999 G. J. Wennagel 
immersion. At the increased immersion, the flow again reseated on the affected region of 
the pod, initial lift and trim were restored, and the process would then repeat itself, causing 
a mild and steady oscillation. A small plate was added on top of the pod and behind the 
strut so as to limit the extent of the air cavity. This change eliminated further oscillation. 
Forward foil design has successfully provided a smooth and stable manner of cavity 
formation over the cruise foils. It is significant that the vehicle has never experienced 
adverse roll due to uneven extent of ventilation, one side to the other. Further, it has 
never experienced abrupt changes in pitch as might be caused if ventilation or flow reseat- 
ing occurred abruptly. This is true for both smooth and rough water operation, and for run- 
ning at either a constant heading or during turning maneuvers. 
CONCLUSIONS 
1. Forced air ventilation, into regions behind the blunt base of a strut or foil, is a 
practical means of drag reduction. 
2. Within the limits of completed testing, predicted propeller and ventilated hydrofoil 
efficiencies have been confirmed. 
3. Ventilated hydrofoil systems can be designed to allow cavity formation in a smooth 
and stable manner. They offer the elimination of abrupt loss in lift associated with some 
subcavitating foil systems when ventilation occurs. Complete flow stability has been 
demonstrated over a wide variety of sea conditions and tuming maneuvers. 
4, Supercavitating foil sections, as compared to subcavitating types, exhibit a reduced 
lift curve slope which minimizes incremental lift changes associated with orbital velocities 
within waves. This feature, together with satisfactory hydrodynamic efficiencies, appears 
to offer an important field for future development. 
ACKNOWLEDGEMENTS 
Appreciation is expressed to the Grumman Aircraft Engineering Corp. and to the General 
Electric Company for freely-given technical assistance and component contribution, to Lear, 
Incorporated for the donation of a linear actuator, and to the Kaman Aircraft Company forthe 
donation of an oil reservoir and deairation device. 
REFERENCES 
[1] Tachmindji, A.J., Morgan, W.B., Miller, M.L., and Hecker, R., “The Design and Perform- 
ance of Supercavitating Propellers,” David Taylor Model Basin Report C-807, Feb. 1957 
[2] Tachmindji, A.J., and Morgan, W.B., “The Design and Estimated Performance of a 
Series of Supercavitating Propellers,” p. 489 in “Second (1958) Symposium on Naval 
Hydrodynamics,” Washington: Office of Naval Research, 1960 
