The aim of this bachelor thesis is to evaluate effect of individual parts of the selected aircraft on its aerodynamic characteristics and to summarize possible directions of aircraft modifications with taking into account increasing its cruising speed while maintaining STOL performances. The first part of this thesis is focused on the description of selected aircraft construction and its legislative categorization. Then follows the theoretical part describing the basic terms of horizontal flight mechanics, the creation of drag and drag types. The practical part contains the evaluation of the drag influence for individual aircraft parts, their possible directions of improving and the final summary how the modified parts influence flight perf...