To test the dynamic behaviour of a free-flying helicopter, a demonstrator model called ‘H9’ was built using the MKSSystem SIMPACK. Along with the general dynamic behaviour of the elastic structure, the primary focus is the coupling effect of the component movement, which occurs due to the mutual influence of the fuselage and the rotor. Distinctive dynamic characteristics of the helicopter are the elastic, orthotropic mounting of the main rotor as well as the modelling of the elastic drive train and the elastic pitch angle controlling. The strong eccentricity in the centre of gravity of the fuselage impedes symmetrical characteristics and, as a consequence, has a noticeable rotation of the main axis of the entire system. This promotes a further coupling of the degrees of freedom of the model movements. Modal analyses of the free system allow the analysis of the rotor–fuselage coupling of the natural (Eigen) form.
Alongside a general look into the structural dynamic behaviour, structural dynamic testing of the free-flying helicopter ‘H9’, in the form of Eigenvalue analyses, can especially help to build up evidence on the stability behaviour of the entire system. The structure-driven instability mechanism can be found in the free-free system. Using the structurally dynamic helicopter ‘H9’, Eigenvalue analyses were carried out to investigate the rotor suspension, drive train and pitch angle control.