Friday Update, February 10, 2012

[Insuber]

Originally Posted by Varrattu

It depends on ...

True airspeed, or TAS, is a measure of the physical speed of the aircraft in relation to the air around it. Just as differences in wind velocity affect groundspeed, differences in air density affect true airspeed. At the same engine power setting, e.g., 75 percent power, an airplane can move faster through air that is less dense. That’s why higher altitudes can
translate to higher true airspeeds.
Like aircraft groundspeed, TAS cannot be measured directly. Rather, the pilot uses outside air temperature (OAT), pressure altitude, and calibrated airspeed CAS to calculate
this value.

Regards Varrattu

You are right about actual T/P vs. standard atmosphere influencing the speed of the plane. As you will know however the eventual decrease in resistance due to lower air density affects not only the plane drag, but also the engine performance and the measure of the pitot tube. For the pitot tube, the ASI will indicate a lower speed than TAS for density lower than the standard atmosphere … in practice, the IAS reported by the ASI during tests must always be corrected for non-standard atmospheric conditions.

Cheers.