The Design of Winglets for Low-Speed Aircraft

Abstract

Although theoretical tools for the design of winglets for low-speed aircraft were initially of limited value, simple methods were used to design winglets that gradually became accepted as benefiting overall aircraft performance.  As understanding was gained, improved methods were developed, which ultimately resulted a number of successful applications of winglets.  The current approach incorporates a detailed component drag buildup that interpolates airfoil drag and moment data across operational lift-coefficient, Reynolds-number, and flap-deflection ranges. Induced drag is initially predicted using a relatively fast multiple lifting-line method.  In the final stages of the design process, a full panel method, including relaxed-wake modeling, is employed.  The drag predictions are used to compute speed polars for both level and turning flight, yielding predicted performance that is in good agreement with flight-test results.  These methods have been successfully applied to the design of winglets to improve the cross-country soaring performance of both span-limited and span-unlimited, high-performance sailplanes, as well as to improve various mission capabilities for several different categories of powered aircraft.