Vmu
Minimum Unstick speed is the lowest calibrated airspeed at and above which the aircraft can safely lift off the ground and continue the take off without encountering critical conditions.
不但要考虑机尾擦地，还要考虑翼尖和发动机擦地的情况

Vmcg
Minimum Control speed on Ground, from which a sudden failure of the critical engine can be controlled by use of primary flight controls only, the other engine remaining at take off power.
水平方向上,飞机必须被控制在跑道中线30Ft以内。
Vmca
Minimum Control speed in the Air at which aircraft can be controlled with a 5° maximum bank angle and no heading change.