Effects of Spanwise Flexibility on Lift and Rolling Moment of a Wingsail

Abstract

Several authors have considered the optimization of spanwise loading on a wing, subject to different constraints. Jones (1) calculated the optimum spanwise lift distribution for a wing subject to a constraint on lift and root bending moment. Tan and Wood (2) applied these ideas to determine the optimum spanwise lift distribution for a yacht sail subject to a constraint on the rolling moment while maximizing forward thrust. Subsequent authors, such as Junge et.al. (3) and Sneyd and Sugimoto (4) extended the analysis to include spanwise variation of wind strength and direction and boat heel. All of these analyses confirm the importance of maximizing lift and/or forward thrust while constraining rolling moment. In the analysis of a yacht, the geometry of the wind direction relative to the yacht direction is such that aerodynamic lift on the wing provides a component of forward thrust on the yacht. Thus we will occasionally use the terms lift and thrust interchangeably.