BRANCH OF AERONAUTICAL ENGINEERING UNIVERSITY OF THE WITWATERSRAND / An experimental investigation was carried out on a half scale model of a helicopter COmbined Infra-Red Suppression and Tail rotor Elimination (CIRSTEL) system to characterise its performance in terms of power consumption, thrust, pressure drops and temperature reduction. The model consists of a Circulation Control Tail Boom and Thruster (CCTB&T) with the hot engine gasses ducted into the tail boom where they are mixed with ambiant air supplied by a fan situated in the body of the helicopter. The CCTB&T replaces the conventional tail rotor on a helicopter and supplies the torque to counter-act the torque applied to the main rotor. The model was tested using both hot and cold air to simulate the flow of hot engine gasses. The performance is defined in terms of thrust, power, and mass flow coefffcients which were found to be constant for the configuration tested. It was shown that the power requirements of the fan are significantly reduced by introducing the hot engine gasses into the tail Boom. The temperature of the hot engine gasses is also reduced from 450°C to approximately 200°C The surface temperature of the model was found to be less than 55'C of the configuration.