The Effect of Winglets on the KC-135A Aircraft

Abstract : To investigate the effects of winglets on the aerodynamic characteristics of the KC-135 aircraft, semispan and full-span wind tunnel models with winglets have been investigated in the NASA/LRC 8-Foot Transonic Pressure Tunnel. At cruise conditions, the full-span tests indicated a total drag reduction of 5.3 percent for the model with the Boeing and NASA upper plus lower winglet configurations and 6.5 percent for the model with the NASA upper winglet configuration. A wing-tip-extension configuration tested on the semispan model had a drag reduction of about 3 percent compared to about 5 to 7 percent for the winglet configurations, however, the tip extension was not optimized for drag reduction. At cruise conditions, the wing tip extension produced the greatest increase in wing root bending moment and the upper winglets the least. The increase in wing root bending moment at cruise conditions varied from about 2.5 percent with the Boeing winglets, to about 3.5 percent with the tip extension. At cruise flight conditions, winglets on the KC-135A aircraft were estimated to reduce the drag about 8.2 percent and increase the maximum lift- drag ratio about 9.5 percent.