Abstract:
Methods and systems are provided to comply with structural load requirements applicable to aircraft additional fuel tank systems. A plurality of aircraft fuel tanks may be positioned adjacent to one another, preferably within the fuselage (e.g., a cargo compartment) of the aircraft so as to be disposed generally along a longitudinal axis of the aircraft. The tank body defining an interior space for holding aircraft fuel, an intercommunication conduit assembly between the fuel tank modules configured to refuel and transfer fuel from the tank modules by a cascade mode and an intentional air-filled ullage space are operatively associated with the tank body to prevent an overpressure condition within the interior space of the fuel tank body. The intentional air-filled ullage is obtained through the predetermined positioning of the terminal open end of the intercommunication tube inside the respective fuel tank module. The intentional air-filled ullage can be configured in all or in only some of the fuel tank modules according to the design of the auxiliary fuel tanks or aircraft structural loads requirements.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims domestic priority benefits under 35 USC §119(e) from U.S. Provisional Patent Application Ser. No. 61/332,136 filed on May 6, 2010, the entire content of which is expressly incorporated hereinto by reference. 
    
    
     FIELD 
     The embodiments disclosed herein relate generally to aircraft fuel systems, and more particularly, to additional fuel tank systems installed in aircraft fuselages and methods to provide compliance with structural load requirements for the fuel tank structures. 
     BACKGROUND 
     Commercial and military transport aircraft are typically designed to carry a given load of passengers, cargo or both, at a given range and/or at a given endurance. Occasionally, the range and/or endurance of the aircraft may need to be increased. Such extended range and/or endurance can be accomplished by installing additional or auxiliary fuel tank systems in the aircraft, typically by positioning fuel tanks physically within the aircraft&#39;s fuselage cargo space (i.e., that space within the aircraft&#39;s pressurized fuselage which is below the passenger deck). Conventional auxiliary fuel tank systems are typically comprised of additional fuel tanks and their respective equipment, manifolds, and harnesses necessary to manage the additional fuel carried in the tanks. 
     These additional fuel tanks and systems may be embodied in diverse configurations, for example, with tanks installed under the wings external to the aircraft or with tanks internal to the fuselage. These additional fuel tanks and systems may be configured to directly supply fuel to the engines or to transfer the fuel to other tanks and from there to feed the aircraft engines and/or to be used to control aircraft center of gravity or even to transfer fuel to other aircraft in flight or to other vehicles on the ground. 
     Auxiliary fuel tank systems are in and of themselves known. For example, it has been proposed in U.S. Pat. Nos. 6,889,940, 7,040,579 and 7,051,979 (incorporated fully by reference herein) to provide auxiliary fuel tank systems that contemplate providing various separate manifold assemblies (e.g., fuel inlet and outlet manifolds, vent manifolds and the like) internally of each tank. By positioning the tank assemblies in adjacent side-by-side configuration, their respective internal manifolds may be connected together to provide a tank system that can be operatively interconnected with the aircraft&#39;s on-board fuel management systems. 
     A difficulty that may be encountered in the conventional auxiliary fuel tank systems noted previously relates to the manifolds that interconnect one tank to another so as to transfer fluids in both directions (i.e., into and out of a respective tank). In case of high accelerations or decelerations in a direction generally parallel to the longitudinal axis of the aircraft (and hence parallel to the row of auxiliary fuel tanks positioned within the aircraft&#39;s fuselage), if the fuel tanks are fluid-connected to one another through one or more manifolds and fuel is allowed to migrate from one fuel tank to another in a cascade fashion, the pressure that responsively develops in the last fuel tank(s) in the row of tanks may reach values well above the tank&#39;s structural limits. As a result, a real risk of potentially damaging or even rupturing the fuel tank exists. 
     More recently, U.S. Pat. No. 7,648,103 (the entire content of which is expressly incorporated hereinto by reference) has disclosed an auxiliary tank assembly having a relief manifold assembly mounted internally within the tank body so as to prevent an overpressure condition occurring within the interior space of the fuel tank body due to an excess volume of fuel being introduced thereinto which exceeds the maximum allowable volume of fuel permitted therewithin. The relief manifold assembly thus includes a buffer vessel which defines an internal buffer chamber within the tank body extending upright between the upper and lower walls of the tank body. The buffer vessel includes an aperture located at a lower end thereof near the lower wall of the tank body and exposed directly to the fuel held in the interior space of tank body. A relief valve associated with a relief branch conduit maintains an air column under pressure within the buffer vessel. When the maximum allowable fuel within the tank body is attained, the pressure of the air column will cause the relief valve to open thereby venting the air column therethrough and allowing some fuel to enter the internal buffer chamber and thereby relieve the overpressure condition. 
     SUMMARY 
     According to one aspect of the present invention, an aircraft fuel tank is provided which includes a tank body defining an interior space for holding aircraft fuel, an intercommunication line between the fuel tank modules configured to refuel and transfer fuel from them by cascade mode and an intentional air-filled ullage space operatively associated with the tank body to prevent an overpressure condition within the interior space of the fuel tank body. 
     According to a preferred embodiment, the intentional ullage can be obtained through the predetermined positioning of the intercommunication tube inside the respective fuel tank module with respect to the height of the tank module. The intentional ullage can thus be configured so that the ullage space may be present in all fuel tank modules or simply in some fuel tank modules according to the design of the auxiliary fuel tanks or structural loads requirements. 
     The fluid intercommunication of the fuel tank modules is accomplished in a cascade manner. By the term “cascade” it is meant that the refueling and/or transferring of fuel, as well as ventilation, from one fuel tank to another adjacent fuel tank, is accomplished by flow of fuel sequentially from one tank to the next in a serially connected set of tanks. The ventilation line is connected in the last fuel tank in the cascade series and thus allows that the air to escape out of the respective auxiliary fuel tank to atmosphere or elsewhere internally of the aircraft. 
     According to some embodiments, the aircraft fuel tank will include intercommunication conduits positioned external to the tank body, an intercommunication access port on a wall of each tank body to allow access therethrough to the interior space defined thereby, an internal recess located on a bottom and on a top wall of the tank body within the interior space defined thereby, and one or more internal branch lines positioned within the interior space of the tank body. 
     The vent line assembly will most preferably comprise a vent conduit positioned external to the tank body, a vent access port in the wall of the last refueled fuel tank module to allow access therethrough to the interior spaced defined thereby, an internal recess located on a top wall of the tank body within the interior space defined thereby, and an internal line positioned within the interior space of the tank body and establishing fluid communication between the internal recess and the external vent conduit through the vent access port. 
     In other aspects, aircraft fuel tank systems are provided which are adapted to being mounted within a fuselage section of the aircraft so as to supplement a main fuel system of the aircraft, the fuel tank systems including at least one fuel tank having a tank body which defines an interior space for containing aircraft fuel and which is sized and configured to be positioned within the fuselage section of the aircraft, at least one fluid interconnection assembly operable coupled to the at least one fuel tank so as to be in fluid communication with the interior space defined thereby; and at least one control box external of the at least one fuel tank and adapted to fluid-connect the at least one fluid interconnection assembly to the main fuel system of the aircraft. 
     According to the embodiments of the present invention, at least one intentional predetermined air-filled ullage in the tank body is provided so as to prevent an overpressure condition during high decelerations. 
     A plurality of aircraft fuel tanks may therefore be positioned adjacent to one another, preferably within the fuselage (e.g., a cargo compartment) of the aircraft so as to be disposed generally along a longitudinal axis of the aircraft. In such an embodiment, a forward fuel tank system may be positioned within a forward section of the fuselage compartment, and an aft fuel tank system may be positioned within an aft section of the fuselage compartment. Each of the forward and aft fuel tank systems will most preferably comprise a plurality of the aircraft fuel tanks positioned adjacent to one another and disposed generally along a longitudinal axis of the aircraft. 
     These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
       The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
         FIG. 1  is a schematic top perspective view of an aircraft with forward and afterward fuselage fuel tank systems in accordance with one preferred embodiment of the present invention; 
         FIG. 2  is a schematic top perspective view of the forward fuselage fuel tank system shown in  FIG. 1  and specifically depicts a cascade type intercommunication system between each of the fuel tank modules (intercommunication lines) including the ventilation line, the transfer control boxes, the transfer line and the refuel line; 
         FIG. 3  is another schematic top perspective view of the forward fuselage fuel tank system shown in  FIG. 2 , showing the tank intercommunication line and the ventilation line; 
         FIG. 4  is a schematic top perspective view of the forward fuselage fuel tank system shown in  FIG. 2 , but showing only the fuel transfer line and fuel refueling line; 
         FIG. 5  is a schematic top perspective view of the forward fuselage fuel tank system shown in  FIG. 2 , but showing only the tank with an ullage relief configuration; 
         FIG. 6  is a schematic detailed view of the tank depicted in  FIG. 5  to maintain the ullage configuration whereby the quantity of the ullage can be configured for each module in equal or different values of ullage volume by preselected setting of the dimension “H”; 
         FIG. 7  is a schematic top perspective view of the aft fuselage fuel tank system shown in  FIG. 1 , and specifically depicts a cascade type intercommunication system between each of the fuel tank modules (intercommunication lines) including the ventilation line, the transfer control boxes, the transfer line and the refuel line; 
         FIG. 8  is another schematic top perspective view of the aft fuselage fuel tank system shown in  FIG. 7 , showing the tank intercommunication line and the ventilation line and also partially showing the refueling line; 
         FIG. 9  is a schematic top perspective view of the aft fuselage fuel tank system shown in  FIG. 6 , but showing only the fuel transfer lines; 
         FIG. 10  is a schematic top perspective view of the aft fuselage fuel tank system shown in  FIG. 7 , but showing only the tank with an ullage relief configuration; 
         FIG. 11  is a schematic detail view of the tank depicted in  FIG. 11  to maintain the ullage configuration whereby the quantity of the ullage can be configured for each module in equal or different values of ullage volume by preselected setting of the dimension “H”; 
         FIG. 12  is a schematic view of the cascade intercommunication system among three of auxiliary fuel tanks modules (forward or aft) depicted during a normal flight or ground attitude and a different intentional ullage volume for each tank; and 
         FIG. 13  is a schematic view similar to  FIG. 12  but showing the intentional ullage volume dumping (cushioning) the fuel column and avoiding the overpressure in the most forward fuel tank module during a high deceleration event, for example a negative (−) 9G force along the longitudinal axis of the aircraft. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure describes modifications, applicable to additional or auxiliary fuel tank systems of aircraft that could improve the production, assembly, installation, inspection and maintenance of such systems and their components. 
     Many of the details, dimensions, angles and other features shown in the figures of the present patent application are merely illustrative of particular embodiments of the invention. Accordingly, other embodiments can have other details, dimensions, angles and features, without departing from the spirit or scope of the present inventions. 
     As shown schematically in accompanying  FIG. 1 , an aircraft  10  has a fuselage  10 - 1 , a pair of wings  10 - 2  extending generally laterally from the fuselage  10 - 1  and wing-mounted engines  10 - 3  to provide the required thrust to the aircraft  10 . In this regard, although multiple wing-mounted engines  10 - 3  are shown, it will of course be understood that the present invention could be utilized satisfactorily with one or more fuselage mounted engines. Stability in the yaw and pitch axes for the aircraft  10  are provided by tail-mounted vertical and horizontal stabilizers  10 - 4 ,  10 - 5 , respectively. 
     As is conventional, the aircraft fuselage  10 - 1  is provided with forward and aft cargo compartments  10 - 1   a ,  10 - 1   b  which are accessed respectively by one or more cargo compartment doors (not shown). Respectively positioned within these forward and aft cargo compartments  10 - 1   a ,  10 - 1   b  are a forward fuel tank system  100  and an aft fuel tank system  200  each having a number of individual tanks  102 ,  202 , respectively. Each of the individual tanks  102 ,  202  comprising the forward and aft fuel tank systems  100 ,  200 , respectively, are most preferably sized and configured to allow for passage through the forward and aft cargo compartment doors for removable positioning within the forward and aft cargo compartments  10 - 1   a ,  10 - 1   b , respectively. Of course, if desired the forward and aft fuel tank systems  100 ,  200  respectively, may be more permanently mounted to the aircraft fuselage structure. 
     The forward and aft fuel tank systems  100 ,  200 , respectively, are operably interconnected to the aircraft&#39;s on-board fuel system FS including, for example, the main aircraft fuel tank system  10 - 6  (e.g., the aircraft&#39;s wing fuel tanks  10 - 2   a  and their associated pumps, conduits, level sensors and the like) and the fuel management system (FMS)  10 - 7  (e.g., the cockpit mounted fuel management instruments, monitors and/or controllers operably coupled to the main aircraft fuel tank system). Interconnection to the on-board fuel management system FMS allows the fuel contained within the forward and aft tank systems  100 ,  200 , respectively, to be monitored and transferred to the aircraft&#39;s main fuel tanks as may be appropriate during the flight to ensure that an adequate supply of fuel is provided to the engines  10 - 3 . 
     Accompanying  FIGS. 2-6  depict in greater detail the structural components of the forward tank system  100 . As shown therein, the tank system  100  comprises a series of adjacently mounted tanks  102  forming a tank row generally extending along the longitudinal axis of the aircraft  10 . The tanks  102  are depicted in dashed line in the accompanying drawing  FIGS. 2-6  for the purpose of enhancing visibility of the various tank components to be discussed in greater detail below. It will also be observed that a few of tanks  102  in the forward tank system  100  are of lesser internal volume (identified in  FIG. 2  as the tanks in the series  100   a ) as compared to the remainder of the tanks  102  rearwardly thereof (identified in  FIG. 2  as the tanks in the series  100   b ). Such a size (and hence internal fuel capacity) difference is to allow the tanks to be positioned within the cargo hold adjacent to other aircraft structures and components (e.g., the retracted nose gear) while yet maximizing the available fuel capacity provided by the forward tank system  100 . 
     It will be understood that the particular size and/or shape of the individual tanks employed in either the forward or aft tank systems  100 ,  200 , respectively, is not critical. As such, virtually any size and/or shape of tank may be provided to be accommodated within a variety of aircraft fuselages. As will be understood from the following discussion, therefore, even though one or more of the individual tanks within the forward and/or aft tank systems  100 ,  200 , respectively, may have a different size and/or shape, they will nonetheless possess similar structural subassemblies and functional attributes. 
     Adjacent pairs of the fuel tanks  102  are interconnected to one another by intercommunication conduit assemblies  104  which include an intercommunication manifold conduit  104 - 1  positioned exteriorly of the tanks  102 . The conduit  104 - 1  will have one end fluid connected to an inlet conduit  104 - 2  and its other end fluid-connected to a discharge conduit  104 - 3 . Each of the conduits  104 - 2  and  104 - 3  is positioned within the internal space of a respective one of the adjacent pairs of tanks  102 . 
     As is perhaps more clearly shown in  FIGS. 5 and 6 , the conduit  104 - 3  is connected at its upper end to the manifold conduit  104 - 1  and extends downwardly so its opposite end terminates near the bottom wall of the tank  102 . The conduit  104 - 2  is connected to its upper end to the manifold conduit  104 - 1  and extends into the tank  102  so as to terminate at an inlet opening (preferably flared)  104 - 4  that is in spaced relationship to the upper wall  102 - 1  of the tank  102  by a dimension “H”. The dimension “H” which separates the inlet opening  104 - 4  of the conduit  104 - 2  from the upper wall of the tank  102  will thus predetermine the ullage  102 - 2  within each of the tanks  102 . 
     The fuel tanks  102  are thus fluid-interconnected to one another by means of the intercommunication conduit assemblies  104  so that each of the fuel tanks  102  is refueled in a cascade mode, that is in such a manner that the fuel tank  102  nearest to the wing main fuel tank is refueled first. After the first tank  102  is supplied with fuel via the fuel supply conduit  103 , the fuel will thus flow thus through that intercommunication conduit assembly  104  and into the next fuel tank  102  in series thereby supplying it with fuel. In a successive like manner, all of the fuel tanks  102  in the forward tank system  100  can be supplied with fuel. 
     The tanks  102  also are ventilated in a cascade mode until the last fuel tank  102  in the series (i.e., for the forward fuel tank system  100  this would be the forward-most one of the tanks  102 ) which then provides a vent path via internal vent conduit  105 - 1 . A ventilation conduit  105  external to the tanks  102  is provided and connected to the internal vent conduit  105 - 1  associated with the last tank of the series so as to provide a vent path to the main tank of the wing and/or to a point directly in the fuselage so that the ventilation of fuel vapors is accomplished in an appropriate region within the aircraft (e.g., surge tank of the wing tank). 
     During the fuel transference from the forward auxiliary tanks  102  to the wing main tanks, the fuel is transferred in an inverse sequence of the refueling operation. That is, the fuel tanks  102  are emptied in a reverse order of the refueling. This can be done by several known means, such as fuel pumps, utilizing differential pressure between the aircraft cabin and atmosphere, air bleed from the engine or APU, compressed air, and the like. A fuel transfer conduit  106  is thus only connected to the fuel tank  102  nearest to the main wing fuel tanks and is thus capable of transferring fuel to the wing main tank or alternatively directly to the engines  10 - 3  as may be controlled by valves located within the transfer control boxes  107   a  and  107   b.    
     The aft tank system  200  is generally quite similar structurally and functionally as compared to the tank system  100  described above. Thus, structures depicted in accompanying  FIGS. 7-11  associated with the aft tank system  200  have similar reference numerals as compared to the structures of the forward tank system  100 , except that the reference numerals for the former are in a “ 200 ” series of numbers whereas the reference numerals for the latter are in a “ 100 ” series of numbers. 
     It will be observed that the aft tank system  200  includes a series  200   a  of larger capacity tanks  202  located generally forwardly of the aircraft and a series  200   b  of smaller capacity tanks  202  located generally rearwardly of the aircraft. The tanks  202  are arranged longitudinally adjacent one another generally along the longitudinal axis of the aircraft  10 . A space  200   c  may exist between the series  200   a  and  200   b  of tanks  202  so as to accommodate the control boxes  207   a  and  207   b  associated operatively with the fuel transfer conduit  206 . 
     As with the forward tank system  100 , the adjacent pairs of the fuel tanks  202  of the aft tank system  200  are interconnected to one another by intercommunication conduit assemblies  204  which include an intercommunication manifold conduit  204 - 1  positioned exteriorly of the tanks  202 . The conduit  204 - 1  will have one end fluid connected to an inlet conduit  204 - 2  and its other end fluid-connected to a discharge conduit  204 - 3 . Each of the conduits  204 - 2  and  204 - 3  is positioned within the internal space of a respective one of the adjacent pairs of tanks  202 . 
     As is perhaps more clearly shown in  FIGS. 10 and 11 , the conduit  204 - 3  is connected at its upper end to the manifold conduit  204 - 1  and extends downwardly so its opposite end terminates near the bottom wall of the tank  202 . The conduit  204 - 2  is connected to its upper end to the manifold conduit  204 - 1  and extends into the tank  202  so as to terminate at an inlet opening (preferably flared)  204 - 4  that is in spaced relationship to the upper wall  202 - 1  of the tank  202  by a dimension “H”. The dimension “H” which separates the inlet opening  204 - 4  of the conduit  204 - 2  from the upper wall  202 - 1  of the tank  202  will thus predetermine the ullage  202 - 2  within each of the tanks  202 . 
     The fuel tanks  202  are thus fluid-interconnected to one another by means of the intercommunication conduit assemblies  204  so that each of the fuel tanks  202  is refueled in a cascade mode, that is in such a manner that the fuel tank  202  nearest to the wing main fuel tank is refueled first. After the first tank  202  is supplied with fuel via the fuel supply conduit  203 , the fuel will thus flow through that intercommunication conduit assembly  204  and into the next fuel tank  202  in series thereby supplying it with fuel. In a successive like manner, all of the fuel tanks  202  in the aft tank system  200  can be supplied with fuel. 
     The tanks  202  also are ventilated in a cascade mode until the last fuel tank  202  in the series (i.e., for the aft fuel tank system  200  this would be the aft-most one of the tanks  202 ) which then provides a vent path via internal vent conduit  205 - 1 . A ventilation conduit  205  external to the tanks  202  is provided and connected to the internal vent conduit  205 - 1  associated with the last tank of the series so as to provide a vent path to the main tank of the wing and/or to a point directly in the fuselage so that the ventilation of fuel vapors is accomplished in an appropriate region within the aircraft (e.g., surge tank of the wing tank). 
     During the fuel transference from the aft auxiliary tanks  202  to the wing main tanks, the fuel is transferred in an inverse sequence of the refueling operation. That is, the fuel tanks  202  are emptied in a reverse order of the refueling. This can be done by several known means, such as fuel pumps, utilizing differential pressure between the aircraft cabin and atmosphere, air bleed from the engine or APU, compressed air, and the like. A fuel transfer conduit  206  is thus only connected to the fuel tank  202  nearest to the main wing fuel tanks and is thus capable of transferring fuel to the wing main tank or alternatively directly to the engines  10 - 3  as may be controlled by valves located within the transfer control boxes  207   a  and  207   b.    
     The cascade mode of fluid intercommunication between fuel tanks  102 ,  202  in the tank systems  100 ,  200 , respectively, allows the adoption of only one fluid line between the fuel tanks. This in turn results in a simpler, lighter and more practical system for manufacture, inspection and/or assembly. 
     The fuel system for the transport category aircrafts must comply with various specific requirements, including that the fuel tank be structurally designed considering high longitudinal decelerations. If it is assumed that the fuel tanks are totally full (i.e., without any internal air space), the pressure of the fuel column during a high deceleration could reach 70 psig because the longitudinal length of the forward and/or aft tanks, during high decelerations, would then be in essence the proper fuel column. In this case, the design of the fuel tank would result in a much heavier auxiliary tank system due the structural reinforcements necessary to withstand such increased design pressure loads. As a result of such increased weight, the entire auxiliary fuel tank design project could be jeopardized as unviable. 
     To solve this problem, auxiliary fuel tank systems may employ a variety of overpressure safety components, such as check valves, swing valves and/or restrictors of all types between each fuel cell to reduce the entire fuel column of all tanks aligned during high decelerations to a single column equivalent to the unique cell. Such techniques are not however ideal solutions to the problem because the components required in such a design present hidden failure possibilities. That is, the flight crew is not provided with any indication about the integrity of the components. This characteristic could therefore adversely affect the reliability and dispatch readiness of the aircraft due the frequent physical inspections that these types of components would require. 
     Another solution to this problem is the use of shut off valves in each fuel cell to control the refueling and transfer operations without hidden failures. In such a solution, these types of valves may then be electronically monitored with various sensors. However, this prior solution increases the complexity and cost of the auxiliary fuel system to such an extent that it may become unviable for medium and small aircraft due the small fuel tanks that these kinds of aircraft could carry. 
     To solve these problems and to maintain the competitiveness of the auxiliary fuel system product, one preferred embodiment of the present invention provides a means to comply with these requirements. Specifically, according to a preferred embodiment of this invention, calculated air volumes are provided intentionally inside at least some or each one of the fuel cells so that during a high deceleration event, the air volumes are available to physically damp the fuel column pressure of the respective cells. In such a manner, therefore, the magnitude of the fuel pressure column may be maintained at a value lower than that which would be reached without such air volumes as depicted in accompanying  FIGS. 12 and 13 . Such a configuration can thus be provided so that the pressure in each fuel tank  102  ( 202 ) is optimally not greater than the pressure that is equivalent to the length of that particular fuel tank  102  ( 202 ). This design flexibility allows that the structures of the fuel tanks can be optimized, with the beneficial consequence being that the fuel tanks can be structurally lighter. 
     Another advantage is that conventional overpressure safety components and/or shut-off valves between the fuel cells are not necessarily required thereby eliminating their attendant hidden failure modes and increasing the dispatch reliability and availability of the aircraft. 
     The air volumes can be induced in all or only some of the tanks  102  ( 202 ) in the series of tank systems  100  ( 200 ), respectively, by the controlled design of the height “H” between an open-ended extremity  104 - 4  ( 204 - 4 ) of the internal conduits  104 - 2  ( 204 - 2 ) and the top walls  102 - 1  ( 202 - 1 ) of each of the tanks  102  ( 202 ), respectively (see  FIGS. 6 and 11 ). In this regard, the greater the dimensional height (i.e., the dimension “H” in  FIGS. 6 and 11 ), the greater will be the stored air volume within the fuel tank  102  ( 202 ). This characteristic thereby allows equal or different air volumes of ullage  102 - 2  ( 202 - 2 ) to be provided in each fuel tank  102  ( 202 ), respectively, by the predetermined setting of the necessary distance between the open-ended extremity  104 - 4  ( 204 - 4 ) within each fuel tank  102  ( 202 ) the internal top wall of such fuel tank  102  ( 202 ). For example, as shown in  FIG. 12 , the distance between the open-ended extremity  104 - 4  ( 204 - 4 ) of the internal conduits  104 - 2  ( 204 - 2 ) and the top walls  102 - 1  ( 202 - 1 ) of each of the tanks  102  ( 202 ) is unequal and increasingly lesser (relative to the aft direction of the aircraft  10  in flight) distances H 1 , H 2  and H 3 , respectively. 
     Each air volume ullage  102 - 2 ,  202 - 2  can thus be optimized. An example for how optimize the air volume ullage  102 - 2 ,  202 - 2  within each fuel tank  102 ,  202 , respectively, can be determined as follows:
         1. Define the capacity of the auxiliary fuel tanks;   2. Define the maintenability, costs, dispachability, market and customer requirements (eventually other requirements can be added or eliminated);   3. Make a conceptual design of the auxiliary fuel system;   4. Calculate the pressure drop of the intercommunication lines;   5. Determine the preliminary definition of how much ullages will be necessary to be left in some modules or in all of them;   6. Considering the structural limits of the each tank, loads of acceleration and deceleration, pressure drop of the intercommunication lines and the requirements, the ullages can be optimized for damping the fuel column during the high acceleration or decelerations; and   7. With the definition of how much ullage will be necessary in each module, the design of the intercommunication conduits can be reviewed to assure that the portion of air inside the fuel tanks can be assisted.       

     The steps 4 to 7 above should be repeated until the all ullages inside each module accomplish all of the defined requirements until the final design can be released. 
     According to the description above, the various embodiments of the present invention will advantageously provide a number of benefits. For example, damping ullage air may be applied in one or more fuel tank modules to comply with load requirements without necessarily using conventional overpressure safety components such check valves, baffle valves, shut off valves, and the like. Damping ullage air may be applied in one or more fuel tank modules to comply with any type of longitudinal, transversal or vertical load requirements without necessarily using conventional overpressure safety components such as check valves, baffle valves, shut off valves, and the like. In addition, damping ullage air may be applied in one or more tank modules for fuel or any kind of liquid (water, waste and the like), to comply with any type of longitudinal, transversal or vertical load requirements in an aircraft without necessarily using conventional overpressure safety components as described above. 
     While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.