Changing Fuel Tanks

Hi everybody!
Just wondering if there is an easy way to add an extra fuel tank to an existing aircraft. I tried looking in the aircraft.cfg file and adding parameters there, but it didn't seem to take.
Any help would be appreciated.
Dwight
Just wondering if there is an easy way to add an extra fuel tank to an existing aircraft. I tried looking in the aircraft.cfg file and adding parameters there, but it didn't seem to take.
Any help would be appreciated.
Dwight