228 G. J. Wennagel 
aspect ratio in this photograph is 1.44. Note the shape of the air cavity at the tip. As in 
the previous test series, the air was not seen to ventilate forward of the trailing edge unless 
a region of separated water existed, such as that caused by stall, extensive cavitation, or 
boundary layer separation. Figure D9 shows this same hydrofoil in two-dimensional flow 
with a very small airflow rate. The vortex pattern seen behind the trailing edge disappears 
when the airflow rate is increased. 
Q20.02¢, R=4; A=c0 
Fig. D9. Hydrofoil of Fig. D8, but 
with a very small airflow rate 
Figure D10 is a plot of the lift-to-drag ratio of the two-dimensional parabolic hydrofoil. 
The lift-to-drag ratio approaches 25 as the airflow rate increases. Higher ratios could have 
been obtained if tunnel blockage had not limited the minimum ventilation to K 2 0.14. 
—_—_ 
pe 25. VENTED 
; k~0.16 
SYMBOL ,f7/SEC eal 
° 30 L/o 
3 20 16 VENTEO 
SHADED SY-MBOL--ULLY WETTED L K~O.90 
CLEAR SYMBOL ~ VENTED 
(R= eo 
&, OLCREES 
of =6igsGe 
Fig. D10. Experimental lift-to-drag ratios of the two-dimensional, cambered, parabolic hydrofoil 
Figure D11 is a table showing an analytical comparison at noncavitating speeds of a 
fully-wetted NACA 16-series hydrofoil and a base-vented parabolic hydrofoil. It is seen 
