| 摘要 |
The blended winglet is a wing-like device comprising a blended lifting surface attachable to each airplane wing tip so as to achieve minimum induced drag for a given surface size. The device consists of a nearly planar, straight section joined to the wing tip through a curved transition section designed to obtain an optimum aerodynamic loading. Surface streamwise cross sections are airfoils having appropriate thickness, camber and twist variations. In a critical departure from the usual winglet design approach, the sensitive transition section features a smoothly varying chord distribution which blends smoothly and continuously with the wing and with the adjoining straight section. In the transition section the leading edge sweep angle is limited to 65 DEG or less and the airfoil nose camber is correspondingly increased to accommodate the high sweep. The transition section also features limited in-plane curvature (i.e., large radius) to accommodate a large chord variation and to provide a practical means of achieving optimum aerodynamic loading. It also minimizes aerodynamic interference and undesirable flow separation and compressibility effects. Specific mathematical guidelines for the selection of winglet geometry are presented as a design framework for achieving maximum drag reduction and performance improvement while maintaining favorable characteristics over a range of operating conditions.
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