CG vs Fuel (kg) 737NG
For those interested here is the effect on MAC% when fuel is being added/used by the aircraft.
As clearly can be seen, from empty (0%) the centre fuel addition moves MAC rearwards to -9% then the centre fuel moves the MAC forwards up to +11%.
On the BBJ where AUX tanks are fitted an additional parallelogram is added to the 21 tons above the centre fuel amount to take these variable configuration tanks into account.
The result of the AUX fuel can easily take the MAC out of limits for the aircraft thus care must be given to how much in which tank and where the hold capability is used as the aircraft operates in the envelope higher than where many airlines publish their maximum weight, in an area than is confined by approximately 4% MAC between forward and aft limit at MTOW.