Flight of jet airplanes operating in airlines around the world is governed by certain calculated values that ensure safe and efficient performance of an aircraft. Of these standardized values, is the take-off speed, calculated by aerospace engineers for a specific type/category of aircraft.
Although these recommended operational speeds associated with take-offs, are given names such as the “Minimum control speed” and “Maximum tire speed,” their values obviously vary with respect to the specific jet airplanes taken into consideration for calculating these values.
As detailed in the Airplane Flying Handbook, by the FAA, a jet airplane taking-off in normal conditions would go through the following three steps sequentially:
- First, the airplane conducts the take-off roll.
- Second, the jet initiates lift-off.
- Finally, the plane begins the initial climb.
The above listed steps are merely a sub-division of a maneuver referred to as the “take-off.” To understand take-off speeds, one must first understand how jet airplanes take-off.
Understanding the Take-off of Jet Airplanes
The take-off procedure may seem complex, but when broken down, it becomes a lot more simple. Here is how a jet plane takes-off:
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- It starts with an aircraft at rest, on a runway, awaiting its clearance for departure from the control tower.
- When cleared, the aircraft accelerates and speeds-up as it travels down the runway.
- As the airplane accelerates, the pilot maintains the aircraft’s attitude and its angle of incidence.
- At a certain speed, referred to as the rotation speed, the pilot uses the elevators to pitch-up the airplane (nose wheel lifts off the ground).
- When the nose wheel leaves the ground, it increases the angle of attack, which consequently increases the plane’s lifting ability.
- As soon as the rapidly developing lift overpowers the airplane’s weight, the main wheels of the aircraft leave the ground.
The take-off maneuver is basically a result of an imbalance between the forces of lift, weight, thrust and drag.
Take-off Speeds of Jet Airplanes
A number of speeds are defined and taken into consideration during the take-off of an airline jet. The need to establish these speeds is a consequence of increasing safety concerns in commercial aviation and a struggle to attain higher efficacy. The following explanation of speed limitations during the three steps listed above is in line with the FAA regulations.
- The decision speed (V1) of an aircraft is a reference to predict take-off ability with respect to the failure of a critical engine.
In simpler words, if the engine fails before V1, the pilot can stop the airplane within the stop distance and if it fails after, the pilot must necessarily take-off.
- Rotation speed (VR) is the speed of an airplane at which its nose wheel leaves the ground.
- The take-off safety speed (V2) is the speed at which the aircraft operates when in the “initial climb” phase. Maintaining this speed ensures a safe operating margin between V2 and stall speed of an aircraft. It also provides a safe speed to operate on, in the event of an engine failure.
Incorporating these speeds into the three subdivisions of take-off:
- Jet airplanes accelerating during the “take-off roll”, take note of V1 to decide whether to take-off or not.
- At VR , the pilot rotates to lift the nose wheel and increase the angle of attack.
- At VLOF (lift off speed), the main wheels “lift off” the ground and the jet airplane enters “initial climb”.
- In this phase, the aircraft flies at V2 to operate within a safe margin with respect to stall speed and possible engine failure.
There are many other speeds involved during the take-off phase in the flight of jet airplanes, such as minimum control speeds, max brake energy absorption speed and maximum tire speed. However, the above listed have a more prominent role in the take-off phase of an aircraft.
The three take-off steps (common in all jet airplanes) can be viewed in the above video of an Emirates Airbus A380 departing from Manchester.
Federal Aviation Administration, Flight standards Service. Airplane Flying Handbook. (2004).
Federal Aviation Administration, Flight standards Service. Pilot’s Handbook of Aeronautical Knowledge. (2008).
Federal Aviation Administration. FAA Regulations. Accessed on 11th November, 2011.
Trevor, T. Aeroplane General Knowledge and Aerodynamics. Aviation Theory Centre. (2004).
Lund University School of Aviation and Nordic Aviation Resources. Performance. (2001).© Copyright 2011 Junaid Ali, All rights Reserved. Written For: Decoded Science