SAT, TAT and OAT?
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SAT, TAT and OAT?
Can somebody please explain the differences to me.
I've read a lot of contradicting and confusing stuff, and looking for an accurate and simple answer.
Would appreciate the help guys.
Thanks n advance.
I've read a lot of contradicting and confusing stuff, and looking for an accurate and simple answer.
Would appreciate the help guys.
Thanks n advance.
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Hi,
You will get a simple, but at the same time accurate answer via this link:
SKYbrary - Air Temperature
or via this link:
The Archive Forum :: View topic - TAT, SAT, & Adiabatic Conversion
For a (much) more comprehensive answer try this link:
Total air temperature - Wikipedia, the free encyclopedia
You will get a simple, but at the same time accurate answer via this link:
SKYbrary - Air Temperature
or via this link:
The Archive Forum :: View topic - TAT, SAT, & Adiabatic Conversion
For a (much) more comprehensive answer try this link:
Total air temperature - Wikipedia, the free encyclopedia
Last edited by grebllaw123d; 12th May 2012 at 22:54. Reason: addition of another link
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SAT and OAT are, for practical purposes, the same.
TAT = SAT + Mach heating, or the temperature the leading edge of the wing and nacelles will feel. The ADC derives SAT from TAT and Mach.
TAT = SAT + Mach heating, or the temperature the leading edge of the wing and nacelles will feel. The ADC derives SAT from TAT and Mach.
Advantage? TAT is what the plane feels. It's like saying, "What's the advantage of wind chill?"
That being said, if the SAT is in the +8 range and you're flying in visible mosture, the TAT will be above 10 if you're flying fast enough so you don't turn on the anti-ice.
That being said, if the SAT is in the +8 range and you're flying in visible mosture, the TAT will be above 10 if you're flying fast enough so you don't turn on the anti-ice.
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Total is the operative word. Total Air Temp is the total or the aggregate of the actual temp. (SAT) and the temperature rise (the increase due to compression).
So if the SAT is -40 and the TAT is - 30, you have a temp. rise of 10. TAT is the reference temp for many on board calculations both systems wise and by the pilot. For example, when you think about the need for engine anti-ice your definition of icing conditions is visual moisture at a temp of 10 deg. TAT or colder if you're airbourne. That's the temp. over the wing so it's more relevant than the actual SAT.
So if the SAT is -40 and the TAT is - 30, you have a temp. rise of 10. TAT is the reference temp for many on board calculations both systems wise and by the pilot. For example, when you think about the need for engine anti-ice your definition of icing conditions is visual moisture at a temp of 10 deg. TAT or colder if you're airbourne. That's the temp. over the wing so it's more relevant than the actual SAT.
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TAT/SAT and Mach Number
I was answering a post on the 'Concorde Question' thread, and thought that I could help clear this one up a bit too:
For a given gas, TAT varies with the square of Mach Number and SAT, and although all temperatures for calculation purposes are obviously ABSOLUTE temperature, they are 'converted back' to °C here. So shown below are a range of TATs shown at four different Mach numbers and three specific SATs (or OAT if you prefer). Altitudes can be assumed as being in the lower stratosphere (ie. above tropopause) and ISA relates to International Standard Atmosphere. ISA is of course -56.25°C, ISA -5 is -61.25°C and ISA +5 is -51.25°C.
MACH 0.5. ISA -5: TAT = -50.6°C. ISA: TAT = -45.3°C. ISA +5 TAT = -40°C
MACH 1.0. ISA -5: TAT = -18.5°C. ISA: TAT = -12.5°C. ISA +5 TAT = -6.5°C
MACH 1.5. ISA -5: TAT = 34.8°C. ISA: TAT = 42°C. ISA +5 TAT = 49.3°C
MACH 2.0. ISA -5: TAT = 109.5°C. ISA: TAT =118.6°C. ISA +5 TAT = 127.6°C
Hopefully it all makes a little more sense with some 'real' numbers. You can see that as Mach Number increases the gap between SAT and TAT increases hugely. As a matter of interest the Mach 2, ISA +5 case was particularly significant for Concorde, as it breached the 127°C/400°K airframe temperature limit and Mach Number would therefore be reduced. Fortunately sustained ISA +5 or above conditions were relatively rare over the North Atlantic but not unheard of either.
For a given gas, TAT varies with the square of Mach Number and SAT, and although all temperatures for calculation purposes are obviously ABSOLUTE temperature, they are 'converted back' to °C here. So shown below are a range of TATs shown at four different Mach numbers and three specific SATs (or OAT if you prefer). Altitudes can be assumed as being in the lower stratosphere (ie. above tropopause) and ISA relates to International Standard Atmosphere. ISA is of course -56.25°C, ISA -5 is -61.25°C and ISA +5 is -51.25°C.
MACH 0.5. ISA -5: TAT = -50.6°C. ISA: TAT = -45.3°C. ISA +5 TAT = -40°C
MACH 1.0. ISA -5: TAT = -18.5°C. ISA: TAT = -12.5°C. ISA +5 TAT = -6.5°C
MACH 1.5. ISA -5: TAT = 34.8°C. ISA: TAT = 42°C. ISA +5 TAT = 49.3°C
MACH 2.0. ISA -5: TAT = 109.5°C. ISA: TAT =118.6°C. ISA +5 TAT = 127.6°C
Hopefully it all makes a little more sense with some 'real' numbers. You can see that as Mach Number increases the gap between SAT and TAT increases hugely. As a matter of interest the Mach 2, ISA +5 case was particularly significant for Concorde, as it breached the 127°C/400°K airframe temperature limit and Mach Number would therefore be reduced. Fortunately sustained ISA +5 or above conditions were relatively rare over the North Atlantic but not unheard of either.
Last edited by M2dude; 16th May 2012 at 22:04. Reason: maffimatikal goof!
