A tailwind is a wind that blows in the direction of travel of an object. A tailwind increases the object's speed and reduces the time required to reach its destination. Tailwinds are commonly measured in relation to the speed of vehicles — commonly air and watercraft — as well as in running events — particularly sprints. The opposite wind is a headwind.
In aeronautics, a tailwind is unfavourable in takeoffs and landings. As a result, aviators and air traffic controllers commonly choose to takeoff or land in the direction of a runway that will provide a headwind.
Tailwind component
Pilots calculate the Headwind Component, Tailwind Component and Crosswind Component of any wind, if they do exist. Headwind and Tailwind are cosine functions of the wind while Crosswind Component is a sine function. Headwind and Tailwind do not occur together in normal conditions.
Assume:
A=Angle of the wind from the direction of travel
WS=The measured total wind speed
CW=Crosswind
TW=Headwind
Then
CW=Sin(A)*WS
TW=Cos(A)*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 and the aircraft is taking-off from runway 24; having heading of 240. We will us the runway side with less than 90 difference from wind direction, in this case Runway 06; heading 060.
Crosswind = Sin(090-060)*15 ≈ 7,5
Headwind = Cos(090-060)*15 ≈ 13
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 side of the runway, it has a heading of 060 in the above mentioned example.
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