TAT versus SAT temperature

Briar Rabbit

Briar Rabbit

Line Up and Wait
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Mar 22, 2017
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Albion, Nebraska
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Rob
After having to cancel my reservations for Oshkosh as everyone canceled on me a week ago I decided to go anyway and then my old college room mate from 48 years ago decided to go along. So I had my Avidyne 540 updated with the recent 10.2.3 update and that wiped out our personalized settings for the data displays. Tonight I updated my Nav and Obstacle databases and re-entered my personal choices for Screen display Data. I thought it a good idea to add outside air temperature and it gives me a choice of TAT or SAT. I assume TAT is True Air Temp. but what is SAT? Only thing I can think of is Sadistic Air Temp after last week. Probably head slapping simple but I've got nothing. What is the S for?
 
Static Air Temperature
 
OK, that makes sense! Thanks, so what is the difference between true OAT and static OAT? And how does the GPS unit adjust it from the one outside probe's signal on the side of the airplane?
 
I researched this on Wikipedia. You are correct SAT is static air temperature while TAT is total air temperature with the difference being heating from the energy change on fast airplanes when the air hits a OAT probe. Negligible at less than 0.2 Mach. So if I fly at less than 135 knots it does not need to be adjusted and TAT is adequate. Over 135 knots SAT may be more accurate and potentially a better predictor of ice?

This seems like rain drops that are super cooled on impact creating ice is counter intuitive to the requirement to adjust TAT to a lower number because the air is actually cooler in reality than the probe? If the air heats when it hits the airplane why doesn’t water heat a small bit too? Maybe evaporation?
 
Briar Rabbit said:
This seems like rain drops that are super cooled on impact creating ice is counter intuitive to the requirement to adjust TAT to a lower number because the air is actually cooler in reality than the probe? If the air heats when it hits the airplane why doesn’t water heat a small bit too? Maybe evaporation?
Click to expand...
Rain drops are already super-cooled before impact. The impact causes a change in state from liquid to solid. The "requirement" to adjust TAT for ram rise is to calculate TAS. In order to somewhat mitigate ice formation, pilots of high performance airplanes have long been counseled to increase IAS in order to take advantage of ram rise. That might just change where the ice accumulates, though, whether the leading edge or back on the unwarmed wing.
 
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