F-16 Autopilot settling

[Exorcet]

The F-16's autopilot has been this way forever and it has always bothered me. When using ALT/ATT hold, AP won't hold the orientation of the aircraft when AP is engaged. Instead the plane will continue to roll until the roll rate is slowly brought to zero. This makes it difficult to point the jet in a precise direction unless the roll trim is perfect. Example, you want to set ALT hold while pointing at a waypoint while the jet is imbalanced (AMRAAM on one wing, not the other, for example). You level the jet, set it on the correct heading,  then engage AP. The jet will roll to one side and no longer be pointing the correct direction.

I would expect the AP to target the bank angle at the moment the AP switch is engaged and for the aircraft to slowly approach that angle. So in my example above, the jet might roll to one side initially, but I would then expect it to reverse the roll and end up level, with a bank angle of 0. If my expectation is wrong, then there is no problem, but in the absence of concrete documentation, the F-16's AP does not seem to be designed well when it comes to roll.

[Frederf]

That's my take as well. It won't exceed +-60 AOB or +-20dps roll rate though. Roll command autopilot branch is mixed in to the command path at 30% the weight of the stick input value. It's not just a piD controller seeking zero D.

[SCPanda]

ED is still tweaking F-16's FLCS so this might change (hopefully). 

[Aquorys]

On 5/28/2022 at 10:59 PM, Exorcet said:

This makes it difficult to point the jet in a precise direction unless the roll trim is perfect. Example, you want to set ALT hold while pointing at a waypoint

If you're flying towards a waypoint anyway, you might as well just go to steerpoint select instead of attitude hold on the roll switch, that should kinda solve your problem.

[RuskyV]

Does the AP have any command or input to the trimming? I know currently the trim is super sensitive and very hard to neutralise role. 
 

I’m wondering if the AP is also fighting this but with less authority over roll it might hunt longer for heading?

[Exorcet]

9 hours ago, Aquorys said:

If you're flying towards a waypoint anyway, you might as well just go to steerpoint select instead of attitude hold on the roll switch, that should kinda solve your problem.

If I'm semi-frequently toggling AP, I don't like to have it set to STRG SEL since I might forget to switch that off and wonder why my jet is suddenly turning. The waypoint thing was just an example for clarity anyway. In other cases tracking the waypoint doesn't help.

3 minutes ago, RuskyV said:

Does the AP have any command or input to the trimming? I know currently the trim is super sensitive and very hard to neutralise role. 
 

I’m wondering if the AP is also fighting this but with less authority over roll it might hunt longer for heading?

AP doesn't have anything to do with trim, and trimming does help with the issue, but I feel like the behavior in the sim is still incorrect, or at least suspicious. I also try to avoid trimming if it's likely that I will soon return to a balanced state just because of how hard it is to trim precisely in DCS.