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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