230 G. J. Wennagel 
lower side is static depth pressure. Once this is accomplished, the lower surface can be 
ventilated in order to reduce frictional drag. In this manner, all the lift is generated by the 
upper surface and the lift-to-drag ratio is optimized. 
Figure D13 is a theoretical plot of the lift-to-drag ratio versus cavitation number of 
several hydrofoil shapes. The strength and lift of each of the hydrofoils was assumed to be 
equal to that of an NACA 16-510 hydrofoil. As the cavitation number was reduced, the 
chord length and thickness of each hydrofoil was varied to prevent cavitation. The assump- 
tions were two-dimensional flow, a fully turbulent boundary layer, zero angle of attack, 
circular-arc camber line, and cavity pressure equal to depth pressure. 
90 iid Paka tio BASE VENTED HYOROFOIL HAVING 
PO OPTIMOM EFFICIENCY 
80 - a, a Ca 
7O - ee = = 
/ 
pe 7 -J BASE VENTED CUT-OFF 16- SERIES 
/ 
Ve SO - -\ FULLY WETTED NACA Le- SERIES 
\ BASE VENTED CAMBERED PARABOLA 
% bette Gee ae 
_ SUPERVENTILATING CIRCULAR ARC 
Jo - Nea Le 
Qo l | | | | 
O O/ 0.2 03 OF AS O06 O.7 
’ ! 1 oO t ! t 
O Al 030 0.95 060 0.75 0.90 LOS 
Opesen = 19 7 
Fig. D13. Comparison of hydrofoils having equal strength and lift 
The following reports published at the U.S. Naval Ordnance Test Station include more 
detailed results of these studies: 
1. Lang, T.G., “Base Vented Hydrofoils,” NavOrd Report 6606, Oct. 19, 1959 
2. Fabula, A.G., “Theoretical Lift and Drag on Vented Hydrofoils for Zero Cavity Num- 
ber and Steady Two-Dimensional Flow,” NavOrd Report 7005, Nov. 4, 1959 
3. Lang, T.G., and Daybell, Dorothy A., Smith, K.E., “Water Tunnel Tests of Hydro- 
foils With Forced Ventilation,” NavOrd Report 7008 
4. Lang, T.G., and Daybell, Dorothy A., “Water Tunnel Tests of a Base-Vented Hydro- 
foil Having a Cambered Parabolic Cross Section,” NavWeps Report 7584, 
Oct 10, 1960 
5. Fabula, A.G., “Application of Thin Airfoil Theory to Hydrofoils With Cut-Off, 
Ventilated Trailing Edge,” NavWeps Report 7571, Sept. 13, 1960 
