Abstract: An improved jet thruster system for use in a helicopter without a tail rotor. A non-rotating outer thruster assembly is attached to the rear of the tail boom which, within it, has a source of low pressure air. The outer thruster assembly has a window on each side. Nested within the outer thruster assembly is an inner thruster assembly with a single window which rotates within the outer thruster assembly in response to commands from the helicopter control system. As the single window in the inner assembly is rotated around to where it overlaps with one or the other of the side windows in the outer assembly, an exit opening is created for the low pressure air which in turn creates a desired side force on the tail boom to counteract the torque created by the main rotor and also to provide yaw control for the helicopter. The interior of the inner thruster assembly contains vanes and an air ramp to efficiently redirect the air flow from axial flow to lateral flow within the inner thruster assembly.