16.885J/ESD. 35J -Sept 2003 Flow Velocities v called the freestream velocity Units ft/sec, mph(I mph=1.47 fps), knot(1 kt=1.69 fps=1. 151 mph) a=speed of sound Function of temperature: a a,=sqrt(T T2) Function of altitude(standard sea level a=1116.4 ft/sec) Mach number is ratio of velocity to speed of sound, M=V/a a Mo< I is subsonic flight, Mo> I is supersonic flight Mo close to 1(approx 0.8 to 1. 2 )is transonic flight16.885J/ESD.35J - Sept 2003 Flow Velocities • Vf called the freestream velocity – Units ft/sec, mph (1 mph = 1.47 fps), knot (1 kt = 1.69 fps=1.151 mph) • a = speed of sound – Function of temperature: a1/a2 = sqrt(T1/T2 ) – Function of altitude (standard sea level a = 1116.4 ft/sec) • Mach number is ratio of velocity to speed of sound, M=V/a – Mf = Vf/ af – Mf < 1 is subsonic flight, Mf > 1 is supersonic flight – Mf close to 1 (approx 0.8 to 1.2) is transonic flight