Takeoff of a multi-engine jet aircraft is a precision maneuvre that must be planned and executed very carefully. The planning starts a few hours before the scheduled departure, where the airline dispatchers prepare a flight plan for the crew and for air traffic controllers. The plan tells them through which way and where the aircraft would like to travel and some basic information about the aircraft and the airline.
Once the weight of the aircraft including fuel, all passengers, and their baggage is known, it's time to calculate several speeds that the aircraft will achieve during the takeoff. We will talk about three of them. These speed are so important for takeoff performance that one of the pilots will announce when each of the speeds is achieved.
The first of these speed numbers is decision speed (V1). If an engine fails during takeoff and the aircraft travels at a speed below the decision speed, the takeoff is aborted and the aircraft stops on the runway. If an engine fails at a speed above the decision speed, the takeoff continues, because flying with one engine and attempting to land again as soon as possible is still better than overshooting the runway and crashing into whatever may be beyond it. There are many factors that determine the decision speed and they include the type and weight of the aircraft, the length of the runway, but also details like the air temperature and airport elevation above sea level.
The second of the speeds that needs to be calculated is rotation speed (Vr). This is the speed where the pilots will start pitching the aircraft's nose up to provide the lift to get the airplane airborne. A typical rotation (and thus takeoff) speed for jetliner is around 145 knots (nautical miles per hour), which is about 270 kilometers per hour.
The third speed that is worth mentioning is the safe climb speed (V2). This is the speed that must be maintained in order to keep the aircraft airborne and climbing even with an inoperative engine.
Assuming no engine failed, the aircraft will reach its cruise altitude (as assigned by the air traffic control) after climbing for a while and then fly to its destination. When cruising in high altitude, a typical speed for jetliners is around Mach 0.78, which is around 515 knots or 955 kilometers per hour.
I don't have any pictures of airliners taking off, but I managed to take some videos. The first video shows a small private jet taking off. The runway was wet, so you can see the trail of water behind the jet. The humming sound that you can hear is not the sound of the jet engines, but of the bus engine (which certainly was not a jet engine).
The second video shows the Speedbird 855 that I already talked about. Unfortunately, I did not manage to capture the end of the takeoff maneuvre, because I lost the airplane from sight.
Copyright notice: Text and images copyright by Michal Řeháček.