headwind n : wind blowing opposite to the path of a ship or aircraft
EtymologyFrom head + wind.
A wind that blows directly against the course of an aircraft or ship
A headwind is a wind that hits a vehicle in the front. This reduces the vehicles' speed and increases the time to reach a destination.
In sailing, it may make forward movement difficult, and necessitate tacking into the wind.
In aeronautics, it is favourable in takeoffs and landings where aviators and Air Traffic Controllers choose the side of the runway with the wind coming against the aircraft.
Headwind ComponentPilots 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 HW=Headwind
For example if the wind is at 24015 that means the wind is currently from heading 240 degrees with a speed of 15 Knots and the aircraft is taking-off from runway 18; having heading of 180.
Crosswind = Sin(240-180)*15 ≈ 13 Headwind = Cos(240-180)*15 ≈ 7.5
The aircraft is said to have 13 knots of crosswind and 7.5 knots of headwind. Aircraft usually have maximum headwind 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 360 in the above mentioned example.