Can you help me with Winglets Design?

Experimented with winglets for several years, using a university's wind tunnel. I wanted to improve my sailplanes performance. My conclusion was that any slight improvement was only at one narrow angle off attack, and they actually added parasite drag above and below the optimum AOA. The fuel burn on a turbine powered aircraft would but it above or below the optimum AOA for over 1/2 of a long flight. My cynical conclusion after all that work and study was that they look "cool" and sell airplanes. Good luck with your project.