Whirl flutter is a dynamic instability that can occur under certain conditions in a motor nacelle with propellers. It involves an aeroelastic instability of the elastically fitted motor nacelle propeller system on the aircraft. This flutter can occur when the connection strength of the motor nacelle, including the propeller, is not sufficiently large, which can lead to problems, especially in aircraft with swivelling propeller nacelles.
Within the scope of the project Bürgernahes Flugzeug (BNF) [civil aircraft] of the Braunschweig research airport, the Institute cooperated with the Braunschweig Technical University and other DLR institutes. One objective within this project was the construction of a wind tunnel model comprising an airfoil with a gap-less Coanda-flap and a driven nine-blade propeller for operations in DNW-NWB. Extensive wind tunnel tests for aerodynamic and aeroacoustic examinations were conducted. The Institute contributed with flutter analyses for the wind tunnel model as well as by examining whirl flutter. Furthermore, the vibration levels in the stationary and rotating model sections was monitored online.