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Thermal spawning, ridge wind and weather configuration

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Thermal spawning, ridge wind and weather configuration

Postby TestSubject » Thu Jun 25, 2020 6:44 pm

Hi everyone,

I'm new to flight gear and looking forward to trying it out for soaring. However, I'm not sure how to setup the weather configuration so that thermals and ridge lift are created.
Does anyone have some idea how to set this up?

Thanks
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Re: Thermal spawning, ridge wind and weather configuration

Postby Isaak » Thu Jun 25, 2020 7:19 pm

When starting FlightGear, make sure 'detailed weather' is selected in the 'settings' tab. Once FlightGear is started, go to environment > Weather, make sure detailed weather is selected and then go to advanced options. There you can select 'Terrain Effects', 'Terrain Presampling' and 'Generate thermals'. Click 'Ok' and 'Ok' again to enable it. Your settings will be stored for your next FG sessions.

Finding thermals is not very easy in FlightGear, as you don't feel the aircraft behaviour with your bum and the vario is always late (as IRL), but flying with Ridge lift is very satisfying ;)

Enjoy!
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Re: Thermal spawning, ridge wind and weather configuration

Postby TestSubject » Fri Jun 26, 2020 5:05 pm

Hi Issak,

Thanks for the tip. Do you know where I can find more information the what we these options?
Also, for thermal are there best "locations" or should I set other weather parameters so something specific to increase the thermal generations such as temperature, humidity?

Thanks
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Fri May 14, 2021 4:16 pm

I would also be very interested in this.
Today i experimented about one and a half hour at zell am see again, but i only got one thermal and even that was not productive enough to get any net altitude with the glider. The surrounding doenward airstream is so strong compared to the very small core, i could not get the core right and so its hard to gain any altitude. Also they seem to be very short lived: despite having a nice cumulus top, i was not able to get any core again after the first pass, derpite trying hard.

I think it is the weather settings and/or location.
For beginners the ridge lift is way more easy to use, but i want to use thermals too!

I will ask on the list if there is any good method to visualize the shape of the thermal.
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Re: Thermal spawning, ridge wind and weather configuration

Postby danielHL » Fri May 14, 2021 4:45 pm

Hm, I can second this: back when the ASK21 was still yasim, I could get several m/s up in the right thermal and get to the cloud base sometimes. The jsbsim model flies much nicer overall, but I never could get any reasonable thermal lift out of it... But this may also be due to my poor glider flying skills and yasim over-estimating things, like usual...
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Re: Thermal spawning, ridge wind and weather configuration

Postby Ysop » Fri May 14, 2021 9:16 pm

According to D-ECHO, that thermal weather engine has been more tested with Yasim.
But it should be possible....

Currently trying to find some wave :)
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Re: Thermal spawning, ridge wind and weather configuration

Postby Michat » Sat May 15, 2021 12:06 am

For those glider's aficionados in FG I'll recommend you to try the Perlan 2 stratospheric glider by HerbyW, under permision of Airbus. This is a complete MP adventure where several gliders will been towed by their respective AI C172 aerotow, to 10000' after that the birdpack will unhook, heading to the west in order to find a shock wave area, see internal map. Not every pilot will success to climb to the top, among the three soaring level, but if you are in luck reaching FL40+ you can break the FG distance glider record, KSFO-KLAX on 17hrs., although you can return to base. Calafate airport and the surroundings is an awesome scenery. Readme file is a must.

Enjoy a lot at: https://github.com/HerbyW/Perlan2

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Re: Thermal spawning, ridge wind and weather configuration

Postby S&J » Sat May 15, 2021 12:26 am

Whoever created the advanced weather screwed up the jsbsim side of things...

I'd explain but would probably be vilified for it.
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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Sat May 15, 2021 6:49 am

Whoever created the advanced weather screwed up the jsbsim side of things...

I'd explain but would probably be vilified for it.


Well, the chances of that happening would be substantially reduced if you'd start with the ex[/]plaining rather than the [i]complaining - as it is, you're setting up a self-fulfilling prophecy.

And, well, there really is no JSBSim-side of things to weather - the weather doesn't know your FDM, it just tells the FDM what the air does.

I'd explain the issue, but since you already started with the complaint...
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Re: Thermal spawning, ridge wind and weather configuration

Postby Maerchenprinz » Sat May 15, 2021 9:45 am

...start with the ex[/]plaining rather than the [i]complaining...
:D

@benih: You may try to use the property-browser (key "/") to (cough) "visualize" the thermals and ridge-lift. Under /environment, you can Shift+Click on the properties to display them at the top-left of your screen. I know, that's not really "visualizing" or "flying with one's bum", but hey!
Please note that the property "thermal-lift-fps" seems to be unused (or left for thermal-scenarios?); "wind-from-down" looks like the one instead.

Ciao,

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Re: Thermal spawning, ridge wind and weather configuration

Postby S&J » Sat May 15, 2021 1:27 pm

Advanced weather interferes with the jsbsim flight model properties that control turbulence.

It's as simple as that. Read and understand it. If you wrote the code you'll know which ones it's effecting, look for yourself.

But don't come on here telling folk we know nothing.

Folks, go manual weather, adjust the properties and have a good look at how jsbsim internally handles the situation and understand how advanced weather instead of working in harmony with it attempts to overwrite the values needed.
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Re: Thermal spawning, ridge wind and weather configuration

Postby benih » Sat May 15, 2021 3:12 pm

And, well, there really is no JSBSim-side of things to weather - the weather doesn't know your FDM, it just tells the FDM what the air does.

I'd explain the issue, but since you already started with the complaint...

Thorsten, i would be pleased if you enlighten me.
I feel understanding things better will allow me to learn soaring better.
In strongly think, the fault is not with the weather system, but my input params and flying skills.

@benih: You may try to use the property-browser (key "/") to (cough) "visualize" the thermals and ridge-lift.

Thank you for the hint, but i already know. What i would need is a visualization, maybe also some weather map, showing me for sure where the thermals are. Currently i don’t know if i just fly wriggly, or if the thermal in question simply is not there or too small
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Re: Thermal spawning, ridge wind and weather configuration

Postby D-ECHO » Sat May 15, 2021 4:27 pm

Hi there,

I have made the same observation that flying thermals with a YASim glider is way easier than flying them with a JSBSim one. Actually, I asked a similar question some time ago, getting the advice to reduce turbulence, which made it already a lot easier than before (see viewtopic.php?f=69&t=36832).

Another thing that I (think I) noticed while trying again today, maybe @Thorsten you could explain on whether this is really the case, is that it seems like the thermals are moving with their cumulus cloud (or their blue cap if there's on cloud, probably), whereas as far as I know in real life thermals are more like a hose, starting at a pretty defined area on the ground (e.g. areas that heat up more easily) and the cap is their effect. Why I think this matters is that I have the feeling that this makes it way more difficult to "center" the thermal, given that it travels at the cloud's altitude's wind speed, whereas the aircraft might be blown into a different direction at a different speed ( as it's at a lower altitude ). Am I getting this halfway correct?
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Re: Thermal spawning, ridge wind and weather configuration

Postby Ysop » Sat May 15, 2021 4:36 pm

Some are stationary but thermals usually separate from the ground and move with their cloud. Picture waterdrops falling from a wet ceiling and being blown sideways.

Any property, which indicate, that there is at least a probability of thermals?

Just trying out in Namibia....usually there should be a good chance.
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Re: Thermal spawning, ridge wind and weather configuration

Postby Thorsten » Sat May 15, 2021 4:49 pm

Advanced weather interferes with the jsbsim flight model properties that control turbulence.


No, it doesn't interfere with these parameters, it sets these parameters (among others). That's the whole point about having a weather system - to tell the FDM what the wind and turbulence is and to tell the renderer what the visibility etc. are.

If you wrote the code you'll know which ones it's effecting, look for yourself.


I just told you that I'd explain the issue for you as it is very known to me and in fact solved long ago - since you don't know that, I feel somewhat justified in treating you as someone who 'knows nothing' as you so eloquently put it :D

Thorsten, i would be pleased if you enlighten me.


Happy to - the issue is that a wind vector has a very well defined mathematical meaning - so setting an updraft or a shear or whatever else works pretty much the same in JSBSim and YaSim. However, turbulence-magnitude-norm (which is the turbulence control parameter for both JSBSim and YaSim) has no well-defined meaning, it more or less is 'some parameter' between 0 and 1 which dials how strong turbulence is simulated.

Unfortunately JSBSim and YaSim treat the parameter very differently - while 1 in YaSim is challenging but very flyable, 1 in JSBSim definitely is not flyable. Add to the mess that some gliders seem to have set a rather funny inertia tensor (which you can see in aerotow, I've done this in real life, and I know how a plane behaves on the tow line, some JSBSim planes behave very different however) - so these planes respond internally consistent and fine in still air, but can't deal with an externa; force like a tow line - or turbulence, they treat it as if it'd be much stronger than it actually is.

Since it'd be vastly unprofessional for the weather system to do a detailed investigation of the FDM before generating weather, the AW GUI has a slider to dial turbulence strength - which you can dial up for YaSim and down for JSBSim, and even further down to virtually no turbulence if you're in one of these funny planes.

So the issue is well known, understood and solved - just some people can't be bothered to simply check the GUI or ask nicely :mrgreen:
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