Methods and apparatus for fuel control using inertial measurement data

Methods and apparatus for fuel control systems using inertial measurement data are disclosed. In one embodiment, a method for controlling a fuel flow includes comparing an acceleration condition of the aircraft with a predetermined threshold at which normal fuel fluid characteristics begin to become unpredictable, and comparing the acceleration condition with a time-based acceleration profile for a given flight profile. Next, the method determines whether the aircraft is about to enter a prolonged negative acceleration regime. The method further includes maintaining normal fuel control and, after a predetermined amount of time has passed, initiating an alternate fuel source to the engine.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for controlling fuel delivery to a propulsion system of an aircraft, and more specifically, to methods and apparatus for fuel control using inertial measurement data.

BACKGROUND OF THE INVENTION

During maneuvers and other types of flight conditions, an aircraft propulsion system typically requires varying rates of fuel flow. Fuel control systems have therefore been developed that provide varying fuel flow rates depending upon a variety of inputs, including, for example, those fuel control systems disclosed in U.S. Pat. No. 6,644,009 B2 issued to Myers, U.S. Pat. No. 6,584,762 B2 issued to Snow et al., U.S. Pat. No. 6,568,189 B2 issued to Blot-Carretero et al., and U.S. Pat. No. 4,344,141 issued to Yates.

One conventional fuel control system employs a sump to endure negative gravitational forces. During a long dive when the engine needs to remain powered throughout the end of the dive, the sump fuel volume can become relatively large. Sumps typically are unable to utilize the entire sump fuel volume, resulting in a substantial percentage of the sump fuel volume not being usable. To reduce the unusable portion of the sump fuel volume, alternate fuel storage systems, such as a fuel accumulator, may be employed. This may reduce the overall sump volume required, and therefore, the unusable portion of the sump fuel volume.

Although desirable results have been achieved using prior art fuel control systems, there is room for improvement. For example, the time to switch from the sump to the alternate fuel storage system (e.g. an accumulator) impacts the sizing of both the sump and the alternate system. In order to provide improved design of these components, a need exists for accurate methods and apparatus for determining the point of handover from the sump to the alternate system.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatus for fuel control using inertial measurement data. Apparatus and methods in accordance with the present invention may advantageously provide improved determination of the point of handover from the sump to the accumulator, thereby permitting a fuel system designer to optimize volumetric space by trading off sump and accumulator volume to achieve the optimum arrangement.

In one embodiment, a method for controlling a fuel flow to an engine of an aircraft includes comparing an acceleration condition of the aircraft with a predetermined threshold at which normal fuel fluid characteristics begin to become unpredictable, and comparing the acceleration condition with a time-based acceleration profile for a given flight profile. Next, the method determines whether the aircraft is about to enter a prolonged negative acceleration regime. The method further includes maintaining normal fuel control and, after a predetermined amount of time has passed, initiating an alternate fuel source to the engine.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to methods and apparatus for fuel control using inertial measurement data. Many specific details of certain embodiments of the invention are set forth in the following description and inFIGS. 1–5to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description.

In brief, embodiments of methods and apparatus in accordance with the present invention may provide improved determination of the point of handover from the sump to the alternate fuel storage system (e.g. an accumulator). More specifically, embodiments of the present invention may utilize inertial measurement data in a fuel control system to provide the required fuel to an engine. In a particular embodiment, the fuel control system may be an open loop control system. Embodiments of the present invention may thereby allow the sizes of the fuel sump and the alternate system to be optimized.

FIG. 1is a flow diagram of a method of controlling fuel flow100to an engine in accordance with an embodiment of the present invention. As shown inFIG. 1, the method100includes controlling fuel flow in a normal manner at a block102. At a block104, a determination is made regarding a flight condition of the aircraft. If a normal flight condition106exists, then the method100returns to the block102and continues controlling fuel flow in the normal manner and continues checking the flight condition at the block104.

If a dive condition108is determined at the block104, then the method100uses an inertial measurement unit (IMU) to determine an acceleration condition at a block110. If the acceleration condition (normally approximately 1 gravitational constant g) is greater than (or equal to) a condition112at which normal fuel fluid characteristics begin to become unpredictable, then the method returns to the block102and continues to perform normal fuel control. As shown inFIG. 1, in one particular embodiment, for example, the condition at which normal fuel fluid characteristics begin to become unpredictable at about a 0.2 g condition.

On the other hand, if the acceleration condition is less than (or equal to) the condition at which normal fuel fluid characteristics begin to become unpredictable (e.g. 0.2 g)114, then at a block116, the method100performs a comparison of the IMU data with a time-based g profile118for the given flight profile to determine if this is a momentary g excursion or if the system is actually about to enter a prolonged negative g regime. In one particular embodiment, the time-based g profile118may be extracted from a pre-existing database of IMU data120for a variety of mission profiles.

As further shown inFIG. 1, if the determination of block116indicates that the acceleration condition is not entering a prolonged negative g regime condition122, then the method100returns to block110and continues to perform the IMU acceleration determination. If, however, the determination of block116indicates that the acceleration condition has entered, or is about to enter, the prolonged negative g regime condition124, then at a block126, the method100begins a counting period while maintaining normal fuel control. At a block128, a determination is made regarding whether the counting period has exceeded a predetermined amount of time. If not, the method returns to the block126to continue the counting period and maintain normal fuel control. In a particular embodiment, the predetermined amount of time may correspond to a maximum amount of sump fuel volume to be used.

Once it is determined that the waiting period (e.g. XX seconds) has passed at the block128, then the alternate fuel storage system (e.g. accumulator) is initiated at the block130. In a particular embodiment, this may be accomplished by energizing an accumulator regulator. The accumulator or other alternate fuel storage system may then become the sole fuel source for the engine until completion of the maneuver.

FIG. 2is a graph200of an acceleration versus time profile of an aircraft during a representative dive mission in accordance with an embodiment of the invention. In this embodiment, the graph200shows both a predicted acceleration versus time profile202(shown in lighter line thickness) and actual IMU-measured acceleration versus time data210(shown in heavier line thickness). The IMU-measured acceleration versus time profile210includes a condition at which normal fuel fluid characteristics begin to become unpredictable204during an initial portion of a dive portion206of the dive mission. The acceleration versus time profile210(or the predicted profile202) is representative of a typical time-based g profile used in the comparison with the IMU data in block116of the method100shown inFIG. 1. Of course, a wide variety of different dive mission profiles may be conceived, and the invention is not limited to the specific acceleration versus time profile210shown inFIG. 2.

FIG. 3is a schematic view of a fuel system300in accordance with another embodiment of the invention. In this embodiment, the fuel system300includes a pressurized gas bottle304that provides pressurization to a fuel tank302via a first regulator306. The gas bottle304also provides pressurization to an accumulator308via a second regulator310. The accumulator308is adapted to provide pressurized fuel to an engine311as needed, including, for example, during engine start, or during a dive or other maneuver. The accumulator308has an orifice312to relieve the gas pressure over a long period of time, allowing the accumulator308to be refilled with fuel during the mission prior to a dive. This out-gassing may be used to supplement the pressurization of the fuel tank302.

As further shown inFIG. 3, the fuel system300includes a fuel pump314and a sump316having a surface tension element318. The fuel pump314is used during the normal fuel control portions of the mission, and pulls fuel from the sump316. A first metering valve319may be coupled to the intake of the fuel pump314. One or more isolation valves320and burst discs321are included to prevent fuel migration during storage, and are typically closed only during storage. A first check valve322downstream of the pump314is used to prevent accumulator fuel flow going through the pump314into the tank302. A second metering valve324downstream of the fuel pump314regulates the fuel flow to the engine311. The fuel system300further includes a fill valve326for the fuel tank302, a fill/drain valve328coupled between the accumulator308and the second metering valve324, and a drain330coupled to the sump316. Finally, the fuel system300includes a control system332operatively coupled to one or more of the above-mentioned components (e.g. to the accumulator308and to at least one of the pump314and the sump316), the control system332being adapted to receive input signals from one or more IMU's and to perform methods of controlling fuel flow in accordance with the present invention, including the method100described above and shown inFIG. 1. The fuel system300is one particular embodiment of fuel system that may utilize inertial measurement data to control fuel flow to the engine311in accordance with the present invention.

FIG. 4is a graph400of a percentage of fuel burned as a function of a representative dive mission time402in accordance with yet another embodiment of the invention. As described above with respect toFIG. 2, the condition at which normal fuel fluid characteristics begin to become unpredictable204during the initial stages of the dive portion206of the dive mission is shown. This point204may then be used as a design point for sizing the sump316and the accumulator308of the fuel system300ofFIG. 3. As shown inFIG. 4, once the maximum dive fuel usage and the corresponding time that the vehicle is in the dive portion206(i.e. from the point204to the end of the dive portion206), the sump316can be sized to provide fuel for a predetermined amount of time. Once the sump fuel usage time is determined, the accumulator can be sized to complete the dive portion206. For example, in the embodiment shown inFIG. 4, the sump316is sized to provide 1.0% of the percentage of fuel burned (designated as reference numeral404), and the accumulator308is sized to provide 1.2% of the percentage of fuel burned (designated as reference numeral406).

Embodiments of methods and apparatus in accordance with the present invention may provide improved determination of the point of handover from the sump to the accumulator (or other alternate fuel storage system). Embodiments of the present invention may advantageously allow prediction of the time the sump is used and the time required for the accumulator, thereby permitting a fuel system designer to optimize volumetric space by trading off sump and accumulator volume to achieve the optimum arrangement. Fuel usage may also be optimized since the size of the accumulator can provide a higher percentage of its fuel volume to the engine.

It will be appreciated that embodiments of methods and apparatus in accordance with the present invention may be employed on a wide variety of aerospace vehicles. For example,FIG. 5is a side view of an aircraft500in accordance with another alternate embodiment of the invention. In this embodiment, the aircraft500includes a fuselage502, a pair of wings504, and at least one engine506. The aircraft500further includes a fuel system510that utilizes inertial measurement data in accordance with the present invention. In one particular embodiment, the fuel system510is of the type described above and shown inFIG. 3, and employs the method100of controlling fuel flow as described above and shown inFIG. 1. Of course, it will be appreciated that a variety of alternate embodiments of fuel systems and fuel control methods in accordance with the invention may be conceived.

Furthermore, although the aircraft500shown inFIG. 5is representative of a well-known fighter aircraft, specifically, an F/A-18E Super Hornet manufactured by The Boeing Company, in alternate embodiments, virtually any other type or variety of military and commercial aircraft may be conceived that include apparatus and methods in accordance with the present invention. In alternate embodiments, for example, the aircraft may be a commercial passenger aircraft, including, for example, the 737, 747, 757, 767, and 777 models commercially-available from The Boeing Company. In still other embodiments, the aircraft may be a rotary aircraft, a bomber aircraft, a cargo aircraft, or any type of unmanned aircraft, including those described, for example, in The Illustrated Encyclopedia of Military Aircraft by Enzo Angelucci, published by Book Sales Publishers, September 2001.