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HIGH fuel costs and environmental concerns provide continuing motivation for research aimed at increasing aircraft efficiency.

Vortexdragisamajorcontributortoaircraftdrag, typicallyaccounting for about 40% of the drag in cruise and about 80–90% of the drag in secondsegmentclimb [1]. Becausewingtipgeometrystronglyaffects vortex drag, wing tip optimization has received a great deal of attention. Improved wing tip design can benefit new designs and can also improve performance of existing wings through retrofits. One of the early wing tip modifications was a simple end plate [2, 3]. These end plates were shown to increase the effective span of the wing and thus reduce the vortex drag. Whitcomb [4] at NASA achieved greater gains in efficiency through carefully designed highaspect-ratio end plates, which he termed winglets. His experimental data published in 1976 showed that a winglet improved the lift-todrag …