Flight Operations Briefing Notes
Understanding Takeoff Speeds

VMU (Velocity of Minimum Unstick)
VMU  is achieved by pitching the aircraft up to the maximum (tail on the runway, for aircraft that are are geometrically-limited) during the takeoff roll (Refer to Figure 2 below). The speed at which the aircraft first lifts off is VMU. Therefore, lift-off is not possible prior to VMU.
Note: All Airbus aircraft types, with the exception of the A318, are geometrically-limited.

Figure 2
VMU Flight Test on an A330

VR : Rotation Speed

The rotation speed ensures that, in the case of an engine failure, lift-off is possible and V2 is reached at 35 feet at the latest. 
Note: Therefore, at 35 feet, the actual speed is usually greater than V2.

The rotation of the aircraft begins at VR, which makes lift-off possible, at the end of the maneuver.
The VR must be such that the lift-off speed is greater than VMU.

Flight Operations Briefing Notes
Understanding Takeoff Speeds

VMCA (Velocity of Minimum Control in the Air)
The rudder is used to compensate for the yaw moment caused by thrust asymmetry. There is a minimum speed at which full rudder will be necessary, in order to fly a constant heading with level wings.

Figure 3
Sideslip Angle in a One Engine-out Condition
To reduce sideslip, this speed can be reduced even more, if the aircraft is banked on the live engine’s side.
The lower the speed, the greater the necessary bank angle. The speed that corresponds to a 5-degree bank angle is defined, by regulations, as the minimum control speed and is referred to as VMCA (Velocity of Minimum Control in the Air).

Figure 4
Roll Angle at VMCA

V2: Takeoff Safety Speed
V2 is the minimum speed that needs to be maintained up to acceleration altitude, in the event of an engine failure after V1. Flight at V2 ensures that the minimum required climb gradient is achieved, and that the aircraft is controllable. V2 speed is always greater than VMCA, and facilitates control of the aircraft in flight.
In an all-engines operative takeoff, V2+10 provides a better climb performance than V2 (Refer to Figure 5 below).

Flight Operations Briefing Notes
Understanding Takeoff Speeds

Figure 5

 Climb Gradient Relative to Speed in a Specific Flaps’ Configuration
If one engine is lost before reaching V2, then the initial climb is flown at V2.
If thrust is lost at a speed between V2 and V2+10, then the current speed is maintained, to ensure the most efficient climb speed.
It is not necessary to increase pitch, in order to reduce the speed to V2, when a higher speed has already been reached.

II.2 Minimum Control Speeds with Derated Thrust
“JAR/FAR: AMJ 25-13 / AC 25-13
(4)(b) Derated takeoff thrust, for an aeroplane, is a takeoff thrust less than the maximum takeoff thrust, for which exists in the AFM a set of separate and independent takeoff limitations and performance data that complies with all requirements of Part 25.”
　
中國航空網 www.k6050.com
航空翻譯 www.aviation.cn
本文鏈接地址：Flight Operations Briefing Notes Takeoff and Departure Operations Understanding Takeoff Speeds(2)