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colwah

OAT / Climb Problem

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Hello All

I feel a bit cheeky coming on here for help seen as I haven't been on the forum for a while.

Lots of thing have happened including work banning the site from our internet which isn't good!

Oh well!

Back in May I asked for some help regarding the PSS 757 not climbing properly. After sending the problem to Just Flight, who are looking into it, one of my friends suggested that there could be a problem with the OAT.

It seems that my friend may be right because when the a/c gets to 10,800 ft or so the OAT is showing as -32C. Now that can't be right?

I was also having the same sort of problem with the Flight1 ATR 72-500 and the Just FLight Airbus Series 1

Does anyone know of a fix for the OAT problem??

Thanks in advance for any help

Best regards

Colwah

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You might try fixed FS WX. It just so happens I just posted the Back to Basics article (in the John's Corner sub-forum) on that last night. You can set layers of fixed WX with different temperatures in different layers. you could set up a few fixed layers at different altitudes and temperatures and experiment to see if that's really what's causing the climb difficulties.

John

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We new you would return.

Sometimes, only the best... is good enough.

:icon_rockon:

Try Johns solution, or just get a decent weather program like Active Sky.

I've not heard of the OAT showing -32 at FL10. Wierd indeed. I have had problems with iced up pitots, at a similar altitude, as the heat wasn't on. It may well have been whilst using the default weather...

.. ergo, it sounds as though John is correct. It is probably typical Microsoft coding, as lack of pitot heating should not really be a problem at 10,000 ft, unless you're in Alaska in January.

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Minus 32 C at 10,000 is pretty extreme but icing at medium altitudes even in the warm months is not at all uncommon. I just pulled up a RW flight planning tool and for a roughly 800 NM line along the SE US East Coast right now - Virginia to Florida (the only place I looked), there is light to moderate icing forecast from about 14,000 all the way up to about 30,000 feet - and it's August. They're showing temperatures in that altitude range from 0 to -30 C.

 

Even accounting for the hurricane, icing in warm climates in summer is not unusual at all. -32 C at 10,000 feet IS pretty unusual, however.

 

John

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Fresh from my Meteorology exam :D .

It's possible for a specific parcel of air to be at or around -32 degrees, assuming a standard Dry Adiabatic Lapse Rate of 3 degrees per 1000ft.

However, the surface temperature would have to be zero or slightly below zero in order for that to happen. Furthermore, for the parcel of air to rise that high, the environment would have to be even colder (as air will only rise if it's warmer than its surrounding environment).

Normally however, the assumed temperature at Fl100 would be -5 (if referenced to the ISA) - 15 degrees surface temperature, and ELR of 2 degrees per 1000ft.

If you're flying through a Thunderstorm, temperatures inside can be abnormally low. Even an environment that's 20 degrees C or higher can host a thunderstorm with supercooled liquid drops down to around -30.

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I think you're mixing standards, Jack. Wiki gives the standard dry adiabatic lapse rate as, "...9.8 °C per 1,000 m (5.38 °F per 1,000 Ft)".

 

Three degrees F per 1,000 feet is an approximation of the SATURATED adiabatic lapse rate, not dry.

 

Bear in mind that a "standard" lapse rate is like a standard atmosphere - it simplifies things wonderfully for conceptual and educational purposes, but you get what you get in the real world. Mother Nature has not signed on and the actual lapse rate can vary significantly from place to place and time to time, and even from elevation to elevation at the same place and time.

 

Having said all that, I think we're all in perfect agreement that the cited -32 degrees C at 10,000 feet with normal summer surface conditions is almost impossibly unlikely, if not physically impossible.

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I think you're mixing standards, Jack. Wiki gives the standard dry adiabatic lapse rate as, "...9.8 °C per 1,000 m (5.38 °F per 1,000 Ft)".

Three degrees F per 1,000 feet is an approximation of the SATURATED adiabatic lapse rate, not dry.

Bear in mind that a "standard" lapse rate is like a standard atmosphere - it simplifies things wonderfully for conceptual and educational purposes, but you get what you get in the real world. Mother Nature has not signed on and the actual lapse rate can vary significantly from place to place and time to time, and even from elevation to elevation at the same place and time.

Having said all that, I think we're all in perfect agreement that the cited -32 degrees C at 10,000 feet with normal summer surface conditions is almost impossibly unlikely, if not physically impossible.

Hi John,

Negative. The Saturated Adiabatic Lapse Rate is 1.5 degrees per 1000ft. The DALR is definitely 3.0 per 1,000ft.

I am correct when I say the DALR = 3.0 degrees per 1,000ft. In fact, you even said in your post 5.38F per 1,000ft, which is equal to 2.98 degrees C per 1,000ft or 3.0 degrees per 1,000ft.

Trust me, I know this! :icon_thumbup:

I can prove this here too:

"The rate of temperature decrease is 9.8 °C per 1,000 m (5.38 °F per 1,000 Ft). The reverse occurs for a sinking parcel of air."

1,000m = 3,280 feet

So that's 9.8 Degrees C per 3,280 feet.

So, we divide both by 3.20 and we get:

3,280/3.20 = 1,000ft

9.8/3.20 = 3.0625 which is almost exactly 3

So:

3 Degrees/1,000ft is the DALR. The SALR is assumed to be exactly half the DALR by the ISA, so that'd be 1.5 degrees per 1,000ft.

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OK, I was looking at degrees C per meter and degrees F per foot, which is what Wiki had listed. You were citing degrees C per foot and I didn't do the conversion.

 

John

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Hi Guys

Thanks for the help and discussion! John I will try your suggestion when I get some free time. Its funny coz it doesn't happen on all my aircraft. My PMDG 737-600/700 is fine so am still non the wiser

Thanks again

Colin

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Hello

I think I have solved the problem. Something made me check the International settings within FS9 and I changed an option from "Altimeter in meters" to "Altimeter in Feet" and pendilng a few more tests and lots of crossed fingers I seem to have solved the problem.

I will let you all know soon!

Thanks

Colin

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