Wind triangle (heading & groundspeed)

To hold a track over the ground you must correct for the wind. Split it against your true course into two parts, one across the track and one along it:

• Crosswind component sets the wind correction angle: WCA = asin(windSpeed · sin WA / TAS), where WA is the wind direction (measured from) relative to course and TAS is true airspeed. The sideways push blows you off track, so you crab into it by the WCA.
• Along-track component sets groundspeed: GS = TAS · cos WCA − windSpeed · cos WA. The cos WCA factor is the little bit of speed you give up to crabbing.

With the wind measured from, cos WA > 0 is a headwind (slows you down) and cos WA < 0 is a tailwind (speeds you up). You subtract the term either way: with a tailwind cos WA goes negative, so subtracting it adds speed. Let the sign do the work; never add a tailwind by hand.

TAS and the answer are in knots, so a wind reported in km/h or mph must be converted first (1 kt = 1.852 km/h = 1.152 mph).

Turn the heading into the wind by the WCA. Trap: swapping the head/cross components, reading groundspeed as TAS, or using a km/h or mph wind speed as knots.

Practice