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National Advisory Committee for Aeronautics, Technical Notes - Rough-Water Impact-Load Investigation of a Chine-Immersed V-Bottom Model Having a Dead-Rise Angle of 10°

A rough-water investigation of a Vébottom chine-immersed model has
been made in the Langley impact basin. The model was 20 inches wide and
5 feet long and had a dead—rise angle of 10° and a beam-loading coeffi-
cient of 5.78. The impacts occurred on waves ranging from ll to 60 feet
in length and from about 1 to 2 feet in height (length-height ratios
from 8.3 to h5.7). The initial flight conditions were held essentially
'constant. The trim angle was held fixed at 12° with respect to the hori-
zontal, the flight-path angle was about 6°, and the resultant velocity
was approximately 65 feet per second. A few planing runs were also made.
Time histories of the runs were obtained, and a few typical time histo-
ries are presented to show the wave shape, the position of the model on
the wave, and the variation of some impact parameters throughout the
impact.

The investigation led to the conclusion that the slope of the wave
is an important impact parameter. Fairly good agreement between the
experiment and an application of smoothdwater theory to rough water was
obtained for the suitable data.

For the landing-impact problem of the operational seaplane, the
roughawater condition is of utmost importance. However, most hydrodynamic
impact-load investigations for large-scale models under controlled con-
ditions have been devoted to smooth water because of the relative simplic-
ity of smooth-water testing and the belief that smoothawater landing con-
ditions are fundamental to many rough-water conditions from the standpoint
of impact loads. Reference 1, for instance, indicates the existence of
a relationship between wave slope and the slope of an equivalent inclined-
plane smooth-water surface for a model without chine immersion. However,
few tests have been made in rough water for the model with immersed chines,
although a few impacts were reported in references 2 and 5. All the
impacts in references 1 to 5 were limited to uniform waves from 3 to
6 model lengths.