If cruising at 40000ft and Mach 0.72, what is the Phenom 100, airspeed?

Answer 1

The speed varies depending on atmospheric conditions; the most important factor is the temperature. Humidity has little effect on the speed of sound, nor does air pressure per se. (Pressure has no effect at all in an ideal gas approximation. This is because pressure and density both contribute to sound velocity equally, and in an ideal gas the two effects cancel out, leaving only the effect of temperature.) Sound usually travels more slowly with greater altitude, due to reduced temperature. An approximate speed of sound in 0% humidity (dry) air, in meters per second (m s-1), at temperatures near 0 °C, can be calculated from:

speed of sound = 331.5 +(0.6*theta)m s-1

where (theta) is the temperature in degrees Celsius(°C),

so the air speed is 0.72*(331.5+(0.6*theta))