Take off is the phase of flight where an aircraft transitions from moving along the ground (taxiing) into the air (see flight), usually from a runway. It is the opposite of landing.
For light aircraft, full power is normally used during take off. Large transport category (airliner) aircraft will usually use a derated power takeoff, where less than full power is used. The aircraft is permitted to accelerate to rotation speed (often referred to as Vr) and then rotated off the ground gently. The term rotation is used, because the aircraft pivots or rotates about its centre of gravity (c.g.) when the flight controls are used to change the aircraft attitude. Usually the rotation is approximately 10 to 15 degrees nose up compared to the position of the nose while on the ground. Autorotation is where an aircraft will do precisely this by itself when it reaches some speed.
Larger planes (such as commercial jet aircraft) have difficulty generating enough lift at the (comparatively) low speeds encountered during take-off. These are therefore fitted with high-lift devices, such as flaps or slats, which increase the lift of the wing at low speed. These are deployed from the front and rear edges of the wing before take-off, and retracted during climb (usually accompanied by a humming noise from the servomotors that move them).
If an obstacle needs to be cleared, the pilot lowers the nose just until the speed for maximum climb angle is achieved, Vx. If no obstacle needs to be cleared, or once an obstacle is cleared, the pilot further lowers the nose to accelerate to Vy, the speed at which climb is the most rapid. At this point the climb phase of flight begins.
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