ONR Hydrofoil Boat XCH-6 227 
Figure D7 is a plot of the lift coefficient versus angle of attack. The upper curve 
refers to fully-wetted flow and the lower curve to vented flow. Note the large decrease in 
YYY YY 
“8 +6 -4 -2 
ANGLE * ATTACK, DEG 
Fig. D7. Lift coefficient of (top curve) fully wetted and (bottom curve) vented hydrofoil 
lift when the hydrofoil is forcibly vented. This type of ventilation can be induced by 
exhausting air through a port at any position on a hydrofoil and therefore may be used as a 
means of controlling the hydrodynamic forces developed by the hydrofoil. It should also be 
noted that the slope of the lift coefficient curve is reduced by ventilation. The references 
cited at the end of this discussion include theoretical work which predicts the lift and drag 
of two-dimensional hydrofoils of arbitrary shape vented at arbitrary chordwise locations for 
the case of zero ventilation number. Good agreement is shown with experiment. 
Figure D8 shows top and side views of a hydrofoil model having a cambered parabolic 
cross section wherein air was exhausted through a hole in the trailing edge. The effective 
kK: 0.100, Qz0.07/, @=8 5 R=1.$4¢ 
Fig. D8. Top and side views of a cambered parabolic 
hydrofoil with air exhausted through a hole in the 
trailing edge 
