leee wrote: > On Monday 08 October 2007 02:17, dave perry wrote: > >> While optimizing the aitopilot config files for the Century IIB and III >> autopilots for the pa24 and the Altimatic IIIc for the SenecaII, a >> significant difference between the values of parameters (gains in >> particular) that give non oscillatory behavior in yasim and jsbsim >> became very apparent. I had to completely turn off turbulence to get >> stability without significant overshoot in >> SenecaII/Systems/ALTIMATICIII.xml. With the values submitted to cvs, >> the Seneca still has a wing rock in LOC REV and LOC modes with the >> default weather that has some turbulence. The pa24 with the same values >> is as solid as a rock with the default turbulence all the way down the >> glide slope. With the turbulence zero, both behave the same. >> >> The SenecaII wing rock with light turbulence appears to result from a >> very exaggerated adverse aileron yaw. So I did the same experiment with >> the c172p and pa28-140 which both use the kap140. With the default >> turbulence, the c172p oscillates so bad that you cannot complete the >> approach with the LOC needle going full stop to full stop near the >> runway. The pa28-161 (also yasim) is as solid as a rock all the way >> down the glide slope with light to moderate turbulence. >> >> If you watch the oscillation for either jsbsim model, you should note >> that when the yoke is rotating counter clockwise, the nose is yawing >> right and then finally swings back left, as would be expected with >> extreme adverse aileron yaw. >> >> Most high performance AC show very little AAY except in significant >> slow flight. I would not expect that small aileron deflections should >> move the nose counter to the roll in a SenecaII or pa24. >> >> Two questions: >> 1. Have others noticed this difference between jsbsim and yasim? >> 2. Can this adverse aileron yaw be toned down in jsbsim? >> >> Regards, >> Dave Perry >> > > Is auto-coordination enabled? I don't think this is effective for YASim > aircraft but it may be complicating things on JSBSim aircraft. Also, are you > getting the same frame-rates with both aircraft? Last time I ran FG I found > that the autopilot PID controllers ran at the frame rate and not at the <Ts> > rate specified in the controller definitions, which could make them unstable > outside a fairly narrow range of fps. > > I have the frame rate throttled to 25 hz as that is achievable with my setup and both AC. I have tried turning on auto coordination. This helps a little. Also, I included a yaw damper in the autopilot config file for the SenecaII. This helps most of the time but can also add to the problem. Toggle for the yaw damper is a SenecaII menu item in the patches I sent to Andy.
Here are the switches from my last test from fgrun. > /usr/local/FlightGear-plib/data/bin/fgfs > --fg-root=/usr/local/FlightGear-0.9/data > > --fg-scenery=/usr/local/FlightGear-0.9/data/Scenery:/usr/local/FlightGear-0.9/Scenery-0.9.10 > --airport-id=KSFO > --aircraft=SenecaII-jsbsim > --control=joystick > --disable-random-objects > --disable-ai-models > [EMAIL PROTECTED] > --turbulence=0.49 > --geometry=1680x1050 > --visibility-miles=15 > --bpp=24 > --fov=65 > --timeofday=dusk > --nmea=socket,out,5,localhost,5500,udp > --prop:/sim/frame-rate-throttle-hz=25 In this test, I turned the turbulence up to 0.49. With this value, the pa24 bounces around a lot and you see the impact of what seems to be thermals and wind shear, but the Century III autopilot flies right down the LOC/GS past the inner marker for RW28R at KSFO. The turbulence means I am constantly adjusting the throttle, but the AP does a good job for all else. LOC and GS stay very nearly centered. With the SenecaII and 0.49 turbulence, it is hardly controllable without the AP, and definitely not controllable with the AP. I think Jon B. is onto something by asking how turbulence is implemented in the various fdms. Thanks for the ideas, Dave ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
