Tas / Sas Definitions - Larsen & Brusgaard PROTRACK II Manual

30 - TAS / SAS Definitions

True Airspeed (TAS) and Skydiver's Airspeed (SAS) are two methods of calculating
the airspeed of a moving/flying/falling object. SAS is a concept developed by LB
ALTIMETERS:
TAS is: The speed of an object relative to the surrounding air regardless of the
altitude, a term used in aviation.
SAS is: The speed of a skydiver calculated as if the complete skydive had been
performed at 4,000 feet MSL.
30.1 TAS
A skydiver's TAS changes as a function of the altitude (air pressure) and temperature,
which makes it difficult to compare fall rates.
Example: A skydiver (in a fixed freefall position) who has a terminal fall rate of 62
meters/sec at 10,000 feet will have a terminal fall rate of 50 meters/sec at 3,000
feet. It will be seen that the difference in altitude (and thereby air pressure) makes it
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difficult to compare the fall rates when measured using TAS.
30.2 SAS
The SAS formula calculates airspeed (using the same metrics used with TAS) from
measurements of air pressure and temperature and converted to a fixed air pressure
(875.3 mb) and a fixed temperature (+7.080C) which corresponds to 4,000 feet MSL.
4,000 feet is chosen as the reference altitude by LB ALTIMETERS since this is the
average altitude at which the working time of a skydive is normally ended.
30.3 Conclusion
Using SAS, skydivers in any body position can express their vertical speed by a number
(SAS). This number remains virtually constant regardless of altitude with little or no
variance due to temperature differences and can be compared with the
airspeeds of other skydivers.
This means that regardless of the elevation of the DZ you are jumping at, SAS will be
the same for the same body position.
SAS is very useful when doing big formation skydiving. If using TAS, it will seem like
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