Hello, I am facing a pitch oscillation issue on a QuadPlane. The problem happens in AUTO mode during the final stage of return/home behavior: the aircraft reaches the home point correctly, then when it starts holding position (VTOL hover hold / QRTL-like hold behavior), it begins oscillating noticeably in pitch (nose up/down bobbing) while trying to maintain position and altitude.
I first encountered this problem on ArduPlane v4.6.3, and then I downgraded back to v4.5.7, but the same behavior still occurs.
From the log graphs, altitude target tracking (QTUN.DAlt vs QTUN.Alt) looks generally good, but the actual climb rate (QTUN.CRt) oscillates significantly compared to the desired climb rate (QTUN.DCRt), and the quad motor outputs show collective thrust activity during the event.
The key observation is: when I manually switch to QHOVER, the oscillation stops immediately and the aircraft becomes stable. This makes me suspect the issue is related to AUTO VTOL position hold / loiter behavior (possibly Q_P_POSXY_ / Q_P_VELXY_ gains, Q_LOIT_BRK_ parameters, or another AUTO/QRTL hold tuning issue), rather than basic QHOVER stabilization itself.
I would appreciate guidance on:
- Which parameters are most likely responsible for this behavior
- Recommended tuning sequence for this exact case (AUTO hold oscillation near home, but stable in QHOVER)
- Whether this points more to XY loiter tuning, pitch/attitude coupling, or vertical Q tuning
I can upload the .bin log and screenshots of QTUN / RCOU graphs if needed.
