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TAT Revisited - Too High Temperature

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So I've been having climb performance issues and I came to the forums to determine what may be wrong. It seems, as others have experienced, that outside temperature is sky-rocketing far too high. So I disabled FSINN Weather, loaded "Real World" FSX Weather, and sat back to watch what would happen. As a side-measure I put the 34A8/FLT64 debugging into FSUIPC (to show ambient temp). I find now, as I pass through 10,000ft, my TAT shows +12c, but the debug from FSUIPC shows +2c. So with FSINN weather disabled, FSX weather being used, why are temperatures so far off in the aircraft? As an FYI, I'm flying the 737NGX-800WL UPDATE: As I pass FL160, the temperature starts climbing again. at +8c and going up. Thanks,Matthew Adair

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I have seen this as well using ASE. Something with this plane is throwing off the TAT. I flew with the exact same weather with the LVLD 767 and got colder TAT temps with that plane. Something buggy with the NGX and the TAT not reporting correctly.


Eric 

 

 

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Did you disable FSInn weather in FSInns options dialog or did you just click the CAVOK button? I have experienced the rising temperature when I just clicked the CAVOK button. After disabling it in FSInns options I never had that problem again.

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I disabled FSINN in the SETTINGS -> WEATHER section, NOT with CAVOK. Would love to find a fix as with this bug, performance is terrible. -Matthew Adair

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TAT is higher than actual outside temperature because TAT is a calculated temperature taking into account air flow over the aircraft (or something along them lines, I'm no expert, this is just what I have read), if you go to PROG page 2, it shows the true outside temperature.

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If I'm correct the TAT doesn't have to be the same on all aircraft because it also takes the shape of the temp probe into account. It's the SAT you are interested in. That is the Saturated Air Temperature and it should be the same in every aircraft flying in the exact same conditions. This value is also importent for performance calculations. Kind regards, Daniel

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As others have pointed out, the TAT (total air temperature) is higher than the SAT (static air temperature) because of adiabatic compression (mainly). Also, for the same SAT, TAT changes with airspeed. TAT is equal to SAT only if you are stationary (zero knots). The difference between SAT and TAT is called the ram rise. Wikipedia has more details: http://en.wikipedia.org/wiki/Total_air_temperature An approximate formula for the ram rise is TAS^2/87^2. The FSUIPC documentation for the variable 34A8 calls it the "ambient temperature" -- I assume this means SAT. Since your TAT is +12 and your SAT is +2, you've got a ram rise of 10 degrees, which corresponds to a TAS of around 280 knots -- that seems about right. An SAT of +2 at 10,000 ft also sounds about right -- at the standard ISA lapse rate of 1.98 degrees per 1,000 ft, that corresponds to +22 degrees at sea level. If the temperature seems to increase as you climb further, that may simply be due to the fact that you're accelerating as you pass 10,000 ft. Let's take your data point of +8 degrees (I assume this is TAT) at 16,000 ft. Assuming the ISA lapse rate, the SAT at that altitude should be -10 degrees. That gives you a ram rise of 18 degrees, corresponding to about 370 knots TAS according to the formula above. That's about 280 knots IAS at that altitude -- sounds about right. So I don't really see anything unrealistic about the temperatures you're observing... Martin Boehme

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I'm having the exact same problem. Yesterday I was flying my PMDG 737NGX climbing to cruise altitude of FL350 while TAT kept rising. At FL300 it couldnt climb anymore and was starting to stall, TAT showed 50c! So i descended to 10.000 and TAT dropped during the the descent to 30c. Then i started climbing again but the same problem occured, the plane couldnt get higher then FL300 while TAT once again showed 50c. Clearly the plane reacts on the too high temperate else it wouldnt stall below cruise altitude. Btw i am using ASE for weather.

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Clearly the plane reacts on the too high temperate else it wouldnt stall below cruise altitude. Btw i am using ASE for weather.
It should certainly react on temperature, I have seen this before in other aircraft although NOT since I started using ASE. When you are getting this what is the Outside Air Temperature, best to see what it is, save the flight (assuming you want to resume) and switch to another aircraft that also has a temp gauge and see what that reports. I suspect it is the same... G

Gary Davies aka "Gazzareth"

Simming since 747 on the Acorn Electron

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The generic formula to pass from SAT to TAT (Kelvin degrees) is TAT=SAT*(1+0,205*(Mach)^2) so i.e. if you're at FL350 ISA and Mach 0,8 (SAT = -55 °C=218 Kelvin) TAT= 218*(1+0,205*(0,8*0,8))= 218*(1+0,1312)= 246,6K= about 247 °K that corresponds at 247-273=-26 °C so in those conditions you'd have SAT=-55 RAT=-26 Best Regards Andrea Buono

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So I've been having climb performance issues and I came to the forums to determine what may be wrong. It seems, as others have experienced, that outside temperature is sky-rocketing far too high. So I disabled FSINN Weather, loaded "Real World" FSX Weather, and sat back to watch what would happen. As a side-measure I put the 34A8/FLT64 debugging into FSUIPC (to show ambient temp). I find now, as I pass through 10,000ft, my TAT shows +12c, but the debug from FSUIPC shows +2c. So with FSINN weather disabled, FSX weather being used, why are temperatures so far off in the aircraft? As an FYI, I'm flying the 737NGX-800WL UPDATE: As I pass FL160, the temperature starts climbing again. at +8c and going up. Thanks,Matthew Adair
The default FSX WX has many issues as well. This is well documented in this and the FSX forums. Switching from FSINN to FSX isn't going to help. The NGX has a very accurate engine model so if the outside temp is not correct the thrust the model produces won't be accurate. Classic example of garbage in garbage out. IMHO, if your not using an external WX engine like ASE, then I would disable real world weather completely.

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There is a well known bug in FSINN that TAT goes too high above approx FL240. Use google to find the various workarounds and pick the one you want to use.

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I dont use FSINN. And TAT doesnt fluctuate it just gradually rises while climbing and drops when descending. @Gazzareth no chance to test it now, am at work. I did find 2 possible workarounds on the internet. 1. Switch from ASE weather to default FSX weather (activate it) and back2. Have a 1 session flight, problem appears to happen when you save a flight and resume later or load a previously saved panel state.

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Hello, I have the sam problem like you TAT temperature with ASE. Tank you JMarc Tibbo

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2. Have a 1 session flight, problem appears to happen when you save a flight and resume later or load a previously saved panel state.
I tend to do a lot of 2 session flights using ASE (normally take-off to cruise and then descent to landing as the second session), I normally save the weather and then reload it back into ASE before I reload FSX - not seen the problem on my machine yet .. .. G

Gary Davies aka "Gazzareth"

Simming since 747 on the Acorn Electron

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