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. LeeE ------------------------------------------------------------------------- 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
