Modeling and simulation are important tools for the development and understanding of technical systems. The consideration of the different physical phenomena involved is often required for a realistic representation but also poses new challenges for developing efficient and effective numerical models. To simulate different domains together, partitioned coupling methods can be applied. For the modeling of the mechanical part of the coupled system, the finite element method is frequently used. To achieve an adequate description of complex systems, however, a fine discretization is necessary which leads to very high-dimensional systems of differential equations. In order to still enable efficient and effective simulations, model order reduction (MOR) is used. By coupling the different domains, though, the individual subsystems often have numerous inputs and outputs that exchange the forces over the common interaction surface. This in turn poses a special challenge for many MOR methods. In this work, projection-based MOR, see e.g. [2], is used to reduce the structural part of the coupled system. Particular attention is thereby devoted to the reduction of input and output directions. One very complex example of a coupled system is a helicopter in flight. The fast rotation of the rotor leads to aerodynamic loads acting on the helicopter cell. These loads can lead to unwanted vibrations that cause discomfort for the pilot and passengers. Furthermore, they deform the structure and cause a change in the aerodynamic flow field.