Jon S. Berndt wrote: > > > I flew the rw29R ILS into Jeffco (KBJC) with the SenecaII Altimatic IIIc > > > autopilot all the way to the runway slowly pulling back the power so the > > > auto trim did the flare out (sort of anyway). Touch down was on the > > > center stripe! > > > > > > But with the no turbulence, you could see the ball move off-center > > I think you meant, with turbulence ON. ? > No, I meant with turbulence OFF. With it on, you get ball motion all the time. With it off, the ball is centered except when the autopilot moves the ailerons. And when the autopilot tries to roll left, the ball moves to the left. When the autopilot tries to roll right, the ball moves to the right. If the ball only moved say 1/4 of a ball width, that would likely be OK. But it moves as much as a ball width. This is much more adverse aileron yaw than one sees with there feet on the floor and initiating a roll in a real high performance airplane. > > > every time the autopilot applied aileron to roll the AC. This > off-center is > > > WAY more than one would see in the real SenecaII. Jsbsim has a very > > > noticeable exaggerated adverse aileron yaw issue. > > > > > > -Dave Perry > > "JSBSim" does not have any "adverse aileron yaw issues". JSBSim only > models an aircraft given the data that is fed to it. Let me elaborate. > There are two issues at work: > > 1) Turbulence is admittedly poorly modeled. Indeed, this has been an > experimental feature for quite a while, and has not gotten the > attention it has needed. > > 2) Adverse yaw is a function as defined in the aircraft model. You can > either have it, or not. It's up to you. The SenecaII adverse yaw is > described in the SenecaII config file beginning with these lines: > > <function name="aero/coefficient/Cnp"> > > <description> > > Yaw moment coefficient due to roll rate(per radian) > > Reduces Dutch Roll damping. Positive value desirable. > > </description> > > <product> > > <property>aero/qbar-area</property> > > <property>metrics/bw-ft</property> > > <property>aero/bi2vel</property> > > <property>velocities/p-aero-rad_sec</property> > > <table> > > <independentVar>aero/alpha-rad</independentVar> > > <tableData> > > -.1396 .4890E-01 > > -.1047 .3126E-01 > > -.6981E-01 .1374E-01 > > -.3491E-01 -.3595E-02 > > .000 -.2134E-01 > > .3491E-01 -.3939E-01 > > .5236E-01 -.4852E-01 > > .6981E-01 -.5772E-01 > > .8727E-01 -.6699E-01 > > .1047 -.7633E-01 > > .1222 -.8576E-01 > > .1396 -.9525E-01 > > .1571 -.1070 > > .1745 -.1195 > > .1920 -.1304 > > .2094 -.1405 > > .2443 -.1597 > > .2793 -.1803 > > .3142 -.1857 > > </tableData> > > </table> > > </product> > > </function> > > I think it is conceivable that the adverse yaw is too high for the > SenecaII. That's easy to adjust. Add the line in red, below, to your > SenecaII file for the above-seen Cnp definition: > > <function name="aero/coefficient/Cnp"> > > <description> > > Yaw moment coefficient due to roll rate(per radian) > > Reduces Dutch Roll damping. Positive value desirable. > > </description> > > <product> > > <!-- a scaling factor for the adverse yaw definition --> > > * <value> 0.30 </value>* > > <property>aero/qbar-area</property> > > <property>metrics/bw-ft</property> > > <property>aero/bi2vel</property> > > <property>velocities/p-aero-rad_sec</property> > > <table> > > <independentVar>aero/alpha-rad</independentVar> > > <tableData> > > -.1396 .4890E-01 > > -.1047 .3126E-01 > > -.6981E-01 .1374E-01 > > -.3491E-01 -.3595E-02 > > .000 -.2134E-01 > > .3491E-01 -.3939E-01 > > .5236E-01 -.4852E-01 > > .6981E-01 -.5772E-01 > > .8727E-01 -.6699E-01 > > .1047 -.7633E-01 > > .1222 -.8576E-01 > > .1396 -.9525E-01 > > .1571 -.1070 > > .1745 -.1195 > > .1920 -.1304 > > .2094 -.1405 > > .2443 -.1597 > > .2793 -.1803 > > .3142 -.1857 > > </tableData> > > </table> > > </product> > > </function> > > The above scale value (0.3) will make the scale factor only 30% of > what it originally was. You can play with that value as much as you > want - even scaling it to zero. > > Let me know if that helps. > 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 ------------------------------------------------------------------------- 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
