One of the factors affecting the aerodynamics and performance of aircraft profiles are flaps. The work presents the influence of selected types of flaps on Diamond DA-20 properties. The aircraft aerodynamics is described in detail. Furthermore, the three types of steady flight are presented and the ways of calculating the basic performance of the airplane are taken into consideration. The techniques used to carry out the research are discussed, the conclusions are drawn and the final results are presented. The aim of this article was to analyse the influence of trailing-edge wing flaps on the aerodynamic characteristics and performance of the Diamond DA-20 aircraft. The research focused on the aircraft in smooth configuration and with four types of trailing-edge wing flaps: pop-up, split flap, single-slotted flap and double-slotted flap in 15° and 45° positions.