Aeroelastic Stability of Lifting Surfaces in High-Density Fluids

The large increases anticipated in speeds of vehicles towed or propelled underwater suggests a re-examination of the problem of stability of flexible lifting surfaces mounted thereon. Experimental and theoretical evidence is assembled which suggests that oscillatory aeroelastic instability (flutter) is very unlikely at the structural-to-fluid mass ratios typical of hydrodynamic operation. It is shown that static instability (divergence) is the more important practical problem but that its occurrence can be predicted with greater confidence. Flutter data obtained in high-density fluids are reviewed, and various sources of inaccuracy in their theoretical prediction are analyzed. The need is expressed for more precise means of analytically representing both dynamic-elastic systems and three-dimensional unsteady hydrodynamic loads. For a simple hydrofoil with single degrees of freedom in bending and torsion, the theoretical influence of several significant parameters on high-density flutter is calculated and discussed. Recommendations are made for refinements to existing techniques of analysis to include the presence of channel boundaries, free surfaces, cavitation or separated flow.