Vmcg, Vmca, Vmcl, Vmu, Vlof, Vr Speeds Explained!

Vmcg – Ground Minimum Control Speed

Vmcg is the calibrated airspeed during the take-off run at which if critical engine fails, it is possible to maintain control of aeroplane with use of primary aerodynamic controls alone (rudder) to enable safe takeoff. In determination of Vmcg it considered that recovery will be done on a path parallel to center line within maximum deviation of 30ft laterally either side.

When an engine fails, the remaining engine continues to generate thrust, causing the aircraft to yaw towards the failed engine side. The amount of yaw is directly related to the thrust produced by the live engine. The only aerodynamic surface available to counteract this yaw and control the aircraft’s direction is the rudder.

The minimum airflow speed over the rudder required to maintain directional control is known as Vmcg (minimum control speed on the ground). If an engine fails below this speed, there is insufficient airflow over the rudder to counteract the asymmetric yaw, making it impossible to continue the takeoff safely.

The primary factor influencing the value of Vmcg is engine thrust. As thrust increases, the rudder needs more airflow to counteract the increased yawing moment. So, Vmcg increases with increase in air density.

Vmcg must be established for most unfavorable CG and maximum available take-off power on operating engine. Engine thrust is sometimes permanently derated as per operators requirement to achieve lower Vmcg, Vmca and Vmcl.

Vmca – Air Minimum Control Speed

Vmca is calibrated airspeed at which if critical engine become inoperative it is possible to maintain the control of aeroplane and straight flight with maximum bank angle of 5 degree. Vmca ensure during the recovery aeroplane should not enter any dangerous attitude or require exceptional pilot skill, alertness or strength to prevent a heading change of more than 20 degrees.

Vmcl – Landing Minimum Control Speed

Vmcl (minimum control speed during landing approach) is the minimum speed at which, with one wing engine inoperative, it is possible to either decrease thrust to idle or increase thrust to maximum takeoff power without encountering dangerous flight characteristics. This speed ensures that the aircraft can be safely controlled during an approach, even with an engine failure, by maintaining sufficient airflow over the control surfaces to manage asymmetrical thrust and maintain stable flight.

Vmbe – Maximum Brake Energy Speed

Vmbe, or maximum brake energy speed, represents the highest speed on the ground from which an aircraft can safely stop within the energy capabilities of its brakes. If a takeoff is aborted at a speed higher than Vmbe, the braking system would not be able to safely bring the aircraft to a stop, regardless of the remaining runway length. At speeds above Vmbe, the brakes would likely overheat, potentially catching fire, melting, or disintegrating due to the excessive energy they would need to dissipate. Vmbe influence V1 (and indirectly V2 when takeoff with higher V2 is desired).

Vmu – Minimum Un-stick Speed

Vmu, or minimum unstick speed, is the slowest calibrated airspeed at which an aircraft can safely lift off the ground and continue the takeoff. It represents the absolute lowest speed at which lift-off is possible. However, in practical operations, Vmu is very close to the stall speed, and aircraft controllability is poor at this speed. Therefore, while Vmu is a critical performance metric, actual lift-off typically occurs at a slightly higher speed, known as Vlof (lift-off speed). This ensures better control and safety during the initial phase of flight, avoiding the risks associated with lifting off at the minimum unstick speed.

Vlof- Lift-off Speed

Vlof, the lift-off speed, must not be less than 110% of Vmu under all-engine operating conditions and 105% of Vmu with one engine inoperative. Vlof is the speed at which the aircraft first becomes airborne, occurring precisely when the main wheels leave the runway. This margin ensures a safe and controlled lift-off, providing a buffer above the minimum unstick speed (Vmu) to account for variations in performance and to enhance aircraft controllability during takeoff.

Vr – Rotation Speed

Vr, or rotation speed, is the speed at which the pilot initiates actions to raise the nose gear off the ground with the intention of becoming airborne. Following are technical considerations of Vr:

  • Vr must not be less than V1.
  • Vr must be at least 1.05 times Vmc.
  • Vr must be a speed that ensures V2 is attained before reaching 35 feet above the runway.
  • Vr must be such that if the aircraft is rotated at the maximum practicable rate, it results in a Vlof of not less than 1.1 times Vmu with all engines operating. For one engine inoperative, Vr must ensure a Vlof of not less than 1.05 times Vmu.

Also Check:

V2 Take-Off Safety Speed | V3 Speed | Take-Off with increased V2 Speed

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