reported Su-27 autopilot and trim

[Volator]

When using the autopilot, e.g. attitude hold mode in the Flanker, shouldn't it give you a more or less trimmed aircraft when you deactivate the autopilot? In its current state, autopilot deactivation can cause radical attitude changes as the autopilot either doesn't use trim at all to maintain a certain flight regime, or it reverts to the trim settings before autopilot activation.

My understanding from (western) real-world aircraft is that AP uses trim to maintain attitude and the a/c will therefore maintain a commanded attitude when you deactivate the AP.

Edited May 18, 2023 by Volator

[BigBorner]

This is the case for the SU25T but unfortunately not for the flanker. 
 

I don’t know if this is „just“ reality driven or a DCS Bug / inaccuracy. 

Edited July 16, 2023 by BigBorner

[Ironhand]

On 5/18/2023 at 3:39 AM, Volator said:

When using the autopilot, e.g. attitude hold mode in the Flanker, shouldn't it give you a more or less trimmed aircraft when you deactivate the autopilot? In its current state, autopilot deactivation can cause radical attitude changes as the autopilot either doesn't use trim at all to maintain a certain flight regime, or it reverts to the trim settings before autopilot activation.

My understanding from (western) real-world aircraft is that AP uses trim to maintain attitude and the a/c will therefore maintain a commanded attitude when you deactivate the AP.

 

What you are experiencing is a bug. You should report it as such. In DCS’s Su-27, when you disengage the ACS, the system seems to revert to the trim setting you had before engaging it. This is impossible as it has no such “memory” function.

The real world manual cautions against disengaging by moving the stick because it can cause transient extreme roll, etc. But the is no such caution in regard to disengaging the system properly.

[Volator]

On 5/18/2023 at 9:39 AM, Volator said:

When using the autopilot, e.g. attitude hold mode in the Flanker, shouldn't it give you a more or less trimmed aircraft when you deactivate the autopilot? In its current state, autopilot deactivation can cause radical attitude changes as the autopilot either doesn't use trim at all to maintain a certain flight regime, or it reverts to the trim settings before autopilot activation.

My understanding from (western) real-world aircraft is that AP uses trim to maintain attitude and the a/c will therefore maintain a commanded attitude when you deactivate the AP.

 

 

6 hours ago, Ironhand said:

What you are experiencing is a bug. You should report it as such. In DCS’s Su-27, when you disengage the ACS, the system seems to revert to the trim setting you had before engaging it. This is impossible as it has no such “memory” function.

The real world manual cautions against disengaging by moving the stick because it can cause transient extreme roll, etc. But the is no such caution in regard to disengaging the system properly.

@Flappie Can you take a look at this please?

[Ironhand]

Here's a TRK file demonstrating the issue. I engage baro altitude hold and, then, disenage it at close to the same airspeed and there is little trim difference. I then reengage baro altitude hold and increase speed. Upon disengaging the ACS, the nose pitches up severely due to the trim reverting to the "lower speed" trim.

Su-27 ACS Issue.trk

[Flappie]

Thank you, @Ironhand.

Issue reported.

[Volator]

Test_Su-27_AP_no_trim.trkTest_Su-25T_AP_trim.trkTest_MiG-29A_AP_trim.trk

 

Su-27 AP still not trimming correctly, Su-25T and MiG-29 APs show expected behavior. Please note the jittering in the aileron trim of the MiG-29, gonna post another bug report on that.