Crabwise · Library
What observations are needed to estimate wind from a flown heading and track?
From true heading 080° at 115 kt and a track of 087° at 101 kt, Crabwise's find-wind mode reconstructs a wind from about 040° at 19.2 kt.
Wind as the difference of two vectors
The find-wind mode turns two observations into vectors with east and north components. The air vector is A = (TAS × sin TH, TAS × cos TH), the ground vector is G = (GS × sin TR, GS × cos TR), and the wind vector is W = G − A. Its length √(Wx² + Wy²) is the wind speed. The vector points where the wind blows to, so the app adds 180° to report the direction it comes from.
All four inputs must describe the same stretch of flight: heading and TAS from the instruments, track made good and ground speed from navigation over the same minutes.
Worked example
An eastbound air vector at 120 kt and an eastbound ground vector at 100 kt differ by a 20 kt opposing wind. The reported FROM direction is 090°.
- Reconstructed wind speed (kt)
- 20
- Reconstructed direction FROM (degrees)
- 90
Collect and enter the observations
- Hold a steady heading and note the true heading and true airspeed.
- Over the same interval, note the track made good and the ground speed.
- Enter all four values with directions referenced to true north.
- Read the wind speed first, then its FROM direction.
Heading 080°, track 087°
With TAS 115 kt on heading 080°, the air vector is about (113.252892, 19.96954). With 101 kt along track 087°, the ground vector is about (100.861583, 5.285932). Their difference is (−12.391309, −14.683609), a wind of about 19.213352 kt blowing towards 220.160589°, so from about 040.160589°.
- Wind vector east component (kt)
- −12.391309
- Wind vector north component (kt)
- −14.683609
- Wind speed (kt)
- 19.213352
- Wind from (°)
- 40.160589
A wind from the left front explains both observations: the track drifts 7° right of the heading and the ground speed is 14 kt below TAS.
Common mistakes
- Entering the compass heading and a GPS track without converting both to true.
- Taking ground speed from a different leg than the heading.
- Reading the vector's direction as the FROM direction without the 180° step.
Scope
The result is the average wind implied by your observations, with their errors included. It is not a weather report. The FAA navigation chapter below explains the wind triangle that this mode inverts.
Educational calculation only. Check current aircraft limits, weather, performance and reserve requirements with approved information.