CS,some of the tanks also have cameras,some are metal and others `plastiqe`/fibreglass,and combinations of.(same with weapons,bombs /rockets)Therefore the `flying characteristics,full/empty have to be determined by `jettison trials` at various airspeeds/manoeuvres in the flight envelope.Even though they may look similar shape /size,their Cof G will determine if they drop clean/roll/tumble/strike the aircraft..