VMCG vs VMCA
in regards to VMCG vs VMCA on the B744, here is the way it was explained to me during an interview prep course: (i am in no way and aerodynamics expert, but it made sense to me)
VMCG on the 744 (and some other A/C) is higher than VMCA because:
VMCG has to do with controllability on the ground - therefore the effective rudder moment is between the tail and the main gear.
VMCA = in the air, so you have an effective rudder moment between the tail and your CofG.
because the rudder moment between the tail and CofG is longer than that between the tail and the main gear on the ground, your rudder will be more effective in the air, therefore VMCA will be lower than VMCG.
does that sounds right?