Thanks Scotflieger.
The ipc control for Smoke is fine, but "Droppable objects" must be an event like "Shift+d" otherwise it will not be read by an external program through SimConnect, so I am told.
In P3D by pressing a joystick button, I need to both send a key event (release droppable objects) and activate the smoke-system via an ipc control. It is important that these actions are separate.
Can anyone help with this?