Laurence Vanek wrote: > dave perry wrote: > >> Laurence Vanek wrote: >> >> >>> dave perry wrote: >>> >>> >>> >>>> Thanks Jon, >>>> >>>> I have not used jsbsim to model any aircraft in flight gear. So I was >>>> not aware of where the adverse-aileron yaw was modeled in jsbsim. I was >>>> only reacting to what seems to me a very exaggerated response. Perhaps >>>> we need to consider such a scaling as default as the c172p also seems to >>>> suffer from this exagferated yaw response. >>>> >>>> -Dave Perry >>>> >>>> >>>> >>>> >>>> >>>> >>> Dave - >>> >>> I tried the 0.3 scale factor. It does calm things down a bit for OSG >>> version. >>> >>> >>> >>> >> I also tried the 0.3 scale factor and agree it helps in the presence of >> turbulence. But even w/o the scaling, if I make sure the turbulence is >> really zero, the cvs SenecaII shows no oscillations all the way to the >> runway using the AP to follow the LOC/GS. >> >> >>> I believe, however, that something else is going on with the A/P during >>> ILS approach. I do not get the behavior you report on approach. The A/P >>> begins to make large over corrections about one mile out, to the point >>> where I need to disable the A/P & make the approach manually using the >>> HSI. Not good if in poor IMC conditions with no visual refs. until at DH >>> (~200 ft). >>> >>> >>> >> I get this behavior with any non zero turbulence even with the 0.3 >> scaling. If I open the Weather menu and the Weather Conditions sub menu >> and make sure all the turbulence tabs are slid all the way to the left >> and then click on apply, the SenecaII settles down and follows the ILS >> down to the runway. You cannot just use the fgrun advanced options >> weather tab to zero the turbulence as it does not really zero the >> turbulence. Make sure the property >> /environment/turbulence/magnitude-norm is '0' (double). With fgrun >> advanced weather turbulence set to zero, this property will still be >> 0.00067 ... which is enough to cause the oscillations on my system. >> >> With the yasim pa24-250 and this value set to 0.33, and the Century III >> AP which is nearly identical to the Altimatic IIIc, I do not get the >> oscillations. I do get what fells like moderate turbulence. But the AP >> takes you right down the GS and the LOC stays centered. The yoke is >> moving in response to the bumps, but the needles stay centered and the >> yaw response is quite realistic. >> >> The fact is that turbulence seems to be well modeled in yasim, and as >> Jon Berndt indicated, it needs significant work in jsbsim. As Jon >> indicated on the developers list, he has modified jsbsim to ignore the >> turbulence setting (i.e. turns off turbulence modeling) in jsbsim cvs. >> This has not been ported to fgfs. >> >> >> >>> Perhaps this is another OSG vs. PLIB difference (although I cant see how)? >>> >>> >>> >> I don't have an osg version running right now. I agree that this is >> unlikely to be the issue. Do any others see this issue with the >> turbulence really zero? >> >> >>> Im running Linux Fedora 8. >>> >>> >>> >> I am running Fedora 7 on a Athlon XP 3200+ with 2G DDR ram and an Nvidia >> GeForce 7800 GS OC. >> >> One other possible AP "tuning" issue. What frame rate are you getting? >> The controller affective time constants vary with frame rate. My >> testing is at frame rates that vary from about 50 to 70 fps. >> >> -Dave Perry >> >> >> > Dave - > > We may be comparing an apple with an orange here, concerning OSG & PLIB :-) > > As I stated I am building from OSG svn & FG cvs head. I find no fgrun in > my install. I do have a " runfgfs.bat" that I do not use (looks like a > windows file). Only these files in /usr/local/bin: > fgrun is a separate compile and not part of fgfs. Here is a link from the FlightGear wiki. http://sourceforge.net/projects/fgrun. The wiki explains what it is and the are many screen shots of an early version there. It is just a convenient "fgfs launch control". > al-info fgfs gl-info metar osgconv osgviewer yasim > est-epsilon fgjs js_demo osgarchive osgversion terrasync > > I run FG (fgfs) directly from there. I set preferences in my ~/.fgfsrc > file (things like --turbulence=0.0). I see that turbulence is also set in my > > ~/FlightGear-0.9/data/preferences.xml > > file, with different values at different elevations. Not sure how the > .fgfsrc file & the preferences.xml reconcile. Maybe thats where we are > different. > I am pretty sure that these elevation turbulence values are what are used at run time. You can check these once fgfs is running by going to "weather" in the drop down menu at the top of the screen and then selecting "weather conditions". The turbulence values that mess up the approach are the "Boundary Layer (AGL)" section. What I notice is that even when I set turbulence = 0.0 before launching fgfs, the tab for 500 ft agl will have a nonzero value. Just slide these tabs all the way to the left and click on Apply. Then you will have no turbulence.
As Jon Berndt said on the developers list, he intends to turn off turbulence in JSBSim for the up-coming release. In other words, it is broken and he plans to reprogram it to match how yasim models it. I am 99.99% sure that this broken turbulence is what is causing your oscillations on the ILS. > Our system capabilities are similar, I have an Intel core 2 duo cpu, 2 G > RAM, Nvidia 7600 GS (256 Megs of VRAM). I am throttled in my ~/.fgfsrc > to give similar frames rates as you with no indication of stutter or > hesitation (thank God, at last). > > My instincts tell me this is a controller issue relating to rate > changes. Is there any possibility that that our > > ~/FlightGear-0.9/data/Aircraft/SenecaII/Systems/CENTURYIII.xml > > files have different controller parameters? Does PLIB version you are > running use identical file? > The only way our CENTURYIII.xml config files could have different values is if you have changed them from what is in cvs. There are no differences between the data cvs for osg and plib. There is just one data repository. Just make sure you really have turbulence zero by moving the tabs I mentioned in the drop-down weather menu all the way to the left and the oscillations will be gone. > thanks for staying with me on this. > > Not a problem. -Dave Perry ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Flightgear-users mailing list Flightgear-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-users
