Both deal with the turning moment created by the rudder offsetting the yawing moment created by asymmetric thrust.
Both speeds are in the least favourable set of circumstances:
eng fail of the critical engine
takeoff thrust on the remaining engines
takeoff flaps
gear up - Vmca
slippery runway - Vmcg
On the B727, the Vmcg is 60 kts, while there is no Vmca, as Vmca is lower than stall speed. Therefore you will stall the aircraft before you will lose control. This may also be the situation on the 747.
Last edited by clear_right; 22nd June 2004 at 03:46.