Types of Airspeed

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Types of Airspeed

Post  Admin on Tue Dec 01, 2009 6:50 am

IAS - Indicated air speed, as visible on the aircraft ASI which is only a measurement of the aerodynamic forces effecting the aircraft, in terms of dynamic pressure.

The dynamic pressure (expressed in hPa) of the airflow, in N/m², is represented by the expression ½rV², where:
r is the density of the air [kg/m³]
V² is the aircraft (or free airstream) speed [m/s²]

CAS - Calibrated air speed, the IAS corrected for position errors, instrument errors and installation errors as stated in an aircrafts unique manual.

EAS - Equivalent airspeed, is the airspeed at sea level which represents the same dynamic pressure as that flying at the true airspeed (TAS) at altitude, in other words, the CAS after having been calibrated for compresabilty errors. The laws of aerospace mechanics sate that 'the speed of an airborne object relative to the atmosphere; in a calm atmosphere, airspeed equals ground speed'.

TAS - True air speed, is the equivalent to EAS after being calibrated for air density errors (function of temperature and altitude). Refer to the Gas Laws.

Cpt. David G. P. Martin

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