At take-off, the pilots concentrate on the speed, or rather the successive speeds of their aircraft. Chronologically they are: V1, VR, or rotation speed and V2 but do you know what they relate to exactly?
Firstly, V1 is the decision speed of take-off. In cases of failure (engine or system) before V1 , the pilot should initiate a braking action to abort the take-off; if the failure occurs after V1, take-off must be continued because otherwise a runway overrun is certain.
Following V1 , there is the rotation speed, known in the jargon as VR . This corresponds to “the speed at which the pilot, by pulling back the control stick, and using a precise technique, noses up the aircraft to the desired angle for take-off.”* This is the time when the aircraft nose wheels begin to leave the ground.
Finally, there is V2. This is the safe take-off speed, or more precisely “the speed at which the take-off is assured. This speed should be reached no later than 35 feet height (10 m) and maintained up to at least 400 feet (120 m).”*
To know when the aircraft has reached V1 and VR , depending on the aircraft, an announcement is given to the pilots by an integrated automatic audio system in the cockpit. For V2 however, verification is carried out by the pilots via the instrumentation panel.
* Excerpts from "Airline Pilot Handbook"