Abstract: An enclosed chamber external combustion rotary engine that converts thermal energy into mechanical energy, comprising of a tapered rotary disc with at least one perimeter quadrilateral vane oscillating inside enclosed expansion chambers formed on alternating sides of the rotary disc. The quadrilateral vane remains centered on the rotary disc, except for the transitional area, allowing fluid to provide force to the top and bottom sections of the quadrilateral vane for the length of the non-transition area. Fluid enters expansion chambers through one or more intake passages. Intake passages are formed with shut-off valves, which control the flow of fluid entering expansion chambers. Fluid pressure propels the vane through the expansion chambers causing the disc to rotate about an axis. Incorporated in the rotary disc is an output shaft from which work can be derived.