Headwind and tailwind

A tailwind increases the object's speed and reduces the time required to reach its destination, while a headwind has the opposite effect.

The terms are also used metaphorically in business and elsewhere about circumstances where progress is made harder (headwind) or easier (tailwind).

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 with 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.

Aircraft carriers usually turn into the wind during takeoffs and landings, and may increase their own speed.

While on take-off and landing, headwinds are good because they allow the aircraft to use a shorter runway, in flight, however, headwinds are bad because they reduce the ground speed of the aircraft, which requires more fuel to get to the destination.

Conversely, tailwinds are bad on take-off and landing, but are good in flight.

In sailing, a headwind may make forward movement difficult, and necessitate tacking into the wind.

It decreases the speed and increases the advantage of drafting, i.e. riding closely together in groups.

The comedian Jacob Haugaard made a pointedly absurd campaign promise of more tailwind on bicycle paths when he successfully ran as an independent in the 1994 Danish parliamentary election.

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 up to 200 metres where athletes run in the same or mostly same direction and wind assistance from a tailwind above two metre per second is not allowed in records.

The direction of wind at a runway is measured using a windsock and the speed by an anemometer, often mounted on the same post.

Determining the ground speed of an aircraft requires the calculation of the head or tailwind.

If the wind exceeds 100 degrees it is common practice to takeoff and land from the opposite end of the runway, it has a heading of 060 in the above-mentioned example.