Pressure-based aircraft fuel capacity monitoring system and method

A system for dynamically monitoring an amount of a liquid contained in a tank having a tank bottom, said system comprising:

• a sensor conduit comprising a first fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank proximate the tank bottom;
• a reference conduit comprising a second fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank at a predetermined height above the tank bottom which defines a vertical spacing h between the first fluid-delivery tube open end and the second fluid-delivery tube open end;
• a regulating valve in each of the first and second fluid-delivery tubes exterior of the tank for delivering a substantially constant volume flow of a fluid to the distal open end of each of the first and second fluid-delivery tubes;
• a pressure sensor in each of the first and second fluid-delivery tubes between the regulating valve and the tank for dynamically measuring a current pressure in each of the sensor conduit and the reference conduit
• a controller for receiving the current pressure measurements from the pressure sensors in the first and second fluid-delivery tubes and operable for calculating at least one of the current weight of the liquid contained in the tank as a function of the measured current pressure in the sensor conduit, the density of the liquid contained in the tank as a function of a fraction in which the numerator is a pressure difference between the measured pressures in the first and second fluid-delivery tubes and the denominator is the vertical spacing h, and the current volume of the contained liquid as a function of a fraction in which the numerator is the calculated current weight of the contained liquid and the denominator is the calculated density of the contained liquid;
• and
• a damping structure disposed at the distal open end of at least one of said first and second fluid-delivery conduits, said damping structure comprising a sidewall protectively surrounding said distal open end to shield the distal open end from shifts of the contained liquid.

A method for dynamically monitoring an amount of liquid contained in a tank having a tank bottom, the liquid contained in the tank has a level that bounds free space in the tank above the liquid level, comprising the steps of:

• delivering a fluid into the contained liquid at a constant volumetric rate through a distal open end of a first fluid-delivery tube tat extends from a proximal end exterior of the tank to the distal open end which is located within the tank proximate the tank bottom;
• continuously measuring a first pressure of the fluid being delivered by the first fluid-delivery tube said step of measuring a first pressure comprises measuring a pressure difference between the fluid being delivered by the first fluid-delivery tube and the free space in the tank;
• calculating a weight of the contained liquid in the tank as a function of the measured first pressure;
• delivering the fluid into the contained liquid at a constant volumetric rate through a distal open end of a second fluid-delivery tube that extends from a proximal end exterior of the tank to the distal open end which is located within the tank at a predetermined height above the tank bottom that defines a vertical spacing h between the first fluid-delivery tube open end and the second fluid delivery tube open end;
• continuously measuring a pressure difference between the fluid being delivered by the first fluid-delivery tube and the fluid being delivered by the second fluid-delivery tube;
• calculating a density of the contained liquid in the tank as a function of a fraction in which the numerator is the measured pressure difference and the denominator is the vertical spacing h;
• and
• calculating a volume of the contained liquid in the tank as a function of a fraction in which the numerator is the calculated weight of the contained liquid and the denominator is the calculated density of the contained liquid.

A system for dynamically monitoring a current weight, density and volume of liquid fuel contained in an aircraft fuel tank having a tank bottom, the contained fuel filling the tank to a level that bounds a free space in the tank above the fuel level, said system comprising:

• a sensor conduit comprising a first fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank closely proximate the tank bottom;
• a reference conduit comprising a second fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank proximate the distal open end of said first fluid-delivery tube and at a predetermined vertical spacing h above the distal open end of said first fluid delivery tube;
• a regulating valve in each of the first and second fluid-delivery tubes exterior of the tank for delivering a substantially constant volumetric flow of nitrogen gas though the respective first and second fluid-delivery tube and outwardly from the distal open end of the respective first and second fluid-delivery tube into the fuel contained in the tank;
• a first differential pressure sensor for continuously measuring a pressure difference between the nitrogen gas being delivered by the respective regulating valve through said first fluid-delivery tube and the free space in the fuel tank above the fuel level;
• a second differential pressure sensor for continuously measuring a pressure difference between the nitrogen gas being delivered by the respective regulating valve though said first fluid-delivery tube and through said second fluid-delivery tube;
• and
• a controller connected to said first and second differential pressure sensors and operable for calculating the current weight of the fuel contained in the tank as a function of pressure difference measured by said first differential pressure sensor, for calculating the current density of the fuel contained in the tank as a function of a fraction in which the numerator is the pressure difference measured by said second differential pressure sensor and the denominator is the vertical spacing h, and for calculating the current volume of the fuel contained in the tank as a function of a fraction in which the numerator is the calculated current weight of the fuel contained in the tank and the denominator is the calculated current density of the fuel contained in the tank.

A system for dynamically monitoring a current weight, density and volume of liquid fuel contained in an aircraft fuel tank having a tank bottom, the contained fuel filling the tank to a level that bounds a free space in the tank above the fuel level, said system comprising:

• a sensor conduit comprising a first fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank closely proximate the tank bottom;
• a reference conduit comprising a second fluid-delivery tube extending from a proximal end exterior of the tank to a distal open end located within the tank proximate the distal open end of said first fluid-delivery tube and at a predetermined vertical spacing h above the distal open end of said first fluid delivery tube;
• a regulating valve in each of the first and second fluid-delivery tubes exterior of the tank for delivering a substantially constant volumetric flow of nitrogen gas though the respective first and second fluid-delivery tube and outwardly from the distal open end of the respective first and second fluid-delivery tube into the fuel contained in the tank;
• a first differential pressure sensor for measuring a pressure difference between the nitrogen gas being delivered by the respective regulating valve through said first fluid-delivery tube and the free space in the fuel tank above the fuel level;
• a second differential pressure sensor for measuring a pressure difference between the nitrogen gas being delivered by the respective regulating valve through said first fluid-delivery tube and through said second fluid-delivery tube;
• and
• a controller connected to said first and second differential pressure sensors and operable for calculating the current weight of the fuel contained in the tank as a function of pressure difference measured by said first differential pressure sensor, for calculating the current density of the fuel contained in the tank as a function of a fraction in which the numerator is the pressure difference measured by said second differential pressure sensor and the denominator is the vertical spacing h, and for calculating the current volume of the fuel contained in the tank as a function of a fraction in which the numerator is the calculated current weight of the fuel contained in the tank and the denominator is the calculated current density of the fuel contained in the tank;
• and
• a fuel perturbation damping structure disposed at the distal open end of at least one of the first and second fluid-delivery tubes, said damping structure comprising a sidewall protectively surrounding at least a portion of said distal open end to shield the distal open end from shifts of the fuel contained in the tank.

A method for dynamically monitoring a current weight, density and volume of liquid fuel contained in an aircraft fuel tank having a tank bottom and in which the liquid fuel fills the tank to a level that bounds a free space in the tank above the libel level, comprising the steps of:

• delivering nitrogen gas into the liquid fuel in the tank at a constant volumetric rate though a distal open end of a first fluid-delivery tube that extends from a proximal end exterior of the tank to the distal open end which is located within the tank proximate the tank bottom;
• continuously measuring a first pressure difference between the nitrogen gas being delivered by the first fluid-delivery tube and the free space in the tank;
• calculating the current weight of the liquid fuel in the tank as a function of the measured first pressure difference;
• delivering the nitrogen gas into the liquid fuel in the tank at the constant volumetric rate trough a distal open end of a second fluid-delivery tube tat extends from a proximal end exterior of the tank to the distal open end which is located within the tank at a predetermined height above the tank bottom that defines a vertical spacing h between the first fluid-delivery tube open end and the second fluid delivery tube open end;
• continuously measuring a second pressure difference between the nitrogen gas being delivered by the first fluid-delivery tube and the nitrogen gas being delivered by the second fluid-delivery tube;
• calculating the current density of the liquid fuel in the tank as a function of a fraction in which the numerator is the measured second pressure difference and the denominator is the vertical spacing h;
• and
• continuously calculating the current volume of the liquid fuel in the tank as a function of a fraction in which the numerator is the calculated current weight of the liquid fuel and the denominator is the calculated current density of the liquid fuel.