[CF-metadata] Four Definitions of Airspeed
chakkarinen at comcast.net
Wed Mar 23 12:57:31 MST 2005
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
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.
Indicated airspeed that is corrected for the calibration error
Examining the Calibration Error
Calibrated airspeed that is corrected for the compressibility error
Examining the Compressibility Error
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.
Dr. Chuck Hakkarinen
2308 Cipriani Blvd
Belmont, CA 94002-1416 USA
email: chakkarinen at comcast.net
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