In wind tunnel testing, the research object is typically mounted on a force balance, which can be internal or external. In the case of an external balance, a mast is required to connect to the object, which inevitably affects the measurements of forces and moments for the entire system. Therefore, understanding the influence of the mast on the generated forces and moments is crucial for the accurate analysis of the aerodynamics of the object under study. It is not always feasible to define this impact experimentally; hence, numerical analyses are conducted, including the investigation of aerodynamic interference between the object and the mast. The study focused on analyzing the impact of a support structure, specifically a cylindrical mast, on the aerodynamic characteristics of a light combat aircraft model. Three methods of determining the aerodynamic characteristics of the aircraft were considered. The analysis was conducted using numerical simulations performed with Ansys Fluent software. The focus was on the qualitative and quantitative assessment of the aerodynamic interference between the mast and the studied model. This allowed for a thorough understanding of this phenomenon and its implications for further aerodynamic tunnel testing.