Why don’t the A380 and A350 have trim wheels?

On the other fly-by-wire Airbus aircraft the trim wheels are there for manual trim in case the aircraft went into direct law since the Airbus sticks do not have a trim control.

Were the trim wheels replaced by another interface? Or is the manual trim option completely removed due to a certain technology?

The trim wheel needs cable/chains that run along the entire length of the airplane to reach the control unit in the back, onto the THS actuator.

It doesn’t actually drive the THS, it just mechanically turns the input gear and the THS actuator follows this gear, drives the main THS jackscrew to position the THS

During normal operations, 3 electrical motors receive commands from flight control computers to drive the THS actuator input gear, which also backdrives the wheel for pilot awareness. Grabbing the wheel cause opposing torque on the input gear, which disengages the motors, so manual input overrides computer commands.

This adds weight and mechanical complexity, which leads to extra cost in building/servicing them.

The need for such mechanical system was proven unnecessary during decades of Airbus operation. The wheel is only ever used in normal operation when setting takeoff trim, which frankly can easily be automated. Flight control degradation is rare, degradation down to the level which needs manual input from the trim wheel is extremely rare, an electrical switch seem to do the job just as well as dozen or even hundreds of KGs of mechanisms.

Airbus experimented with fully electronically commanded rudder on some A340 models. Previous Airbus models also had mechanically commanded rudder, not so on these A340. They flew just fine. So they proceeded to axe the trim wheel and associated mechanisms on A380 & A350, replace it with a backup trim switch.

The Airbus A350 uses a fly-by-wire control system, which eliminates the need for a traditional trim wheel. Instead, the aircraft’s computer automatically adjusts the trim to maintain the desired flight attitude. This allows for greater precision and stability, and eliminates the potential for human error in the trimming process. Additionally, the A350’s fly-by-wire system also provides greater protection against overspeed, stall and other potential hazards.