Pitch attitude unstable during autoland

sun2515 commented 3 weeks ago

Aircraft Version

Development

Build info

{
    "built": "2024-10-31T15:50:20+00:00",
    "ref": "refs/tags/v0.12.0",
    "sha": "2fe89113291f2478347dde0dc3228b55dc924f74",
    "actor": "FoxtrotSierra6829",
    "event_name": "manual",
    "pretty_release_name": "stable/v0.12.0",
    "version": "a380x-v0.12.0-rel.2fe8911"
}

Describe the bug

Pitch attitude is unstable when the autopilot is engaged, the nose keeps fluctuating up and down slightly when maintaining an altitude causing the vertical speed to also fluctuate. When performing an auto landing. The amplitude increases as the altitude decreases, and causes a heavy touchdown.

Expected behavior

Maintain a proper pitch and VS.

Steps to reproduce

Start an auto land.
Keep AP on till touchdown.

References (optional)

https://youtu.be/SBzPU86km3E

Additional info (optional)

No response

Discord Username (optional)

chengli76

vossiniko commented 1 week ago

I second that. It looked like the A380 is trying to follow the Glidepath too long into the TDZ, and once it goes up when reaching the TDZ, it goes into Flare but a milisecond too late after starting to follow the up trend of the GP again. Maybe engaging Flare Mode a bit earlier will be better? I know the real one does it at the same time on the FMA, but it could start a few milliseconds before being displayed.

sun2515 commented 2 days ago

I think the problem lies in the control delay of the aircraft. In both manual flying and auto flying, the aircraft's reaction to pitch control input is slow. So I think reducing the moment of Inertia on the pitch axis may help. Or maybe the delay is caused by the FBW system? (not sure)

发件人: vossiniko @.> 发送时间: 2024年11月17日 18:53 收件人: flybywiresim/aircraft @.> 抄送: sun2515 @.>; Author @.> 主题: Re: [flybywiresim/aircraft] Pitch attitude unstable during autoland (Issue #9327)

I second that. It looked like the A380 is trying to follow the Glidepath too long into the TDZ, and once it goes up when reaching the TDZ, it goes into Flare but a milisecond too late after starting to follow the up trend of the GP again. Maybe engaging Flare Mode a bit earlier will be better?

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flybywiresim / aircraft