FSX Student
Apparently there is some misunderstanding in the interpretation of MZFW and ZFW : in fact MZFW is a certified weight, and basically is a weight that cannot be exceeded by nothing else than fuel.
ZFW is not a certified weight ; it can be translated as something as ‘dry weight’ or ‘equipped weight’ and is just the weight of a/c, baggages, pilot and passengers but with empty tanks … just before filling it with fuel.
Therefore, you need to know the ZFW in order to know the TOW (which is the ‘loaded weight’ ) , and to verify if it is below the MTOW (which is a ‘certified’ weight) – just add the weigth of the fuel to the ZFW.
Before filling the a/c with fuel, you need as well to know the ‘dry aircraft ’ CG position (in other words: the ‘dry aircraft’ moment) so that, adding fuel, you will be able to verify that the TO CG position (or ‘moment’) is inside the TO GC (or moment) envelope.
Most of the small general aviation aircraft do not have a MZFW - it means that you can mix whatever combination of fuel, pilots and baggages until you remain below the MTOW and inside the TO CG envelope.
Vittorio