VEHICLE FUEL SYSTEM

[00011 This patent application is related to and claims the priority benefit of U.S.

Provisional Patent Application No. 60/859,243, filed November 16, 2006, entitled "WICKING PICCOLO TUBE FOR AIRCRAFT FUEL SYSTEM BLADDER," the entirety of which is hereby incorporated by reference.

TECHNICAL FIELD

[0002] This patent application relates generally to vehicle fuel systems and more particularly to fuel systems having fuel pickup and/or air/fuel vapor venting devices.

BACKGROUND [0003] UAVs and other aircraft typically include a fuel system that includes a fuel bladder for holding fuel. The fuel bladder can be located, for example, within the hollow wings of the UAV. The fuel system also typically includes one or more fuel pickups located within the bladder. The fuel pickup transports the fuel inside the bladder to transfer lines located outside of the bladder. The transfer lines transfer the fuel to downstream components, such as a fuel pump or fuel filter, and the fuel is ultimately delivered to an engine.

[0004] As the engine consumes the fuel contained in the fuel bladder, the air/fuel ratio inside the bladder increases. As the air/fuel ratio reaches high levels (e.g., greater than 1 : 1), the chances of air or fuel vapor ingestion increases. Vaporized fuel in the system can result, for example, from vaporized fuel present in a closed fuel system. Air can enter the fuel system, for example, due to improper fueling procedures, or leaking fuel line connections or fittings.

[0005J When the engine ingests air or fuel vapor, it typically stalls. With conventional fuel pickups, the engine often stalls due to air and/or fuel vapor ingestion prior to consumption of all of the fuel contained in the fuel bladder. As a result, the run time of the engine is unduly shortened. [0006] Additionally, closed (i.e., unvented) fuel systems conventionally rely on the integrity of the vacuum created and maintained within sealed containers or collapsible bladders to prevent the intrusion of air and/or vapor into the system. Such systems generally do not provide countermeasures to remove internally generated fuel vapor and/or air that enters due to improper fueling or leaks. Accordingly, the total volume of air and/or fuel vapor inside the various components (e.g., fuel bladders, tanks, lines, etc.) of a closed system can reach critical

levels capable of progressing through the fuel lines into the engine and thereby inducing engine- seizure.

[0007] In contrast, open (i.e., vented) fuel systems typically incorporate a mechanism that allows the removal of undesirable air or fuel-vapor from the fuel lines. Such mechanisms, however, are usually independent from the system fuel sump and are not electronically controlled or modulated based on system conditions. Furthermore, the mechanism may not typically be located immediately before the engine and significant distance between the mechanism and the engine can allow for the intrusion of air through leaks or poorly sealed connections, or additional fuel vapor generated in the lines subsequent to the mechanism, thereby obviating the advantages of an open system.

SUMMARY

[0008] Embodiments of the present invention may use the capillary transport properties of a wicking material to increase the amount of fuel that can be reliably drawn by a fuel pickup prior to engine seizure or fuel starvation, even in the presence of excessive ratios of air to fuel (e.g., greater than 1 :1), and despite variations in temperature, altitude, and orientation.

The wicking material can be associated with the fuel pickup and can have numerous microporous conduits that extend within a fuel container. For example, in the case of a fuel bladder located within the wing of an UAV, the fuel bladder and the wicking material located therein can extend across nearly the entire span and chord of the wing. The wicking material expands the accessible fuel region within the bladder to nearly any location within the bladder that the wicking material contacts. As a result, the proportion of fuel within the bladder that is consumed prior to engine seizure or fuel starvation is increased.

[0009] According to an exemplary embodiment, a fuel pickup may include a fuel pickup tube including a plurality of holes for receiving fuel from inside a fuel container; and a wicking material enveloping at least one of the plurality of holes.

[00010] According to another exemplary embodiment, an aircraft fuel system may include a fuel container; a fuel pickup tube located in the fuel container; and a wicking material located in the fuel container and contacting at least a portion of the fuel pickup tube. [00011 J According to yet another exemplary embodiment, an aircraft fuel system may include an aircraft wing defining a hollow interior; a fuel container located in the hollow

interior; and a fuel pickup located in the fuel container, the fuel pickup comprising a wicking material.

[00012] In another exemplary embodiment of the present invention, a fuel sump and a vehicle fuel system having such a fuel sump are disclosed. [00013] According to yet another exemplary embodiment, a fuel sump may include a pressurized vessel and at least two sensors configured to detect a level of fuel within the vessel. A valve coupled to the vessel may be configured to release air and/or fuel vapor to the atmosphere. The fuel sump may also include a programmable electronic controller configured to modulate the valve between a closed position and an open position based on signals received from the at least two sensors corresponding to the fuel level. The valve may be configured to remain in the closed position until the fuel level drops below a predetermined level and the controller sends a signal to open the valve to release air and/or fuel vapor from the vessel into the atmosphere.

|00014| hi another exemplary embodiment of the present invention, a vehicle fuel system may include a fuel bladder and an engine having an intake. The fuel system may include a fuel sump with a pressurized vessel having a fuel inlet coupled to the fuel bladder and a fuel outlet coupled to the engine intake. The fuel sump may include at least two sensors configured to detect a level of fuel within the vessel and a valve coupled to the vessel. The fuel sump may also include a programmable electronic controller configured to modulate the valve between a closed position and an open position based on signals received from the at least two sensors corresponding to the fuel level. The valve may be configured to remain in the closed position until the fuel level drops below a predetermined level and the controller sends a signal to open the valve to release air and/or fuel vapor from the vessel into the atmosphere.

[00015] In still another exemplary embodiment of the invention, a vehicle fuel system may be provided which may include a fuel container and a fuel pickup located in the fuel container. The fuel pickup may include a fuel pickup tube including a plurality of holes for receiving fuel from inside the fuel container, and a wicking material enveloping at least one of the plurality of holes. The vehicle fuel system may further include an engine having an intake and a fuel sump. The fuel sump may include a pressurized vessel having a fuel inlet coupled to the fuel container and a fuel outlet coupled to the engine intake. The fuel sump may include at least two sensors configured to detect a level of fuel within the vessel and a valve coupled to the

vessel. A programmable electronic controller may be configured to modulate the valve between a closed position and an open position based on signals received from the at least two sensors corresponding to the fuel level. The valve may be configured to remain in the closed position until the fuel level drops below a predetermined level and the controller sends a signal to open the valve to release air and/or fuel vapor from the vessel into the atmosphere.

[00016] Further features and advantages of the invention, as well as the structure and operation of various embodiments of the invention, are described in detail below with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[00017] The foregoing and other features and advantages of the invention will be apparent from the following, more particular description, as illustrated in the accompanying drawings wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. [00018] FlG. 1 is a perspective view of an exemplary fuel pickup;

[00019] FIGS. 2A-2C depict exemplary embodiments of a fuel pickup tube wrapped in a wicking material, shown schematically and in cross-section;

[00020] FlG. 3 is a top view of three exemplary embodiments of a fuel pickup tube wrapped in a wicking material; [00021] FIG. 4 is a perspective view of an exemplary embodiment of a fuel pickup tube attached to a wicking material;

[00022] FlG. 5 is a top, schematic representation of an exemplary aircraft wing enclosing a fuel bladder in conjunction with a fuel pickup tube and wicking material, wherein the wing is shown with its top sheet removed to permit viewing of components inside the wing; [00023] FlG. 6 is a schematic, cross-sectional view of FlG. 5, taken along lines VI-VI of FIG. 5;

[00024] FIG. 7 is a graph indicating the amount of fuel volume remaining in a fuel bladder after first engine shutoff for various exemplary configurations of a fuel pickup, wherein the fuel bladder is oriented at -5° pitch attitude during the engine run;

[00025] FIG. 8 is a graph indicating the amount of fuel volume remaining in a fuel bladder after first engine shutoff for various exemplary configurations of a fuel pickup, wherein the fuel bladder is oriented at +10° roll during the engine run;

[00026] FIG. 9 depicts a schematic view of a fuel sump according to an exemplary embodiment of the present invention;

[00027] FIG. 10 depicts another schematic view of the fuel sump of FIG. 9 when the fuel sump is completely full of fuel;

[00028] FIG. 1 1 depicts another schematic view of the fuel sump of FIG. 9 when the fuel sump is partially full of fuel; [00029] FIG. 12 depicts another schematic view of the fuel sump of FIG. 9 when the fuel level in the sump is at a critical level and air and/or fuel vapor is vented from the sump; and

[00030] FIG. 13 depicts a schematic view of a fuel system including a fuel sump according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION

[00031] Various exemplary embodiments of the invention are discussed in detail below. In describing embodiments, specific terminology is employed for the sake of clarity.

However, the invention is not intended to be limited to the specific terminology so selected.

While specific embodiments are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations can be used without departing from the spirit and scope of the invention.

[00032] In the following description of certain embodiments of the invention, directional words such as "top," "bottom," "upwardly," and "downwardly" are employed by way of description and not limitation with respect to the orientation of the apparatus and its various components as illustrated in the drawings. Similarly, directional words such as "axial" and

"radial" are also employed by way of description and not limitation.

Exemplary Definitions

[00033] In describing the invention, the following definitions are applicable throughout (including above).

[00034| A "computer" may refer to one or more apparatus and/or one or more systems that are capable of accepting a structured input, processing the structured input according to prescribed rules, and producing results of the processing as output. Examples of a computer may include, e.g., but not limited to: a computer; a stationary and/or portable computer; a computer having a single processor, multiple processors, and/or multi-core processors, which may operate in parallel and/or not in parallel; a general purpose computer; a special purpose computer; a supercomputer; a mainframe; a super mini-computer; a mini-computer; a workstation; a microcomputer; a server; a client; an interactive television; a web appliance; a telecommunications device with internet access; a hybrid combination of a computer and an interactive television; a portable computer; a tablet personal computer (PC); a personal digital assistant (PDA); a portable telephone; application-specific hardware to emulate a computer and/or software, such as, for example, but not limited to, a digital signal processor (DSP), a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), an application specific instruction-set processor (ASIP), a chip, chips, and/or a chip set; a system on a chip (SoC), or a multiprocessor system-on-chip (MPSoC); an optical computer; a quantum computer; a biological computer; and/or an apparatus that may accept data, may process data in accordance with one or more stored software programs, may generate results, and typically may include input, output, storage, communications, arithmetic, logic, and/or control units, etc.

[00035| "Software" may refer to prescribed rules to operate a computer. Examples of software may include, for example, but not limited to: software; code segments; instructions; applets; pre-compiled code; compiled code; interpreted code; computer programs; and/or programmed logic. Detailed Description of Some Exemplary Embodiments

[00036] Referring to FIG. 1, an exemplary fuel pickup tube is shown generally as reference number 10. Fuel pickup tube 10 may be of the type typically referred to in the art as a "piccolo tube," although other configurations are possible. As shown in FIG. 1 , fuel pickup tube 10 can comprise an elongated section of tubing 12 including one or more openings 14 for taking up fuel, for example, from a fuel container. The openings 14 may be of various shapes and sizes, and may be located along the length of the tubing 12, as well as at the terminal end of the tubing 12. As also shown in FIG. 1 , fuel pickup tube 10 can include a fitting 16 located at one end, for example, a threaded connector or a quick-connector. Fitting 16 can connect fuel pickup

tube 10 to downstream hoses, etc., to facilitate fuel delivery, for example, to an aircraft engine. According to an exemplary embodiment, fuel pickup tube 10 may include a RQ-7B piccolo tube _^ having a length of approximately 35 inches, an outer diameter of approximately 1/8 to 1/2 inches, and holes spaced approximately 2 to 3 inches apart, although other configurations are possible. As shown in FIG. 5, for example, and discussed in more detail below, pickup tube 10 can be located within a fuel container 50 that may be located, for example, in the wing of an aircraft, such as a UAV. Fuel pickup tube 10 is not limited to the circular and/or oval cross- sectional shape and configuration shown. For example, fuel pickup tube 10 can alternatively have a square, triangular, polygonal or other cross-section. Additionally or alternatively, fuel pickup tube 10 can be curved or bent. Fuel pickup tube 10 can be flexible or rigid.

[00037] Referring generally to FIGS. 2-4, a wicking material 20 can be associated with fuel pickup tube 10, for example, to increase the amount of fuel that can be reliably drawn up by an engine connected to the fuel pickup tube 10 prior to engine seizure or fuel starvation. The fuel pickup tube 10 can exploit the capillary transport abilities of the wicking material 20 (e.g., both in static equilibrium and across a pressure gradient), to increase the fuel uptake. Exemplary materials suitable for the wicking material 20 include materials that wick liquids ;against a gravity potential when standing upright. This capillary wicking capacity allows the materials to exploit a pressure gradient across their surface to enhance the delivery of fuel to downstream fuel transfer lines. [00038J According to an exemplary embodiment, the wicking material 20 can have a vinyl composition, and/or can have a microporous molecular structure. The microporous molecular structure can act as conduits to take up fuel across substantially the entire area of the wicking material 20, thereby expanding the accessible fuel region with a fuel container to nearly any location the wicking material 20 contacts. According to an exemplary embodiment, the wicking material 20 may include a saran-based fabric such as, for example, but not limited to, NF-900 Saran-Fabric from Asahi-Kasei America Inc., of New York, NY, USA.

[00039| Referring to the exemplary embodiments of FIGS. 2A-2C, the wicking material 20 can be wrapped tightly around the tubular portion 12 of fuel pickup tube 10, for example, such that the wicking material 20 may conform closely to the outer circumference of the tubular portion 12. As shown in the exemplary embodiment of FIG. 2 A, a single layer 20a of the wicking material 20 can be wrapped completely around the tubular portion 12, and joined

together, for example, with stitches 22 or other fastening structures known in the art. Alternatively, layer 20a can comprise a unitary, tube-shaped piece of the wicking material 20 that is slid over the tubular portion 12 of the fuel pickup tube 10. FIG. 2B is similar to the embodiment of FIG. 2 A, except that it may include two layers 20a, 20b of wicking material 20 wrapped tightly around the fuel pickup tube. FIG. 2C is also similar to the embodiment of FIG. 2A, except that it includes four layers 20a, 20b, 20c, 2Od of wicking material 20 wrapped tightly around the fuel pickup tube. Layering the wicking material can increase the amount of wetted surface area exposed to fuel, for example, during flight, and can increase the fuel retention and wicking potential of the wicking material 20. As a result, layering the wicking material 20 can increase the fuel uptake properties of the fuel pickup tube 10. Based on the specific configuration of the wicking material 20, and its weight, it is expected that the wicking material may add between about 0.2 and about 1.0 pounds to the weight of a fuel system according to an exemplary embodiment.

|00040| Still referring to FIGS. 2A-C, the one or more layers of wicking material 20 can envelope each of the holes 14 in the tubular portion 12 of the fuel pickup tube, including the hole 14 located in the terminal end of portion 12. For example, as shown, the wicking material 20 can be held tightly over each of the holes 14, such that the wicking material may completely cover each of the holes 14 in a flush manner. As a result, any pressure gradient applied to the fuel pickup tube can create a pressure-gradient across the one or more layers of wicking material 20, thereby maximizing the amount of fuel available to the fuel pickup tube 10 by drawing through each of the one or more layers of wicking material 20. Therefore, the wicking material 20 may prevent vapor or air ingestion into an engine and may mitigate fuel system related mishaps. Additional benefits can include water/fuel separation and/or in-tank fuel filtration. The fuel pickup tube 10 and wicking material 20 can be used with closed-loop fuel systems, and/or electronic fuel injection systems (e.g., to provide air- and vapor- free fuel delivery to injectors). According to an exemplary embodiment, the wicking material 20 and/or fuel pickup tube 10 can be retrofitted to existing fuel systems without substantially affecting their configuration and/or operation. For example, a conventional fuel bladder and fuel pickup may be replaced with one described herein. Alternatively, an entire wing containing a conventional system may be replaced with a wing containing a fuel system described herein.

[00041] Still referring to FIGS. 2A-C, the wicking material 20 can include one or more tabs 24 extending along the length of the tubular portion 12 of the fuel pickup tube 10. The tab(s) 24 can comprise a single layer of material folded over on itself, as shown in FIG. 2A, or alternatively, can comprise multiple layers of material folded over upon themselves, as shown in FIGS. 2B and 2C. The tab(s) 24 can extend away from the tubular portion 12 in a radial direction, as shown. The tab(s) 24 can be formed integrally with the one or more layers of wicking material 20, as shown in FIGS. 2A-C, or alternatively, can comprise separate pieces of material attached, for example, by sewing. The tab(s) 24 can act as outward extensions of the wicking material 20 that increase the reach and/or fuel-retention of the wicking material 20 during flight maneuvers, for example, where fuel location is subject to change.

[00042] Referring to FIG. 3, three exemplary configurations of tab(s) 24 are shown in top view. The exemplary embodiment at the top of FIG. 3 may include four intermittent tabs 24 extending along the length of the tubular portion 12 of the fuel pickup tube 10. The tabs 24 are generally evenly spaced apart, and have open spaces located between adjacent tabs 24. The tabbed configuration can allow for wicking of fuel from substantially the entire bladder, while at the same time reducing the volume and weight of the wicking material 20. Reducing the volume of the wicking material 20 can allow for more fuel to be contained in the bladder. Reducing the weight of the wicking material 20 can reduce the overall weight of the fuel system or aircraft. According to an exemplary embodiment, the tabs 24 are approximately two inches wide, extend approximately three inches away from the tubular portion in the radial direction, and are spaced approximately four inches apart from one another. The wicking material 20 in the embodiment at the top of FIG. 3 includes two layers 20a, 20b of wicking material 20 (see FIG. 2B), however, other configurations are possible.

[00043] The exemplary embodiments of fuel pickups shown at the middle and bottom of FlG. 3 each may include a single, uninterrupted tab 24', 24", respectively, that may extend along the length of the tubular portion 12. The embodiment in the middle of FIG. 3 may include a relatively thin tab 24' of wicking material 20 (e.g., 1 to 2" across). The embodiment in the middle of FIG. 3 may also include four layers 20-2Od of wicking material 20 (see FIG. 2C), although other configurations are possible. The configuration at the bottom of FIG. 3 may include a relatively wide tab 24" (e.g., 4" across) and includes a single layer 20a of wicking material 20 (see FIG. 2A), although other configurations are possible. In all three exemplary

embodiments shown in FlG. 3, the wicking material 20 may cover the entire length of the tubular portion 12 of fuel pickup tube 10, including the hole 14 located at the terminal end of tubular portion 12.

100044] Referring to FIG. 4, another exemplary embodiment of the wicking material 20 is shown. According to this embodiment, one or more layers of the wicking material 20 may be formed into a bag 40, and all or part of the tubular portion 20 of the fuel pickup tube 10 extends into the bag 40, for example, through an appropriately shaped hole in the wicking material 20. A portion of the wicking material 20 can be wrapped tightly around all or a part of the tubular portion 12, for example, similar to the exemplary embodiments of FIGS. 2 and 3. Alternatively, all or a portion of the tubular portion 12 can be positioned freely within the bag 40 (e.g., not rigidly connected to the wicking material). According to another exemplary embodiment, the wicking material 20 can be used in place of the tubular portion 12. For example, a truncated tubular portion 12 can abut the bag 40 at its perimeter (e.g., along an edge), and extend only slightly into the bag 40, for example, by approximately Vi to 2 inches, or alternatively, not extend into the bag 40 at all.

[00045] Referring to FIGS. 5 and 6, an exemplary aircraft fuel system located with a portion of an aircraft wing 52 is shown. The fuel system may include a fuel container 50, which can comprise a flexible bladder (as shown), or alternatively, a rigid or semi-rigid container. According to an exemplary embodiment, the fuel container 50 can comprise a block IA bladder supplied by Aero Tec Laboratories, Inc. USA (ATL) of Ramsey, New Jersey, USA, without baffles, although other configurations are possible.

[00046] As shown in FIGS. 5 and 6, the fuel container 50 can be located within an aircraft wing 52, for example, in the hollow region formed between the leading and trailing edges 54, 56, and between ribs 58, 60, although other configurations and arrangements are possible. According to an exemplary embodiment, the size and shape of the fuel container 50 may be constrained only by the interior dimensions of the wing. For example, according to an exemplary embodiment, a flexible fuel bladder 50 can extend across nearly the entire span and chord of the wing 52.

[00047| The fuel container 50 can contain at least a portion of the fuel pickup tube 10, as well as the wicking material 20. The wicking material 20 can be in any of the exemplary configurations discussed above. In the exemplary embodiment of FIGS. 4 and 5, the wicking

material 20 is in the bag-like configuration, according to which embodiment, the bag 40 can define an outer perimeter 42 that is of substantially the same shape and dimensions as the outer perimeter 59 of the fuel container 50, thereby maximizing the area within the fuel container 50 that can be reliably used for fuel uptake. The wicking material 20 can alternatively have the tabbed configurations shown in FIGS. 2 and 3, although, other configurations are also possible, for example, those not including tabs.

[00048] As shown in FIG. 5, the fuel container 50 can include an access hatch 51, to provide access to the fuel pickup tube 10 and/or wicking material 20 located inside the fuel container 50. According to an exemplary embodiment, the access hatch is manufactured by ATL of Ramsey, NJ.

Example

[00049] FIGS. 7 and 8 contain graphs depicting the amount of unused fuel remaining in fuel bladders after first engine kill (cutout) for various fuel systems described herein, as well as for a conventional fuel system. The tests were run using a fully functional Shadow 200 fuel system with fuel flow metering, supplied by ATL Fuel Bladders of New Jersey. For the tests, the fueling and de-fueling procedure replicated those used in the field for UAVs. The fuel container -used in the tests was a Block IA bladder having a volume of approximately 36 Liters, and having no baffles.

|00050) FIG. 7 depicts the amount of fuel remaining in the fuel bladder after first engine kill for a fuel bladder oriented at -5° pitch attitude, and at fuel-to-air ratios of 3: 1 and 1.5:1 for five different configurations. The first configuration, labeled "no wick," did not include the wicking material described herein. For this configuration, approximately 4 liters of unused fuel were left in the bladder after first engine kill, for both 3:1 and 1.5:1 fuel-to-air ratios. The configuration labeled "large wick" included wicking material in the bag-like configuration shown in FIG. 4. For this configuration, approximately 3.8 liters of unused fuel were left in the bladder after first engine kill, for both 3:1 and 1.5: 1 fuel-to-air ratios. The configuration labeled "single layer wick 4" wide" included wicking material in the configuration shown at the bottom of FIG. 3, and in FIG. 2A. For this configuration, approximately 2 liters of unused fuel were left in the bladder after first engine kill, for both 3:1 and 1.5:1 fuel-to-air ratios. The configuration labeled "2 layer wick with tabs" included wicking material in the configuration shown at the top of FIG. 3, and in FIG. 2B. For this configuration, approximately 1 liter of unused fuel was left in

the bladder after first engine kill for the 3:1 fuel-to-air ratio, and approximately 0.7 liters of unused fuel were left for the 1.5:1 fuel-to-air ratio. The configuration labeled "4 layer wick" included wicking material in the configuration shown in the middle of FIG. 3, and in FIG. 2C. For this configuration, approximately 1.6 liters of unused fuel were left in the bladder after first engine kill for both the 3:1 and 1.5:1 fuel-to-air ratios. Thus, for a fuel bladder at a -5° pitch attitude, the presence of the wicking material decreased the amount of unused fuel by up to approximately 3 liters, depending on the configuration of the wicking material and/or the fuel-to- air ratio. NF-900 Saran-Fabric was used for all embodiments.

[00051] FIG. 8 depicts the amount of fuel remaining in the fuel bladder after first engine kill for a fuel bladder oriented at +10° roll, and at fuel-to-air ratios of 3:1 and 1.5:1 for three different configurations. The first configuration, labeled "no wick," did not include the wicking material described herein. For this configuration, approximately 7.6 liters of unused fuel were left in the bladder after first engine kill for the 3:1 fuel-to-air ratio, and approximately 6.6 liters of unused fuel were left for the 1.5:1 fuel-to-air ratio. The configuration labeled "2 layer wick with tabs" included wicking material in the configuration shown at the top of FIG. 3, and in FIG. 2B. For this configuration, approximately 5.1 liters of unused fuel were left in the bladder after first engine kill for the 3:1 fuel-to-air ratio, and approximately 4.4 liters of unused fuel were left for the 1.5:1 fuel-to-air ratio. The configuration labeled "4 layer wick" included wicking material in the configuration shown in the middle of FIG. 3, and in FIG. 2C. For this configuration, approximately 4.4 liters of unused fuel were left in the bladder after first engine kill for the 3:1 fuel-to-air ratio, and approximately 4.0 liters of unused fuel were left for the 1.5:1 fuel-to-air ratio. Thus, for a fuel bladder at +10° roll orientation, the presence of the wicking material decreased the amount of unused fuel by up to approximately 2.5 liters, depending on the configuration of the wicking material and/or the fuel-to-air ratio. NF-900 Saran-Fabric available from Asahi Kasei America Inc. of New York, NY, was used for all embodiments.

[00052] Based on the data shown in FIGS. 7 and 8, and discussed above, it is estimated that the addition of the wicking material to the fuel pickup tube can result in approximately a 3 liter to 6 liter reduction in the amount of unused fuel in the fuel bladder for a bladder having a capacity of 36 Liters. It is expected that this reduction in unused fuel may result in an increase in the engine run times for aircraft. For example, for a Shadow® UAV, available from AAI Corporation of Hunt Valley, Maryland, USA, having a fuel consumption rate

of 6 Liters per hour, extracting an extra 3 to 6 Liters of fuel from the fuel bladder can result in a flight time increase of approximately '/2 to one hour.

[00053] FIG. 9 depicts a schematic view of a fuel sump 110 according to another exemplary embodiment of the present invention. In operation, the fuel sump 110 may provide a "vent-on-demand" feature to selectively remove air and/or fuel-vapor from a fuel system to which the fuel sump 1 10 is connected. This may allow a closed-loop fuel system to operate in conditions where the generation of fuel vapor or the intrusion of air can occur in large enough quantities to induce engine seizure. As shown in FIG. 9, the fuel sump 110 may include a pressurized vessel 112 having a top 114, a bottom 1 16, and a side wall 118 to define an interior volume capable of storing a liquid such as, for example, fuel for direct delivery to an engine (not shown in FIG. 9). The pressurized vessel 112 may also be capable of accumulating air and/or fuel vapor that may be present in the system to which fuel sump 110 is connected. The pressurized vessel 112 may include a fuel inlet 122 and a fuel outlet 124. The fuel inlet 122 may be configured to be coupled to a fuel tank 120 which may be, for example, a collapsible bladder. The fuel outlet 124 may be configured to be coupled directly to the engine intake (not shown in FIG. 9). A pair of sensors 126, 128 such as, for example, optical sensors, may be disposed on -the pressurized vessel 112 and may be arranged to detect a level of fuel within the vessel 112. In the embodiment depicted in FIG. 9, for example, the pair of sensors may include a first (upper) sensor 126 and a second (lower) sensor 128. One of skill in the art will recognize that the sensors could be any of a number of different types of lightweight sensors such as, for example, but not limited to, capacitance or other non-intrusive automotive type sensors. An exhaust valve 130 may be coupled to the vessel 1 12 and may be configured to vent or release air and/or fuel vapor that has accumulated in the vessel 1 12 when predetermined conditions are reached within the vessel 112 as detected by the sensors 126, 128. The exhaust valve 130 may be, for example, a solenoid valve or any other valve that can be activated at a high frequency to allow exhaust without losing pressure in the vessel 112. In one embodiment (not shown), the valve 130 may be connected to a fuel line attached to an aperture in the top 1 14 of the vessel 1 12.

[00054| As shown in the embodiment depicted in FIG. 9, the vessel 112 may define a total unit height measured from the bottom (base) 1 16 up to the top 114. The fuel inlet 122 and the fuel outlet 124 may be positioned along the side wall 1 18 of the vessel 1 12 such that the fuel inlet 122 may be above the fuel outlet 124. In one embodiment, the fuel inlet 122 may be

positioned at approximately 90% of the total unit height of the vessel 1 12 and the fuel outlet 124 may be positioned at approximately 8% of the total unit height of the vessel 112. Similarly, the first and second sensors 126, 128 may be positioned along the side wall 1 18 of the vessel 112 such that the first sensor 126 may be located above the second sensor 128. In the embodiment shown in FIG. 9, the first sensor 126 may be positioned at approximately 85% of the total unit height of the vessel 1 12 and the second sensor 128 may be positioned at approximately 15% of the total unit height of the vessel 112. The first and second sensors 126, 128 may be angularly offset from the fuel inlet and outlet 122, 124 about a central vertical axis (not shown) defined by the vessel 112 so that fuel entering the vessel 112 via the inlet 122 does not inadvertently contact the sensors 126, 128 and cause a false signal to be generated regarding the conditions within the vessel 1 12. In the embodiment depicted in FIG. 9, the inlet 122 and outlet 124 may be located 90° off-axis from the sensors 126, 128 to avoid splashing the sensors 126, 128 with incoming fuel and producing false "wet" signals when the vessel 112 is only partially full.

|00055] FIG. 10 depicts another schematic view of the fuel sump 1 10 of FIG. 9 when the vessel 112 is completely full of fuel (i.e., no air and/or fuel vapor is present in the vessel 12). Each of the first and second sensors 126, 128, as well as the valve 130 are shown as being •electrically coupled to a programmable electronic controller 132. In the depicted embodiment, electrical leads emerging from the sensors 126, 128 and valve 130 may be coupled to the controller 132, which may be a programmable electronic board with an embedded software controller. In general, the programmable electronic controller 132 may be, for example, a computer or other application-specific hardware configured to emulate a computer, and which is capable of receiving input, processing data in accordance with one or more stored software programs, and generating output. The controller 132 may be electrically coupled to the sensors 126, 128 and to the valve 130 by hard-wired connections (e.g., electrical leads or wires, coaxial cable, twisted pair, optical fiber, waveguides, etc.) and/or wireless connections (e.g., radio frequency waveforms, free-space optical waveforms, acoustic waveforms, etc.).

[00056) FIGS. 10-12 depict an exemplary embodiment of the fuel sump 110 in various states depending on the level of fuel within the vessel 112. In any given state, the sensors 126, 128 may output signals to the controller based on the level of fuel in the vessel 112. The controller 132 may receive and process the logical on/off signals from the sensors 126, 128 and may determine the appropriate position of the valve 130 for the particular state detected in the

vessel 112. The controller 132 may include software configured to vary the on/off cycle time of the valve 130 to achieve a pulsed activation that can increase or decrease the time required to expel the volume of air and/or fuel vapor in the vessel 112. An example logic table of the controller 132 is shown below in Table 1 :

Table 1: Solenoid Valve Controller Logic

[00057] In FIG. 10, the vessel 112 is shown as being completely full of fuel, i.e., prior to any air or fuel vapor intrusion into the system. In this state, sensors 126 and 128 may both return signals of "wet" to the controller 132 and the valve 130 remains closed. After time, air and/or fuel vapor may be present in the system and enter the pressurized vessel 112. The air and/or fuel vapor may buoyantly accumulate along a direction perpendicular to the gravity gradient (the top 1 14 in equilibrium flight), thereby displacing the fuel volume. When the vessel .1 12 is partially full of fuel, as shown in FIG. 1 1, the vessel 1 12 may contain some volume of air and/or fuel vapor in addition to the fuel. In FIG. 11, the fuel level shown is sufficient to cover both sensors 126, 128 and, as a result, both sensors 126, 128 may return signals of "wet" to the controller 132 and the valve 130 remains closed. Even when the fuel level drops below the first

(upper) sensor 126 and the controller receives a signal of "dry" from the first (upper) sensor 126, the valve 130 may remain closed so long as the second sensor 128 still returns a signal of "wet".

|00058] As shown in FIG. 12, the air and/or fuel vapor may continue to accumulate in the vessel 1 12 until the displacement of fuel causes the second (lower) sensor 128 to return a "dry" signal to the controller 132, resulting from a loss of fuel covering the sensor 128. At this point, the fuel level in the vessel 1 12 has dropped to a critical level and both sensors 126, 128 may return a signal of "dry" to the controller 132. The controller 132, in turn, may output a signal to the valve 130 to open and air and/or fuel vapor may be vented from the vessel 112 through the valve 130. In an exemplary embodiment in which the valve 130 is a solenoid valve, the signal from the controller 132 may charge the inductor, opening the solenoid valve for an amount of time determined by the controller 132. The positive pressure inside the vessel 1 12 may cause the air and/or fuel vapor to eject through the valve 130, thereby allowing incoming

fuel to fill the evacuated volume of the vessel 112. Fuel may continue to flow into the vessel 112 through the inlet 122 until both sensors 126, 128 are immersed in fuel and return "wet" signals to the controller 132 indicating a full fuel volume within the vessel 1 12. The valve 130 may be controlled to ensure near constant pressure in the vessel 112 (e.g., by pulse width modulated timing of the valve 130). The fuel sump 110 may ensure reliable fuel delivery to a carburetor or injector of an engine at any throttle position.

[00059] As shown in Table 1, failure modes may also be addressed in the controller's logic and safe-guards may be implemented to accommodate different failure modes of the system. The first safe-guard relates to the signals received from the first and second sensors 126, 128. For example, the sensors 126, 128 may be designed to return "wet" signals only when on or in the presence of fuel and "dry" signals only when off or in the absence of fuel. In the event that the first (upper) sensor 126 returns a signal of "wet" and the second (lower) sensor 128 returns a signal of "dry," the controller 132 may recognize that one or both of the sensors 126, 128 are malfunctioning and the valve 130 may default to a closed position. When sensor failure is detected, the valve 130 may be shut off and the system may operate as a closed (unvented) system preventing fuel ejection due to failure. In an embodiment where the fuel sump 1 10 is used in an aircraft fuel system, sealing the valve 130 for the remainder of a flight after detecting a sensor malfunction may prevent the potential release of fuel during flight.

[00060] Another safe-guard may include a time-out sequence in the controller software to prevent the valve 130 from remaining on when receiving false "dry" signals from the sensors 126, 128. This logic may compensate for a possible fault in the sensors 126, 128 that may indicate that the vessel 1 12 is empty when it is actually full of fuel. The controller 132 may place a time-limit on the maximum duration the valve 130 may remain open. The valve 130 may be instructed to close after a maximum time limit that, if reached, indicates a fault exists within the system and the valve 130 may be permanently shutoff. This may return the fuel- system to a closed system with no damage or impact to fuel system performance. In addition, the controller 132 may provide a software warning based on the time and frequency of valve open conditions. In the exemplary embodiment where the fuel sump 1 10 is included in a aircraft fuel system, the operator can receive a return home warning in such conditions. [00061] FIG. 13 depicts a schematic view of a vehicle fuel system 200 incorporating the fuel sump 1 10 according to an exemplary embodiment of the present invention. Fuel may be

initially received and stored in a fuel tank 120 such as, for example, but not limited to, a collapsible bladder. When the vehicle is started, fuel may be drawn from the fuel tank 120 through a filter 202 by a fuel pump 204. A pressure gauge 206 may monitor the fuel pressure at an outlet of the pump 204 and air may be injected via line 207 prior to a pressure regulator 208. The fuel sump 110 may receive the fuel after it has passed through the regulator 208 and may function as substantially set forth above based on the controller 132. That the sump 110 operates aft of a pressure regulator 208 may allow a constant higher than atmospheric internal pressure in the vessel 112. Fuel may be drawn directly from the outlet 124 of the vessel 112 to the intake 211 of an engine 212. The sump 1 10 may be located immediately prior to the engine intake 211 to minimize the possibility of air and/or fuel vapor intrusion between the sump 110 and the engine 212 and allow for maximum effectiveness and efficiency. A pressure gauge 210 may monitor the fuel pressure at the outlet 124. Fuel may return to the tank 120 via return line 214. The ability of the controller 132 to vary the ejection time of air and fuel vapor by varying the open/closed timing of the valve 130 may allow manipulation of the ejection rate of air or fuel vapor. Each component of the fuel system 200 may be lightweight and/or miniature so as to be ideal for use on aircraft.

|00062] One of ordinary skill in the art will recognize that the optimum size, shape, and material of the vessel 1 12 may depend on chosen system characteristics and variables. In one embodiment, the vessel 1 12 may be composed of an acrylic and/or composite material. One of skill in the art will also recognize that additional valves and/or sensors could be employed. [00063] The fuel sump and any fuel system incorporating such a fuel sump may be adapted for use in a closed vehicle fuel system with collapsible bladders and with an Electronic Fuel Injection (EFI) equipped engine. EFI high pressure injectors are generally incompatible with closed fuel systems because the injectors are generally less intolerant to air or vapor, which can cause immediate engine seizure. The exemplary fuel sump described herein may permit the coupling of the two technologies by ensuring clean fuel delivery to the injectors under all conditions.

|00064] The above-described exemplary embodiments may be utilized separately or in combination within a vehicle fuel system. |00065] The exemplary embodiments illustrated and discussed in this specification are intended to teach those skilled in the art how to make and use the invention including the best

way known by the inventors. Nothing in this specification should be considered as limiting the scope of the present invention. All examples presented are representative and non-limiting. The above-described embodiments of the invention may be modified or varied, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.