Abstract: Wingtip slots, where the outer primary feathers of birds split and spread vertically, are regarded as an evolved favorable feature that could eff ectively improve their aerodynamic performance. They have inspired many to perform experiments and simulations as well as to relate their results to aircraft design. This paper aims to provide guidance for the research on the aerodynamic mechanism of wingtip slots. Following a review of previous wingtip slot research, four imperfections are put forward: vacancies in research content, inconsistencies in research conclusions, limitations of early research methods, and shortage of the aerodynamic mechanism analysis. On this basis, further explorations and expansion of the infl uence factors for steady state are needed; more attention should be poured into the application of fl ow fi eld integration method to decompose drag, and evaluation of variation in induced drag seems a more rational choice. Geometric and kinematic parameters of wingtip slot structure in the unsteady state, as well as the fl exibility of wingtips, should be taken into account. As for the aerodynamic mechanism of wingtip slots, the emphasis can be placed on the study of the formation, development, and evolution of wingtip vortices on slotted wings. Besides, some research strategies and feasibility analyses are proposed for each part of the research.

Key words: Slotted wingtip, Tip vortex, Drag reduction, Unsteady state, Flexibility