Hi Julian,
thanks for the information/links
But my understanding of how flaps/gears are supported by Pixhawk4 and how to configure it are not satisfied.
I studied the ArduCopter documentation about that and found easy documentaion with all the basic knowledge id need.
But it seems to me that this feature is completely renewed in Pixhawk4 so it does not help anymore.
In Manual, Stabilize, or FBW-A modes your flaps will operate manually and you can set them with your transmitter.
In FBW-B the target airspeed is set by the position of the throttle stick. If set up properly you should see flaps deploy as you lower the throttle stick through the two flap airspeed ranges.
In RTL, Guided, and Auto modes flaps settings are determined by the schedule in your parameters and the current value of cruise_speed. You can change cruise_speed to a value in one of the flap ranges from the GCS and should see the flaps deploy. Also, if you use the Do_Change_Speed command in mission flaps will be deployed when the target speed is changed into one of the flap speed ranges.
Source: Using Flaps
Any help appreciated