Patent Description:
The precise measurement of fuel quantity, used to estimate energy available for operation of the aircraft engines, is valuable for maximizing operational efficiency. The most widely used method utilizes capacitive sensors to measure the height (and thus quantity) of fuel in the tank, combined with a capacitive compensator to measure the variance in fuel dielectric, and a densitometer to measure fuel density. From these three measurements, the fuel mass and energy is estimated.

Another emerging method is a pressure based approach, where the fuel mass is estimated based on measurement of fuel pressure and density. This method utilizes optical sensors, which reduces the amount of electrical energy in the fuel tank as well as accomplishing a similar accuracy measurement as the traditional system, yet with less sensors. Sensor count reduction reduces installation cost and improves safety.

Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved fluid quantity sensor systems. The present disclosure provides a solution for this need.

<CIT> discloses a prior art system according to the preamble of claim <NUM>.

In one aspect, a fluid quantity sensor system for sensing a fluid quantity in a fluid tank is provided according to claim <NUM>.

In another aspect, an aircraft wing tank system is provided according to claim <NUM>.

In another aspect, a method of determining a weight of a fluid in a tank is provided according to claim <NUM>.

Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject disclosure. For purposes of explanation and illustration, and not limitation, an illustrative view of an embodiment of a system in accordance with the disclosure is shown in <FIG> and is designated generally by reference character <NUM>. Other embodiments and/or aspects of this disclosure are shown in <FIG> and <FIG>.

In accordance with at least one aspect of this disclosure, referring to <FIG>, a fluid quantity sensor system <NUM> for sensing a fluid quantity in a fluid tank <NUM> (e.g., fuel in a fuel tank) can include one or more strain sensors 103a, 103b configured to be disposed in physical communication with (e.g., directly or indirectly attached to) the tank <NUM> to sense a strain on one or more portions (e.g., a top, a bottom, one or more sides, etc.) of the tank <NUM>. The system <NUM> can include a weight module <NUM> configured to be operatively connected to the one or more strain sensors 103a, b and configured to determine a strain and/or a weight of a fluid <NUM> in the tank <NUM> based on received strain signals from the one or more strain sensors 103a, b.

In certain embodiments, the weight module <NUM> can include an optical output (e.g., a laser) to interrogate the one or more strain sensors 103a, b (e.g., using a tuned swept laser method, or a broadband response method). The weight module <NUM> can include any suitable optical hardware.

The weight module <NUM> can include weight correlation data (e.g., a map or any other suitable table) configured to correlate the strain with the weight of the fluid <NUM>. The one or more strain sensors 103a, b can be integral with a structure <NUM> forming and/or supporting the tank <NUM>. The structure <NUM> forming and/or supporting the tank <NUM> can be a composite material formed in layers (e.g., a composite airframe). In certain embodiments, the one or more strain sensors 103a, b can be disposed between a plurality layers. Any suitable material for the tank (e.g., metal) is contemplated therein, and the one or more strain sensors can be integrated into the tank structure material in any suitable manner.

Referring additionally to <FIG> and <FIG>, the one or more strain sensors 103a, b can be one or more fiber Bragg grating (FBG) sensors, e.g., as shown. Any other suitable strain sensors (e.g., a Fabry Perot sensor, a foil type) configured to sense strain are contemplated herein.

The one or more strain sensors 103a, 103b can include a first strain sensor 103a disposed in physical communication with a first portion (e.g., a bottom) of the tank <NUM>, and a second strain sensor 103b disposed in physical communication with the second portion (e.g., a top) of the tank <NUM> such that the first strain sensor 103a is configured to sense a strain of the first portion of the tank <NUM> and the second strain sensor 103b is configured to sense a strain of the second portion of the tank <NUM>. The first strain sensor 103a and the second strain sensor103b can be positioned such that externally induced stress on a structure (e.g., a wing, a strut) forming and/or supporting the tank can be cancelled out such that such that a strain caused by only the fluid in the tank can be determined to determine a weight of the fluid in the tank.

In certain embodiments, the first strain sensor 103a can be disposed in an opposite strain location of the second strain sensor 103b. For example, the first portion of the tank 103a can be a gravitational bottom of the tank <NUM>, and a second portion of the tank can be a gravitational top of the tank <NUM>. In certain embodiments, the sensors 103a, 103b can be disposed diametrically opposite from each other (e.g., in the same x-axis and y-axis position on a wing tank, and at different z-axis positions on the wing structure, e.g., as shown).

The weight module <NUM> can be configured to receive strain signals from the first strain sensor 103a and the second strain sensor 103b (e.g., via one or more optical cables <NUM>). The weight module <NUM> can be configured to cancel out externally induced stress on a structure <NUM> (e.g., stress on a wing structure <NUM> in flight) forming and/or supporting the tank <NUM> such that a strain caused by only the fluid <NUM> in the tank <NUM> can be determined to determine a weight of the fluid <NUM> in the tank <NUM>. The weight module <NUM> can include any suitable optical hardware, computer hardware and/or computer software module(s) configured to perform any suitable function(s) (and/or any combination thereof) disclosed herein (e.g., as described above), and/or any other suitable function as appreciated by those having ordinary skill in the art.

In accordance with at least one aspect of this disclosure, an aircraft wing tank system (e.g., system <NUM> as shown in <FIG>) can include a fuel tank (e.g., tank <NUM>), and a fluid quantity sensor system (e.g., system <NUM> as disclosed above) for sensing a fuel quantity in the fuel tank <NUM>. The fluid quantity measuring system can be any suitable system disclosed herein, e.g., as described above. The one or more strain sensors can be integral with a wing structure forming and/or supporting the tank. The wing structure forming and/or supporting the tank can be a composite material formed in layers, wherein the one or more strain sensors are disposed between a plurality layers.

In accordance with at least one aspect of this disclosure, a method of determining a weight of a fluid in a tank can include receiving a first optical signal from a first strain sensor disposed at a first location of the tank and receiving a second optical signal from a second strain sensor disposed at a second location of the tank. The method can include cancelling out externally induced strain on the tank using both the first and second strain signals and determining the weight of the fluid in the tank based on the a remaining strain on the tank determined from the first optical signal and/or the second optical signal. The method can include any other suitable method(s) and/or portion(s) thereof.

Embodiments can use multiple sensors in any suitable position and any suitable strain cancelling methodology, for example. Embodiments can include multiple pairs of sensors, e.g., each in positions that can be correlated to relative strain. Certain embodiments can assume a structure acts as a cantilever, and can cancel out externally induced strain on both top and bottom and be left with only additional strain on the bottom of structure due to weight of fuel.

Embodiments can include an integrated fiber optic strain gauge integrated into a structure that forms tank (e.g., or any wall that forms tank, for example). An optical cable can come out of the structure, e.g., a wing at any desired location (e.g., a wing root). Embodiments can be employed in a wet wing/rigid tank structure, but may also be applicable to a bladder tank.

In certain embodiments, while a strain measurement correlates to a weight of fuel directly, each strain gauge itself or a stiffness of structure can have temperature dependency. As a result, certain embodiments can include a temperature correction module associated with the weight module for correcting for temperature if desired (e.g., using temperature correlation data and a temperature reading from a temperature sensor). Certain embodiments may accept temperature variance and utilize a simple chart correlating strain to weight without a temperature correction.

Embodiments include an alternative strain-based method, which would enable estimation of fuel energy without a need for pressure sensors inside of the tank. Instead, embodiments can utilize fiber bragg-grating strain sensors embedded in the composite structure of the wing to measure the fuel quantity, for example. As aircraft utilize more and more to composite structures, metal wiring and sensors in the wing fuel tanks represent a more challenging problem for lightning protection. Additionally, the installation of sensors into the aircraft fuel tanks can be a high cost aspect of aircraft build on the assembly line. Any methods that can remove sensors from the tank for both safety and cost reasons will have a distinct advantage in the industry.

Embodiments can measure the load in aircraft fuel tanks (or any other suitable fluid in any other suitable tank), by measuring the strain on the tank structure. Different fuel quantities impart different loads on the fuel tank (due to more or less weight). Embodiments can utilize traditional foil strain gages, or with fiber optic strain measurement techniques. Benefits of the fiber optic technique includes the ability to embed the fiber optic sensors into the tank structure, if it is composite, for example. To accommodate loads due to aircraft motion, sensors could be placed in/on the upper and lower surfaces of the tanks, and differential measurement of the sensor sets can eliminate extraneous load factors.

Strain sensing is the practice of measuring a structure's reaction to an applied load. It is a unit-less measurement, because the measure is displacement/length. For instance, if a weight is hung from the free end of a cantilevered beam, the strain along the top of the beam will increase proportionally to the load, as the top elongates. Conversely, if someone pushes upwards on the free end of the beam (e.g., as shown in <FIG>), the strain along the top of the beam decreases proportionally to the load, as the top compresses.

Fiber optic strain sensing can be accomplished by etching a repeating pattern (the fiber bragg grating) over a small section of the optical fiber. The distortion in the fiber medium due to this grating results in a predictable response pattern or frequency from the interrogation method. When the fiber experiences displacement due to an applied strain, the grate pattern changes (elongates or compresses, depending on the applied load) which proportionally changes the interrogation response. Based on the response change, the applied strain can be calculated very accurately, often to less than <NUM>µstrain.

There are two popular interrogation methods for fiber optic sensors. Broadband optical spectroscopy, and tuned swept laser. Embodiments utilizing such fiber optic sensors can utilize either interrogation method, or any other suitable interrogation method, for measuring strain from a fiber-bragg grating. An example response from broadband light interrogation is shown in <FIG>.

Traditional foil based strain gages are notoriously fragile. Unless embedded in a hermetic enclosure, such as a load cell, strain gages are prone to delamination (due to adhesive bond failure), impact damage, and wire de-bonding. A large portion of aircraft fuel storage can be within the wings, where the wing structure itself can act as the fuel tank. Embodiments can include embedded fiber optic strain sensing cables in between the composite fiber layers. This installation method can provide long term reliability of the strain sensors, removing the potential for damage due to maintenance personnel over the life of the aircraft, as well as shielding the strain sensors from other environmental hazards.

Embodiments can measure the reaction of the vessel holding the fuel to the applied load. By embedding strain sensors in the wing structure, the structural reaction can be measured directly, for example. While there are other factors that can impact the measured strain (aircraft flight attitude, variable cargo loads within the aircraft, temperature, etc.), embodiments can provide the capability to compensate for a number of the external factors through a differential measurement. By placing strain sensors in both the upper and lower sections of the wing structure, a differential measurement can remove the common components that influence load across the entire aircraft structure. The load induced by fuel mass can be the majority (if not all) of the remaining generated strain signal between the upper and lower wing structure.

Currently, all production systems use capacitance based height level sensors. Embodiments can remove in tank sensors all together. Any other suitable uses are contemplated herein.

Aspects of this disclosure may be described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of this disclosure. It will be understood that each block of any flowchart illustrations and/or block diagrams, and combinations of blocks in any flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in any flowchart and/or block diagram block or blocks.

Claim 1:
A fluid quantity sensor system (<NUM>) for sensing a fluid quantity in a fluid tank (<NUM>), comprising:
strain sensors (103a, 103b) configured to be disposed in physical communication with the tank (<NUM>) to sense strain on portions of the tank (<NUM>),
wherein the strain sensors (103a, 103b) include at least a first strain sensor (103a) disposed in physical communication with a first portion of the tank (<NUM>), and a second strain sensor (103b) disposed in physical communication with the second portion of the tank (<NUM>) such that the first strain sensor (103a) is configured to sense a strain of the first portion of the tank (<NUM>) and the second strain sensor (103b) is configured to sense a strain of the second portion of the tank (<NUM>);
characterised in that:
the first strain sensor (103a) and the second strain sensor (103b) are positioned such that externally induced stress on a structure forming and/or supporting the tank (<NUM>) can be cancelled out such that a strain caused by only the fluid (<NUM>) in the tank (<NUM>) can be determined to determine a weight of the fluid (<NUM>) in the tank (<NUM>); and
a weight module (<NUM>) is configured to receive strain signals from the first strain sensor (103a) and the second strain sensor (103b) and to cancel out externally induced stress on a structure forming and/or supporting the tank (<NUM>) such that a strain caused by only the fluid (<NUM>) in the tank (<NUM>) can be determined to determine a weight of the fluid (<NUM>) in the tank (<NUM>).