As previously mentioned, the Institute of Aeroelasticity is responsible for the aeroelastic verification management of the modifications made to DLR’s research aircraft within DLR development operations.
A flight vibration test was carried out on the research aircraft HALO, marking the last stage of approving certain modifications. In essence, flight vibration tests enable evaluations directly on board the aircraft or on the ground. Finally, a telemetry system is needed. As part of the flight test on the modifications made to the research aircraft HALO, the on-board variant was selected, where one of the Institute's employees belonged to the test crew. Over several test flights, the entire flight envelope could be opened according to the basis configuration, and in such a way that it was possible, for the purpose of the desired approval, to demonstrate the verification management in a computational manner, as well as sufficient aeroelastic damping properties during flight. This provides a significant contribution to the process of obtaining a Supplemental Type Certificate (STC) from the aviation authorities. The aviation authorities then approve the deployment and use of DLR research aircraft worldwide.
In the case of the HALO flight test, DLR was limited to the suggestions made by pilots of the control surface deflections and thus to excitation frequencies. As such, the Institute of Future Flight Tests at DLR is preparing for the use of alternative methods, which will make use of resources from suitable exciters in order to provide sufficient energy to the structure, ensuring that all relevant vibration patterns are excited during the flight. In terms of system identification, there is a new generation of output only methods (OMA - operational modal analysis), which have already been used in, for example, taxi vibration tests (TVT), and which are considered particularly suitable for flight vibration tests because they only use system responses for modal system identification.