Since Andy's working on the virtual cockpit idea right now and I'm still
studying ssg code, I'd like to do some more work on the autopilot before
returning to the panel.

Basically what I'd like to do is make some adjustments so that the autopilot 
functions more closely model real world devices.  Some of these buttons are
new and some exist but would have a slightly different effect.  Also some of
the features are in the code already, some not.

ButtonName - Description of function

TEST - illuminate the display indicators breifly (or while held???)
Engage/Disengage (aka AP button) - this will lock in the current heading and
pitch (when multiaxis supported).

HDG - will switch heading hold over to the Bug.

ALT - will the override pitch-hold angle and level at current altitude.

ARM - will continue at pitch-hold angle until altitude set with dial is    
reached then it will override pitch-hold angle and level off.

NAV - will switch heading hold over to NAV1.  Clicking on NAV when APR is on
will turn APR off and release AP from glideslope (see APR).

APR - will lock on ILS and GS indicator will light when GS is found.  If and
only if the GS is found the pitch-hold angle is overriden. It will also turn
off the NAV mode and APR indictor will show that the localizer has been found.

REV - same as APR except backwards no GS.

PITCH Up/Down - clicking these buttons will change the pitch-hold angle by 1
degree.

FD - Flight director.  This needs a little more investigation before I know
what exactly it does.  My guess at this point is that it'll allow manual
inputs via controls to change heading and pitch or continue flying the plane
until the pilot wants the AP to take over again (which it will do automatically).

This is my impression of how an autopilot like the kap140 should work.  Of
course not all aircraft can support more than 1 axis.  As I go along I will
probably add properties to the per aircraft configuration, so that the
behavior of APR will be modified if only 1 axis support is desired.  It would
seem that an aircraft with no vertical axis will have no ALT or UP/DOWN buttons.

One critical change here will be locking into a pitch-angle for climb and
descent rather than a climb-rate and zeroing in on a pitch-angle for to
achieve that rate.  This should make the ride a little smoother, doing away
with the wild pitch oscillations that sometimes occur.

Of course this means that it'll also be possible to hold a pitch angle that
will stall the aircraft if the throttle is lowered enough.  I'm not sure how
or if a real world autopilot deals with this type of error.

Comments would be welcome, especially from anyone who has actually used 
these devices.

Best,

Jim

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