Editing Indicated airspeed (section)

== Calculation ==

Indicated airspeed measured by [[pitot tube|pitot-tube]] can be approximately expressed by the following equation delivered from [[Bernoulli's equation]].

:<math>IAS \approx \sqrt{\frac{2 (p_t - p_s)}{\rho(0)}}</math>

'''NOTE:''' The above equation applies only to conditions that can be treated as incompressible. Liquids are treated as incompressible under almost all conditions. Gases under certain conditions can be approximated as incompressible. See [[Compressibility]].

The compression effects can be corrected by use of [[Poisson constant]]. This compensation corresponds to [[equivalent airspeed]] (EAS){{Citation needed|date=December 2022}}.
:<math>u = \sqrt{ \frac{2 \gamma}{\gamma - 1} \frac{p_s}{\rho} \left[\left(\frac{p_t}{p_s}\right)^\frac{\gamma-1}{\gamma}-1 \right] }</math>

where:
* <math>u</math> is indicated airspeed in m/s,
* <math>p_t</math> is [[Stagnation pressure|stagnation]] or total pressure in pascals,
* <math>p_s</math> is static pressure in pascals,
* <math>\rho(0)</math> is standard atmosphere fluid density in <math> kg/m^3</math> at sea level, and
* <math>\ \gamma\,</math> is the [[Heat capacity ratio|specific heat capacity ratio]] (≈1.401 for air<ref>{{Cite web |year=2003 |title=Air - Specific Heat Ratio |url=https://www.engineeringtoolbox.com/specific-heat-ratio-d_602.html |url-status=live |archive-url=https://web.archive.org/web/20220712214737/https://www.engineeringtoolbox.com/specific-heat-ratio-d_602.html |archive-date=12 July 2022 |access-date=26 December 2022 |publisher=The Engineering ToolBox}}</ref>).