SAILPLANE WINGLET DESIGN

Abstract

Although the accuracy of methods for the design and analysis of winglets has been limited, the performance gains achieved through their use are now well established. To further these gains, an improved methodology for winglet design has been developed. This methodology incorporates a detailed component drag buildup that includes the ability to interpolate input airfoil drag and moment data across operational lift coefficient, Reynolds number, and flap-setting ranges. Induced drag is initially predicted using a relatively fast discretized, 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 tuning flight. This information can then be used to obtain cross country performance over a range of thermal strengths and profiles. The performance predictions agree well with flight-test results, and are consistent with the winglet design experiences obtained thus far. Example designs for the Schempp-Hirth Discus and the Schleicher ASW-20 demonstrate that winglets can provide a small but important performance advantage over much of the operating range for both Standard and Racing Class sailplanes.