[Flightgear-devel] Generic Autopilot Rework Proposal

[Josh D. <jos...@gm...>]

Hi,
For years the generic AP has irritated me as it just flies very poorly. In
my view a generic AP should be able to fly most aircraft with plausible
FDM, but the generic AP can barely do that. (No offense intended to the
original creator)

I created some prototype of a reworked generic AP last year but forgot
about it, it was designed to be able to fly any aircraft with a
plausible FDM.

To be clear - this is not anything like IT-AUTOFLIGHT. IT-AUTOFLIGHT is
designed to facilitate development of realistic airliners autopilots, which
is totally different goal then a default generic AP.

This generic AP I wrote last year was designed to be a *drop-in replacement*
of the existing - no aircraft side edits required. It uses the existing
properties to maintain compatibility and is designed to fly as many types
as possible. The control system design is very specifically made so that
different FDMs and feeling aircraft can still be flown with some stability.

The primary issues with the current generic:
- Unstable response in all heading/route manager, altitude, and speed on
pitch control
- Overshoots/undershoots due to bad integrator use/cascade design
- Oscillation/vibration on sensitive aircraft
- Oscillation/overshoots on heavier flying aircraft
- Bad pitch control handling
- A few more I can't remember now

I made a quick demo showing the heading, altitude, and trim issues:
https://youtu.be/9b1e9aVzT7Q
Did not have time to film/demo all the other issues, this is just a small
subset of the issues. If weather comes into play, it just gets much more
unstable

I also think some configurability can be added, for example, whether to use
the baro altimeter or the standard altitude shown in the HUD and /position.
This would not require any aircraft side changes for the default behavior.
Meaning, when the setting is not there, the file falls back on the default
behavior (ex, standard altitude prop), and when the setting is there, it
uses the defined behavior. That way any airplanes use the default behavior,
and also there is some minimal configurability possible by the developer.

Appreciate your thoughts and feedback, and if there is interest, I will put
together a demo using the prototype file I created, and you can tell me
what you think! I really think this would improve alot of the "unfinished"
planes that are borderline un-autopilotable with the current generic AP.

Kind Regards,

--
Josh Davidson