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RAS/EAS Errors  
User currently offlineNovice From United Kingdom, joined Aug 2012, 90 posts, RR: 0
Posted (3 years 7 months 5 days 5 hours ago) and read 4151 times:

If rectified airspeed is indicated airspeed corrected for pressure error and equivalent airspeed is rectified airspeed corrected for compressibility error, what is the differences in these two corrections?

3 replies: All unread, jump to last
User currently offlinelarshjort From Denmark, joined Dec 2007, 1945 posts, RR: 0
Reply 1, posted (3 years 7 months 5 days 1 hour ago) and read 4106 times:

Quoting Novice (Thread starter):
rectified airspeed is indicated airspeed corrected for pressure error

RAS=CAS Calibrated Airspeed
As far as I remember calibrated airspeed is corrected for the pressure drop that comes with increasing altitude. EAS then takes that number and corrects it for the compressability that happens when you reach near supersonic speeds.

At low speeds CAS=EAS


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User currently onlineMir From United States of America, joined Jan 2004, 22785 posts, RR: 53
Reply 2, posted (3 years 7 months 5 days ago) and read 4091 times:

Quoting larshjort (Reply 1):
As far as I remember calibrated airspeed is corrected for the pressure drop that comes with increasing altitude.

Calibrated airspeed is indicated airspeed corrected for instrument error. When you correct for pressure dropping with altitude, you end up with true airspeed (correction for non-standard temperature is a part of that as well).


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User currently onlinePihero From France, joined Jan 2005, 5143 posts, RR: 78
Reply 3, posted (3 years 7 months 4 days 23 hours ago) and read 4076 times:
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A simpler way to remember all the relationships between the airpeeds :
IAS + ki --> CAS x kc -->EAS x 1/sqrt d --> TAS
- ki is the instrument and position (of the pitot tube) error
- kc is the compreessibility error (to be ignored below 200 kt and 5000 ft )
- d is the air density

EAS is only ueed for aircraft performance, never in everyday piloting.

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