Re: Converting speeds

Date:         24 Jan 98 02:53:18 
From:         Arthur Utay <awutay@worldnet.att.net>
Organization: AT&T
References:   1
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Marc Schaeffer wrote:
> I'm looking for the formula to convert speed from Mach to mph.

M= V/sqrt(gamma*R*T)

where 	M= Mach No.
		gamma = gas constant = 1.4 for air
		R = universal gas constant = 53.352 ft-lbf/lbm-R
					   = 287.04 J/Kg-K
		T= ambient Temperature = degrees Rankine or Kelvin
		V = local velocity = ft/s or m/s

you also have to multiple the term under the square root by a conversion
factor either (gravitational constant) 32.2 ft/s^2 or 9.8 m/s^2 to get
the units to come out right. (better check my SI units - I don't use
them often)

for example M=0.5 (in english units) on a 80 °F day:

V= .5 * (1.4 * 53.352 * 32.2 * (459+80)) ^.5
 = 569 ft/s or 388 MPH

--
A. W. Utay
awutay@worldnet.att.net
C180 N180Y