DOUBLE DUCTED FAN (DDF) By

This technical paper describes a novel ducted fan inlet flow conditioning concept that will significantly improve the performance and controllability of V/STOL ‘vertical/short take off take-off and landing ” UAVs ‘uninhab-ited aerial vehicles ” and many other ducted fan based systems. The new concept that will significantly reduce the inlet lip separation related perfor-mance penalties in the forward flight zone is named ‘DOUBLE DUCTED FAN (DDF)”. The current concept uses a secondary stationary duct sys-tem to control ‘inlet lip separation ” related momentum deficit at the inlet of the fan rotor occurring at elevated forward flight velocities. The DDF is self-adjusting in a wide forward flight velocity range. DDFs corrective aero-dynamic influence becomes more pronounced with increasing flight velocity due to its inherent design properties. The DDF can also be implemented as a ‘Variable Double Ducted Fan ” (VDDF) for a much more effective inlet lip separation control in a wide range of horizontal flight velocities in UAVs, ai