Effect of Sweep and Drag on Hydrofoil Stability

The stability of hydrofoils is currently estimated by plots of the log decrement versus flutter frequency and forward speed. Herein is suggested a method used by electrical or electronic engineers to determine the relative stability of a linear system. This “root contour” method is discussed and it is shown how it can be applied to a hydrofoil analysis. The strip method of analysis is used with strength of material estimates for foil stiffness. Both drag and sweep angle effects are included in the analysis to determine their effect on foil stability as defined by the root contour method.