Answer: Fuel Tank Switching
Right now the GlobalFlyer fuel system is set on "Auto Mode". Fuel from the wings gravity feeds into the boom tanks, and from there is fed to the tank behind Steve. The engine draws its fuel from the tank behind Steve for use in combustion. When in "Auto Mode" the fuel is taken from one of the 4 main boom tanks, 2 in each boom, and moved into the tank behind Steve. The system will switch between the tanks automatically every time 50lbs of fuel is burned.