Re: Converting speeds

Date:         24 Jan 98 02:53:21 
From:         eertink@nlr.nl (Johan Eertink)
Organization: National Aerospace Laboratory NLR
References:   1
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Marc Schaeffer (marcmsc@geocities.com) wrote:
: Sorry if this a very basic one.
:
: I'm looking for the formula to convert speed from Mach to mph.

        Speed = Mach * Speed of sound

Now the tricky part: Speed of sound depends on temperature, according to:

        Speed of sound = sqrt(gamma*R*T), where gamma = 1.4
                                                R     = 287.05 K m2/s2
                                                T     = temp in Kelvin

at sea level, T = 288,15 K, so Speed of Sound = 340.29 m/s = 761 mph

According to standard Atmosphere (ISA):
With increasing altitude, T decreases by 6.5 deg per 1000 m, up to 11000 m
(troposphere).
then it remains constant up to 20000 m (stratosphere), then it increases
again through the mesosphere.

Johan.