In this paper, we consider a method for determining the feasibility of using a wing strut and non-retractable landing gear on a light multi-purpose aircraft. In a certain range of cruising speeds and flight ranges, it is advisable to use non-retractable landing gear and wing strut. With an increase in cruising speed and flight range, these engineering solutions must be abandoned to improve aerodynamic characteristics. The dependencies obtained in this work make it possible to make decisions on the use of a wing strut and non-retractable landing gear at the early design stages. To obtain aerodynamic characteristics in the Siemens NX program, a three-dimensional model of a light multi-purpose aircraft was created and an aerodynamic experiment was performed in the FloEFD program. Then the calculation of flight performance was carried out. As a result of the study, the dependence of the speed up to which it is advisable to use the undercarriage strut and fixed landing gear on the flight range for a light multi-purpose aircraft weighing 2000 kg was obtained. When designing an aircraft, it is necessary to make decisions about the use of one or another engineering solution, which, on the one hand, has a positive effect on aerodynamics and negatively on the weight of the aircraft, and vice versa. In this article, using the example of a wing strut and fixed landing gear in the first version of the aircraft, and a cantilever wing and retractable landing gear in the second version, a model for solving such a problem is shown.