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Convert Units of Velocity

On March 17, 2004, Russell from New York contacted me about calculating the miles-per-hour equivalent of Mach 0.91 which was the maximum velocity of the original Cessna Citation X aircraft. Mach numbers, which indicate velocity relative to the speed of sound, vary greatly with temperature (and therefore with altitude) but only minimally with humidity. The following links may be useful:

• Sound of Speed in Air — the formula v sound in air = 331.4 + 0.6T_c m/s (where T_c is the temperature in degrees Celsius and m/s is velocity in meters per second) provides a good approximation.
• Speed of Sound at nasa.gov — includes a Java applet for calculating the speed of sound at various altitudes.
• Speed of Sound, Mach Number, and the Sound Barrier at Aerospaceweb.org
• Mach vs. Altitude Tables at Aerospaceweb.org
• Measuring the Speed of Sound — Relative humidity does have an effect, but it is minimal.