Headwind
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A tailwind is a
wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...
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. The terms are also used metaphorically in business and elsewhere about circumstances where progress is made harder (headwind) or easier (tailwind).


Travel

In
aeronautics Aeronautics is the science or art involved with the study, design, and manufacturing of air flight–capable machines, and the techniques of operating aircraft and rockets within the atmosphere. The British Royal Aeronautical Society identif ...
, a headwind is favorable in
takeoff Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff. For aircraft that take off horizontally, this usually involves starting with a ...
s and
landing Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown" or ...
s because an
airfoil An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of an object whose motion through a gas is capable of generating significant lift, such as a wing, a sail, or the blades of propeller, rotor, or tur ...
moving into a headwind is capable of generating greater
lift Lift or LIFT may refer to: Physical devices * Elevator, or lift, a device used for raising and lowering people or goods ** Paternoster lift, a type of lift using a continuous chain of cars which do not stop ** Patient lift, or Hoyer lift, mobile ...
than the same airfoil moving through tranquil air, or with a tailwind, at equal
ground speed Ground speed is the horizontal speed of an aircraft relative to the Earth’s surface. It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight. An aircraft diving ve ...
. As a result,
aviator An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they a ...
s and
air traffic controller Air traffic control specialists, abbreviated ATCS, are personnel responsible for the safe, orderly, and expeditious flow of air traffic in the global air traffic control system. Usually stationed in air traffic control centers and control ...
s commonly choose to take off or land in the direction of a
runway According to the International Civil Aviation Organization (ICAO), a runway is a "defined rectangular area on a land aerodrome prepared for the landing and takeoff of aircraft". Runways may be a man-made surface (often asphalt concrete, as ...
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 Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the ''water'' ( sailing ship, sailboat, raft, windsurfer, or kitesurfer), on ''ice'' ( iceboat) or on ''land'' ( land yacht) over a chose ...
, a headwind may make forward movement difficult, and necessitate tacking into the wind. In
motor vehicle A motor vehicle, also known as motorized vehicle or automotive vehicle, is a self-propelled land vehicle, commonly wheeled, that does not operate on rails (such as trains or trams) and is used for the transportation of people or cargo. The ...
s, wind can affect fuel consumption and top speed but is usually ignored by the driver who chooses the speed from speed limits and road conditions. In
cycling Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from tw ...
, headwind is felt strongly by cyclists. It decreases the speed and increases the advantage of
drafting Drafting or draughting may refer to: * Campdrafting, an Australian equestrian sport * Drafting (aerodynamics), slipstreaming * Drafting (writing), writing something that is likely to be amended * Technical drawing, the act and discipline of compo ...
, i.e. riding closely together in groups. This can affect tactics in
road bicycle racing Road bicycle racing is the cycle sport discipline of road cycling, held primarily on paved roads. Road racing is the most popular professional form of bicycle racing, in terms of numbers of competitors, events and spectators. The two most common ...
. The comedian Jacob Haugaard made a pointedly absurd campaign promise of more tailwind on
bicycle path Cycling infrastructure is all infrastructure cyclists are allowed to use. Bikeways include bike paths, bike lanes, cycle tracks, rail trails and, where permitted, sidewalks. Roads used by motorists are also cycling infrastructure, except ...
s when he successfully ran as an independent in the 1994 Danish parliamentary election. Cycling in Denmark is very popular. Tailwinds and headwinds are commonly measured in relation to the speed of vehicles — commonly air and watercraft — as well as in
running Running is a method of terrestrial locomotion allowing humans and other animals to move rapidly on foot. Running is a type of gait characterized by an aerial phase in which all feet are above the ground (though there are exceptions). This is ...
events — particularly sprints up to 200 metres where athletes run in the same or mostly same direction and
wind assistance In track and field, wind assistance is the benefit that an athlete receives during a race or event as registered by a wind gauge. Wind is one of many forms of weather that can affect sport. Due to a tailwind helping to enhance the speed of the a ...
from a tailwind above two
metre per second The metre per second is the unit of both speed (a scalar quantity) and velocity (a vector quantity, which has direction and magnitude) in the International System of Units (SI), equal to the speed of a body covering a distance of one metre in a ...
is not allowed in records. This limit also applies to
long jump The long jump is a track and field event in which athletes combine speed, strength and agility in an attempt to leap as far as possible from a takeoff point. Along with the triple jump, the two events that measure jumping for distance as a gr ...
and
triple jump The triple jump, sometimes referred to as the hop, step and jump or the hop, skip and jump, is a track and field event, similar to the long jump. As a group, the two events are referred to as the "horizontal jumps". The competitor runs down t ...
.


Aeronautics calculations

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 A windsock (also called a wind cone) is a conical textile tube that resembles a giant sock. It can be used as a basic indicator of wind speed and direction, or as decoration. They are typically used at airports to show the direction and strengt ...
and the speed by an
anemometer In meteorology, an anemometer () is a device that measures wind speed and direction. It is a common instrument used in weather stations. The earliest known description of an anemometer was by Italian architect and author Leon Battista Alberti ...
, 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 Ground speed is the horizontal speed of an aircraft relative to the Earth’s surface. It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight. An aircraft diving ve ...
of an aircraft requires the calculation of the head or tailwind. Assume: A=\text WS=\text CW=\text TW=\text HW=\text Then CW=\sin(A) \cdot WS HW=\cos(A) \cdot WS For example, if the wind is at 09015 that means the wind is currently from heading 090 degrees with a speed of 15 
knots A knot is a fastening in rope or interwoven lines. Knot may also refer to: Places * Knot, Nancowry, a village in India Archaeology * Knot of Isis (tyet), symbol of welfare/life. * Minoan snake goddess figurines#Sacral knot Arts, entertainmen ...
and the aircraft is taking-off from runway 24; having heading of 240. The pilot prefers the runway side with less than 90 difference from wind direction, in this case Runway 06; heading 060. Here, A=30^\circ. \text = \sin 0^\circ\cdot 15 \mathsf \approx 7.5 \mathsf \text = \cos 0^\circ\cdot 15 \mathsf \approx 13 \mathsf The aircraft is said to have 7.5 knots of crosswind and 13 knots of headwind on runway 06, or 13 knots of tailwind on runway 24. Aircraft usually have maximum tailwind and crosswind components which they cannot exceed. If the wind is at eighty degrees or above it is said to be full-cross. 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.


See also

*
Crosswind A crosswind is any wind that has a perpendicular component to the line or direction of travel. This affects the aerodynamics of many forms of transport. Moving non-parallel to the wind's direction creates a crosswind component on the object and th ...
*
Air navigation The basic principles of air navigation are identical to general navigation, which includes the process of planning, recording, and controlling the movement of a craft from one place to another. Successful air navigation involves piloting an air ...
*
Thrust Thrust is a reaction force In physics, a force is an influence that can change the motion of an object. A force can cause an object with mass to change its velocity (e.g. moving from a state of rest), i.e., to accelerate. Force can al ...
*
Wind assistance In track and field, wind assistance is the benefit that an athlete receives during a race or event as registered by a wind gauge. Wind is one of many forms of weather that can affect sport. Due to a tailwind helping to enhance the speed of the a ...
*
Windsock A windsock (also called a wind cone) is a conical textile tube that resembles a giant sock. It can be used as a basic indicator of wind speed and direction, or as decoration. They are typically used at airports to show the direction and strengt ...


References

{{reflist Aerodynamics