Biplane and Tail Effects in Flapping Flight

Abstract

A numerical investigation is performed on the interference effects in single or biplane flapping airfoil propulsion in the presence of a stationary downstream tail. At a Reynolds number of 1000, this corresponds to the regime of small micro aerial vehicles. The objective of this study is to provide insight into the complex wing–tail interaction effects occurring in flapping-wing propulsion configurations. The effect of the relative distance between the airfoils, as well as the positioning and incidence angle of the tail, is investigated. Adding a tail behind a single flapping airfoil increases the efficiency and average thrust by up to 10 and 25%, respectively. For the biplane flapping airfoils without tail, overall efficiency and average thrust per airfoil increase up to 17 and 126%, respectively, with respect to the single airfoil due to the formation of a strong momentum jet. The effect of adding a tail behind the biplane flapping airfoils depends on the tail’s orientation and location. Increasing the incidence angle of the tail generates higher lift, although at the expense of decreased efficiency and thrust. Lastly, shifting the vertical position of the tail to have it coincide with the middle heaving position of the leading top airfoil gives the best overall performance.