novice
Topic Author
Posts: 90
Joined: Tue Aug 07, 2012 2:55 pm

### RAS/EAS Errors

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?

larshjort
Posts: 1440
Joined: Wed Dec 19, 2007 6:54 pm

### RE: RAS/EAS Errors

 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

/Lars
139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,

Mir
Posts: 19383
Joined: Mon Jan 05, 2004 3:55 am

### RE: RAS/EAS Errors

 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).

-Mir
7 billion, one nation, imagination...it's a beautiful day

Pihero
Posts: 4318
Joined: Mon Jan 31, 2005 5:11 am

### RE: RAS/EAS Errors

A simpler way to remember all the relationships between the airpeeds :
IAS + ki --> CAS x kc -->EAS x 1/sqrt d --> TAS
where
- 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.
Contrail designer

### Who is online

Users browsing this forum: 767333ER, Google Adsense [Bot], ianhAU, OMP777X and 25 guests

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos