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List:       flightgear-devel
Subject:    Re: [Flightgear-devel] =?utf-8?q?Need_help_to_commit_extension_for_as?=
From:       "polzer.thomas () t-online ! de" <polzer ! thomas () t-online ! de>
Date:       2015-09-25 16:50:28
Message-ID: 4677067256057b54ded947.80843086 () email ! t-online ! de
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Hi Thorsten,

I have 25 years of experience as a glider pilot with PPL-C and PPL-C. Aerotow and \
Aerobatic authorization as well. That no longer seems relevant, no doubt.

The ASK 13 goes very well with both the thermal_demo thermals and with the "advanced \
weather" thermals too.

ASK-13 is a YASim aircraft. The asw20 (DG-101G) are both JSBsim aircraft.

I myself have had good experiences and beautiful flights with asw20 and DG-101G.

Was thinking to make a good contribution to make other users gliding interesting to \
me. Interest appears to exist. Will I still repeatedly addressed via chat by ATC or \
pilot.

No interest in my idea? Then it's good for me. I want anyone bored.

With best regards
Thomas Polzer


-----Original-Nachricht-----
Betreff: Re: [Flightgear-devel] Need help to commit extension for asw20 (setting \
                thermals arround plane)
Datum: Fri, 25 Sep 2015 18:30:29 +0200
Von: "Renk, Thorsten" <thorsten.i.renk@jyu.fi>
An: FlightGear developers discussions <flightgear-devel@lists.sourceforge.net>

> For some time, I developed a love for gliding in FGFS. If, however,  
> dealt with quite simplified. To make thermal gliding possible, I've come  
> up with something practical.

I've responded somewhat unenthusiastically to the idea in the forum. The reason is \
that this uses the 'old style' AI scenario thermals and distributes them around the \
plane using a script, i.e. the plane brings its own weather - which I frankly don't \
like conceptually.

The argument for introducing the thermals that way given in the forum is that AW \
thermals use some amount of turbulence (actually selectable in the GUI) and Thomas \
found them too hard to use in the ASW-20. There's some history to that as well, the \
scripted thermals were first introduced by the DG-101G which had the same issues with \
turbulence.

Initially I suspected that this is a JSBSim vs. YaSim issue so that a plausible \
amount of turbulence for YaSim planes makes JSBSim handling impossible and so we \
would need to adjust the meaning of turbulence-magnitude-norm in one of the engines \
to get comparable behavior. After some time, I'm less sure. I've flown the DG-101G \
under aerotow (I might add that I have flown aerotow in real life and know quite well \
how a glider should handle in that situation). The DG-101G was bouncing wildly and \
did not handle like a real glider under tow at all - this made me suspect that the \
inertia tensor somehow has a problem - which would not really show up in still air as \
many aerodynamic properties are dimensionless, but would show up in turbulence or for \
external forces.

In addition, I've done a test flight with the SenecaII in turbulent conditions, and \
the plane handled like I would expect - certainly not impossible to control. 

As a result my current theory is that there's some FDM-side issue in the JSBSim \
gliders which makes them behave oddly under turbulence (and aerotow) and rather than \
fixing the root cause, using plane-generated thermals is a quick fix to hide the \
underlying issue bu getting rid of the turbulence.

I think this needs to be investigated thoroughly and fixed either plane-side (or if \
it turns out that JSBSim genuinely handles turbulence different from YaSim by a \
scaling factor FG-side), but not by a workaround.

My two cents.

* Thorsten
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