In this paper, a mathematical model of a helicopter NO TAil Rotor (NOTAR) antitorque system is developed for real-time flight simulations. The model consists of the circulation control tail boom, direct jet thruster, and the vertical stabilizers. The airflow inside the tail boom is modeled by dividing the flow into aerodynamic control volumes. The model features a bladeelement-type approach for modeling the mass flow through the axial fan blades as well as aerodynamic mass and momentum conservation calculations in each control volume. The side force produced by the direct jet thruster and circulation control tail boom is calculated at different flight conditions. A simple rectangular plan form with symmetrical airfoil shape is used to model the vertical tail. The developed NOTAR antitorque model is integrated with a nonlinear helicopter model. Flight tests are performed on the MD600N, and the data obtained are used for verification. Results show a reasonable match between the model and flight-test data in the antitorque response in hover and forward flight to pilot pedal input.