Within the European Integrated Project NACRE (New Aircraft Concept REsearch) led by Airbus, a team of research centers and universities developed a multidisciplinary flying testbed called IEP (Innovative Evaluation Platform). Under the form of a dynamically scaled model of a future civil transport aircraft, its role is to assist engineers during the assessment of flight dynamics characteristics and noise reduction capabilities.
After the feasibility study during which potential scientific and economical benefits of such new test facility have been identified, the team decided to design and manufacture the IEP. Because of the dual aspect of the system (it is a flying unmanned aerial vehicle and a test facility), an extensive requirement analysis has been carried out by the partners in order to identify the necessary operational modes and their associated navigation and control strategies.
The navigation algorithm implemented in the IEP is based on a control geometry around the airplane which is used to sense the target flight path progression in three dimensions. This approach provides a look ahead functionality to increase the control performance without increasing the complexity of the controller architecture. Studies emphasized that the computation of the control geometry combined with a “low cost” controller architecture increases performance and requires a lower computational effort.
In addition to these studies, a robust controller insensitive to modelling errors has been developed. The chosen method has been Incremental Nonlinear Dynamic Inversion. This is a robust extension of the well-known Nonlinear Dynamic Inversion (NDI) technique based on properties of general mechanical systems by feeding back angular acceleration measurements. The controller performance has been evaluated and its robustness properties were verified, demonstrating thus the asset of the approach over NDI techniques.
During the entire IEP project, from conceptual design to taxi tests, partners gathered an important know-how on the development of the flying test facility made of a Modular Flying Platform and a Ground Control Station. Based on this important experience, several paths for future developments of the IEP have been identified.