As a 300 hour user of a KAP140 I would caution you on several things
depending on the
plane its fitted to.

The short list of gotchas a

Easy to inadvertantly fly an ILS instead of a GPS if you mistune the NAV
receiver

Because its pitch information is based on rate of climb , mountain waves,
buump clouds,
thermals can cause significant airspeed and pitch chnage attitudes,
including stalling the plane!

Inadvertant engagement of the AP on teh ground can cause uncontrollable trim
excursions

If you tweak a nav system whilst its connected it may appear to be connecte
dto teh njav solution but
its actually disenegaged

apart from thats its fine!

PS make sure you can hand fly in real iFR when it lets go!

peter


"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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