Dave,

You have confused me even more!
If I am flying a radial with a cross wind, should the HDG bug be on the
radial or should it be on the estimated course made good with the wind
correction?

Thanks,
Ross
"Dave Butler" wrote in message
...
News wrote:
snip
What algorithm is the autopilot is using? How does it uses the
Heading bug info in conjunction with the OBS and CDI? I noticed that
once I
am tracking a radial if I change the HDG bug the aircraft turns. My
mental
model has the autopilot just using the CDI deflection and OBS setting to
hold a course, but obviously I am missing something. If anyone can
point me
to some more detailed information on how the AP uses the Heading Bug
while
in NAV or APR mode I would appreciate it.

I don't have specific experience with the KAP140, but it sounds like it
may work
just like a couple of other ones I have used.

I think you understand how it works in HDG mode, right? There is an error
signal
from the heading bug, and the aircraft is turned so as to correct the
error. In
NAV mode, the CDI error is (conceptually) added to the heading error, so
that
the effective zero-error heading will be slightly off the heading bug
setting
when the CDI is not centered.

In a crosswind, theoretically the aircraft will track a course offset from
the
radial on the downwind side, with a heading offset into the wind. The CDI
will
be offset upwind, and the heading flown will be offset into the wind from
the
heading bug. In other words, it doesn't track the center of the radial, it
tracks just enough off to the side so that the error signal from the CDI
plus
the error signal from the heading bug cancel each other.

Dave

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