TAS and Conversion Factor

Question: How can I calculation a True Air Speed and obtain the conversion factor?

In the SDK we use the IndicatedAirSpeed struct which has a few different constructors to handle a different temperature variation, the full API documentation can be found here. Two values are required, these are an Airspeed and an Altitude value.  So an example call to the API would be:

 IndicatedAirSpeed iasComputed = new IndicatedAirSpeed(
                   new AirSpeed(250, AirSpeedUnits.Kt), 
                   new Altitude(600, AltitudeUnits.Metres));

A speed of 250 knots at 600 metres is used to instantiate the IndicatedAirSpeed struct. Once this is complete the struct has some member properties that expose the True Air Speed and the conversion factor. The properties are:

  • .TrueAirSpeed – True Airspeed
  • .K – Conversion factor (ICAO)

The calculation used is that defined in ICAO Doc. 8168

    TAS = IAS × 171233 [(288 ±VAR) − 0.006496H]0.5 ÷ (288 – 0.006496H)2.628

where: VAR = Temperature variation about ISA in °C

2018-08-24T17:11:46+00:00August 24th, 2018|FPAssistant SDK/API News|