Starling 2: No climb above ~20 cm at 2400 m ASL (high altitude), suspect thrust limit

[j-angel]

We have a Starling 2 that normally flies at approximately 1000-1300 m above sea level. It starts struggling around 1800 m, and at approximately 2400 m above sea level, it only climbs about 20 cm. Even in manual/PostCtrl mode, it does not climb.

Observations:

• Battery charge: 7.3-8 V.

• Rotor speed: 12,000 RPM.

• Takeoff is detected, but the drone cannot climb.

• Geofence and altitude parameter limits were checked (no strict limits were found).

• The drone's position is estimated using VIO (OpenVins). GPS is disabled, and a barometer is not used to aid in altitude estimation.

Hypothesis:

• At high altitude (2400 m), air density reduces thrust; the hover throttle is likely saturated. We increased MPC_THR_MAX and adjusted MPC_THR_HOVER, pending testing.

Request: Are any adjustments to the PX4 (acceleration/hover/air density) or propeller/motor modifications recommended so that the Starling 2 can maintain flight at approximately 2600 m above sea level?

Attachment: PX4 Flight log from 2400 meters above sea level.
https://review.px4.io/plot_app?log=45254900-3c62-4bc8-bcb3-6cf669b0e9e2