The problem of modelling the airflow through the gap between a main wing part and a slat is investigated. Numerical studies of the aerodynamics of a wing with a slat at beyond stall angles characteristic for a spin are carried out. The features of the flow near the slotted slat of the wing model and full-scale wing are revealed. It is shown that with the observance of the geometric similarity on the spin model, the flow and aerodynamic characteristics are somewhat distorted, respectively. It is proposed to simulate the flow around the gap according to the local jet momentum coefficient of the full-scale aircraft and its model.