Takeoff is the phase of flight where an aircraft goes through a transition from moving along the ground (taxiing) to flying in the air (see flight), usually on a runway. For a balloon, helicopter and some specialized fixed wing aircraft (VTOLs) vertical takeoff aircraft (such as the Harrier), no run up is needed. Takeoff is the opposite of landing.

For light aircraft, full power is used during takeoff. Large transport category (airliner) aircraft will usually use a derated power take-off, where less than full power is used. The engines are normally applied to 80% power before this to check for engine-related problems. The aircraft is permitted to accelerate to rotation speed (often referred to as V_r). The term rotation is used because the aircraft pivots around the axis of its main landing gear due to manipulation of the flight controls to make this change in aircraft attitude. The nose is usually brought to a 5 - 20 degree nose up attitude to create sufficient lift from the wings. Autorotation is when the wings have created sufficient lift to overcome the weight of the aircraft and obtain a nose-up attitude without flight control inputs.

Larger planes (such as commercial jet aircraft) have difficulty generating enough lift at the (comparatively) low speeds encountered during takeoff. These are therefore fitted with high-lift devices, often including slats and usually flaps, which increase the effectiveness of the wing at low speed, thus creating more lift. These are deployed from the front and rear edges of the wing prior to takeoff, and retracted during the climb out.

The speeds needed for takeoff are relative to the motion of the air (indicated airspeed). A headwind will reduce the ground speed needed for takeoff, as there is a greater flow of air over the wings. Typical take-off air speeds for jetliners are in the 130 to 155 knot range (150 to 180 miles/hour, 250 - 290 km/hour.) Light aircraft, such as a Cessna 150, take off at around 55 knots (63 miles/hour, 100 km/hour). Ultralights have even lower take-off speeds. The take off speed is directly proportional to the aircraft weight; the heavier the weight, the greater the speed needed.

The speed required varies according to many factors, including airport altitude, outside temperature, aircraft gross weight, power setting, and flap position. The altitude and the temperature are linked and expressed as density altitude which can best be related to what the wing thinks its altitude is. Pilots of multi-engine aircraft calculate a decision speed (V₁) for each takeoff that dictates action to be taken in case an engine fails. Below V₁ the takeoff is aborted; above V₁ the pilot should continue to take off. After the co-pilot calls V1, he/she will call VR or "rotate" in meaning for the captain to change the pitch of the aircraft for takeoff. Then V2 is called for safety climb-out speed or, maximum ground speed limit. In a single engine aircraft the pilot should calculate the length of runway required to take off and clear any obstacles, prior to take off.

If an obstacle needs to be cleared, the pilot lowers the nose just until the speed for maximum climb angle is achieved, V_x. This is to take advantage of the ground affects where the drag is slightly decreased so the aircraft can climb at a faster rate. If no obstacle needs to be cleared, or once an obstacle is cleared, the pilot can further lowers the nose to accelerate to V_y, where the aircraft will get to altitude in the fastest rate of time. There are other rates of climb where the aircraft will gain the largest altitude in the shortest ground distance, or just a normal cruise rate of climb

Gliders take off using a variety of methods (see article on gliding), but most commonly they use winching-launching and towing behind a light aircraft.

See also

• Cruise
• Landing

Aviation

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