Fluid quantity sensor systems

An aircraft wing tank system, comprising:

• a fuel tank;
• and
• a fluid quantity sensor system for sensing a fuel quantity in the fuel tank, comprising
• one or more strain sensors configured to be disposed in physical communication with the tank to sense a strain on one or more portions of the tank, wherein the one or more strain sensors include at least a first strain sensor disposed in physical communication with a first portion of the tank, and a second strain sensor disposed in physical communication with the second portion of the tank such that the first strain sensor is configured to sense a strain of the first portion of the tank and the second strain sensor is configured to sense a strain of the second portion of the tank, wherein the first strain sensor and the second strain sensor are positioned such that externally induced stress on a structure 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.

A method of determining a weight of a fluid in a tank, comprising:

• receiving a first optical signal from a first strain sensor disposed at a first location of the tank;
• receiving a second optical signal from a second strain sensor disposed at a second location of the tank;
• 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.