Sat & Tat
 

Hi,
My Question is in two parts,

Can any one please explain to me the meaning of these two terms please?.

I understand that they are very important when determining if you require engine anti-ice on big jets however what do both Sat & Tat represent on big jets?

Thank You:confused:

SAT : Static Air Temperature
TAT : Total Air Temperature

Some people prefer to think of SAT as OAT or TOAT (assuming that there is no instrument error involved), and TAT as indicated OAT allowing for compressibility problems at the thermometer.

TAT will exceed SAT by an amount depending on mach number and the characteristics of the transducer design, the latter determining how much of the temperature rise associated with the mach number is registered by the system.

Icing-wise it is all the same ... if the temperature is in the range determined during certification to present an icing risk, then you do the things appropriate to the aircraft to minimise the effects.

As the air is brought to rest there is an associated temperature rise is the simlple explanation. This rise is linked to airspeed (Mach No). SAT is usually the more useful of the two... well, for the work I do anyway.

The quations used to get from TAT to SAT are quite lengthy, but they can be found in good aero/met books for engineers.

If we make the normal isentropic flow assumptions, temperature rise is calculated simply as

temperature rise = k/5 x M^2 x SAT

k is the rise factor for the aircraft system
M is the Mach Number
SAT in degrees K (deg K = deg C + 273)

ie TAT = SAT + temperature rise

The various graphs you find in your OMs will be this equation plotted .. so you can easily reverse a few points to work out the k factor if that interests you.

Thank you for the replies, very informative.