Norman Vine writes:
> >Interesting.  I've seen the problem consistently for quite a few
> >months (the AP holds the DG about 10 deg off the heading bug).
> 
> Yep this changed recently.
> 
> It is almost as if the magnetic deviation is being added in twice ??
> I haven't really checked into this though

I took a quick peek this morning.  I think the autopilot and heading
values are correct.  What I'm seeing (and this behavior did change
recently) is that the JSBSim C172 now requires significant right
aileron/rudder to hold straight level flight, even at full throttle,
full speed, level flight.  Even in a descent I see a lot of turning
force and need to compensate with right rudder/aileron to maintain a
straight path.

The autopilot heading hold is just 'proportional' so it assumes that
neutral controls correspond to straight flight and slight offset's
either way will produce a slight turn in that direction.  So, if there
is constant left turn bias, the autopilot heading hold will never
quite get there.  At full throttle level flight with the JSBSim C172,
the closest I can get is about 3 degrees off the desired heading.
The error is much bigger in a climb.

Note that the YASim C172 doesn't have this same effect and the
autopilot holds the heading well for it.

So, I hearby decree that this is a problem with JSBSim (or at least
the JSBSim C172 model) and not the autopilot or FlightGear or recent
property manager changes.

Regards,

Curt.
-- 
Curtis Olson   IVLab / HumanFIRST Program       FlightGear Project
Twin Cities    [EMAIL PROTECTED]                  [EMAIL PROTECTED]
Minnesota      http://www.menet.umn.edu/~curt   http://www.flightgear.org

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