How this calculator works
The calibrated-speed method converts sea-level-calibrated impact pressure to local Mach number using the isentropic pitot relation for dry air with gamma = 1.4. Local sound speed then gives true airspeed. Indicated altitude and altimeter setting estimate station pressure with ISA. The rule-of-thumb option adds 2% per 1000 ft of pressure altitude and a square-root temperature correction relative to ISA; it is a rough comparison, not an exact E6B result. Vector mode subtracts the wind-to vector from the ground-velocity vector. Correct instrument and position errors before treating indicated speed as calibrated speed.
Formula
q_c = p0[(1+0.2(CAS/a0)^2)^3.5-1]; M = sqrt(5[(1+q_c/p)^(2/7)-1]); TAS = M sqrt(1.4 R T). Vector TAS = sqrt(GS^2+W^2-2 GS W cos(theta_to)).
Worked example
A ground speed of 100 m/s with a 20 m/s tailwind gives true airspeed 80 m/s. A 3 m/s ground vector perpendicular to a 4 m/s wind vector gives 5 m/s.
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Frequently asked questions
Is indicated speed the same as calibrated speed?
No. Calibrated speed corrects instrument and installation errors. Use aircraft data for those corrections.
Is wind direction from or to?
This input is wind-to, measured relative to ground track. A wind blowing along the track is zero degrees and acts as a tailwind.
Can I use this above Mach one?
No. Supersonic pitot flow requires a shock-wave relation. The tool rejects a sonic or supersonic result.