Aerodynamic Characteristics of a Straight Wing with a Spiroid Wingtip Device

Spiroid wingtip devices (WD) offer a promising way of improving the lift drag ratio of UAVs, but may on the other hand lead to negative aerodynamic interference of the wing with the WD and deterioration of the aerodynamic characteristics as compared to a wing without the WD. Determining the influence of the geometric parameters of a spiroid WD on aerodynamic wing characteristics, however, remains an understudied field. In our study, we investigated the influence of the following geometrical parameters on wing aerodynamic characteristics with WD: area, radius, camber angle, constriction, and pitch of the spiroid. We found that the positive effect of the WD is present at a relative radius > 0.05, as well as with an increase in the lift coefficient C_L as a result of an increase in the proportion of inductive resistance. For example, with the Reynolds number Re = 2.1×10⁵ for a rectangular wing with an aspect ratio θ = 5.12 equipped with a spiroid WD with =0.15 the quality gain is almost 10% at C_L = 0.5, and at C_L = 0.7 is almost 20% and at C_L = 0.7 – almost 20% compared to a wing without WD. Moreover, we found that a change in the camber angle WD θ provides an increase in the derivative of the lift coefficient with respect to the angle of attack in the range from θ = 0° to θ = 130°. By changing the camber angle, it is possible to increase the lift drag ratio of the layout up to 7.5% at θ = 90° compared to θ = 0° at the Reynolds number Re = 2.1×10⁵. From the point of view of ensuring maximum lift drag ratio and minimum inductive drag, the angle θ = 90° is the most beneficial.