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2 Answers

Differences between SAT OAT RAT and TAT

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Hello! I'm Brian and i'm an student pilot from Peru. I was wondering myself about 2 words, OAT (outside air temperature) and TAT (total Air temperature).. then searching on the web RAT and SAT came out. I can't find a good definition of these four. I need a good definition to understand, i mean they all have to do with outside temperature but they have a kind of correction due to friction and high speeds.

Thanks and looking forward for your answers !

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2 Answers

  1. Jay on Jan 21, 2012

    OAT is just as it sounds, it is the temperature of the air outside cabin. On aircraft that fly at higher speeds this indication is usually corrected due to the heating effects of skin friction on the probe. Static Air Temperature is the temperature of the air as measured by a probe that isn’t in motion with respect to the air around it. Although I’ve heard people use both of these terms in reference to OAT.
    As far as I know, Ram Air Temperature and Total Air Temperature are interchangeable terms, they both mean the same thing. The TAT is a measurement of air temperature due to compression. Recall that energy is always conserved, and that moving air has kinetic energy. When moving air is slowded down like it is inside of a TAT probe it loses kinetic energy, but that energy has to go somewhere. So it is converted into heat, which raises the temperarture of the air being measured.  
    On modern, high speed aircraft, the TAT sensor slows down the air to a near standstill and then measures the temperature. It then sends the info to the air data computer so that it can calculate true airspeed.
    Most of these terms don’t really apply to a light training aircraft. A Cessna travelling around 100KIAS doesn’t  experience a lot of compressibility problems! 
    Hope this helps!

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  2. JB on Aug 13, 2012

    Hi Brian, since you’re a student pilot I’m going to try to simplify this.

    SAT – what the temp “feels” like if you were outside the plane, motionless.

    TAT- what the leading edge of the wing “feels” as it is moving through the air. The faster you go, the warmer it gets.

    A normal demonstration of the differences of the two can be seen during climb in icing conditions. Ice will build up on the un-heated portions of a jet, then when you accelerate, the TAT rises and the ice starts shedding. Pretty cool to see.

    +6 Votes Thumb up 11 Votes Thumb down 5 Votes

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