Unmanned aerial vehicles (UAV's) are increasingly fulfilling long surveillance missions where endurance and efficiency are amongst the most important considerations. Naturally, the wing aspect ratio of such airplanes is large, to improve lift to drag ratio. The objective of the present study is to investigate if further improvements in endurance are possible for an existing high altitude UAV. One possibility for such improvements is the addition of wing tip devices, and for practical reasons, this work is focused on upward pointing winglets. Such winglets are successfully used on numerous passenger airplanes, but the magnitude of improvement for the high aspect ratio wing considered here was not clear. Therefore, in this study, various geometrical parameters were investigated such as wing tip dihedral, sweep, twist, and length. Computed results indicate, that the 30° dihedral with 0° rearward sweep provided the best improvement of about 5.68% (in terms of improving CL/CD). However, the increased lift of the wing resulted in an increased wing-root bending moment of about 15.61%.