Aircraft fuel gauging method using virtual probes
A method of fuel gauging includes the use of limited physical probes and a number of virtual probes that are mathematically represented despite having no physical representation. Each probe determines the volume of fuel in a particular section of the fuel tank. The calculation method includes using the attitude of the fuel tank to calculate the rotation of each physical probe, using this information to determine the height of the fuel at each physical probe, and extrapolating the physical height information to determine the position of each virtual probe. Once the information on each physical and virtual probe is obtained, a total fuel volume can be calculated.
1. A method of fuel gauging for an aircraft, the method comprising:
determining an attitude and an acceleration of a fuel tank;
obtaining measured capacitances from physical probes within the fuel tank;
determining a height of fuel in the fuel tank relative to each of the physical probes using the measured capacitances of the physical probes and the attitude of the fuel tank;
estimating a height of fuel relative to each of a plurality of virtual probes based on the heights of fuel relative to the physical probes and the attitude of the fuel tank; and
determining a total volume of fuel in the fuel tank using the heights of fuel relative to the physical probes, the heights of the fuel relative to the virtual probes, and the attitude of the fuel tank;
wherein determining a height of fuel in the fuel tank relative to each of the physical probes comprises:
calculating a fractional fuel coverage relative to each of the physical probes;
calculating an effective top for each of the physical probes;
calculating an effective bottom for each of the physical probes; and
calculating a height of fuel in the fuel tank relative to each of the physical probes using the fractional fuel coverage, the effective top, and the effective bottom.
2. The method of claim 1 , wherein the physical probes are spaced throughout the fuel tank such that at least one physical probe is always intersected by a surface of the fuel.
3. The method of claim 1 , wherein determining the attitude and acceleration of the fuel tank comprises referencing a default attitude and acceleration for the aircraft.
4. The method of claim 1 , further comprising determining the rotation and the pitch of the physical probes within the fuel tank from the attitude of the fuel tank.
5. The method of claim 1 , wherein the physical probes are each assigned coordinates within the fuel tank, and wherein the assigned coordinates of each probe are used in combination with the measured capacitances of each probe and the attitude of the fuel tank to determine the height of fuel in the fuel tank relative to each of the physical probes, and to estimate the height of fuel relative to each of the plurality of virtual probes.
6. The method of claim 1 , wherein calculating the fractional fuel coverage comprises using the measured capacitance, a dry capacitance, and an active capacitance to calculate the fractional fuel coverage.
7. The method of claim 1 , wherein calculating heights of fuel relative to virtual probes comprises extrapolating the heights of fuel relative to the physical probes to the virtual probe locations.
8. The method of claim 1 , wherein each physical probe is assigned to a zone of the fuel tank, and each virtual probe is assigned a zone of the fuel tank.
9. The method of claim 8 , wherein determining a total volume of fuel in the fuel tank comprises:
inserting the height of fuel relative to each physical probe in to a look-up table to obtain a zone fuel volume corresponding to each physical probe;
inserting the height of fuel relative to each virtual probe in to a look-up table to obtain a zone fuel volume corresponding to each virtual probe; and
adding together the zone fuel volumes corresponding to each physical probe and the zone fuel volumes corresponding to each virtual probe.
10. The method of claim 8 , further comprising determining a fuel mass of the fuel tank by multiplying the total volume of fuel in the fuel tank by a density of fuel in the fuel tank.
11. A fuel gauging system for an aircraft comprising:
a fuel tank containing a plurality of physical probes;
a data concentrator configured to receive signals from the plurality of physical probes;
an avionics system configured to calculate attitude of the aircraft; and
a fuel quality processing unit designed to receive data from the data concentrator and the avionics system, the fuel quality processing unit configured to calculate a total volume of fuel in the fuel tank based on received signals from the plurality of physical probes indicative of the heights of fuel relative to the plurality physical probes, simulated signals from a plurality of virtual probes indicative of the heights of fuel relative to the plurality virtual probes, and the attitude of the aircraft
wherein the fuel quality processing unit is configured to determine a height of fuel in the fuel tank relative to each of the plurality of physical probes by:
calculating a fractional fuel coverage relative to each of the plurality of physical probes;
calculating an effective top for each of the plurality of physical probes;
calculating an effective bottom for each of the plurality of physical probes; and
calculating a height of fuel in the fuel tank relative to each of the plurality of physical probes using the fractional fuel coverage, the effective top, and the effective bottom.
12. The system of claim 11 , further comprising an aeronautical radio configured to communicate between the fuel quality processing unit and the avionics system.
13. The system of claim 11 , wherein the avionics system is configured to calculate attitude based on aircraft bank and tilt.
14. The system of claim 11 , wherein each physical probe and each virtual probe is assigned to a zone of the fuel tank.
15. The system of claim 11 , wherein the physical probes are spaced throughout the fuel tank such that at least one of the plurality of physical probes is always intersected by a surface of the fuel.
16. The system of claim 11 , wherein the physical probes are capacitive probes.
17. The system of claim 11 , wherein the fuel quantity processing unit calculates the total volume of fuel using a model of the fuel tank comprising a plane representing the fuel, the plane calculated from heights of fuel at each physical probe.
18. The system of claim 17 , wherein the plane can be extrapolated to calculate a height of fuel at each virtual probe location.
19. The system of claim 18 , wherein the total volume of fuel in the fuel tank is calculated by summing volumes corresponding to each virtual probe location and each physical probe location, the volumes calculated from the height of fuel at each virtual or physical probe location.
20. The system of claim 11 , wherein calculating the fractional fuel coverage comprises using a measured capacitance, a dry capacitance, and an active capacitance to calculate the fractional fuel coverage.