The effects of multiple winglets (sails) on finite wing performance and vortex wake

This thesis attempts to answer the question, "What is the function of tip feathers of soaring birds?"

Multiple sails (feathers) are added to a plain wing and changes in the trailing tip vortex are measured. The same tests are repeated in a wind tunnel to measure changes in the aerodynamic forces. A computer simulation of the shed vortex pattern is also used as a model.

Although incomplete, this study is a good basis for future work, and the results indicate that bird tip feathers increase the effective aspect ratio of the wing, reducing the induced drag.