This report is a collection of notes which were intended to be short communications. Main target of the work presented is to supply new approaches to stability investigations of wind turbines. The author's opinion is that an efficient, systematicstability analysis can not be performed for large systems of differential equations (i.e. the order of the differential equations > 100), because numerical "effects" in the solution of the equations of motion as initial value problem, eigenvalue problem orwhatsoever become predominant. It is therefore necessary to find models which are reduced to the elementary coordinates but which can still describe the physical processes under consideration with sufficiently good accuracy. Such models are presented.