Bug: Temperature at high altitudes doesn't fall bellow -57C

[DackSter94]

I found a temperature bug, while testing different planes performance:

 

Here is a screenshot of temperature from A-10C CDU at 11000m(mission temperature is set to +15C on the ground):

 

 

Here is a screenshot of temperature from A-10C CDU at 11000m(mission temperature is set to 0C on the ground):

 

 

As you can see temperature at 11000 still same even though on the ground it was lowered by 15C. And it's the same for any lower temperature on the ground.

This is further confirmed by planes performance. Their max speed is always equal when the temperature is stuck at -57C.

Edited February 8, 2018 by DackSter94

[L-39beeratros]

That's roughly the temperature of IRL stratosphere, and it's constant. Look for international standard atmosphere :)

[DackSter94]

That's roughly the temperature of IRL stratosphere, and it's constant. Look for international standard atmosphere :)

 

ISA assumes that temperature at surface is always 15, no?

[Ironhand]

I found a temperature bug, while testing different planes performance...

 

As you can see temperature at 11000 still same even though on the ground it was lowered by 15C. And it's the same for any lower temperature on the ground.

This is further confirmed by planes performance. Their max speed is always equal when the temperature is stuck at -57C.

Not sure I'd call it a bug. As mentioned, that number is almost straight out of the Standard Atmosphere Heights and Temperatures chart. Starting at around 11,600 m (38,000 ft) the temp would be a constant for awhile. Prior to that there can be some variation. But the variation wouldn't necessarily be linear. So I think they're just using the chart as a sort of shorthand to simplify life.

[DackSter94]

Not sure I'd call it a bug. As mentioned, that number is almost straight out of the Standard Atmosphere Heights and Temperatures chart. Starting at around 11,600 m (38,000 ft) the temp would be a constant for awhile. Prior to that there can be some variation. But the variation wouldn't necessarily be linear. So I think they're just using the chart as a sort of shorthand to simplify life.

 

It will be constant temperature, but if its 0 or -15 on the surface(and not 15 as in ISA), it will be a lower constant, no?

https://www.digitaldutch.com/atmoscalc/

 

PS: sorry for editing a lot :)

Edited February 8, 2018 by DackSter94

[L-39beeratros]

That application just takes formula for standard temperature decrase (0.65°C each 100m) and calculates from that. However, that's not how it works in real life and apparently also not how it works in DCS, where there's just set stratospheric temperature (-57) at set altitude (11000m) - so the decrease is not as linear as in ISA.

I'd agree using the standard formula in DCS might be nicer, but it's still just an approximation.

[Ironhand]

It will be constant temperature, but if its 0 or -15 on the surface(and not 15 as in ISA), it will be a lower constant, no?

https://www.digitaldutch.com/atmoscalc/

 

PS: sorry for editing a lot :)

Perhaps. I don't think it's necessarily linear, though. My point is simply that I suspect that what you're seeing is by design rather than the result of a bug.

[DackSter94]

Perhaps. I don't think it's necessarily linear, though. My point is simply that I suspect that what you're seeing is by design rather than the result of a bug.

 

Yes, it doesn't have to be linear, but it should be able to go lower then -57C. Reason I'm reporting this is Because you can't even get full performance from some aircraft(and may be all of them).

For example viggen is supposed to be able to go like mach 1.98 with no stores at ISA -15, and at ISA it's only supposed to be able to go 1.82. Since we are locked at -57, no matter what surface temperature we set, we can't push aircraft to the limits.

[Krippz]

+1

[Ironhand]

Yes, it doesn't have to be linear, but it should be able to go lower then -57C. Reason I'm reporting this is Because you can't even get full performance from some aircraft(and may be all of them).

For example viggen is supposed to be able to go like mach 1.98 with no stores at ISA -15, and at ISA it's only supposed to be able to go 1.82. Since we are locked at -57, no matter what surface temperature we set, we can't push aircraft to the limits.

Ahhh...now I understand your point. :)

[DackSter94]

Here is an example with numbers from the sim to make it clearer:

 

I tested flanker at 59% fuel + full cannon ammo (infinite fuel enabled, so that mass of aircraft is always the same), level flight at 11000m full afterburner under 3 different conditions:

 

1) Temperature set to 25C(surface) in mission editor(ISA+10).

2) Temperature set to 15C(surface) in mission editor(ISA).

3) Temperature set to 0C(surface) in mission editor(ISA-15).

 

Resulting temperature readout from a-10C at 11000m:

 

1) -47C

2) -57C

3) -57C (the issue)

 

Resulting top speed in flanker:

 

1) TAS: 2666.7km/h (Mach: 2.507)

2) TAS: 2754.3km/h (Mach: 2.589)

3) Exactly same as 2)

 

As you can see there was significant gain in top speed (almost 90km/h) from ISA+10 to ISA. But from ISA to ISA-15 there is 0 change in performance (obviously because temperature at high alt at ISA-15 = temperature at high alt at ISA).

[NeilWillis]

According to Pooley's (A UK air pilot's manual for PPL licence qualifications), the minimum temperature above 36,000 feet is minus 57 degrees centigrade, and that is a constant as seen in nature.

 

So what you're seeing appears to me to be deliberate, and realistic.

 

In other words, to quote Scottie "Ye cannae change the laws of physics Jim"

[Mammatus]

Not a bug.... Real life stuff!!!! ;-)

 

Environmental lapse rate[edit]

 

The environmental lapse rate (ELR), is the rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location. As an average, the International Civil Aviation Organization (ICAO) defines an international standard atmosphere (ISA) with a temperature lapse rate of 6.49 K/km[15] (3.56 °F or 1.98 °C/1,000 ft) from sea level to 11 km (36,090 ft or 6.8 mi). From 11 km up to 20 km (65,620 ft or 12.4 mi), the constant temperature is −56.5 °C (−69.7 °F), which is the lowest assumed temperature in the ISA. The standard atmosphere contains no moisture. Unlike the idealized ISA, the temperature of the actual atmosphere does not always fall at a uniform rate with height. For example, there can be an inversion layer in which the temperature increases with altitude.

Edited February 9, 2018 by Mammatus

[Ironhand]

Not a bug.... Real life stuff!!!! ;-)

 

Environmental lapse rate[edit]

 

The environmental lapse rate (ELR), is the rate of decrease of temperature with altitude in the stationary atmosphere at a given time and location. As an average, the International Civil Aviation Organization (ICAO) defines an international standard atmosphere (ISA) with a temperature lapse rate of 6.49 K/km[15] (3.56 °F or 1.98 °C/1,000 ft) from sea level to 11 km (36,090 ft or 6.8 mi). From 11 km up to 20 km (65,620 ft or 12.4 mi), the constant temperature is −56.5 °C (−69.7 °F), which is the lowest assumed temperature in the ISA. The standard atmosphere contains no moisture. Unlike the idealized ISA, the temperature of the actual atmosphere does not always fall at a uniform rate with height. For example, there can be an inversion layer in which the temperature increases with altitude.

All of that assumes a static atmosphere, while the real atmosphere is far from static and the temps vary: NOAA Aviation Weather Center. You'll probably need to select the altitude. Unfortunately they don't use meters and 34K is the closest you get to the OP's reference altitude.

[FSKRipper]

All of that assumes a static atmosphere, while the real atmosphere is far from static and the temps vary: NOAA Aviation Weather Center. You'll probably need to select the altitude. Unfortunately they don't use meters and 34K is the closest you get to the OP's reference altitude.

 

Maybe I'm a bit misguided but when following your link, choosing 53000ft I'm seeing not less then -70° there which corresponds to the post above as I would expect these are °F.

[Ironhand]

Maybe I'm a bit misguided but when following your link, choosing 53000ft I'm seeing not less then -70° there which corresponds to the post above as I would expect these are °F.

°C

 

Select "Hover" under Plot Options and hover over the wind barb for confirmation.

Edited February 9, 2018 by Ironhand

[Mammatus]

All of that assumes a static atmosphere, while the real atmosphere is far from static and the temps vary: NOAA Aviation Weather Center. You'll probably need to select the altitude. Unfortunately they don't use meters and 34K is the closest you get to the OP's reference altitude.

 

 

Earth atmosphere is a lot more complicated than just saying it will loose 2 degrees Celcius / 1000ft... At a certain point, the air temperature will stop to decrease with altitude. This is the tropopause, the boundary between the troposphere and the stratosphere... Going higher in the stratosphere, the temperature will even begin to increase.

 

 

 

 

 

I do agree with you that real atmosphere is far from being static. The tropopause height will change according to many different factors... Actually, the colder it is, the lower will be the tropopause. Generally, it will be also be lower at the earth pole than at the equator. More locally, the height of the tropopause could also vary with low/high pressure systems and even with the amount of humidity in the air below it... Consequently, you will always have a point where the temperature will stop decreasing (at the tropopause). This temperature of 56,5 deg Celcius is a mean value, but you will always have this point, at about plus or minus 10 deg Celcius (so about -55 to -65), where an increase/decrease of altitude will not result in any temperature change.

 

 

And assuming that lowering to ISA -15 like you did will result to lower temperature at tropopause is false.

 

 

First because if temperature is lower, tropopause will also be lower and youll consequently reach this point where temperature remain constant faster while climbing... Inversely, when its warmer than ISA, tropopause will be higher, so you can climb higher before reaching the tropopause. That partially explain why whatever temperature you have on the ground, the temperature will aways be somewhere -56,5C at the tropopause.

 

 

In fact, the coldest temperature that you can have at the tropopause will be over or near the equator, where the temperature is hotter and consequently, the tropopause higher...

 

 

This is confirmed by the wedsite that you posted (NOAA). Look at higher altitude, you will see that the coldest temperature at those altitude are those that are further South of the map...

 

 

So basically, -56 is a mean value, for a point somewhere between the equator and an earth pole with standard temperature (at ISA). But at the end, you will always have a point close to this -56,5C where temperature will remain constant with any altitude variation, and thats what you are seeing in DCS.

 

 

Pretty sweet that the devs have modelled this...

[Art-J]

First because if temperature is lower, tropopause will also be lower and youll consequently reach this point where temperature remain constant faster while climbing... Inversely, when its warmer than ISA, tropopause will be higher, so you can climb higher before reaching the tropopause. That partially explain why whatever temperature you have on the ground, the temperature will aways be somewhere -56,5C at the tropopause.

 

That, however, is source of the problem OP is asking about - apparently in DCS tropopause transition altitude might be fixed at 11k no matter what remaining parameters are, thus he won't be able to replicate what you've written in your post.

 

Without someone form the ED coming in and sheding some light on how their tropo- and stratosphere are modelled, we don't know if it's a bug, or a result of some non-ISA model simplification.

[DackSter94]

That, however, is source of the problem OP is asking about - apparently in DCS tropopause transition altitude might be fixed at 11k no matter what remaining parameters are, thus he won't be able to replicate what you've written in your post.

 

Without someone form the ED coming in and sheding some light on how their tropo- and stratosphere are modelled, we don't know if it's a bug, or a result of some non-ISA model simplification.

 

No, no 11km was just random high alt i picked up..

[DackSter94]

Inversely, when its warmer than ISA, tropopause will be higher, so you can climb higher before reaching the tropopause. That partially explain why whatever temperature you have on the ground, the temperature will aways be somewhere -56,5C at the tropopause.

 

Interesting tho, if you set ISA+10, you can't get below -47 high up... So, if what you wrote is correct then there is still something wrong with the implementation?

Edited February 9, 2018 by DackSter94

[Mammatus]

No, it's not fixed....

 

 

The proof is that he is at -47c at 11000m at ISA+10.

 

 

"Quote"

 

 

1) Temperature set to 25C(surface) in mission editor(ISA+10).

2) Temperature set to 15C(surface) in mission editor(ISA).

3) Temperature set to 0C(surface) in mission editor(ISA-15).

 

Resulting temperature readout from a-10C at 11000m:

 

1) -47C

2) -57C

3) -57C (the issue)

 

 

"End of Quote"

 

 

1- He is at -47C at 11000 and not at the tropopause temp of -57C because he is not yet at the tropopause. Tthe temperature is higher (ISA+10) and consequently, the tropopause is higher too... He should have climb a little bit more to reach the tropopause and the -57C.

 

 

2- He is right at the tropopause, 11000m, 57C and ISA temp

 

 

3- He is at -57C like number 2 because he is probably over the tropopause (the area where the temp remain constant). The temperature is below ISA (ISA-15) so the tropopause is below 11000. He should have reached -57C well below 11000m.

 

 

So tropopause is not fixed and seems to be very well modeled!!!!

Edited February 9, 2018 by Mammatus

[DackSter94]

No, it's not fixed....

 

 

 

1- He is at -47C at 11000 and not at the tropopause temp of -57C because he is not yet at the tropopause. Tthe temperature is higher (ISA+10) and consequently, the tropopause is higher too... He should have climb a little bit more to reach the tropopause and the -57C.

 

No, I just did separate test, where i spanwed a-10c at 13000m+ at ISA+10 and temperature is still -47 just like at 11000m.

[FSKRipper]

Maybe this one get's some more light into the discussion:

 

On average, the static temperature decrease is about 0.65 °C per hundred meters, which is called geometrical temperature gradients. If there is no further decrease in temperature, the tropopause has been reached. If this tropopause is particularly high, as in the tropics, minimum temperatures of -80 °C can also develop in the troposphere.

In the further course of time the temperature rises again after a stationary phase, normally from an altitude of 25 km upwards. This is due to the relatively high ozone concentration and the associated radiation absorption in this layer of the atmosphere, which is known as the stratosphere. The maximum temperature is reached with about 0 °C at the level of the stratopause. In the following mesosphere the temperature sinks again and reaches a new minimum at the mesopause of -100 °C. This is followed by the thermosphere and finally the exosphere with a rising temperature again, although at these altitudes one can hardly speak of air and they actually belong to space. The particle density here is so low that even a temperature of several thousand degrees Celsius would not require any significant heat transfer processes.

[zhousaifu]

@BIGNEWY Hiya! Is there any definite answer from the ED Team on how the atmosphere IS modeled in DCS 2.7?   Is there a lapse rate modeled? This would effect density altitude and how engine and aerodynamic performance is modeled.