[CF-metadata] Four Definitions of Airspeed

[Chuck Hakkarinen]

Besides "Indicated Air Speed" (what a pilot would see, in theory, on his airspeed gauge), there are at least 3 other definitions of airspeed, as I learned at http://www.mathworks.com/access/helpdesk/help/toolbox/aeroblks/aero_s16.html

Measuring Airspeed

To measure airspeed, most light aircraft designs implement pilot-static airspeed indicators. Pilot-static airspeed indicators measure airspeed by an expandable capsule that expands and contracts with increasing and decreasing dynamic pressure. This is known as calibrated airspeed (CAS), which denotes the airspeed that a pilot would see in the cockpit of an aircraft. 
To help compensate for measurement errors, airspeed is divided into three definitions of measurement.

Airspeed Type
Description
See Also

Calibrated 
Indicated airspeed that is corrected for the calibration error
Examining the Calibration Error

Equivalent 
Calibrated airspeed that is corrected for the compressibility error
Examining the Compressibility Error

True 
Equivalent airspeed that is corrected for the density error
Examining the Density Error


The differencies are not trivial in many instances, particularly when aircraft accidents are being investigated.


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Dr. Chuck Hakkarinen 
2308 Cipriani Blvd 
Belmont, CA 94002-1416 USA 
email: chakkarinen at comcast.net 
ph: +1.650.593.9112 
cell: 650.703.6404 
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