Aviation Speeds Definitions 1.0

Aviation Speeds Definitions 1.0



Stall speed (Vs):


Minimum flight speed which the aircraft is controllable, it is calculated with the center of gravity as forward as possible, and idle power.

Why a forward center of gravity?

If the center of gravity is in the most forward position the moment made by the rudder is greater, resulting in it is easier to stall

Vs 1g: Stall speed when the plane is subjected to a load factor of 1 g Vs = 0.94Vs 1g

Vm: Maneuver speed Vm = √n Vs. By regulation it must hold a maximum load factor of 2.5(g +) and 1 (g -).


Minimum Control Speed in Ground Vmcg:


Minimum ground speed at which the aircraft can be controlled satisfactorily with the use of the primary aerodynamic controls (rudder) in case of engine failure, assuming:

Critical motor inoperative.

Maximum power.

Maximum take off weight and Cg in the most unfavorable position (rear limit).

Airplane in take off configuration and trimmed for takeoff.

When it is recovered it must not deviate more than 30 feet from the central axis of the runway

Factors that affect the Vmcg

This speed it is different from the others as this one is regulated by the quantity of air that the rudder needs to counteract the yaw effect made by an engine failure.

So the higher the power available is, the stronger the yaw would be, and the more force the rudder need, so we required more speed.

If the power required is big, we will required more power to move the plane, so this would lead in a less strong yaw. What makes that the power required for the rudder drops down, leading in a less speed.


  • If the temperature raises, the density altitude raises  the  power available decreases which means that our rudder does not need as much air and in consequence much power to controlled the plane, for this reason the Vmcg decreases.

           Temperature ↑ DA ↑ Pd ↓ Vmcg ↓


Pressure ↓ ρDA ↑ Pd ↓ Vmcg ↓


  • If the humidity increases, the density decreases resulting in a decrease of the power available. So our rudder does not need as much air and in consequence Vmcg decreases.

           Humidity ↑ ρDA ↑ Pd ↓ Vmcg ↓


  • High stage of Flap provokes the power required is increased, which means that the drag increases, so the yaw will be less powerful ending up in we need less power from the rudder.


Flap ↑ Pn ↑ Vmcg ↓

  • Wind: because the plane behaves like a wind vane. It faces to the wind 

           The windward engine failure : Vmcg ↑

           The leeward motor failure : Vmcg ↓






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