Airspeed
From the number on the airspeed indicator to true airspeed and Mach, and back.
Turns the number on the airspeed indicator into calibrated airspeed, true airspeed, and Mach, and works back from a true airspeed or Mach to the calibrated airspeed to fly. Pilots use it for flight planning, the wind triangle, and checking cruise performance. Start with the true airspeed tool, which shows the 2% per 1,000 ft rule beside the exact answer. Correct indicated airspeed to calibrated first, from the calibration table in your POH or AFM, because the rest of the chain assumes calibrated airspeed.
Planning and education aid. Not for primary navigation. Full disclaimer
I want to turn indicated or calibrated airspeed into true airspeed and Mach
- True airspeed from indicated or calibrated airspeed
True airspeed, Mach, and equivalent airspeed from IAS or CAS, pressure altitude, and outside air temperature, by the exact compressible-flow path, with the 2% per 1,000 ft rule beside it.
I want to find the calibrated airspeed to fly for a true airspeed or Mach
- Calibrated airspeed from true airspeed or Mach
The calibrated airspeed to fly for a true airspeed or Mach number at a pressure altitude and temperature, with Mach, EAS, and impact pressure.
I want to get outside air temperature from a total air temperature probe
- Total and static air temperature
Static (outside) air temperature from the total air temperature a probe reads, or the reverse, with the ram rise at your Mach number.
IAS → CAS → EAS → TAS → Mach
- IAS is what the airspeed indicator shows. Correcting it for instrument and position error, from the calibration table in the POH or AFM, gives calibrated airspeed (CAS). True airspeed from indicated or calibrated airspeed
- Correcting CAS for the compression of air in the pitot tube gives equivalent airspeed (EAS). The difference is small below about 200 kt and 10,000 ft and grows with speed and altitude.
- Correcting EAS for air density, from pressure altitude and outside air temperature, gives true airspeed (TAS): your speed through the air mass. True airspeed from indicated or calibrated airspeed
- TAS divided by the local speed of sound, which depends only on temperature, is the Mach number. A probe reads total air temperature, warmer than the outside air at speed, so convert it first. Total and static air temperature
- To plan the other way, from a TAS or Mach you want to the CAS to fly, run the chain in reverse. Calibrated airspeed from true airspeed or Mach