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National Advisory Committee for Aeronautics, Report - The Hydrodynamic Characteristics of Modified Rectangular Flat Plates having Aspect Ratios of 1.00, 0.25, 0.125 and Operating Near a Free Water Surface

An investigation has been conducted to determine the hydro-
dynamic forces and moments acting on modified rectangular flat
plates with aspect ratios of 1.00, 035, and 0.125 mounted on a
single strut and operating at several depths of submersion. A
simple method has been developed by modification of Falkner’s
vortex-lattice theory which enables the prediction of the lift
characteristics in unseparated flow at large depths. This
method shows good agreement with experimental data from the
present tests and with aerodynamic data at all angles investi-
gated for aspect ratios of 1.00 and 0.25 and at angles up to 16°
for aspect ratio 0.125. Above 16° for aspect ratio 0.125, the
predicted lift proved too high.

The experimental investigation indicated that decreasing the
aspect ratio or depth of submersion caused a decrease in the lift
coefiicient, drag coefiicient, and lift-drag ratio. The center of
pressure moved aft with decreasing aspect ratio and forward
with decreasing depth of submersion except for the aspect-ratio—
0.12b' plate at angles of attack above 8°. For these angles of
attack, the center of pressure moved aft with decreasing depth
of submersion.

Cavitation at the leading edge caused a gradual decrease in
lift coeficient and a gradual increase in drag coefficient with
little change in moment coefiicient.

Two types of leading-edge separation at high angles of attack
were encountered. One type, called “white water” and found
only for the aspect-ratio—I.00 surface, caused a slight decrease
in the lift and moment coefficients and a slight increase in the
drag coefl‘icient. The other type, called the “planing bubble”
and found for all three surfaces, caused a sharp drop in the
lift, drag, and moment coefiicients primarily because of the loss
of upper surface lift. The ventilation boundaries defining the
start of the high—angle separation moved to higher speeds and
higher angles as the aspect ratio was decreased.