Wind tunnel testing was carried out to evaluate the reduction of induced drag using wing-tip blowing, fixed and adaptive multi-winglets. Different arrangements of each device were tested on a semi-span wing, with additional investigations performed on a half-body model of a trainer aircraft. Results include: aerodynamic coefficients; surface pressure distributions; and wake surveys with a multi-hole Pitot probe. The influence of each wing-tip arrangement on aircraft performance was estimated, considering the energy requirements of the blowing system. All devices tested were able to minimize induced drag; however, for practical applications in commercial airplanes, multi-winglets are a more promising alternative due to the large amount of energy required by wing-tip blowing.

The aim of this research is to study the potential use of adaptive multi-winglets for the reduction of induced drag through variations of winglet cant angles. Different studies have shown that the flow around and over the wing tip can be redirected using small aerodynamic surfaces, thereby reducing the induced drag. The model tested is composed of a rectangular wing using an NACA 65₃-018 profile with three winglets called ‘tip-sails,’ which are small wings without sweep along the 25 per cent chord line. The tests were made at a Reynolds number of 350 000. The results are analysed in terms of lift and drag. Results show that it is possible to find the best configuration of the three winglets to obtain the optimum aerodynamic performance for each flow regime in climb and cruise.