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ISA Definition

Discussion in 'Technical Talk' started by majorityof1, Jan 30, 2008.

  1. majorityof1

    majorityof1 New Member

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    It seems as though this would be an easy google but I am coming up short...

    What is the difference between celsius and ISA celsius. Moreover, which one is commonly used in weather (ATIS, etc..). Why have two different ones?

    Thanks in advance.
  2. tgrayson

    tgrayson New Member

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    Can you quote the context?

    I would be inclined to say that "ISA Celsius" is merely quoting the International Standard Atmosphere (ISA) temperatures in Celsius; normally, they'd use Kelvin. Celsius = Kelvin - 273.15.
  3. majorityof1

    majorityof1 New Member

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    Sure can. I am reviewing the dash limitations and the ambient temperature limit is the lower of +48.9 degrees celsius or ISA +35 degrees celsius. Besides being really hot which one is the Celsius that I know and love from ATIS reports?
  4. surreal1221

    surreal1221 Well-Known Member

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    What is ISA?

    And add 35 degrees to that.

    So, ISA + 35 = 15+35 = 50C.

    Hopefully that clears up any confusion.

    There is only ONE Celsius, and ONE Fahrenheit.
  5. Clocks

    Clocks Well-Known Member

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    I think this is referring to the fact that the standard temperature changes with altitude.

    At sea level ISA+35 = 15+35 = 50C. At 1000' MSL ISA+35 is 48C. At 2000' its 46C. At FL200 its -5C, etc.

    The ERJ has a similar limitation. ISA+35 is the max temperature for the aircraft. But max temperature for takeoff is 52C. How is that possible? Its because we can take off at -1000MSL, where ISA+35 is 52C.
  6. tgrayson

    tgrayson New Member

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    I agree with Clocks analysis.
  7. majorityof1

    majorityof1 New Member

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    Well that makes some sense. What does ISA stand for?
  8. Clocks

    Clocks Well-Known Member

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    International Standard Atmosphere

    http://en.wikipedia.org/wiki/International_Standard_Atmosphere

    The basic number to remember (as it relates to those temperature limitations) is standard temperature at sea level is 15 C, and it changes at a rate of -2C per thousand feet you go up in the troposphere (and +2C for every thousand feet you descend)
  9. Olympic

    Olympic Well-Known Member

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    1.98C just to be exact ... JAA guys understand.
  10. wzgrza

    wzgrza Well-Known Member

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    And im thinking of converting.. this is gonna be a pain in the ass :banghead::banghead:
  11. Olympic

    Olympic Well-Known Member

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    I use 2 but for the exams they will have 1.98 and 2 .... damn JARS.

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