The Rotary Engine is ideally suited to ducted fan propulsion systems. The obvious features of high power density and low vibration are complemented by the basic round shape and compatible shaft speed. These advantages contribute to enhanced aircraft propulsion.Moller International is developing a family of Vertical Take-Off and Landing (VTOL) aircraft, both manned and unmanned, which utilize ducted fans powered by rotary engines.For initial evaluation, Moller has redesigned the 33 kW Rotary Engine produced by OMC in the 1 970's.(l)* The modifications required to adapt this engine to the ducted fan are outlined in detail. Performance data from the engine's static test platform are offered as representative of operation in the aircraft.A new engine design incorporating changes in basic engine geometry and the adaptation of direct fuel injection for multi-fuel capability are presented as future developments.