Aviation Speeds

Aviation Speeds

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

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. ( check the definition of critical motor)

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 (everything that affects the available power because it affects the yaw):

           Temperature ↑ DA ↑ Pd ↓ Vmcg ↓




Pressure ↓ ρ ↓ DA ↑ Pd ↓ Vmcg ↓


           So our rudder does not need as much air and in consequence much power to controlled the plane, for this reason the Vmcg decreases .

           Humidity ↑ ρ ↓ DA ↑ Pd ↓ Vmcg ↓


  • High stage of Flap 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 (the factors that affect the power available ).

Flap ↑ Pn ↑ Vmcg ↓


  • Wind: because the plane behaves like a wind vane is approached by the wind

           The windward engine failure (where the wind comes): Vmcg ↑

           The leeward motor failure (where the wind is going): Vmcg ↓

Minimum control speed in the air (Vmca):

  • Minimum flight speed to which the aircraft is controllable assuming (Vmca):

                        Critical motor inoperative (check the definition of critical motor)

                        Operating motor with maximum thrust

                        Maximum take of mass and the Center of gravity at the rear limit

                        Compensated and configured for take-off except the landing gear

                        Maximum rolled is 5 degrees to the operative engine

                        By law all airplanes must accomplish that the Vmca => 120% Vs

Engine failure speed. Vef:

Speed ​​used for calculation effects of the takeoff performances.

Minimum unstick speed. Vmu:

Minimum speed at which the aircraft can take off from the ground and continue the takeoff safetly, not considering the ground effect ( not to crash the tail of the plane into the ground).

Lift off speed Vlof:

Speed ​​at which the wheels of the airplane rise up from ground. It depends on the thrust & weight ratio, Vlof => 1,1Vmu (two engines operative), Vlof => 1,05 Vmu (1 engine operative).

Maximum tire speed. Vmax tire:

The tires are exposed to very high centrifugal forces during the take off run, the manufacturer must ensure that the wheels support them.

It is the upper limit of the Vlof.

Maximum braking speed Vmbe:

When the airplane brakes, all the kinetic forces are absorbed by the brakes, and it is transformed into heat. The faster the plane brakes the hotter it becomes.

It is the upper limit of V1.

Decision speed. V1:

It is the speed at which the pilot decides to continue or perform a rejected take off. If a failure occurs before this speed the pilot must perform a rejected take off, before this speed you have enough runway to stop safely, however if the failure occurs after this speed, the pilot must continue the take off. If the failure occurs at this speed you can decide if continue or rather perform a rejected take off.

Here there is a video showing how to perfrom a rejected take off :

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