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Turbulence numbers

Postby gierschi@flightgear » Mon Dec 21, 2015 4:49 pm

Hey guys,

i have the following question to you: When you start flightgear it is possible to set the turbulence strength to a number between 0 (no turbulence) and 1 (severe turbulence). What exactly does this number mean and in which part of the code is this value important.

Thank you very much in advance for your response.
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Re: Turbulence numbers

Postby Johan G » Sun Dec 27, 2015 8:03 pm

Where do you set it? In a wizard/launcher, in a menu or in the property browser, and if the last, what property would that be?
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Re: Turbulence numbers

Postby gierschi@flightgear » Tue Dec 29, 2015 3:32 pm

Dear Johan,

i am starting flightgear via the console (OpeneSuse) with the following command:

fgfs --turbulence=n

You can Set turbulence (n) from completely calm (0.0) to severe (1.0). It's an Environment Option.
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Re: Turbulence numbers

Postby wkitty42 » Tue Dec 29, 2015 6:15 pm

if this number is like other of similar format and use, then it would seem to be a percentage where 1.0 is 100%, 0.90 is 90%, 0.30 is 30% and so on... i think this answers your question of "What exactly does this number mean"... as far as the portion of the code that this number affects, i would hazard a guess that it is working with the two weather engines... which one depends on if you are using basic weather or detailed weather (aka AW or advanced weather)...
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Turbulence numbers

Postby Thorsten » Tue Dec 29, 2015 6:18 pm

No, it's a message to JSBSim or YaSim to do something - turbulence isn't generated in the weather system, since it has to do with very fine eddies, you need to treat them inside the FDM to get it properly done.

It's basically 'a number' that JSBSim and/or YaSim decide to treat in 'some way'. As we used to say - some quantity in arbitrary units.

I think you really need to look into the FDM-specific code to find out what the number means, I honestly don't know.
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Re: Turbulence numbers

Postby wkitty42 » Tue Dec 29, 2015 7:32 pm

ahhh, yeah... i keep forgetting that the weather engines don't affect the craft... that's all done in the FDM... even the rocking in high winds while sitting tied down in a parking place... as i noted, it was a guess ;)

the number is a percentage as i described, right?
"You get more air close to the ground," said Angalo. "I read that in a book. You get lots of air low down, and not much when you go up."
"Why not?" said Gurder.
"Dunno. It's frightened of heights, I guess."
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Re: Turbulence numbers  

Postby gierschi@flightgear » Thu Dec 31, 2015 4:15 pm

Looking into the code from the FDM was my first guess, too. I specified myself to the JSBSim code now but can't find the place where this turbulence number could play an important role. :-( The turbulence itself is calculated in FGWinds.cpp. Maybe you can tell me which file handles all the inputparameter from the console ? Then I can try to find out how the number n is interpreted.
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Re: Turbulence numbers

Postby gierschi@flightgear » Fri Mar 04, 2016 3:56 pm

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