively opening or closing the ram air intake openings so as to control the inlet flow of ram air. For example, in the Airbus A320 aircraft, it is known to arrange only a single individual inlet flap in the ram air intake. On the other hand, in the Airbus A330 and A340 aircraft, it is known to provide both an inlet flap and an outlet flap for controlling the flow of the ram air.  
      It has been found that the existing ram air inlet flap arrangements still leave room for improvement, i.e. for optimizing the airflow control and flow characteristics of the ram air through the air intake channel, as well as the total air resistance or drag generated by the air inlet arrangement in the open position, the closed position, and any intermediate position.  
     SUMMARY OF THE INVENTION  
      In view of the above it is an object of the invention to provide a ram air inlet arrangement for an aircraft, of which the intake opening is let into the outer contour of a lifting wing structure, and which has an inlet flap arrangement that achieves improved or optimized airflow of the ram air through the ram air channel in open or partially open positions of the flap arrangement, and improved or optimized airflow of the outside ambient air over the wing, so as to avoid any negative influence on the aerodynamics or especially the total aerodynamic resistance of the lifting wing. The invention further aims to avoid or overcome the disadvantages of the prior art, and to achieve additional advantages, as apparent from the present specification. The attainment of these objects is, however, not a required limitation of the claimed invention.  
      The above objects have been achieved according to the invention, in an aircraft including an aircraft fuselage and lifting wings connected to the fuselage, as well as a ram air intake arrangement including a ram air inlet at the upstream end of a ram air channel extending inside the aircraft. The invention especially provides an improved ram air inlet arrangement in which the air intake opening is let into the outer contour of the leading edge of the lifting wing of the aircraft, and the ram air channel extends from the air intake opening along or substantially parallel to a wing profile chord of the wing, in a direction of the wing chord or depth thereof. “Substantially parallel” means within an angular range around parallel, for example up to the sweepback angle of the wing, or as another example within +/−20° of parallel to the wing chord.  
      The ram air inlet arrangement further comprises a closure flap arrangement supported in the inlet channel on plural rotation or pivot bearings that each respectively have a bearing axis or pivot axis extending in the wing span direction, whereby the closure flap arrangement is pivotable about the pivot axes defined by these bearings. The arrangement further comprises an actuating mechanism, which includes an actuator and/or a spring, that is connected through a drive linkage to the ram air inlet flap arrangement so as to selectively close, partially open, or fully open the air intake opening with the flap arrangement.  
      Preferably, the ram air inlet flap arrangement includes a front flap and a rear flap that are movably supported and connected to each other via the above mentioned bearings. A first bearing is a fixed bearing that pivotably supports the front flap at a fixed location. A second bearing may be a fixed or movable bearing that pivotably supports the rear flap at a fixed or movable location. Preferably, the second bearing is a constrained or guided movable bearing, e.g. a linearly movable bearing, that can move linearly along one or more guide tracks in the wing chord or depth direction. The third bearing is a movable bearing that pivotably interconnects the front flap with the rear flap along a pivot axis that is movable in both the wing chord or depth direction and the wing height or thickness direction. Also, the drive linkage or transmission mechanism of the actuating mechanism is preferably connected to the third bearing, so as to apply the flap opening and closing drive actuation to this bearing.  
      Further preferably according to the invention, the front flap is outwardly convexly curved with a curvature matching the contour curvature of the sectional profile of the leading edge of the wing, while the rear flap is substantially flat or planar. With this arrangement, the front flap can be actuated to close the air intake opening, while providing a substantially flush and uninterrupted outer aerodynamic contour of the leading edge of the wing. This achieves a low disruption of the optimized aerodynamic contour of the leading edge of the wing, and thus does not produce any significant increase of the overall air resistance, and does not cause any significant airflow disturbance, separation, or turbulence of the incident airflow forming one or more boundary layers over the leading edge of the wing. On the other hand, when the flap arrangement is partially opened, the combination of the front flap and the rear flap joined to each other at the third bearing forms a constricted throat with a nozzle-like cross section of the open passage of the ram air channel. This achieves an efficient control of the airflow of the ram air through the channel. Finally, in a completely open position, the front and rear flaps can be completely contracted from the open flow cross-section of the air channel, to allow unobstructed airflow therethrough, or can still provide a slight nozzle effect by forming a slightly narrower smoothly confined nozzle throat or constriction. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      In order that the invention may be clearly understood, it will now be described in connection with example embodiments thereof, with reference to the accompanying drawings, wherein:  
       FIG. 1  is a schematic cross sectional view of a ram air inlet arrangement according to the invention, including an air intake opening in the leading edge of a lifting wing, and a flap arrangement including two flaps and an actuating mechanism in an open position in the air inlet channel;  
       FIG. 2  is a schematic sectional view similar to  FIG. 1 , but with the flap arrangement in a closed position in which the air intake opening is closed by the front flap;  
       FIG. 3  is a schematic sectional view similar to  FIG. 1 , but showing a partially opened position, in which the cross-section in the air inlet channel is partially closed or constricted by the flap arrangement;  
       FIG. 4  is a schematic sectional view similar to that of  FIG. 2 , in an almost-closed position of the flap arrangement, additionally including a contact stop plate structurally strengthening the floor of the channel;  
       FIG. 5  is a schematic sectional view similar to  FIG. 4 , but showing an alternative embodiment of the flap arrangement that is supplemented by a mounting lever arrangement; and  
       FIG. 6  is a schematic sectional view similar to  FIG. 4 , but showing a further alternative embodiment of the flap arrangement in which the rear flap is made up of two flap members interconnected by a movable pivot bearing.  
    
    
     DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE BEST MODE OF THE INVENTION  
      The drawings schematically illustrate several example embodiments of a ram air inlet or intake arrangement according to the invention, of which the air intake opening  14  is let into the outer contour of the leading edge  12  of a lifting wing  1  of an aircraft. This location is selected because the incident airflow of ambient air  19  surrounding the wing  1  forming a ram airflow  18  will develop the maximum stagnation or ram air pressure along the curved nose of the leading edge  12  of the lifting wing  1  during flight of the aircraft. Thus, the selected location of the air intake opening  14  is preferably the optimum ram or stagnation point on the wing leading edge  12 . By moving the ram air intake opening from the conventional location in the belly fairing to the leading edge of the wing, this frees additional space in the belly fairing for other systems. The flap arrangement as described in detail below is very simple, and the length of the ram air channel  2  can be reduced to a minimum, whereby the total weight of the arrangement is also significantly reduced.  
      The air intake opening  14  is at the upstream end of a ram air channel or duct  2  that extends rearwardly from the opening  14  into the wing structure  22  of the wing  1 , substantially in the wing chord or depth direction t along or substantially parallel to a profile chord  23  of the wing. For example, the ram air channel  2  preferably extends parallel to the airflow direction of the incident wind of the ram air  18 . The ram air channel  2  preferably has a channel height in the wing height or thickness d direction that increases slightly from the air intake opening  14  rearwardly in an expanding front end portion of the channel  2 , until it reaches a maximum height that is then maintained substantially uniformly along the rest of the length of the channel  2 . The width of the channel in the wing span s direction is not visible in the present drawings, but may have a uniform continuous width or may expand similarly as the expansion in the height direction. The top of the channel is bounded by a channel ceiling  20 ; and the bottom of the channel is bounded by a channel floor  21 . For example, the channel ceiling  20  and the channel floor  21  may each exhibit a kink or slight bend that extends along a line parallel a wing span s direction at the transition from the expanding portion to the uniform-height portion of the ram air channel  2 . The height and width dimensions define an open channel cross-section  15  of the channel  2 .  
      The ram air channel  2 , e.g. the channel ceiling  20  and the channel floor  21  thereof as well as the sidewalls thereof (not shown), may be constructed as a massive metal component, e.g. a solid-walled pipe or duct or channel within and secured to the aircraft wing structure  22 . As mentioned above, the channel ceiling  20  of this air channel or duct  2  may have a recess or even an opening to accommodate the flap  13  (and a movable third bearing  16  as discussed below) therein or moving therethrough.  
      The ram air channel  2  extends and is connected to a ram air heat exchanger  9  such as a main or primary heat exchanger of an air conditioning pack, which may be installed near the root of the wing  1  where it joins the fuselage of the aircraft. After passing through the ram air heat exchanger  9 , and thereby extracting heat from the air cycle process air flowing through the heat exchanger  9 , the ram outlet air  18 A continues through an air outlet channel  10  to be returned back to the ambient environment  19  surrounding the aircraft, for example at an air outlet located at a lower pressure location on the outer skin of the aircraft, in comparison to the ram air inlet  14 . For example, the air outlet can be arranged at a lower pressure area of the outer skin of the lifting wing  1 .  
      In view of these further features of the ram air channel and the like, the location of the ram air opening  14  in the leading edge  12  of the wing also aims to achieve a short total ram air channel length serving the heat exchanger  9  of the air conditioning pack. Thus, such a position of a ram air intake opening  14  is advantageous in connection with the location of an air conditioning pack near the wing root, but would not be as advantageous for supplying ram air to an air conditioning pack located in the aircraft belly fairing on the bottom or belly of the aircraft fuselage, due to the resulting long length of the required air channel.  
      The ram air intake arrangement according to the invention further includes a ram air inlet flap  13  that is especially embodied as a flap assembly or flap arrangement  13  including a front inlet flap  3  and a rear inlet flap  4  that are respectively pivotably supported by a first bearing  16 A and a second bearing  16 B, and that are pivotably connected to each other by a third bearing  16 . The flap  13 , that is to say the front flap  3  and rear flap  4  may, for example, be metal plates or fiber reinforced composite material plates that are each substantially stiff or rigid and formed with the required curvature (for the front flap  3 ) or the required flat planarity (for the rear flap  4 ). These flaps may be slightly flexible but in any event stiff enough to be self-supporting and to maintain the respective initial curved or planar shape thereof.  
      The overall arrangement further includes an actuating mechanism that comprises an actuator  8  and/or a spring  8 B connected through a transmission arrangement or actuating linkage  8 A to the ram air inlet flap  13  for moving the flap  13  selectively into different positions. The transmission arrangement or linkage  8 A may be a mechanical transmission arrangement such as a rack and pinion arrangement, a threaded screw or spindle with a threaded follower nut, a rod linkage, a push-pull cable linkage (e.g. a Bowden cable), or the like. In any event, the transmission or linkage  8 A transmits the actuating motion and power from the actuator  8  onto the ram air inlet flap  13  to selectively move the flap  13  so as to close or open or partially open the air intake opening cross-section  14  of the ram air channel  2 , as follows.  
      In this regard, the ram air inlet flap  13  can take on a fully opened position as shown in  FIG. 1 , in which the flap  13  is retracted fully against the channel ceiling  20 , or is retracted into a recess or cavity for this purpose in the channel ceiling  20 , or is pulled upwardly through an opening in the channel ceiling  20 , so that the flap  13  effectively forms this flush area of the channel ceiling  20 . As can be seen in  FIG. 1 , in this fully open position, the flap  13  does not or does not significantly block or constrict the air intake opening cross-section  14 , so that a full flow of the ram air  18  into the ram air channel  2  and then further through the heat exchanger  9  is permitted.  
      Alternatively, the flap  13  can be driven by the actuator  8  to the fully closed position shown in  FIG. 2 . In this position, the front flap  3  has completely (or substantially) closed and blocked the air intake opening cross section  14 , so that (substantially) no ram air  18  flows into the ram air channel  2 . Namely, the front flap  3 , in this closed position, spans the opening cross section  14  between the channel ceiling  20  and the channel floor  21 , whereby the lower and rear edge of the front flap  3  is pressed against the forward edge of the channel floor  21 , so as to close the air intake opening. It should be understood that the closed position does not require a complete air tight seal of the air inlet opening cross-section, but may allow some insignificant air leakage or a mandatory minimum airflow (e.g. to prevent overheating of the heat exchanger  9 ) therethrough into the ram air channel  2 .  
      In this regard, it is advantageous that the front flap  3  has a convex curvature, with the convexity oriented downward and outward, as can be seen in  FIGS. 1, 2  and  3 . Particularly, this convex curvature of the front flap  3  matches the curvature of the cross-sectional outer contour of the leading edge  12  of the lifting wing  1  at this location of the air intake opening cross-section  14 . In this regard, the curvature of the flap  3  “matching” the curvature of the wing leading edge  12  means “matching” sufficiently so that there is no disruption or only an insignificant disruption of the overall aerodynamics of the wing. Thus, in the closed position shown in  FIG. 2 , the front flap  3  effectively closes and completes the outer contour of the wing leading edge  12 , so that there is no significant disruption of the ram air  18  or the outside ambient air  19  as it flows in its normal flow pattern as a boundary layer or layers over the leading edge  12  of the wing  1 , without suffering significantly increased separation or turbulence. Thereby, the total air resistance, e.g. the coefficient of drag, of the aircraft is not significantly increased by the provision of the ram air inlet and flap arrangement in the leading edge of the wing. In contrast to the shape of the front flap  3 , the rear flap  4  may conveniently or simply have a flat planar shape without curvature.  
       FIG. 3  shows a further possible position of the flap  13 , namely a partially open position. In this partially open position, the curved front flap  3  and the straight or planar rear flap  4  together form a smooth constriction in the form of a nozzle throat, having a variable opening depending on the particular selected position of the inlet flap  13 . Thereby, the flow velocity and the mass flow throughput of the ram air  18 , flowing through the ram air channel  2  as cooling air to the heat exchanger  9 , can be effectively controlled. This nozzle configuration can also serve to increase the total cooling air mass flow, which means that the cooling capacity of the air conditioning system can be increased, so that correspondingly the system weight of the air conditioning system and the dimensions of the ram air channel can be reduced, which also can lead to weight savings.  
      In any such intermediate or partially open position, the convexly curved front flap  3  forms the inwardly curving convergent inlet of the ram air channel  2 , while the adjoining rear flap  4  forms the divergent or expanding portion of the achieved nozzle configuration. Excess ram air  18  is effectively diverted away from the inlet opening cross-section  14 , to continue in its normal flow pattern over the leading edge  12  of the wing  1 .  
      Each of the above described positions of the ram air inlet flap  13  can be actively selected by appropriate actuation of the actuator  8 . Moreover, the flap  13  is securely held in any selected position between the fully open position and the fully closed position, i.e. over a range of partially open positions, for example by the unpowered actuator&#39;s resistance against movement. The established position of the flap arrangement  13  can also be held in a self-locking manner, for example due to a purposeful degree of friction in the bearings or in the slide guide track as will be described below. In this regard, the actuator  8  can have any conventionally known construction, arrangement and operation. For example, the actuator  8  may comprise an electrically powered stepper motor, which is preferably regulatable in an infinitely positionable or stepless manner. Alternatively, the actuator  8  may comprise a pneumatic or hydraulic linear actuator such as a piston-cylinder device, or a rotary actuator such as a pneumatic or hydraulic motor. In any event, the transmission or linkage arrangement  8 A couples, and if necessary converts, the output drive power of the actuator  8  to a complex motion of the ram air inlet flap  13 , for example as a linear actuation while additionally allowing a pivoting motion of the third bearing  16 . In other words, it is simply necessary that the actuator  8  and the transmission or linkage  8 A can exert a push-pull actuation to the third bearing  16  and/or the connected front flap  3  and rear flap  4 , relative to the wing structure  22 .  
      Additionally, or alternatively, a pre-stressed spring  8 B can be arranged parallel to the actuator  8  or instead of the actuator  8 . This spring  8 B (see  FIG. 1 ) has a defined stiffness or spring constant and exerts a defined pre-stress pushing downwardly and outwardly against the flap  13 , namely against the front flap  3  and the rear flap  4  or the third bearing  16  connected thereto, to bias the flap from the open position toward the closed position. Particularly, this spring  8 B is thus a compression spring that has one end thereof secured and bearing against the wing structure  22 , and the other end thereof exerting a spring pressing force against the third bearing  16  of the flap  13 . In this manner, the spring force of the spring  8 B acts against the force of the ram air  18  pressing on the flap  13 , and especially the front flap  3 . Thus, if the spring  8 B is used without the actuator  8 , the flap  13  will exhibit a self-regulated operation to open or close the ram air inlet depending on the prevailing ram air pressure. On the other hand, if the spring  8 B is used together and parallel with the actuator  8 , the spring will simply serve to counteract the ram air force, so as to relieve the actuator  8  of this ram air force. In any event, the combination of the actuator  8 , the spring  8 B, and the transmission and the linkage  8 A serve to move the flap  13  to any desired position and hold any such desired position in the range from the fully open position to the fully closed position and any intermediate partially open position.  
      The particular mechanics and motion of the two flaps, namely the front flap  3  and the rear flap  4  making up the flap  13 , as well as the three bearings  16 ,  16 A and  16 B, will now be described in further detail in connection with FIGS.  1  to  3 .  
      As mentioned above, the convexly curved front flap  3  and the planar rear flap  4  are pivotably connected to each other by the third bearing  16  at the third pivot point  6 , i.e. to allow the two flaps  3  and  4  to pivot relative to each other about the third bearing axis  17  extending substantially in the wing span s direction. This third bearing  16  is freely movable in the wing chord or depth t direction and in the wing height or thickness d direction. This can be seen by comparing the positions of the bearing  16  in the open position according to  FIG. 1 , the closed position according to  FIG. 2 , and the partially opened position according to  FIG. 3 .  
      On the other hand, the first bearing  16 A is a fixed bearing, namely a rotational pivot bearing that is fixedly connected to the wing structure  22  at a fixed position near the ram air inlet opening cross section  14 , i.e. at the area of the leading edge  12  within the wing structure  22 . The forward and upper edge of the front flap  3  is connected to the first bearing  16 A so as to be pivotable about the first pivot point  5  established by this bearing, i.e. about the first bearing axis  17 A extending substantially in the wing span s direction. Thus, the front flap  3  is enabled to pivot about this axis  17 A between the open position shown in  FIG. 1  through various intermediate positions as shown in  FIG. 3 , to the fully closed position as shown in  FIG. 2 . In connection with such pivoting of the front flap  3  about the first bearing axis  17 A, the third bearing  16  moves along a corresponding arc as discussed above.  
      Meanwhile, the rear flap  4 , which is also pivotably connected to the third bearing  16  to be pivotable about the axis  17  relative to the front flap  3 , must also move together with or corresponding to the motion of the movable bearing  16 . To allow this, the upper and rear edge of the rear flap  4  is connected to the second bearing  16 B so as to allow the rear flap  4  to pivot about the second pivot point  7  established by the second bearing  16 B, i.e. about the second axis  17 B extending substantially in the wing span s direction. Furthermore, the complex motion of the flaps  3  and  4  requires the second bearing  16 B to be movable at least in one direction generally along the profile chord  23 , i.e. a longitudinal direction of the channel parallel to or generally along the wing chord or depth t direction. For example, the movable second bearing  16 B, particularly embodied as a linearly movable bearing, may comprise an axial bearing that is supported in one or more guide tracks  16 B′ that extend generally parallel to the wing chord or depth t direction. Note that the guide track  16 B′ can tilt or slope somewhat in the wing height or thickness d direction. Nonetheless, preferably the majority motion component of the motion of the movable second bearing  16 B is directed in the longitudinal direction extending longitudinally along the air channel  2 , while a lesser motion component may be oriented in the wing thickness or height d direction.  
      The actuator  8  is connected via the transmission or the linkage  8 A to the movable third bearing  16 . Thereby, when the actuator  8  and linkage  8 A exert a pushing force onto the movable bearing  16 , the flap arrangement  13  will be moved from the open position shown in  FIG. 1  through the intermediate position shown in  FIG. 3  to the closed position shown in  FIG. 2 . That involves the third bearing  16  moving downwardly toward the channel floor  21  and forwardly toward the inlet opening cross-section  14  of the ram air channel  2 , while the front flap  3  pivots downwardly and forwardly about the first bearing axis  17 A (in a clockwise direction), and while the rear flap  4  pivots downwardly (in a counterclockwise direction) about the second bearing axis  17 B and is simultaneously pulled forward by the motion of the third bearing  16 . Thus, the second bearing  16 B slides forwardly along the guide tracks  16 B.  
      In the opposite sense, when the flap arrangement  13  is to be moved from the closed position of  FIG. 2  to the intermediate position of  FIG. 3  or the open position of  FIG. 1 , the actuator  8  through the linkage  8 A exerts a pulling force onto the third bearing  16 . This causes the bearing  16  to pivot upwardly with the front flap  3  (in a counterclockwise direction) about the first bearing axis  17 A, while the bearing  16  moves upwardly and rearwardly. As a consequence, the rear flap  4  connected to the third bearing  16  is also pivoted upwardly (in a clockwise direction) about the second bearing  16 B, while the second bearing  16 B is additionally pushed rearwardly and thus caused to slide along the guide tracks  18 B in a direction away from the channel intake opening  14 .  
      In this regard, the particular length of the front flap  3  between the bearings  16 A and  16 , and of the rear flap  4  between the bearings  16  and  16 B, relative to each other and relative to the length and height of the inlet throat of the ram air channel can be designed and selected as necessary to achieve and optimize the required opening and closing motion pattern of the flap arrangement. As mentioned above, the front flap  3  has a convex curvature preferably matching the outer contour curvature of the leading edge  12  of the wing  1 , while the rear flap  4  is substantially flat or planar. The curved contour of the front flap  3  is preferably a circular arc contour for simplicity, or can be more exactly matched to the geometry of the leading edge of the wing. These curvatures can also be specially adapted to optimize the nozzle effect achieved by the flap arrangement in the partially open positions. The most important factor is simply that the front flap  3  must pivot downwardly to close the air intake opening cross section  14  as shown in  FIG. 2 .  
      Moreover, while the embodiment shown in the present drawings involves the actuating mechanism arranged in the wing structure  22  above the ram air channel  2 , and the flap arrangement  13  also arranged above and extending downwardly into the channel  2  for closing the channel, either or both of these aspects could be reversed. Namely, the actuating mechanism  8 ,  8 A,  8 B and or the flap arrangement  13  could be mounted at the bottom side of the channel  2  rather than at the top side of the channel  2 .  
      Preferably to achieve the desired motion pattern, the extended flap length of the front flap  3  is less than or equal to the extended flap length of the rear flap  4 . As mentioned above, the flaps in the open position may be retracted flush with or above the actual plane of the channel ceiling  20 , for which purpose there must be a recess or an opening provided in the channel ceiling  20  into which or through which the flaps  3  and  4  as well as the third bearing  16  can freely move.  
       FIG. 4  shows a further feature of the invention, generally in connection with the embodiment discussed above with reference to FIGS.  1  to  3 . In other words, the embodiment of  FIG. 4  corresponds to that of FIGS.  1  to  3 , except for the additional feature of a mechanical contact stop  11  such as a contact stop plate  11  that serves to structurally strengthen the channel floor  21  near its end adjoining the wing leading edge  12 . This contact stop plate  11  serves to avoid or reduce the possibility of wear and/or pressing damage of the channel floor  21  due to the repeating pressing of the front inlet flap  3  and/or the movable third bearing  16  against the floor  21 . Namely, in this embodiment, the closure of the air intake opening cross-section  14  is achieved by the pressing of the front flap  3  and/or the bearing  16  against the contact stop plate  11  rather than directly against the channel floor  21 . The contact stop plate  11  can be easily replaced whenever necessary, for example at routine maintenance or service intervals.  
      Also, the surface of the contact stop plate  11  can be configured and/or constructed to achieve an improved seal relative to the front flap  3  and/or the bearing  16 . Alternatively, the contact stop plate  11  can purposely prevent a complete closure of the air intake opening cross-section  14 . For example, the contact stop plate  11  may have slots or grooves extending therein in the wing chord direction, to allow at least a defined minimum flow of ram air  18  into the channel  2  even when the front flap  3  and/or the bearing  16  is pressed against the contact stop plate  11 . The contact stop may alternatively be arranged as several individual plates  11  spaced apart from one another on the channel floor  21  in the wing span s direction, so as to leave the minimum airflow opening at the spaces between the successive plates  11  in the wing span s direction. This guaranteed minimum flow of ram air  18  through the channel  2  to the heat exchanger  9  avoids unintended overheating of the heat exchanger  9 , which could lead to a malfunction or shutdown of the air conditioning system.  
      A modified embodiment of the ram air intake arrangement of  FIG. 4  is shown schematically in  FIG. 5 . This embodiment of  FIG. 5  generally corresponds to the features of the embodiments of FIGS.  1  to  4 , except that the second bearing  16 B, instead of being a linearly movable bearing, is now a fixed bearing that is secured at a fixed location relative to the wing structure  22 . Further; in this regard, a pivotable lever  27  is pivotably connected to the fixed second bearing  16 B, and the opposite free end of this lever  27  is secured substantially perpendicularly (e.g. at 80 to 100°) to the rear and upper end of the rear inlet flap  4 , i.e. at the end thereof opposite the end connected to the third bearing  16 .  
      Thereby, the lever-mounting of the upper rear end of the rear flap  4  via the lever  27  is carried out to allow a flexing or kinking. This permits a displacement of the rear flap  4  in the wing chord and/or wing thickness directions, to permit the pivoting motion of the third bearing  16  along with the front flap  3  about the pivot axis of the first bearing  16 A. While the front flap  3  and the third bearing  16  pivot up and back from the closed position to the open position, the rear flap  4  is also pushed back and up via the flexing or kinking connection through the lever  27  to the fixed second bearing  16 B.  
      With this arrangement, however, it will not be possible to achieve the totally flush or recessed open position of the flap arrangement  13  as shown in  FIG. 1 , but instead the flap arrangement  13  will always protrude somewhat into the cross-sectional area of the ram air channel  2 . This merely needs to be taken into account when designing the dimensions for the required ram air flow volume and velocity. In any event, this mounting or support of the rear upper end of the rear flap  4  via a flexible or kinkable lever  27  and the fixed pivot bearing  16 B represents another embodiment of the pivotable and movable mounting or support at this end of the rear flap  4 , instead of the linearly slidable pivot bearing  16 B of the embodiment of FIGS.  1  to  3 . Namely, even with the fixed-position bearing  16 B in  FIG. 5 , the interposed flexible or kinkable lever  27  provides the required additional degree of mobility in one or more directions.  
       FIG. 6  shows a further modified or varied embodiment of a pivotable and movable mounting arrangement for the rear end of the rear flap  4 . This embodiment of  FIG. 6  looks somewhat similar to the embodiment of  FIG. 5 , and is also generally similar to the embodiment of FIGS.  1  to  3  as well as the embodiment of  FIG. 4 . Instead of the linearly slidable mounting of the second bearing  16 B in  FIG. 1 , the embodiment of  FIG. 6  provides a pivoting support or motion of a fourth bearing  16 C as a movable bearing. More particularly, in this embodiment, the rear flap  4  is made up of a first rear flap member  4 A and a second rear flap member  4 B, which are pivotably connected to each other by the fourth movable bearing  16 C, so that the two flap members  4 A and  4 B are pivotable relative to each other about the pivot bearing axis  17 C extending substantially parallel to the wing span s direction. The forward end of the second flap member  4 B, i.e. the forward end of the rear flap  4 , is connected to the movable third bearing  16  just as described above. The opposite or upper end of the first flap member  4 A, i. e. representing the rear and upper end of the rear flap  4 , is connected to the second bearing  16 B, which here can be embodied as a fixed-position bearing  16 B having a fixed position relative to the wing structure  22 .  
      With this arrangement, the first flap member  4 A of the rear flap  4  can pivot about the pivot point  7  of the second bearing  16 B, i.e. about the pivot axis  17 B. Thereby, the fourth bearing  16 C can swing or pivot about the second pivot axis  17 B, while its fourth pivot axis  17 C moves correspondingly in an arc about the second axis  17 B, as these two axes  17 B and  17 C remain parallel to each other. Thereby, the two flap members  4 A and  4 B of the rear flap  4  will be pivotable relative to one another about the fourth bearing pivot point  25  identifying the location of the fourth pivot axis  17 C.  
      In this embodiment of  FIG. 6 , the front flap  3  is once again convexly curved, just as in the above described embodiments, while the first flap member  4 A and the second flap member  4 B together forming the rear flap  4  are each flat or planar and not curved. The flap length of the first and second flap members  4 A and  4 B differ from one another. For example, the first flap member  4 A is shorter than the second flap member  4 B, but it may alternatively be of the same length or longer than the second flap member  4 B. In any event, the length of the individual flap components must simply be selected or designed to achieve the required motion pattern of the overall flap arrangement.  
      With this arrangement, when the third bearing  16  is pulled up by the actuator  8  to move the flap arrangement to the open position, the first flap member  4 A of the rear flap  4  can be pivoted rearwardly and upwardly to lie flush against or recessed into the channel ceiling  20 , while the second flap member  4 B of the rear flap  4  lies against and overlaps the first flap member  4 A, to also extend flushly along or recessed into the channel ceiling  20  in the maximum open position. In this manner, the front flap  3  and the second flap member  4 B of the rear flap  4  will together form a portion of the channel ceiling  20 . If a recess or opening is provided in the channel ceiling  20 , then this recess or opening is large enough to allow the second bearing  16 B and the fourth bearing  16 C together with the flap components to be recessed into or above the channel ceiling.  
      Various different actuating mechanisms can be used instead of the above described preferred example embodiment that acts on the third bearing  16  with a push-pull actuation in a direction transverse relative to the longitudinal direction of the air channel  2 . For example, a push-pull actuation in the longitudinal direction of the channel can be applied to the movable second bearing  16 B. As a further example, a rotary actuation can be applied to the shaft of the front flap  3  in the first bearing  16 A.  
      Although the invention has been described with reference to specific example embodiments, it will be appreciated that it is intended to cover all modifications and equivalents within the scope of the appended claims. It should also be understood that the present disclosure includes all possible combinations of any individual features recited in any of the appended claims.