TAS GS and IAS help
 

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?.

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.

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

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).

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".

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

GS = TAS +/- Wind

TAS = IAS + corrections as noted previously.

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

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