Patent Application
20050166967
This application relates to copending U.S. patent application Nos. [Attorney Docket Nos. 03004.8113US and 03004.8114US] entitled “Auxiliary Fuel Tank Systems for Aircraft and Methods for Their Manufacture and Use,” filed concurrently herewith and incorporated herein in their entireties by reference.
The following disclosure relates generally to aircraft fuel tank systems and, more particularly, to auxiliary fuel tank systems that can be installed in aircraft fuselages.
Commercial transport aircraft are typically designed to carry a given load of passengers, cargo, or passengers and cargo over a given range. Occasionally, however, the need arises to increase the range of the aircraft to serve other routes. Increasing the range generally requires increasing the fuel capacity of the aircraft.
Another situation in which it may be necessary to increase the fuel capacity of an aircraft occurs when the role of the aircraft changes. For example, some military aircraft may serve as aerial refueling tankers at one point in time and cargo carriers at another. In the refueling tanker role, auxiliary fuel tanks can be installed in the body (i.e., the fuselage) to increase the amount of fuel that can be off-loaded to other aircraft in flight. In the cargo carrier role, the body tanks can be removed to increase cargo capacity. Whether auxiliary fuel tanks are added to increase range or to increase fuel off-load capacity, they should be relatively easy to install and remove so that the aircraft can be quickly changed into the desired configuration.
One known type of auxiliary fuel tank system includes an auxiliary tank installed in a fuselage of an aircraft. The system uses pneumatic pressure to transfer fuel from the auxiliary tank to a center-wing tank of the aircraft. The source of the pneumatic pressure can be cabin air. Alternatively, a supplemental blower system can be used to deliver pneumatic pressure when the cabin air is not sufficient to transfer the fuel. This particular auxiliary fuel tank includes double-wall construction.
Another known type of auxiliary fuel tank system includes a group of three tanks linked together in a fuselage of an aircraft in a cascading fill/empty arrangement. Like the system described above, this system also uses pneumatic pressure to transfer fuel from the auxiliary tanks to a center-wing tank of the aircraft. In this system, however, the separate tanks are filled in sequence with the first tank overflowing into the next and continuing until all the tanks are full. Fuel is transferred out of the tanks in reverse. That is, the last tank empties first and then the next tank until all of the tanks are empty. The first tank in the group to fill is connected to the main fuel system of the aircraft. The last tank in the group to fill is connected to the aircraft vent system and the pressurization source.
A further known type of auxiliary fuel tank system includes a group of three tanks having individual fuel inlet, fuel outlet, and vent manifolds. Each tank includes individual valves to control the inflow and outflow of fuel from the tank. In addition, a single electric motor-driven fuel pump can be installed in each tank for transferring fuel out of the tank. Alternatively, pneumatic pressure from an aircraft bleed air system can be individually provided to each of the tanks for fuel transfer.
Yet another known type of auxiliary fuel tank system includes two or more auxiliary tanks ganged together with slip-together, low-level interconnects that maintain a uniform fuel level across all the tanks. Fuel is added to the tanks via a main fueling manifold of the aircraft. Pneumatic pressure from an aircraft bleed air system is used to flow fuel from the auxiliary tanks into integral aircraft fuel tanks. Venting of the auxiliary tanks is provided via existing aircraft fuel system vents.
A further known type of auxiliary fuel tank system can be found on KC-135 series aircraft. This system uses a number of flexible bladders that are permanently laced into a lower section of the fuselage structure. The bladders include low-level interconnects that allow fuel to migrate from one bladder to the next. An aircraft fueling manifold provides fuel to the bladders for filling. Motor-driven pumps are used to move fuel out of the bladders and return it to the aircraft fuel system or to an aerial refueling system. In this system, the auxiliary tank structure (i.e., the bladder) is single-wall construction.
The present invention is directed generally toward auxiliary fuel tank systems for aircraft and methods for their manufacture and use. A fuel outlet manifold configured in accordance with one aspect of the invention includes a duct and a valve assembly operably coupled to the duct. The duct can include a fuel inlet configured to draw fuel out of a tank. The valve assembly can be configured to at least reduce the flow of fuel through the inlet when fuel in the tank drops to or below a selected level. In one embodiment, the valve assembly can include a valve movably positioned in the duct, and a float operably coupled to the valve. Movement of the float can cause the valve to move between a first position in which the duct is at least approximately open and a second position in which the duct is at least approximately closed.
In another aspect of the invention, the duct is a first duct having a first fuel inlet and the valve assembly is a first valve assembly operably coupled to the first duct. In this aspect, the fuel outlet manifold further includes a second duct and a second valve assembly operably coupled to the second duct. The second duct can have a second fuel inlet configured to draw fuel out of the tank. The second valve assembly can be configured to at least reduce the flow of fuel through the second fuel inlet when fuel in the tank drops to or below the selected level.
In a further aspect of the invention, the duct is a first duct configured to transfer fuel out of a first tank via a first fuel inlet, and the valve assembly is a first valve assembly operably coupled to the first duct. In this aspect, the fuel outlet manifold further comprises a second duct and a second valve assembly operably coupled to the second duct. The second duct can include a second fuel inlet configured to draw fuel out of a second tank body positioned adjacent to the first tank body. The second valve assembly can be configured to at least reduce the flow of fuel through the second fuel inlet when fuel in the second tank body drops to or below a selected level.
In yet another aspect of the invention, a method for providing fuel to at least one of an engine and an aerial refueling manifold on an aircraft includes drawing fuel through a duct having a fuel inlet positioned in an auxiliary fuel tank assembly on the aircraft. The method can further include automatically closing a valve in the duct before fuel in the tank assembly drops below the fuel inlet to avoid ingesting air or other gaseous substances into the duct. In one embodiment, automatically closing the valve in the duct includes mechanically closing a valve by movement of a float operably coupled to the valve.
The following disclosure describes auxiliary fuel tank systems for aircraft and methods for their manufacture and use. Certain details are set forth in the following description and in
Many of the details, dimensions, angles, and other features shown in the Figures 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 invention. In addition, further embodiments of the invention may be practiced without several of the details described below.
In the Figures, identical reference numbers identify identical or at least generally similar elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refer to the Figure in which that element is first introduced. For example, element 110 is first introduced and discussed with reference to
As described in greater detail below, both the forward and aft tank groups 112 and 114 can be operably coupled to an aircraft fuel system 130, an aircraft vent system 132, and a fuel management system (FMS) 134 (all shown schematically in
In another aspect of this embodiment, the forward tank group 112 includes a first master tank assembly 120a and a first end tank assembly 122a. The aft tank group 114 can include a second master tank assembly 120b, a mid tank assembly 121, and a second end tank assembly 122b. In the illustrated embodiment, the mid tank assembly 121 and the end tank assemblies 122 are all “slave” tank assemblies. As described in greater detail below, these tanks are slave tanks because they are filled and drained via equipment positioned in the corresponding “master” tanks 120.
In a further aspect of this embodiment, each of the tank assemblies 120, 121, and 122 is shaped and sized to individually fit through the cargo doors 107 without substantial disassembly. For example, referring to the forward tank group 112, the first master tank assembly 120a is configured to pass through the forward cargo door 107a and be removably positioned proximate to an aft bulkhead 103a in the forward cargo compartment 106. Enough space is provided between the first master tank assembly 120a and the bulkhead 103a so that maintenance personnel can access the interfaces between the forward tank group 112 and the aircraft fuel system 130, the aircraft vent system 132, and the FMS 134. The first end tank assembly 122a is also configured to pass through the forward cargo door 107a, and is further configured to be operably coupled to the first master tank assembly 120a. Referring to the aft tank group 114, the second master tank assembly 120b is configured to pass through the aft cargo door 107b and be positioned proximate to a forward bulkhead 103b in the aft cargo compartment 108. Like the first master tank assembly 120a, the second master tank assembly 120b is spaced apart from the forward bulkhead 103b so that maintenance personnel can access the interfaces between the aft tank group 114 and the aircraft fuel system 130, the aircraft vent system 132, and the FMS 134. The mid tank assembly 121 and the second end tank assembly 122b are also configured to pass through the aft cargo door 107b, and they are further configured to be operably coupled to the second master tank assembly 120b in series.
The number and arrangement of auxiliary fuel tanks positioned in either the forward cargo compartment 106 or the aft cargo compartment 108 can be varied to meet particular range and/or fuel off-load requirements. For example, two auxiliary fuel tanks can be positioned in the forward cargo compartment 106 as illustrated in
In the illustrated embodiment, both the forward tank group 112 and the aft tank group 114 are positioned outside a five-degree rotor burst cone (not shown) of the engines 105 in compliance with applicable regulatory standards. However, the first master tank assembly 120a can be positioned within a broader 15-degree engine rotor burst cone (also not shown). Accordingly, in one aspect of this embodiment, the forward cargo compartment 106 can include shielding if necessary to adequately protect the first master tank assembly 120a from a rotor burst. In addition or as an alternative, the first master tank assembly 120a can include reinforced tank walls to prevent a rupture in the event of a rotor burst. In another embodiment, the proximity of the second master tank assembly 120b to a landing gear system (not shown) of the aircraft 100 may make it susceptible to damage in the event of a landing gear collapse. In such an embodiment, the second master tank assembly 120b can be made smaller than the corresponding slave tank assemblies 121 and 122 to prevent damage to the second master tank assembly 120b in the event of a landing gear collapse.
The auxiliary fuel tank system 110 illustrated in
In a further aspect of this embodiment, the forward tank group 112 includes a fuel system interface 231 configured to be operably coupled to the aircraft fuel system 130 (
The fuel outlet manifold 230 extends into both the master tank assembly 120a and the end tank assembly 122a, and is coupled together by a first tank interconnect 232a bridging the gap between the two fuel tanks. Similarly, the fuel inlet manifold 240 extends into both the master tank assembly 120a and the end tank assembly 122a, and is coupled together by a second tank interconnect 232b. The tank interconnects 232 can provide sealed interfaces between adjacent fuel tanks and corresponding sections of the fuel outlet manifold 230. In one embodiment, they can have double-wall construction and can include telescoping and gimbaling features that accommodate relative misalignment or motion between the fuel tanks.
In yet another aspect of this embodiment, the forward tank group 112 includes a vent system interface 251 configured to be operably connected to the aircraft vent system 132 (
In a further aspect of this embodiment, the forward tank group 112 includes an FMS interface 261 configured to be operably coupled to the FMS 134 (
In a further aspect of this embodiment, many portions of the mid tank assembly 121 are at least generally similar in structure and function to corresponding portions of the end tank assembly 122b. One difference between these two tank assemblies, however, is that a number of extensions can be added to the vent and fuel system manifolds in the mid tank assembly 121 to extend the manifolds for coupling to the end tank assembly 122b. For example, outlet manifold extensions 332a can be added to the fuel outlet manifold 230, and inlet manifold extensions 332b can be added to the fuel inlet manifold 240. Similarly, vent manifold extensions 332c can be added to the vent manifold 250. In addition to the manifold extensions 332, additional tank interconnects 232 are also required to operably couple the mid tank assembly 121 to the end tank assembly 122b.
One feature of embodiments described above and illustrated in
In another aspect of this embodiment, the tank body 225 includes a top access port 453 and a side access port 452. The top access port 453 can include an outer top door 454a and an inner top door 454b. The outer top door 454a can removably cover a corresponding aperture in the outer tank skin 442. The inner top door 454b can be positioned directly below the outer top door 454a, and can removably cover a corresponding aperture in the inner tank skin 441. Removal of the top doors 454 can provide access to the interior of the tank body 225 for inspection or maintenance of one or more of the systems installed within as described in greater detail below.
The side access port 452 can include an outer side door 455a and an inner side door 455b. The outer side door 455a can removably cover a corresponding aperture in the outer tank skin 442. Removal of the outer side door 455a can provide access to a dry bay 458 extending between the outer tank skin 442 and the inner tank skin 441. As described in greater detail below, a number of fuel tank interface controls can be housed in the dry bay 458 so that they can be easily accessed by maintenance personnel if needed when the tank body 225 is full of fuel. The inner side door 455b can be positioned directly inboard of the outer side door 455a, and can removably cover a corresponding aperture in the inner tank skin 441. Removal of the inner side door 455b can provide additional access to the interior of the tank body 225. In a further aspect of this embodiment, the inner tank skin 441 forms a fuel sump 446 extending downwardly from the bottom of the tank body 225. As further described in detail below, use of the fuel sump 446 helps to reduce the amount of fuel remaining in the tank body 225 after draining.
In yet another aspect of this embodiment, the tank body 225 includes a first end wall 443a and an opposite second end wall 443b. In the illustrated embodiment, the end walls 443 have profiles that maximize the available cross-sectional space in the aircraft cargo compartment. Accordingly, in this embodiment, the end walls 443 include beveled corner portions 445 toward the bottom of the tank body 225 that follow the contour of the cargo compartment. As mentioned above, in other embodiments, the tank body 225 can be made smaller and/or narrower to prevent damage during a landing gear collapse. In such embodiments, the beveled corner portions 445 are not required and the end walls 443 can accordingly be rectangular in shape.
In a further aspect of this embodiment, the first end wall 443a includes two fuel outlet apertures 432a, two fuel inlet apertures 432b, and two vent apertures 432c. These apertures are configured to accommodate passage of the fuel outlet manifold 230, the fuel inlet manifold 240, and the vent manifold 250, respectively, described above with reference to
One feature of the embodiment described above and illustrated in
In another aspect of this embodiment, the master tank portion 670 of the fuel outlet manifold 230 is operably coupled to a dual-purpose fuel inlet/outlet manifold 671. The fuel inlet/outlet manifold 671 includes the aircraft fuel system interface 331, and bifurcates into a first branch 673a and a corresponding second branch 673b. Each branch 673 of the fuel inlet/outlet manifold 671 can include an inlet manifold interface 678 (identified individually as a first inlet manifold interface 678a and a second inlet manifold interface 678b). As described below in reference to
In a further aspect of this embodiment, each branch 673 of the fuel inlet/outlet manifold 671 also includes an outlet manifold interface 679 (identified individually as a first outlet manifold interface 679a and a second outlet manifold interface 679b). The first outlet manifold interface 679a can be operably coupled to a corresponding first branch 675a of the master tank portion 670. Similarly, the second outlet manifold interface 679b can be operably coupled to a corresponding second branch 675b of the master tank portion 670. Each branch 675 of the master tank portion 670 can include a pump outlet check valve 676 (identified individually as a first pump outlet check valve 676a and a second pump outlet check valve 676b) operably coupled in series to a fuel transfer pump 672 (identified individually as a first fuel transfer pump 672a and a second fuel transfer pump 672b). Because they are positioned within the inner tank volume of the master tank assembly 120b and exposed to fuel, the fuel transfer pumps 672 of the illustrated embodiment can be hydraulically driven. In other embodiments, such as embodiments in which the fuel transfer pumps 672 are positioned within a dry bay 458 of the master tank assembly 120b, the fuel transfer pumps 672 can be electrically driven.
In yet another aspect of this embodiment, a pump pressure switch 674 is operably coupled to each of the fuel transfer pumps 672 and is accessibly mounted in the dry bay 458. The pump pressure switches 674 can be operably connected to the FMS 134 (
In a further aspect of this embodiment, the basic tank portion 660 of the fuel outlet manifold 230 includes a first fuel inlet duct 661a operably coupled to the first branch 675a of the master tank portion 670 and a second fuel inlet duct 661b operably coupled to the second branch 675b of the master tank portion 670. Each of the fuel inlet ducts 661 can include a corresponding fuel inlet 662 positioned at least generally within the fuel sump 446. As described in greater detail below, in a further aspect of this embodiment, each fuel inlet 662 can include a corresponding shutoff valve assembly 664 configured to close the corresponding fuel inlet 662 before the fuel inlet 662 loses prime, that is, before the fuel level in the tank falls below the fuel inlet 662. Closing the fuel inlet 662 while it is still submerged in fuel can prevent the fuel outlet manifold 230 from ingesting air. This can minimize loss of pump prime when any one of two or more tanks in a tank group empties before one or more of the other tanks in the group. Accordingly, when fuel is no longer available in one of the tanks, the corresponding fuel inlets 662 close to isolate the tank from the others in the group.
In a further aspect of this embodiment, the extension portion 632 of the fuel outlet manifold 230 includes two outlet manifold extensions 332a. Each of the outlet manifold extensions 332a can be operably coupled to a corresponding one of the fuel inlet ducts 661. As described above with reference to
When fuel is being flowed into the master tank assembly 120b through the fuel system interface 331, the pump outlet check valves 676 on the outlet manifold 230 are closed causing the fuel to flow into the inlet manifold 240 (
Referring next to
The shutoff valve assembly 664 is but one type of mechanical shutoff valve that can be used with the fuel outlet manifold 230 to avoid losing prime on one or more of the fuel transfer pumps 672. In other embodiments, other types of shutoff valves can be used. For example, in one other embodiment, an electrically actuated valve can be used. In a further embodiment, a hydraulically actuated valve can be used. In still further embodiments, the shutoff valve assembly 664 can be omitted and, instead, a fuel level sensor can be used to command a valve, such as an electrically actuated valve, to close the corresponding fuel inlet before the fuel level drops below the inlet.
In another aspect of this embodiment, the master tank portion 870 of the fuel inlet manifold 240 includes a first branch 873a operably coupled to the fuel inlet/outlet manifold 671 at the first inlet manifold interface 678a and a second branch 873b operably coupled to the fuel inlet/outlet manifold 671 at the second inlet manifold interface 678b. Each branch 873 of the master tank portion 870 can include a primary fueling valve 872 (identified individually as a first primary fueling valve 872a and a second primary fueling valve 872b) operably coupled in series to a secondary fueling valve 874 (identified individually as a first secondary fueling valve 874a and a second secondary fueling valve 874b). In addition, each branch 873 of the fuel inlet manifold 240 can also include a refuel shutoff pressure switch 891 and a ground fueling solenoid valve 892 positioned in the dry bay 458. The refuel shutoff pressure switch 891 and the ground fueling solenoid valve 892 can be operably coupled between the secondary fueling valve 874 and a corresponding pilot float valve 894. The pilot float valve 894 is configured to command the secondary fueling valve 874 closed when the fuel in the tank rises above the pilot float valve 894, thereby stopping the flow of fuel into the master tank assembly 120b. If desired, the ground fueling solenoid valve 892 can be used to override the pilot float valve 894 and increase the fuel level in the master tank assembly 120b above that normally allowed by the pilot fuel valve 894. The refuel shutoff pressure switch 891 can be configured to send a signal to the FMS 134 (
In a further aspect of this embodiment, the master tank portion 870 of the fuel inlet manifold 240 can also include a solenoid pre-check valve 896 positioned within the dry bay 458. The solenoid pre-check valve 896 can be operably coupled to both of the pilot float valves 894. The solenoid pre-check valve 896 can provide a means for verifying that the pilot float valves 894 are functioning properly. For example, in one embodiment, the solenoid pre-check valves 896 can be commanded through the FMS 134 (
In yet another aspect of this embodiment, the basic tank portion 860 of the fuel inlet manifold 240 includes a first fuel outlet duct 861a operably coupled to the first branch 873a of the master tank portion 870 and a second fuel outlet duct 861b operably coupled to the second branch 873b of the master tank portion 870. In the illustrated embodiment, each of the fuel outlet ducts 861 includes a piccolo tube 862 (identified individually as a first piccolo tube 862a and a second piccolo tube 862b) having a plurality of fuel outlets 863. The fuel outlets 863 distribute incoming fuel into the interior of the master tank assembly 120b.
In a further aspect of this embodiment, the extension portion 832 of the fuel inlet manifold 240 includes two inlet manifold extensions 332b. Each of the inlet manifold extensions 332b can be operably coupled to a corresponding one of the fuel outlet ducts 861. As described above with reference to
To fill the master tank 120b and any corresponding slave tanks (not shown) with fuel, the primary and secondary fueling valves 872 and 874 are opened and fuel is introduced into the fuel inlet/outlet manifold 671 via the fuel system interface 331. From the inlet/outlet manifold 671, the fuel flows past the opened primary fueling valves 872 and the opened secondary fueling valves 874 to the fuel outlet ducts 861. From there, the fuel flows into the master tank assembly 120b from the corresponding piccolo tubes 862. Concurrently, the fuel also flows to any adjoining tanks (e.g., the mid tank assembly 121 and the end tank assembly 122 of
In another aspect of this embodiment, the master tank portion 970 of the vent manifold 250 includes a first branch 971a and a second branch 971b extending outwardly from the vent system interface 251. The basic tank portion 960 of the vent manifold 250 can include a first vent duct 961a operably coupled to the first branch 971a and a second vent duct 961b operably coupled to the second branch 971b. The extension portion 932 of the vent manifold 250 can include two vent manifold extensions 332c. Each of the vent manifold extensions 332c can be operably coupled to a corresponding one of the vent ducts 961. As described above with reference to
In a further aspect of this embodiment, each of the vent ducts 961 includes a first vent port 962a and a second vent port 962b. In the illustrated embodiment, the first vent port 962a remains open at all times, but the second vent port 962b includes a vent float valve 964 configured to close the second vent port 962b if the fuel level rises above the second vent port 962b. The arrangement of the vent float valves 964 can minimize the amount of fuel flowing into the vent manifold 250 as the fuel sloshes around in the master tank assembly 120b.
The basic tank assembly 1190 of
Referring next to
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.
