Airspeed - Fluke RPM4-AD Operation And Maintenance Manual

7. APPENDIX
Low Altitude: H < 36089 ft and P > 6.6832426 inHg
Mid Altitude: 65617ft > H > 36089 ft and 1.6167295 inHg < P < 6.6832426 inHg
High Altitude: H >65617ft and P < 1.6167295 inHg
7.2.3

AIRSPEED

RPM-AD has the ability to determine true airspeed, calibrated air speed and the Mach
number. True airspeed unit selections are indicated by using upper case for the unit symbol
(e.g. KTS, MPH). Mach and true airspeed unit of measure are dependent on static pressure
and/or temperature. Calibrated airspeed is a function of differential pressure only. All
airspeed calculations are based on the international standard ISO 1151-5.
Calibrated Airspeed
Calibrated airspeed is the expected airspeed at sea level atmospheric conditions. Some texts
refer to this version of airspeed as "calibrated" airspeed because the value is corrected for
specific atmospheric conditions. Other texts refer to it as "indicated airspeed" since the displayed
value is what one would expect to see on a mechanical airspeed indicator in a plane.
The equations below are used to determine calibrated airspeed from a given differential
pressure. There are two cases: 1) when the calculated airspeed is less than the speed of
sound at sea level, 2) when the calculated airspeed is greater than the speed of sound at sea
level. For the second case, the Mach number is determined assuming atmospheric static
pressure. The Mach number times the speed of sound is the resultant air speed. In both
cases, the resultant airspeed value is in meters per second. Length and time unit
conversions are applied to yield all cases of airspeed units.
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