ASI under-read or over read?

[funfly]

I seem to remember that someone bought Concord's ASI as a souvenir and was surprised that the maximum was well below the speed of sound.

[overmars]

if i remember correctly, the mach number is dependent on the ambient temperature and pressure. and if i also remember correctly, it is easier to reach Mach 1 at a higher altitude.

[Old Smokey]

overmars,

Mach Number is totally dependant upon dynamic pressure (CAS or EAS) and the static pressure (Ps). Temperature does not come into play.

For example 300 Kt CAS at 30,000 feet (EAS = 285.0), Mach Number is always 0.7905, regardless of temperature.

Calculation of TAS WILL require Mach Number and Temperature.

It is easier to reach any Mach Number at a higher aktitude. Total drag is the sum of the High speed polars, (wave drag due to mach number above Mcrit) and Low speed drag polars due to EAS (dynamic pressure). As altitude increases, for a given mach number, the low speed drag polar decreases due to decreasing EAS/CAS.

Regards,

Old Smokey