TAS GS and IAS help

[dantebarba]

Hi ppl

I'm having a discussion with a friend about the difference between TAS GS and IAS.

He claims that GS=TAS=IAS+-Wind speed which I argued that it's incorrect, I gave him proof but he is still insisting that he's right.

Just to know, is he right?. And if he's wrong, why?.

[DaveReidUK]

Forget IAS for the time being.

Just ask your friend if they think a headwind or tailwind affects an aircraft's speed over the ground.

[HEATHROW DIRECTOR]

Hmmmmm..Ask him why TAS and IAS are apparently the same.

[bfisk]

No, your friend is incorrect.

Indicated airspeed (IAS) +- instrument, position and calibration errors ---> Calibrated airspeed (CAS)
CAS +- density correction ---> True airspeed (TAS)
TAS +- head/tailwind component ----> Ground speed (GS).

[Mad (Flt) Scientist]

And to put some example numbers to show how far off TAS is from IAS:

Mach 0.70, 25,000ft, standard atmosphere:

CAS 292 knots

TAS 421 knots

CAS to IAS relationship is dependent on the type, but for a modern aircraft with corrections in the air data system, IAS likely is within a few knots of "true CAS". In any case you're looking at an IAS more than 100knots away from TAS, "guaranteed".

[dantebarba]

Thanks guys, keep it coming I want as much reply's as possible.

[Intruder]

GS = TAS +/- Wind

TAS = IAS + corrections as noted previously.

For most people/airplanes/situations, CAS ~= IAS, so don't worry too much about CAS...

[DaveReidUK]

Thanks guys, keep it coming I want as much reply's as possible.

Keep us up to date with your friend's responses. :O