Catastrophic Hydroelastic and Side Ventilation Phenomena on High-Speed Hydrofoil Struts

Struts capable of safely supporting hydrofoils at speeds up to 80 knots cannot be designed using existing strut data. High-speed struts are most susceptible to the hydroelastic problems of flutter and divergence, and the hydrodynamic problem of side ventilation than are low-speed struts. Any one of these three phenomena can produce catastrophic failure of the hydrofoil craft. Divergence is a static loading problem which can be avoided by estimating maximum loads on the strut and designing the strut to withstand those loads. Flutter and side ventilation are complex problems which are not understood completely and which are only now being characterized experimentally. Neither can be predicted by theoretical means at present. There are known technological gaps in the available strut design data which can be filled by the appropriate research recommended in this report. These gaps must be filled to meet the long-range requirement for a design base for high-speed hydrofoils. The immediate requirement for a strut capable of supporting hydrofoils at speeds up to 80 knots demands a practical solution based on experimental model data. The design approach to satisfy this requirement should be threefold: a. Determine the strut profile best suited to avoiding side ventilation even while supporting a possibly superventilating foil. b. Design the strength and sweepback of the strut to be divergence-free by calculation. c. Construct a dynamic model of the semi-final strut-pod-foil system to determine that it is free from flutter. (Author)