7. APPENDIX
Page 137
© 2005-2007 DH Instruments, a Fluke Company
Airspeed dimension/time corrections
AIRSPEED
UNIT
CORRECTION FACTOR
MULTIPLY V
C
BY
m/s 1.0
ft/s 1/0
.3048
mph 2.236936292054
km/h 3.6
knot 1.9438444924
Mach Number
The Mach number is defined as the ratio of true airspeed to the local speed of sound. Mach
number is converted based on the international standard
ISO 1151-5
. The conversion of
Mach number requires two pressure inputs: differential pressure and static pressure.
The equations below are used to determine the Mach number. There are two cases: 1)when
the Mach number is less than 1; 2) when the Mach number is greater than 1. For the second
case, an iteration is performed on the Mach number starting with the Mach number
calculated for the subsonic case. The iteration continues until the change in calculated Mach
number between iteration cycles is less than 0.01 parts per million.
For M<1