Abstract: A motorized operator for opening and closing a window sash relative to a window frame via an arm mechanism connected to the window frame and being adapted to be installed in a cavity defined in the window frame. The operator comprises a motor, a drive axle rotated by the motor, and first and second gears in meshed engagement. The first gear is mounted on the drive axle, while the second gear is mounted to the arm mechanism such that motorized rotation of the first gear rotatably drives the second gear thereby causing the arm mechanism to pivot for opening and closing the window sash. A manual operator is adapted to disengage the first and second gears from one another while becoming engaged to the second gear for manually rotating the second gear and so manually operate the arm mechanism. The manual operator comprises a handle and a manual actuator which includes a sprocket.