“Unusable fuel” is an industry-wide phenomenon which affects not just aircraft, but any vehicle with a fuel tank – cars being the most common example. In essence, this is the fuel which forms as puddles inside the tanks in areas which the fuel pump intake valve can't reach. For large aircraft this has meant carrying some excess weight – several hundred kilogrammes could be typical. Not only is this 'dead' weight, but it is also fuel which is not being used to power the aircraft. To tackle this, and to increase the efficiency of its aircraft, Airbus has assembled a dedicated “Sprint" team of engineers with extensive experience from across Airbus. The results from the project are promising: Several proposed solutions could more than halve the amount of unusable fuel. Furthermore, the retrofit solutions would keep costs down by avoiding having to alter any structural components.

Airbus' dedicated “ProtoSpace” innovation facility provided the team with advanced tools and rapid-prototyping equipment, including 'additive layer manufacturing' (ALM) machines to create '3D-printed' test components and models. An example was a full-scale, quarter-size A330 centre fuel tank demonstrator with root-joint and stringers to validate how liquid actually moves around the tank and where the puddles form and explore how fuel can be redistributed to where the pump can extract it. To complement the physical models, digital modelling analysed fluid behaviour inside the wing for different flight phases.