Wind from heading and track
Fly a leg and you know four things: the heading you held, your true airspeed, the track you actually made good, and your groundspeed. Those four are enough to work out the wind that produced them.
Calculator
This is an educational and planning aid. Use current official weather, your aircraft flight manual, and the rules that apply to your flight before you act on any figure here. See the aviation disclaimer.
What the result means
The answer is the wind the aircraft genuinely experienced over that leg, not a forecast. If it differs from the forecast wind, the aircraft is right and the forecast is out of date.
The drift angle shown alongside is the difference between where you pointed and where you went. It is the most visible sign of wind in the cockpit.
When this is useful
- Early in a cross country, to check the forecast wind before it costs you time and fuel on later legs.
- When the groundspeed readout does not match what was planned, to find out which part of the plan was wrong.
- As a training exercise, because working the triangle in both directions is what makes the relationship stick.
How it is calculated
The air vector, which is true airspeed along the heading, and the ground vector, which is groundspeed along the track, are both broken into north and east components. Subtracting one from the other leaves the wind vector.
That vector points in the direction the air is moving. Aviation reports the direction wind comes from, so the calculator adds 180 degrees before giving the answer.
wind vector = ground vector - air vector, then report the reciprocal of its direction
Worked example
- True heading flown
- 011.5 degrees
- True airspeed
- 100 kt
- Track made good
- 000 degrees
- Groundspeed
- 98 kt
The wind is from 090 at 20 kt.
Check: These are exactly the outputs of the forward wind triangle example run in reverse, and it returns the original wind of 090 at 20 kt. Solving the problem both ways and getting back to the start is the strongest check available for this calculation.
Limitations
- It gives the average wind over the leg you flew. A short leg, or one flown while climbing, gives a figure that is a blend of several winds.
- Accuracy depends entirely on the four inputs. Groundspeed and track from a GPS are reliable, but a heading read from a drifting gyro is not.
- Everything must be in degrees true. Mixing a magnetic heading with a GPS track in degrees true produces a wind that is wrong by the local variation.
Common mistakes
- Entering indicated airspeed instead of true airspeed, which throws the whole vector subtraction out.
- Swapping heading and track. Heading is where the nose points, track is the path over the ground.
- Expecting the answer to match the forecast. If it does not, that is the calculator doing its job.
Sources
- Pilot's Handbook of Aeronautical Knowledge, navigation chapter , US Federal Aviation Administration
- Aviation Formulary , Ed Williams