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National Advisory Committee for Aeronautics, Technical Notes - Hydrodynamic Loads in Smooth Water for a Prismatic Float Having an Angle of Dead Rise of 40°

A prismatic-float forebody with an angle of dead rise of #00 was
subjected to smooth-water impacts in the Langley impact basin. The tests
were made at fixed trims of 3°, 6°, 9°, and 12° for a range of flight~
path angles from approximately 2° to 22°. '

The data are presented and converted into dimensionless variables
for correlation of the experimental results with hydrodynamic impact
theory and for comparison of the runs among themselves. The average
value of the dead-rise function for an angle of dead rise of #00 is
evaluated and compared with similar values for angles of dead rise
of 30° and 225 and with the theoretical dead-rise function. The experi-
mental data are shown to be in good agreement with values predicted by
theory.

The development of seaplanes having high aerodynamic performance
accompanied by high stalling speeds and high wing loadings has resulted
in increased impact loads. The designer of the modern seaplane is con-
fronted with the dual prdblem of predicting the water loads and of
devising means of reducing these loads.

In order to provide a more rational basis for the prediction of
impact loads, reference 1 presented an analysis which showed that the
motion and time characteristics of an impact may be represented by
means of generalized variables. The variation of the generalized vari-
ables is governed solely by the magnitude of the approach parameter K
which may be considered a criterion of impact similarity.

One possible means of reducing the water loads on seaplanes is the
use of sharper angles of dead rise. A program undertaken at the
Langley impact basin to determine the variation of impact loads with
angle of dead rise has therefore been expanded to include tests of a
seaplane float having a #00 angle of dead rise. Data were obtained at
fixed trim.with a VFbottom prismatic-float forebody of MOO dead-rise
angle. The data were obtained at the Langley impact basin in smooth
water for a wide range of trim angles, velocities, and flight-path angles.
The test simulated flight conditions in which the effects of the presence
of the afterbody is small. The data are compared with the generalized
theoretical results previously mentioned and the effect of dead-rise
angle on hydrodynamic loads is analyzed.