Mach 1 = sqrt(gamma*R*temperature)
Mach 1 (in meters/sec) = sqrt(1.4*287*(288.15+OAT))
Multiply that by 1.944 to get knots.
The final equation is below. It's accurate to within about 1 knot.
Mach No. x 1.944 x sqrt(401.8(273.15+OAT)).
Last edited by CessnaCitationX; 04-28-2009 at 03:49 PM.