Roll Trim can never return to Center

[pauldy]

Seems that once you trim left or right.. the jet can never go back to perfect center trim again.. Even with trim reset, engaging auto pilot modes, etc..

The same thing also happens to the F-15 ..so i guess this is an FC3 quirk or something?

Pretty much i'm careful not to trim for left or right roll.. unless needed for asymmetric loads for landings.. (e.g. there are more remaining missiles on one side)
 

[Ironhand]

Never noticed it in the Flanker, perhaps because of how I fly her. Non-recentering  is certainly an issue in the MiG-29. In AP you can watch the MiG’s trim continually shift right-left in an effort to maintain level flight.

EDIT: Just checked. You are correct for the Su-27. Even LAlt+3 (Transition to Level Flight) does not correct the issue. Goes out of trim as soon as you exit the mode.

Edited January 22, 2022 by Ironhand

[pauldy]

I see, glad i'm not the only one that noticed this.

iirc, this has been a nuisance since 1.5. I'm surprised it wasn't addressed even up to now.. or perhaps no one really reported it or something.

==
for the record I have the current DCS Stable 2.7.9.18080 installed

[Flappie]

From Yo-Yo:

 

This thread could be of interest, too:

 

[Ironhand]

Forgot about Ctrl-T, if that still exists. But the issue isn’t pitch trim. I, at least, have no difficulty trimming for level flight without use of the AP—up until extremely high altitudes, that is, but that’s because the throttle is involved. OTOH, pitch trimming is extremely dicey at, say, 16,000 m for the same reason. But roll trim is another matter. Once you move it off center, you can’t trim it back—I guess without Ctrl-T.

[Flappie]

I'll give it a go.

[Flappie]

Just tested: trim reset (Ctrl + T) works just fine. It resets all 3 axis, as stated in the manual.

[Ironhand]

43 minutes ago, Flappie said:

Just tested: trim reset (Ctrl + T) works just fine. It resets all 3 axis…

Kind of figured it would, though I haven’t used it in years. I find it’s resetting of all three axes to neutral to be more of a PITA than dealing with the slight mis-trim of a single axis.

[Cmptohocah]

Try trimming along the roll axis an aircraft with asymetric loadout -it's impossible.

What ever you do, it will keep on rolling to one side or the other.

[okopanja]

I had this issue since ages. Then I tuned axis dead zones. Since then way less severe.

My joystick is old and shaked on its own.

[pauldy]

Sorry for getting back late on this. 

Anyways I made a track.
I forgot the exact specifics i did but things i did after take off:

1. Tried to be in a relatively level attitude, then i fired an ET from the left pylon.

2. The jet now has asymmetric weight distribution.

3. I then tried engaging either Alt = 2 Altitude Hold or Alt + 3 Return to level flight to somehow correct the trim.

4. It didn't, so I tried manually trimming the jet myself. Now the jet seems so have an over trim to the right.

5. I fired my right ET, hoping to make the jet "balanced" again.

6. I repeated what i did in numbers 3 to 4, but the jet seems to have some slight over trim either to the left or right side.

I always thought Trimming will always make you aircraft return to a neutral state, regardless if there's some asymmetric load.

trim off center.trk

Edited January 29, 2022 by pauldy

[Ironhand]

10 hours ago, pauldy said:

3. I then tried engaging either Alt = 2 Altitude Hold or Alt + 3 Return to level flight to somehow correct the trim.

4. It didn't, so I tried manually trimming the jet myself. Now the jet seems so have an over trim to the right.

It is how it should function. While in the appropriate AP mode, the aircraft should be trimmed. Upon exiting the AP mode, the aircraft returns to the prior trim state.

 

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6. I repeated what i did in numbers 3 to 4, but the jet seems to have some slight over trim either to the left or right side

What's interesting is that, even with that slight roll, the neutral trim lamp will illuminate. (Not sure if your TRK displayed this but that's what I saw after taking control and making an adjustment.) So the system, as designed, may not be sufficiently "fine grained" to allow exact trimming. Of course, this doesn't explain why the AP holds it rock solid. In the MiG-29 you can watch the system constantly adjusting. In the Su-27, there's no evidence of that.

 

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I always thought Trimming will always make you aircraft return to a neutral state, regardless if there's some asymmetric load.

See above. One solution, at least while in transit, is to use the appropriate AP mode, use the temporary override to change direction, altitude, etc, then re-engage the AP. It's sufficiently fine grained that, with the neutral lamp lit, when maneuvering the aircraft (active hands on stick) you're not going to really notice it.

Edited January 29, 2022 by Ironhand

[pauldy]

I only have the standalone Su-27 though, so i can't verify with the Fulcrum. I guess the Flanker's Autopilot is still the same as with LOMAC/FC 1.12a/b. That's why it's rock solid when engaged? or at least in Altitude Hold..

Anyways I've tried again, this time focusing on Trim Reset.

It seems to return to Neutral now. I guess my error was not letting the control stick return to it's true neutral position in the cockpit. 

 

But yeah.. it feels indeed PITA,

because by the time the stick returns to neutral position, the jet is already in crazy pitch attitudes, especially when you have a high airspeed.. needing to compensate any attitude changes with brute force.
 

Edited February 1, 2022 by pauldy