[ADDED] Do contrail altitudes scale with temperature at sealevel?

[RockPaperScissors]

Hi ,

I continue to be impressed about the level of detail in this simulator (so a big compliment to the devs).
This brings me to a question about one of these details ... the altitude at which contrails are modeled.
From the MegaFAQ I understand that CMANO uses the following approach,

"TECHNICAL DETAILS: Contrails will only form at altitudes greater than 8000m, and at temperatures
below -40 deg C. The simulator has a ‘standard atmosphere’ model that checks if the temperature is
lower than 233 deg Kelvin at the aircraft’s current altitude."

According to the U.S. Standard Atmosphere Heights and Temperatures model (with 15°C at sea level)
the -40°C altitude is approx. 27600 feet. CMANO seems to follow this model. However when playing
around with the average temperature in the editor, the altitude does not appear to scale. For instance
with a temperature of 28°C at sea level, you would expect the -40°C altitude to be around 34200 feet.
Instead the contrail altitude still seems to be 27600 feet [&:]

Is the WAD and does the model not scale with sea level temperature (or am I doing something wrong)?

Thanks in advance for the clarification!

KR, RPS

[Dimitris]

Hi,

That's an interesting observation. Is there a standard formula for calculating the -40C altitude based on different values at SL?

I found this resource: https://www.engineeringtoolbox.com/stan ... d_604.html - But this states only figures for the assumption of 15C at SL. Does the temperature-at-altitude change at the same rate as at SL, or is there a lon-linear association?

[Dimitris]

Found also this: https://www.digitaldutch.com/atmoscalc/

[c3k]

Well, there is the Adiabatic Lapse Rate. See: https://en.wikipedia.org/wiki/Lapse_rate

About 3.3F per 1,000 feet. Roughly. That's ~1.8C per 1,000 feet. (A lot of rule of thumb approximates it as 2C/1,000ft.)


And, here's a pic to show something: http://apollo.lsc.vsc.edu/classes/met13 ... p_all.html
The temperature starts to INCREASE at a certain altitude. (It varies.)

There are certain layers where contrails form, and then, if you go high enough, they stop forming. Until you go too high, and they form again.

[RockPaperScissors]

Thank you for responding and it is indeed captured in the Barometric Formula. I simply ignored the pressure and used a calculator (similar to the one shared by Dimitris) to find the altitude crossing -40ºC, and in the example applied an offset of 13ºC to the 15ºC standard atmospheric model.

As requested, the linear relationship between the temperature at sea level (TSL in ºC) and altitude of -40ºC (Hcontrail in feet) can be described as:

Hcontrail = 504.87 x TSL + 20192

Perhaps it is not too difficult to incorporate into the existing contrail model (I can always try [;)]).

In any case, thanks for reading!

KR, RPS

[Dimitris]

Added the true calculation of the -40C threshold (dependent on actual sea-level temp) for the next build.

(Yes, six years after. Sometimes good things take time )