How to use
- 1Enter the runway number (e.g. 27) or exact heading, the wind direction and speed, and any gust.
- 2Read the crosswind (from the left or right), headwind or tailwind and the wind angle on the diagram.
- 3Switch tabs for density altitude, true airspeed, time-distance-fuel and unit conversions.
- 4Cross-check every result against your aircraft’s POH/AFM before using it in planning.
Crosswind and headwind components
The wind is split into two parts relative to the runway: crosswind = wind speed × sin(angle) and headwind = wind speed × cos(angle), where the angle is the difference between the wind direction and the runway heading. A 20-knot wind 30° off the runway gives a 10 kt crosswind and about a 17.3 kt headwind; at 60° the crosswind rises to about 17.3 kt. A two-digit entry is read as a runway number (09 = 090°), a three-digit entry as an exact heading. If you enter a gust, the components are calculated for it too — compare the gust value with the maximum demonstrated crosswind in your POH. Note that METAR and TAF winds are referenced to true north, while runway numbers and ATIS or tower winds are magnetic.
Density altitude and true airspeed
Pressure altitude is field elevation corrected for non-standard pressure — roughly 1,000 ft per inch of mercury (about 30 ft per hPa) away from 29.92 inHg / 1013.25 hPa; the tool uses the exact standard-atmosphere formula. Density altitude then corrects for temperature: at a 5,000 ft field with standard pressure and 30 °C, density altitude is about 7,800 ft, meaning a longer takeoff roll and a weaker climb. The airspeed tab converts calibrated airspeed to true airspeed from pressure altitude and temperature: 120 KCAS at 8,000 ft and 0 °C is about 136 KTAS, while the +2%-per-1,000-ft rule of thumb gives about 139 kt.
Time, distance and fuel
Flight time is distance ÷ ground speed, trip fuel is fuel flow × time, and reserve fuel is fuel flow × reserve minutes. For 250 NM at 110 kt ground speed with a fuel flow of 30 per hour, the flight time is 2 h 16 min, trip fuel about 68.2 and a 45-minute reserve 22.5, for a minimum of about 90.7 — in whatever unit you entered (US gal, L, kg or lb). The Units tab converts kt↔km/h, ft↔m, inHg↔hPa, NM↔km and °C↔°F. All results are for training and planning only, not for operational use; always use your aircraft’s POH/AFM and official data.
Frequently asked questions
How do I estimate crosswind in my head?
Use the clock method: 15° off the runway ≈ ¼ of the wind speed, 30° ≈ ½, 45° ≈ ¾, and 60° or more ≈ the full wind. A 20 kt wind 30° off gives about 10 kt of crosswind.
What is the maximum demonstrated crosswind?
The highest crosswind component tested during certification, listed in the POH — for many light training aircraft around 15–17 kt. It is not necessarily a structural limit, but beyond it you are outside what was demonstrated.
Should I use true or magnetic wind?
Runway headings are magnetic. Winds in METARs and TAFs are true; winds from ATIS and the tower are magnetic. For precise results, convert using the local magnetic variation.
Why does density altitude matter?
Engine power, propeller efficiency and lift depend on air density, not on the altitude shown on the altimeter. On hot days and at high fields, a high density altitude noticeably reduces takeoff and climb performance.
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