Effectiveness of Large-Camber Circular Arc Airfoil at Very Low Reynolds Numbers

The objective of this study is to ascertain the steady-state aerodynamic characteristics of a thin circular arc airfoil with a large-camber by comparing its camber with various cambers at Reynolds numbers ranging from 1×103 to 10×103, similar to that of insect flight. A large camber of over 20% chord is seen in the elytra of beetles (Coleoptera), many of which fly by opening the elytra. A low-pressure wind tunnel that we uniquely designed was used to measure the very small forces and moment acting on the wing. As a result, a high maximum lift coefficient was obtained for a large-camber circular arc airfoil, even at Reynolds numbers less than 3×103. In addition, the pitching moment of the airfoil was found to be zero in a wide range of angles of attack when the moment center was set to the appropriate position. The large-camber circular arc airfoil will be useful in designing very-low Reynolds number aircraft such as insect-sized micro-air vehicles (MAVs).