Headwind
A tailwind is a wind that blows in the direction of travel of an object, while a headwind blows against the direction of travel. A tailwind increases the object's speed and reduces the time required to reach its destination, while a headwind has the opposite effect. Tailwinds and headwinds are commonly measured in relation to the speed of vehicles — commonly air and watercraft — as well as in running events — particularly sprints.
In aeronautics, a headwind is favorable in takeoffs and landings because an airfoil moving into a headwind is capable of generating greater lift than the same airfoil moving through tranquil air or a tailwind at equal ground speed. As a result, aviators and air traffic controllers commonly choose to take off or land in the direction of a runway that will provide a headwind. In sailing, a headwind may make forward movement difficult, and necessitate tacking into the wind.
Pilots calculate the Headwind or Tailwind Component and the Crosswind Component of local wind before takeoff. The direction of wind at a runway is measured using a windsock and the speed by an anemometer, often mounted on the same post. Headwind and Tailwind are opposite interpretations of the wind component which is parallel to the direction of travel, while Crosswind represents the perpendicular component. Determining the ground speed of an aircraft requires the calculation of the head or tailwind.
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