# Total Air Temperature

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Can someone explain to me just ##### "[1+ .2(M**2)] in normal air (degrees celsius * 256)" means? I am trying to use the TOTAL_AIR_TEMP token variable, and I have no clue what this means.Thanks in advanceMatt

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Total Air Temperature (TAT) is the air temperature as measured by a temperature probe. It's greater than the static (ambient) air temperature because of the heating that occurs as air moving past the aircraft is slowed down. May I ask why you want to use TAT if you don't know what it is?

Gerry Howard

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Thanks for that next to useless response. As I posted in the panel design forum, one would suspect that I am working on a panel. Another clue would have been the mention of the token variable TOTAL_AIR_TEMP, which is described in the SDK as "[1+.2(M**20] in normal air (degrees celsius*256)." which means absolutely nothing to me. Sarcasm aside, what difference does it make WHY I want to use something. The fact is, I need a TAT display on a gauge I'm working on and I don't understand any of the displays I'm getting from the variable. Hence the question, what does the definition mean. Also, I KNOW what TAT is in reality, but I don't know how to calculate it. Is this clear enough for you? Now can I get some assistance, or is the entrance exam not over yet?

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"I am trying to use the TOTAL_AIR_TEMP token variable, and I have no clue what this means."I gave you a working definition.The formula you have is self-evident. The TAT is calculated as 1 + 0.2*M**2. The value returned By FS is in deg Celsius multiplied by 256, so you have to divide the returned value by 256.Simple isn't it when you think about it instead of WTFing?

Gerry Howard

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>Can someone explain to me just ##### "[1+ .2(M**2)] in normal>air (degrees celsius * 256)" means? I am trying to use the>TOTAL_AIR_TEMP token variable, and I have no clue what this>means.Matt,This is a simplified formula for calculating TAT from known variables. Since it is done for you internally, all that you need to know to use the variable is to divide the reported value by 256 in order to obtain a useful number in degrees Celsius, e.g.,double tat = 0;tat = TOTAL_AIR_TEMPvar.var_value.n / 256 ;ortat = CELSIUS_TO_FARENHEIT( TOTAL_AIR_TEMPvar.var_value.n / 256 ) ;The formula is 1 plus (.2 times Mach squared)The actual formula is quite a bit more complex. See here for details:http://mtp.jpl.nasa.gov/notes/sat/sat.html

Fr. Bill

AOPA Member: 07141481 AARP Member: 3209010556

Avsim Board of Directors | Avsim Forums Moderator

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You said you hadn't a clue so I gave you a working definition of TAT.I politely asked by you wanted to use TAT if you hadn't a clue, to try to understand what you needed.In return I got childish abuse.

Gerry Howard

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>Thanks, Bill, I was actually expecting you to have a useful>response. I appreciate your assistance! I couldn't figure>out what I was getting back from the Token Variable, and the>description in the SDK didn't exactly explain that I was>getting my return in DegC. The formula didn't make much sense>to me at all, considering I've never learned to calculate TAT>and I had no idea that's what I was looking at. So thanks a>lot!Well, thank goodness for the "dual SDK descriptions," since the XML "Parameters.doc" simply says - get this! - "Self-explanatory" ... :-grr Of course to be fair, the XML token will actually convert the return "automatically" based on the "units" specified in the variable declaration, e.g., (A:TOTAL AIR TEMP, celsius) or (A:TOTAL AIR TEMP, farenheit)... ;)For certain variables I simply find it more convenient to take the extra steps needed using aircraft_varget to 'fetch' the XML token rather than mess around with converting the C variable!As for "##### moments," I've certainly had my share of those myself lately... For example, there's no logical reason why perfectly valid, and well-formed XML code should cause a CTD on a very few user's computer systems, but work as designed for 99 out of 100!Evidently there's something "missing" on those few user's systems that will choke and puke on the "Transparent" and "UseTransparency" attributes. The error returned during the CTD isn't very helpful either, since it is seemingly random: ntdll.dll, gdiplus.dll, panels.dll and systems.dll... :-hangEven in C, C++ and GDI+ there are some compilers that will choke and puke on syntactically correct code... It's very frustrating at times! :-bang

Fr. Bill

AOPA Member: 07141481 AARP Member: 3209010556

Avsim Board of Directors | Avsim Forums Moderator

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>You said you hadn't a clue so I gave you a working definition>of TAT.He asked what the FORMULA meant. You did not answer the question asked...However, even so the response you received was a bit 'over the top' admittedly...

Fr. Bill

AOPA Member: 07141481 AARP Member: 3209010556

Avsim Board of Directors | Avsim Forums Moderator

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"I am trying to use the TOTAL_AIR_TEMP token variable, and I have no clue what this means."OK, so I misunderstood his question but I did at least try to help. In return I got abuse. At times I wonder why I bother?

Gerry Howard

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mgh,Okay, having re-read the original post, I can certainly understand why you'd misread the question. I'll admit my culpability in this misunderstanding and try to be less irritable in the future. It's extremely frustrating to sit here hour after hour and not get the results you need, much less understand some of them.

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Ok. Matter closed :)

Gerry Howard

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> there's no logical reason why perfectly valid, and well-formed > XML code should cause a CTD on a very few user's computer > systems, but work as designed for 99 out of 100!To quote someone: "... computers have minds of their own ..." :9 adam

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On 8/31/2005 at 1:58 PM, mgh said:

You said you hadn't a clue so I gave you a working definition of TAT.I politely asked by you wanted to use TAT if you hadn't a clue, to try to understand what you needed.In return I got childish abuse.

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4 hours ago, PebbleBeach said:

You do realize that you have responded to a post that is 17 years old?

Jim Barrett

Licensed Airframe & Powerplant Mechanic, Avionics, Electrical & Air Data Systems Specialist. Qualified on: Falcon 900, CRJ-200, Dornier 328-100, Hawker 850XP and 1000, Lear 35, 45, 55 and 60, Gulfstream IV and 550, Embraer 135, Beech Premiere and 400A, MD-80.

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