Characteristics of locked and free-wheeling ducted fan based on wind tunnel tests and CFD analyses

The presented paper is describing ducted fan tests performed for a new generation of joined wing aircraft. . In order to fully integrate propulsion system with an aircraft and get reliable results from flight tests, propulsion systems must be thoroughly tested. Due to the recent development in electric propulsion systems, new possibilities are arising. Stopping and restarting the motor in flight allows better determination of aircraft performance (for example lift to drag ratio) during flight tests of dynamically scale flight models. Free-wheeling and braked tests of ducted fan and unshrouded propellers for comparison have been performed in different conditions. In a conventional unshrouded fixed pitch propeller in a free spinning (wind milling) situation such prop has much more drag than when it is stationary (locked). Wind tunnel tests have proven than ducted fans have much different results and the lowest drag is possible when the fan is free spinning. In order to validate it and find the mechanism of this occurrence, CFD analyses have been performed. As the results of ducted fans’ free-wheeling and locked characteristics are different to unshrouded propeller they also make emergency procedures different in case of an engine cut off during the flight.